Supervisors


Professional Education


  • Doctor of Philosophy, Northwestern University (2017)
  • Bachelor of Science, Universita Degli Studi Di Perugia (2008)
  • Master of Science, Universita Degli Studi Di Bologna (2010)

All Publications


  • Electrochemical Switching of a Fluorescent Molecular Rotor Embedded within a Bistable Rotaxane JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wu, Y., Frasconi, M., Liu, W., Young, R. M., Goddard, W. A., Wasielewski, M. R., Stoddart, J. 2020; 142 (27): 11835–46

    Abstract

    We report how the nanoconfined environment, introduced by the mechanical bonds within an electrochemically switchable bistable [2]rotaxane, controls the rotation of a fluorescent molecular rotor, namely, an 8-phenyl-substituted boron dipyrromethene (BODIPY). The electrochemical switching of the bistable [2]rotaxane induces changes in the ground-state coconformation and in the corresponding excited-state properties of the BODIPY rotor. In the starting redox state, when no external potential is applied, the cyclobis(paraquat-p-phenylene) (CBPQT4+) ring component encircles the tetrathiafulvalene (TTF) unit on the dumbbell component, leaving the BODIPY rotor unhindered and exhibiting low fluorescence. Upon oxidation of the TTF unit to a TTF2+ dication, the CBPQT4+ ring is forced toward the molecular rotor, leading to an increased energy barrier for the excited state to rotate the rotor into the state with a high nonradiative rate constant, resulting in an overall 3.4-fold fluorescence enhancement. On the other hand, when the solvent polarity is high enough to stabilize the excited charge-transfer state between the BODIPY rotor and the CBPQT4+ ring, movement of the ring toward the BODIPY rotor produces an unexpectedly strong fluorescence signal decrease as the result of photoinduced electron transfer from the BODIPY rotor to the CBPQT4+ ring. The nanoconfinement effect introduced by mechanical bonding can effectively lead to modulation of the physicochemical properties as observed in this bistable [2]rotaxane. On account of the straightforward synthetic strategy and the facile modulation of switchable electrochromic behavior, our approach could pave the way for the development of new stimuli-responsive materials based on mechanically interlocked molecules for future electro-optical applications, such as sensors, molecular memories, and molecular logic gates.

    View details for DOI 10.1021/jacs.0c03701

    View details for Web of Science ID 000550639000027

    View details for PubMedID 32470290

  • F4-TCNQ as an Additive to Impart Stretchable Semiconductors with High Mobility and Stability ADVANCED ELECTRONIC MATERIALS Mun, J., Kang, J., Zheng, Y., Luo, S., Wu, Y., Gong, H., Lai, J., Wu, H., Xue, G., Tok, J., Bao, Z. 2020
  • Reversible Symmetry-Breaking Charge Separation in a Series of Perylenediimide Cyclophanes JOURNAL OF PHYSICAL CHEMISTRY C Coleman, A. F., Chen, M., Zhou, J., Shin, J., Wu, Y., Young, R. M., Wasielewski, M. R. 2020; 124 (19): 10408–19
  • Fine-Tuning Semiconducting Polymer Self-Aggregation and Crystallinity Enables Optimal Morphology and High-Performance Printed All-Polymer Solar Cells. Journal of the American Chemical Society Wu, Y., Schneider, S., Walter, C., Chowdhury, A. H., Bahrami, B., Wu, H., Qiao, Q., Toney, M. F., Bao, Z. 2019

    Abstract

    Polymer aggregation and crystallization behavior play a crucial role in the performance of all-polymer solar cells (all-PSCs). Gaining control over polymer self-assembly via molecular design to influence bulk-heterojunction active-layer morphology, however, remains challenging. Herein, we show a simple yet effective way to modulate the self-aggregation of the commonly used naphthalene diimide (NDI)-based acceptor polymer (N2200), by systematically replacing a certain amount of alkyl side-chains with compact bulky side-chains (CBS). Specifically, we have synthesized a series of random copolymer (PNDI-CBSx) with different molar fractions (x = 0-1) of the CBS units and have found that both solution-phase aggregation and solid-state crystallinity of these acceptor polymers are progressively suppressed with increasing x as evidenced by UV-vis absorption, photoluminescence (PL) spectroscopies, thermal analysis, and grazing incidence X-ray scattering (GIWAXS) techniques. Importantly, as compared to the highly self-aggregating N2200, photovoltaic results show that blending of more amorphous acceptor polymers with donor polymer (PBDB-T) can enable all-PSCs with significantly increased PCE (up to 8.5%). The higher short-circuit current density (Jsc) results from the smaller polymer phase-separation domain sizes as evidenced by PL quenching and resonant soft X-ray scattering (R-SoXS) analyses. Additionally, we show that the lower crystallinity of the active layer is less sensitive to the film deposition methods. Thus, the transition from spin-coating to solution coating can be easily achieved with no performance losses. On the other hand, decreasing aggregation and crystallinity of the acceptor polymer too much reduces the photovoltaic performance as the donor phase-separation domain sizes increases. The highly amorphous acceptor polymers appear to induce formation of larger donor polymer crystallites. These results highlight the importance of a balanced aggregation strength between the donor and acceptor polymers to achieve high-performance all-PSCs with optimal active layer film morphology.

    View details for DOI 10.1021/jacs.9b10935

    View details for PubMedID 31793773

  • Choosing sides: unusual ultrafast charge transfer pathways in an asymmetric electron-accepting cyclophane that binds an electron donor CHEMICAL SCIENCE Zhou, J., Wu, Y., Roy, I., Samanta, A., Stoddart, J., Young, R. M., Wasielewski, M. R. 2019; 10 (15): 4282–92

    Abstract

    Constructing functional molecular systems for solar energy conversion and quantum information science requires a fundamental understanding of electron transfer in donor-bridge-acceptor (D-B-A) systems as well as competitive reaction pathways in acceptor-donor-acceptor (A-D-A) and acceptor-donor-acceptor' (A-D-A') systems. Herein we present a supramolecular complex comprising a tetracationic cyclophane having both phenyl-extended viologen (ExV2+) and dipyridylthiazolothiazole (TTz2+) electron acceptors doubly-linked by means of two p-xylylene linkers (TTzExVBox4+), which readily incorporates a perylene (Per) guest in its cavity (Per ⊂ TTzExVBox4+) to establish an A-D-A' system, in which the ExV2+ and TTz2+ units serve as competing electron acceptors with different reduction potentials. Photoexcitation of the Per guest yields both TTz+˙-Per+˙-ExV2+ and TTz2+-Per+˙-ExV+˙ in <1 ps, while back electron transfer in TTz2+-Per+˙-ExV+˙ proceeds via the unusual sequence TTz2+-Per+˙-ExV+˙ → TTz+˙-Per+˙-ExV2+ → TTz2+-Per-ExV2+. In addition, selective chemical reduction of TTz2+ gives Per ⊂ TTzExVBox3+˙, turning the complex into a D-B-A system in which photoexcitation of TTz+˙ results in the reaction sequence 2*TTz+˙-Per-ExV2+ → TTz2+-Per-ExV+˙ → TTz+˙-Per-ExV2+. Both reactions TTz2+-Per+˙-ExV+˙ → TTz+˙-Per+˙-ExV2+ and TTz2+-Per-ExV+˙ → TTz+˙-Per-ExV2+ occur with a (16 ± 1 ps)-1 rate constant irrespective of whether the bridge molecule is Per+˙ or Per. These results are explained using the superexchange mechanism in which the ionic states of the perylene guest serve as virtual states in each case and demonstrate a novel supramolecular platform for studying the effects of bridge energetics within D-B-A systems.

    View details for DOI 10.1039/c8sc05514a

    View details for Web of Science ID 000465271800013

    View details for PubMedID 31057755

    View details for PubMedCentralID PMC6471873

  • Fine-Tuning Aromatic Stacking and Single-Crystal Photoluminescence Through Coordination Chemistry EUROPEAN JOURNAL OF ORGANIC CHEMISTRY Chen, C., Wu, Y., Li, H. 2019: 1778–83
  • Covalent Radical Pairs as Spin Qubits: Influence of Rapid Electron Motion between Two Equivalent Sites on Spin Coherence JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wu, Y., Zhou, J., Nelson, J. N., Young, R. M., Krzyaniak, M. D., Wasielewski, M. R. 2018; 140 (40): 13011–21

    Abstract

    Ultrafast photodriven electron transfer reactions starting from an excited singlet state in an organic donor-acceptor molecule generate a radical pair (RP) in which the two spins are initially entangled and, in principle, can serve as coupled spin qubits in quantum information science (QIS) applications, provided that spin coherence lifetimes in these RPs are long. Here we investigate the effects of electron transfer between two equivalent sites comprising the reduced acceptor of the RP. A covalent electron donor-acceptor molecule (D-C-A24+) including a p-methoxyaniline donor (D), a 4-aminonaphthalene-1,8-imide chromophoric primary acceptor (C), and a m-xylene bridged cyclophane having two equivalent phenyl-extended viologens (A24+) as a secondary acceptor was synthesized along with the analogous molecule having one phenyl-extended viologen acceptor and a second, more difficult to reduce 2,5-dimethoxyphenyl-extended viologen in a very similar cyclophane structure (D-C-A4+). Photoexcitation of C within each molecule results in subnanosecond formation of D+•-C-A23+• and D+•-C-A3+•. The spin dynamics of these RPs were characterized by time-resolved EPR spectroscopy and magnetic field effects on the RP yield in both CH3CN and CD3CN. The data show that rapid electron hopping within A23+• promotes spin decoherence in D+•-C-A23+• relative to D+•-C-A3+• having a monomeric acceptor, while the interaction of the RP electron spins with the nuclear spins of the solvent have little or no effect on the spin dynamics. These observations provide important information for designing and understanding novel molecular assemblies of spin qubits with long coherence times for QIS applications.

    View details for DOI 10.1021/jacs.8b08105

    View details for Web of Science ID 000447354800052

    View details for PubMedID 30211549

  • Hybrid 2D Dion-Jacobson perovskites and application in solar cells Man, L., Ke, W., Pedesseau, L., Wu, Y., Katan, C., Even, J., Wasielewski, M., Stoumpos, C., Kanatzidis, M. AMER CHEMICAL SOC. 2018
  • ExTzBox: A Glowing Cyclophane for Live-Cell Imaging JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Roy, I., Bobbala, S., Zhou, J., Nguyen, M. T., Nalluri, S., Wu, Y., Ferris, D. P., Scott, E., Wasielewski, M. R., Stoddart, J. 2018; 140 (23): 7206–12

    Abstract

    The ideal fluorescent probe for live-cell imaging is bright and non-cytotoxic and can be delivered easily into the living cells in an efficient manner. The design of synthetic fluorophores having all three of these properties, however, has proved to be challenging. Here, we introduce a simple, yet effective, strategy based on well-established chemistry for designing a new class of fluorescent probes for live-cell imaging. A box-like hybrid cyclophane, namely ExTzBox·4X (6·4X, X = PF6-, Cl-), has been synthesized by connecting an extended viologen (ExBIPY) and a dipyridyl thiazolothiazole (TzBIPY) unit in an end-to-end fashion with two p-xylylene linkers. Photophysical studies show that 6·4Cl has a quantum yield ΦF = 1.00. Furthermore, unlike its ExBIPY2+ and TzBIPY2+ building units, 6·4Cl is non-cytotoxic to RAW 264.7 macrophages, even with a loading concentration as high as 100 μM, presumably on account of its rigid box-like structure which prevents its intercalation into DNA and may inhibit other interactions with it. After gaining an understanding of the toxicity profile of 6·4Cl, we employed it in live-cell imaging. Confocal microscopy has demonstrated that 64+ is taken up by the RAW 264.7 macrophages, allowing the cells to glow brightly with blue laser excitation, without any hint of photobleaching or disruption of normal cell behavior under the imaging conditions. By contrast, the acyclic reference compound Me2TzBIPY·2Cl (4·2Cl) shows very little fluorescence inside the cells, which is quenched completely under the same imaging conditions. In vitro cell investigations underscore the significance of using highly fluorescent box-like rigid cyclophanes for live-cell imaging.

    View details for DOI 10.1021/jacs.8b03066

    View details for Web of Science ID 000435525500024

    View details for PubMedID 29771509

  • Shuttling Rates, Electronic States, and Hysteresis in a Ring-in-Ring Rotaxane ACS CENTRAL SCIENCE Lipke, M. C., Wu, Y., Roy, I., Wang, Y., Wasielewski, M. R., Stoddart, J. 2018; 4 (3): 362–71

    Abstract

    The trisradical recognition motif between a 4,4'-bipyridinium radical cation and a cyclo-bis-4,4'-bipyridinium diradical dication has been employed previously in rotaxanes to control their nanomechanical and electronic properties. Herein, we describe the synthesis and characterization of a redox-active ring-in-ring [2]rotaxane BBR·8PF6 that employs a tetraradical variant of this recognition motif. A square-shaped bis-4,4'-bipyridinium cyclophane is mechanically interlocked around the dumbbell component of this rotaxane, and the dumbbell itself incorporates a smaller bis-4,4'-bipyridinium cyclophane into its covalently bonded structure. This small cyclophane serves as a significant impediment to the shuttling of the larger ring across the dumbbell component of BBR 8+ , whereas reduction to the tetraradical tetracationic state BBR 4(+•) results in strong association of the two cyclophanes driven by two radical-pairing interactions. In these respects, BBR·8PF6 exhibits qualitatively similar behavior to its predecessors that interconvert between hexacationic and trisradical tricationic states. The rigid preorganization of two bipyridinium groups within the dumbbell of BBR·8PF6 confers, however, two distinct properties upon this rotaxane: (1) the rate of shuttling is reduced significantly relative to those of its predecessors, resulting in marked electrochemical hysteresis observed by cyclic voltammetry for switching between the BBR 8+ /BBR 4(+•) states, and (2) the formally tetraradical form of the rotaxane, BBR 4(+•) , exhibits a diamagnetic ground state, which, as a result of the slow shuttling motions within BBR 4(+•) , has a long enough lifetime to be characterized by 1H NMR spectroscopy.

    View details for DOI 10.1021/acscentsci.7b00535

    View details for Web of Science ID 000428801200011

    View details for PubMedID 29632882

    View details for PubMedCentralID PMC5879476

  • Hybrid Dion-Jacobson 2D Lead Iodide Perovskites JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Mao, L., Ke, W., Pedesseau, L., Wu, Y., Katan, C., Even, J., Wasielewski, M. R., Stoumpos, C. C., Kanatzidis, M. G. 2018; 140 (10): 3775–83

    Abstract

    The three-dimensional hybrid organic-inorganic perovskites have shown huge potential for use in solar cells and other optoelectronic devices. Although these materials are under intense investigation, derivative materials with lower dimensionality are emerging, offering higher tunability of physical properties and new capabilities. Here, we present two new series of hybrid two-dimensional (2D) perovskites that adopt the Dion-Jacobson (DJ) structure type, which are the first complete homologous series reported in halide perovskite chemistry. Lead iodide DJ perovskites adopt a general formula A'A n-1Pb nI3 n+1 (A' = 3-(aminomethyl)piperidinium (3AMP) or 4-(aminomethyl)piperidinium (4AMP), A = methylammonium (MA)). These materials have layered structures where the stacking of inorganic layers is unique as they lay exactly on top of another. With a slightly different position of the functional group in the templating cation 3AMP and 4AMP, the as-formed DJ perovskites show different optical properties, with the 3AMP series having smaller band gaps than the 4AMP series. Analysis on the crystal structures and density functional theory (DFT) calculations suggest that the origin of the systematic band gap shift is the strong but indirect influence of the organic cation on the inorganic framework. Fabrication of photovoltaic devices utilizing these materials as light absorbers reveals that (3AMP)(MA)3Pb4I13 has the best power conversion efficiency (PCE) of 7.32%, which is much higher than that of the corresponding (4AMP)(MA)3Pb4I13.

    View details for DOI 10.1021/jacs.8b00542

    View details for Web of Science ID 000427910700042

    View details for PubMedID 29465246

  • X-Shaped Oligomeric Pyromellitimide Polyradicals JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wu, Y., Han, J., Hong, M., Krzyaniak, M. D., Blackburn, A. K., Fernando, I. R., Cao, D. D., Wasielewski, M. R., Stoddart, J. 2018; 140 (1): 515–23

    Abstract

    The synthesis of stable organic polyradicals is important for the development of magnetic materials. Herein we report the synthesis, isolation, and characterization of a series of X-shaped pyromellitimide (PI) oligomers (Xn-R, n = 2-4, R = Hex or Ph) linked together by single C-C bonds between their benzenoid cores. We hypothesize that these oligomers might form high-spin states in their reduced forms because of the nearly orthogonal conformations adopted by their PI units. 1H and 13C nuclear magnetic resonance (NMR) spectroscopies confirmed the isolation of the dimeric, trimeric, and tetrameric homologues. X-ray crystallography shows that X2-Ph crystallizes into a densely packed superstructure, despite the criss-crossed conformations adopted by the molecules. Electrochemical experiments, carried out on the oligomers Xn-Hex, reveal that the reductions of the PI units occur at multiple distinct potentials, highlighting the weak electronic coupling between the adjacent redox centers. Finally, the chemically generated radical anion and polyanion states, Xn-Hex•- and Xn-Hexn(•-), respectively, were probed extensively by UV-vis-NIR absorption, EPR, and electron nuclear double resonance (ENDOR) spectroscopies. The ENDOR spectra of the radical monoanions Xn-Hex•- reveal that the unpaired electron is largely localized on a single PI unit. Further reductions of Xn-Hex•- yield EPR signals (in frozen solutions) that can be assigned to spin-spin interactions in X2-Hex2(•-), X3-Hex3(•-), and X4-Hex4(•-). Taken together, these findings demonstrate that directly linking the benzene rings of PIs with a single C-C bond is a viable method for generating stabilized high-spin organic anionic polyradicals.

    View details for DOI 10.1021/jacs.7b12124

    View details for Web of Science ID 000422813300085

    View details for PubMedID 29215275

  • Probing Distance Dependent Charge-Transfer Character in Excimers of Extended Viologen Cyclophanes Using Femtosecond Vibrational Spectroscopy JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wu, Y., Zhou, J., Phelan, B. T., Mauck, C. M., Stoddart, J., Young, R. M., Wasielewski, M. R. 2017; 139 (40): 14265–76

    Abstract

    Facile exciton transport within ordered assemblies of π-stacked chromophores is essential for developing molecular photonic and electronic materials. Excimer states having variable charge transfer (CT) character are frequently implicated as promoting or inhibiting exciton mobility in such systems. However, determining the degree of CT character in excimers as a function of their structure has proven challenging. Herein, we report on a series of cyclophanes in which the interplanar distance between two phenyl-extended viologen (ExV2+) chromophores is varied systematically using a pair of o-, m-, or p-xylylene (o-, m-, or p-Xy) covalent linkers to produce o-ExBox4+ (3.5 Å), m-ExBox4+ (5.6 Å), and p-ExBox4+ (7.0 Å), respectively. The cyclophane structures are characterized using NMR spectroscopy in solution and single-crystal X-ray diffraction in the solid state. Femtosecond transient mid-IR and stimulated Raman spectroscopies show that the CT contribution to the excimer states formed in o-ExBox4+ and m-ExBox4+ depends on the distance between the chromophores within the cyclophanes, while in the weak interaction limit, as represented by p-ExBox4+ (7.0 Å), the lowest excited singlet state of ExV2+ exclusively photo-oxidizes the p-Xy spacer to give the p-Xy+•-ExV+• ion pair. Moreover, the vibrational spectra of the excimer state show that it assumes a geometry that is intermediate between that of the locally excited and CT states, approximately reflecting the degree of CT character.

    View details for DOI 10.1021/jacs.7b08275

    View details for Web of Science ID 000413057100049

    View details for PubMedID 28880547

  • Exploring viscosity, polarity and temperature sensitivity of BODIPY-based molecular rotors PHYSICAL CHEMISTRY CHEMICAL PHYSICS Vysniauskas, A., Lopez-Duarte, I., Duchemin, N., Thanh-Truc Vu, Wu, Y., Budynina, E. M., Volkova, Y. A., Pena Cabrera, E., Ramirez-Ornelas, D. E., Kuimova, M. K. 2017; 19 (37): 25252–59

    Abstract

    Microviscosity is a key parameter controlling the rate of diffusion and reactions on the microscale. One of the most convenient tools for measuring microviscosity is by fluorescent viscosity sensors termed 'molecular rotors'. BODIPY-based molecular rotors in particular proved extremely useful in combination with fluorescence lifetime imaging microscopy, for providing quantitative viscosity maps of living cells as well as measuring dynamic changes in viscosity over time. In this work, we investigate several new BODIPY-based molecular rotors with the aim of improving on the current viscosity sensing capabilities and understanding how the structure of the fluorophore is related to its function. We demonstrate that due to subtle structural changes, BODIPY-based molecular rotors may become sensitive to temperature and polarity of their environment, as well as to viscosity, and provide a photophysical model explaining the nature of this sensitivity. Our data suggests that a thorough understanding of the photophysics of any new molecular rotor, in environments of different viscosity, temperature and polarity, is a must before moving on to applications in viscosity sensing.

    View details for DOI 10.1039/c7cp03571c

    View details for Web of Science ID 000412271600002

    View details for PubMedID 28718466

  • Mechanical-Bond-Protected, Air-Stable Radicals JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Sun, J., Liu, Z., Liu, W., Wu, Y., Wang, Y., Barnes, J. C., Hermann, K. R., Goddard, W. A., Wasielewski, M. R., Stoddart, J. 2017; 139 (36): 12704–9

    Abstract

    Radical templation centered around a heterotrisradical tricationic inclusion complex DB•+⊂DAPQT2(•+), assembled from an equimolar mixture of a disubstituted 4,4'-bipyridinium radical cation (DB•+) and an asymmetric cyclophane bisradical dication (DAPQT2(•+)), affords a symmetric [2]catenane (SC·7PF6) and an asymmetric [2]catenane (AC·7PF6) on reaction of the 1:1 complex with diazapyrene and bipyridine, respectively. Both these highly charged [2]catenanes have been isolated as air-stable monoradicals and characterized by EPR spectroscopy. X-ray crystallography suggests that the unpaired electrons are delocalized in each case across two inner 4,4'-bipyridinium (BIPY2+) units forming a mixed-valence (BIPY2)•3+ state inside both [2]catenanes, an observation which is in good agreement with spin-density calculations using density functional theory. Electrochemical studies indicate that by replacing the BIPY2+ units in homo[2]catenane HC•7+-composed of two mechanically interlocked cyclobis(paraquat-p-phenylene) rings-with "zero", one, and two more highly conjugated diazapyrenium dication (DAP2+) units, respectively, a consecutive series of five, six, and seven redox states can be accessed in the resulting SC·7PF6 (0, 4+, 6+, 7+, and 8+), HC·7PF6 (0, 2+, 4+, 6+, 7+, and 8+), and AC·7PF6 (0, 1+, 2+, 4+, 6+, 7+, and 8+), respectively. These unique [2]catenanes present a promising prototype for the fabrication of high-density data memories.

    View details for DOI 10.1021/jacs.7b06857

    View details for Web of Science ID 000411043900059

    View details for PubMedID 28806074

  • Tunable White-Light Emission in Single-Cation-Templated Three-Layered 2D Perovskites (CH3CH2NH3)(4)Pb3Br10-xClx JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Mao, L., Wu, Y., Stoumpos, C. C., Traore, B., Katan, C., Even, J., Wasielewski, M. R., Kanatzidis, M. G. 2017; 139 (34): 11956–63

    Abstract

    Two-dimensional (2D) hybrid halide perovskites come as a family (B)2(A)n-1PbnX3n+1 (B and A= cations; X= halide). These perovskites are promising semiconductors for solar cells and optoelectronic applications. Among the fascinating properties of these materials is white-light emission, which has been mostly observed in single-layered 2D lead bromide or chloride systems (n = 1), where the broad emission comes from the transient photoexcited states generated by self-trapped excitons (STEs) from structural distortion. Here we report a multilayered 2D perovskite (n = 3) exhibiting a tunable white-light emission. Ethylammonium (EA+) can stabilize the 2D perovskite structure in EA4Pb3Br10-xClx (x = 0, 2, 4, 6, 8, 9.5, and 10) with EA+ being both the A and B cations in this system. Because of the larger size of EA, these materials show a high distortion level in their inorganic structures, with EA4Pb3Cl10 having a much larger distortion than that of EA4Pb3Br10, which results in broadband white-light emission of EA4Pb3Cl10 in contrast to narrow blue emission of EA4Pb3Br10. The average lifetime of the series decreases gradually from the Cl end to the Br end, indicating that the larger distortion also prolongs the lifetime (more STE states). The band gap of EA4Pb3Br10-xClx ranges from 3.45 eV (x = 10) to 2.75 eV (x = 0), following Vegard's law. First-principles density functional theory calculations (DFT) show that both EA4Pb3Cl10 and EA4Pb3Br10 are direct band gap semiconductors. The color rendering index (CRI) of the series improves from 66 (EA4Pb3Cl10) to 83 (EA4Pb3Br0.5Cl9.5), displaying high tunability and versatility of the title compounds.

    View details for DOI 10.1021/jacs.7b06143

    View details for Web of Science ID 000409286000048

    View details for PubMedID 28745881

  • White-Light Emission and Structural Distortion in New Corrugated Two-Dimensional Lead Bromide Perovskites JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Mao, L., Wu, Y., Stoumpos, C. C., Wasielewski, M. R., Kanatzidis, M. G. 2017; 139 (14): 5210–15

    Abstract

    Hybrid inorganic-organic perovskites are developing rapidly as high performance semiconductors. Recently, two-dimensional (2D) perovskites were found to have white-light, broadband emission in the visible range that was attributed mainly to the role of self-trapped excitons (STEs). Here, we describe three new 2D lead bromide perovskites incorporating a series of bifunctional ammonium dications as templates which also emit white light: (1) α-(DMEN)PbBr4 (DMEN = 2-(dimethylamino)ethylamine), which adopts a unique corrugated layered structure in space group Pbca with unit cell a = 18.901(4) Å, b = 11.782(2) Å, and c = 23.680(5) Å; (2) (DMAPA)PbBr4 (DMAPA = 3-(dimethylamino)-1-propylamine), which crystallizes in P21/c with a = 10.717(2) Å, b = 11.735(2) Å, c = 12.127(2) Å, and β = 111.53(3)°; and (3) (DMABA)PbBr4 (DMABA = 4-dimethylaminobutylamine), which adopts Aba2 with a = 41.685(8) Å, b = 23.962(5) Å, and c = 12.000(2) Å. Photoluminescence (PL) studies show a correlation between the distortion of the "PbBr6" octahedron in the 2D layer and the broadening of PL emission, with the most distorted structure having the broadest emission (183 nm full width at half-maximum) and longest lifetime (τavg = 1.39 ns). The most distorted member α-(DMEN)PbBr4 exhibits white-light emission with a color rendering index (CRI) of 73 which is similar to a fluorescent light source and correlated color temperature (CCT) of 7863 K, producing "cold" white light.

    View details for DOI 10.1021/jacs.7b01312

    View details for Web of Science ID 000399353800037

    View details for PubMedID 28306254

  • Photoluminescent phenalenyl-type radical Anamimoghadam, O., Wu, Y., Pezzato, C., Minh Nguyen, Samanta, A., Gozem, S., Mosca, L., Krylov, A., Wasielewski, M., Stoddart, F. AMER CHEMICAL SOC. 2017
  • Spin frustrated organic trisradical triangle Wu, Y., Krzyaniak, M., Wasielewski, M. AMER CHEMICAL SOC. 2017
  • Intramolecular Energy and Electron Transfer within a Diazaperopyrenium-Based Cyclophane JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Gong, X., Young, R. M., Hartlieb, K. J., Miller, C., Wu, Y., Xiao, H., Li, P., Hafezi, N., Zhou, J., Ma, L., Cheng, T., Goddard, W. A., Farha, O. K., Hupp, J. T., Wasielewski, M. R., Stoddart, J. 2017; 139 (11): 4107–16

    Abstract

    Molecules capable of performing highly efficient energy transfer and ultrafast photoinduced electron transfer in well-defined multichromophoric structures are indispensable to the development of artificial photofunctional systems. Herein, we report on the synthesis, characterization, and photophysical properties of a rationally designed multichromophoric tetracationic cyclophane, DAPPBox4+, containing a diazaperopyrenium (DAPP2+) unit and an extended viologen (ExBIPY2+) unit, which are linked together by two p-xylylene bridges. Both 1H NMR spectroscopy and single-crystal X-ray diffraction analysis confirm the formation of an asymmetric, rigid, box-like cyclophane, DAPPBox4+. The solid-state superstructure of this cyclophane reveals a herringbone-type packing motif, leading to two types of π···π interactions: (i) between the ExBIPY2+ unit and the DAPP2+ unit (π···π distance of 3.7 Å) in the adjacent parallel cyclophane, as well as (ii) between the ExBIPY2+ unit (π···π distance of 3.2 Å) and phenylene ring in the closest orthogonal cyclophane. Moreover, the solution-phase photophysical properties of this cyclophane have been investigated by both steady-state and time-resolved absorption and emission spectroscopies. Upon photoexcitation of DAPPBox4+ at 330 nm, rapid and quantitative intramolecular energy transfer occurs from the 1*ExBIPY2+ unit to the DAPP2+ unit in 0.5 ps to yield 1*DAPP2+. The same excitation wavelength simultaneously populates a higher excited state of 1*DAPP2+ which then undergoes ultrafast intramolecular electron transfer from 1*DAPP2+ to ExBIPY2+ to yield the DAPP3+•-ExBIPY+• radical ion pair in τ = 1.5 ps. Selective excitation of DAPP2+ at 505 nm populates a lower excited state where electron transfer is kinetically unfavorable.

    View details for DOI 10.1021/jacs.6b13223

    View details for Web of Science ID 000397477700029

    View details for PubMedID 28225610

  • Size-Matched Radical Multivalency JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Lipke, M. C., Cheng, T., Wu, Y., Arslan, H., Xiao, H., Wasielewski, M. R., Goddard, W. A., Stoddart, J. 2017; 139 (11): 3986–98

    Abstract

    Persistent π-radicals such as MV+• (MV refers to methyl viologen, i.e., N,N'-dimethyl-4,4'-bipyridinum) engage in weak radical-radical interactions. This phenomenon has been utilized recently in supramolecular chemistry with the discovery that MV+• and [cyclobis(paraquat-p-phenylene)]2(+•) (CBPQT2(+•)) form a strong 1:1 host-guest complex [CBPQT⊂MV]3(+•). In this full paper, we describe the extension of radical-pairing-based molecular recognition to a larger, square-shaped diradical host, [cyclobis(paraquat-4,4'-biphenylene)]2(+•) (MS2(+•)). This molecular square was evaluated for its ability to bind an isomeric series of possible diradical cyclophane guests, which consist of two radical viologen units that are linked by two ortho-, meta-, or para-xylylene bridges to provide different spacing between the planar radicals. UV-Vis-NIR measurements reveal that only the m-xylylene-linked isomer (m-CBPQT2(+•)) binds strongly inside of MS2(+•), resulting in the formation of a tetraradical complex [MS⊂m-CBPQT]4(+•). Titration experiments and variable temperature UV-Vis-NIR and EPR spectroscopic data indicate that, relative to the smaller trisradical complex [CBPQT⊂MV]3(+•), the new host-guest complex forms with a more favorable enthalpy change that is offset by a greater entropic penalty. As a result, the association constant (Ka = (1.12 ± 0.08) × 105 M-1) for [MS⊂m-CBPQT]4(+•) is similar to that previously determined for [CBPQT⊂MV]3(+•). The (super)structures of MS2(+•), m-CBPQT2(+•), and [MS⊂m-CBPQT]4(+•) were examined by single-crystal X-ray diffraction measurements and density functional theory calculations. The solid-state and computational structural analyses reveal that m-CBPQT2(+•) is ideally sized to bind inside of MS2(+•). The solid-state superstructures also indicate that localized radical-radical interactions in m-CBPQT2(+•) and [MS⊂m-CBPQT]4(+•) disrupt the extended radical-pairing interactions that are common in crystals of other viologen radical cations. Lastly, the formation of [MS⊂m-CBPQT]4(+•) was probed by cyclic voltammetry, demonstrating that the radical states of the cyclophanes are stabilized by the radical-pairing interactions.

    View details for DOI 10.1021/jacs.6b09892

    View details for Web of Science ID 000397477700016

    View details for PubMedID 28170237

  • Spin Frustration in the Triradical Trianion of a Naphthalenediimide Molecular Triangle JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wu, Y., Krzyaniak, M. D., Stoddart, J., Wasielewski, M. R. 2017; 139 (8): 2948–51

    Abstract

    Crystalline supramolecular frameworks consisting of charged molecules, held together by hydrogen bonds and Coulomb interactions, have attracted great interest because of their unusual structural, chemical, electronic, and magnetic properties. Herein, we report the preparation, structure, and magnetic properties of the triradical trianion of a shape-persistent chiral equilateral molecular triangle having three naphthalene-1,4:5,8-bis(dicarboximide)s ((+)-NDI-Δ3(-•)). Single-crystal X-ray diffraction of its tris(cobaltocenium) salt ([(+)-NDI-Δ3(-•)(CoCp2+)3]) reveals accessible one-dimensional tubular cavities, and variable-temperature electron paramagnetic resonance spectroscopy shows that a dilute solution of [(+)-NDI-Δ3(-•)(CoCp2+)3] in an organic glass has a spin-frustrated doublet ground state and a thermally accessible quartet state. Furthermore, SQUID magnetometry from 5 to 300 K of solid [(+)-NDI-Δ3(-•)(CoCp2+)3] shows ferromagnetic ordering with a Curie temperature TC = 20 K. The successful preparation of hybrid ionic materials comprising macrocyclic triradical trianions with spin-frustrated ground states and accessible 1D pores offers routes to new organic spintronic materials.

    View details for DOI 10.1021/jacs.7b00515

    View details for Web of Science ID 000395493400023

    View details for PubMedID 28194969

  • Enabling singlet fission by controlling intramolecular charge transfer in pi-stacked covalent terrylenediimide dimers NATURE CHEMISTRY Margulies, E. A., Miller, C. E., Wu, Y., Ma, L., Schatz, G. C., Young, R. M., Wasielewski, M. R. 2016; 8 (12): 1120–25

    Abstract

    When an assembly of two or more molecules absorbs a photon to form a singlet exciton, and the energetics and intermolecular interactions are favourable, the singlet exciton can rapidly and spontaneously produce two triplet excitons by singlet fission. To understand this process is important because it may prove to be technologically significant for enhancing solar-cell performance. Theory strongly suggests that charge-transfer states are involved in singlet fission, but their role has remained an intriguing puzzle and, up until now, no molecular system has provided clear evidence for such a state. Here we describe a terrylenediimide dimer that forms a charge-transfer state in a few picoseconds in polar solvents, and undergoes equally rapid, high-yield singlet fission in nonpolar solvents. These results show that adjusting the charge-transfer-state energy relative to those of the exciton states can serve to either inhibit or promote singlet fission.

    View details for DOI 10.1038/NCHEM.2589

    View details for Web of Science ID 000389225700009

    View details for PubMedID 27874873

  • Dopant-Free Hole Transporting Polymers for High Efficiency, Environmentally Stable Perovskite Solar Cells ADVANCED ENERGY MATERIALS Liao, H., Tam, T., Guo, P., Wu, Y., Manley, E. F., Huang, W., Zhou, N., Soe, C., Wang, B., Wasielewski, M. R., Chen, L. X., Kanatzidis, M. G., Facchetti, A., Chang, R. H., Marks, T. J. 2016; 6 (16)
  • Chiral redox-active isosceles triangles for energy storage applications Nalluri, S., Liu, Z., Wu, Y., Hermann, K., Samanta, A., Kim, D., Stoddart, J. AMER CHEMICAL SOC. 2016
  • Enabling singlet fission by controlling intramolecular charge transfer in pi-stacked covalent terrylenediimide dimers Wasielewski, M., Margulies, E., Miller, C., Wu, Y., Ma, L., Young, R., Schatz, G. AMER CHEMICAL SOC. 2016
  • Radical multivalency via Goldilocks size matching of a diradical host and guest Lipke, M., Cheng, T., Wu, Y., Arslan, H., Wasielewski, M., Goddard, W., Stoddart, J. AMER CHEMICAL SOC. 2016
  • Sliding-Ring Catenanes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Fernando, I. R., Frasconi, M., Wu, Y., Liu, W., Wasielewski, M. R., Goddard, W. A., Stoddartt, J. 2016; 138 (32): 10214–25

    Abstract

    Template-directed protocols provide a routine approach to the synthesis of mechanically interlocked molecules (MIMs), in which the mechanical bonds are stabilized by a wide variety of weak interactions. In this Article, we describe a strategy for the preparation of neutral [2]catenanes with sliding interlocked electron-rich rings, starting from two degenerate donor-acceptor [2]catenanes, consisting of a tetracationic cyclobis(paraquat-p-phenylene) cyclophane (CBPQT(4+)) and crown ethers containing either (i) hydroquinone (HQ) or (ii) 1,5-dioxynaphthalene (DNP) recognition units and carrying out four-electron reductions of the cyclophane components to their neutral forms. The donor-acceptor interactions between the CBPQT(4+) ring and both HQ and DNP units present in the crown ethers that stabilize the [2]catenanes are weakened upon reduction of the cyclophane components to their radical cationic states and are all but absent in their fully reduced states. Characterization in solution performed by UV-vis, EPR, and NMR spectroscopic probes reveals that changes in the redox properties of the [2]catenanes result in a substantial decrease of the energy barriers for the circumrotation and pirouetting motions of the interlocked rings, which glide freely through one another in the neutral states. The solid-state structures of the fully reduced catenanes reveal profound changes in the relative dispositions of the interlocked rings, with the glycol chains of the crown ethers residing in the cavities of the neutral CBPQT(0) rings. Quantum mechanical investigations of the energy levels associated with the four different oxidation states of the catenanes support this interpretation. Catenanes and rotaxanes with sliding rings are expected to display unique properties.

    View details for DOI 10.1021/jacs.6b04982

    View details for Web of Science ID 000381715700029

    View details for PubMedID 27398609

  • Ultrafast Two-Electron Transfer in a CdS Quantum Dot-Extended-Viologen Cyclophane Complex JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Young, R. M., Jensen, S. C., Edme, K., Wu, Y., Krzyaniak, M. D., Vermeulen, N. A., Dale, E. J., Stoddart, J., Weiss, E. A., Wasielewski, M. R., Co, D. T. 2016; 138 (19): 6163–70

    Abstract

    Time-resolved optical spectroscopies reveal multielectron transfer from the biexcitonic state of a CdS quantum dot to an adsorbed tetracationic compound cyclobis(4,4'-(1,4-phenylene) bipyridin-1-ium-1,4-phenylene-bis(methylene)) (ExBox(4+)) to form both the ExBox(3+•) and the doubly reduced ExBox(2(+•)) states from a single laser pulse. Electron transfer in the single-exciton regime occurs in 1 ps. At higher excitation powers the second electron transfer takes ∼5 ps, which leads to a mixture of redox states of the acceptor ligand. The doubly reduced ExBox(2(+•)) state has a lifetime of ∼10 ns, while CdS(+•):ExBox(3+•) recombines with multiple time constants, the longest of which is ∼300 μs. The long-lived charge separation and ability to accumulate multiple charges on ExBox(4+) demonstrate the potential of the CdS:ExBox(4+) complex to serve as a platform for two-electron photocatalysis.

    View details for DOI 10.1021/jacs.5b13386

    View details for Web of Science ID 000376331000017

    View details for PubMedID 27111529

  • Chiral Redox-Active Isosceles Triangles JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Nalluri, S., Liu, Z., Wu, Y., Hermann, K. R., Samanta, A., Kim, D., Krzyaniak, M. D., Wasielewski, M. R., Stoddart, J. 2016; 138 (18): 5968–77

    Abstract

    Designing small-molecule organic redox-active materials, with potential applications in energy storage, has received considerable interest of late. Herein, we report on the synthesis, characterization, and application of two rigid chiral triangles, each of which consist of non-identical pyromellitic diimide (PMDI) and naphthalene diimide (NDI)-based redox-active units. (1)H and (13)C NMR spectroscopic investigations in solution confirm the lower symmetry (C2 point group) associated with these two isosceles triangles. Single-crystal X-ray diffraction analyses reveal their rigid triangular prism-like geometries. Unlike previously investigated equilateral triangle containing three identical NDI subunits, both isosceles triangles do not choose to form one-dimensional supramolecular nanotubes by dint of [C-H···O] interaction-driven columnar stacking. The rigid isosceles triangle, composed of one NDI and two PMDI subunits, forms-in the presence of N,N-dimethylformamide-two different types of intermolecular NDI-NDI and NDI-PMDI π-π stacked dimers with opposite helicities in the solid state. Cyclic voltammetry reveals that both isosceles triangles can accept reversibly up to six electrons. Continuous-wave electron paramagnetic resonance and electron-nuclear double-resonance spectroscopic investigations, supported by density functional theory calculations, on the single-electron reduced radical anions of the isosceles triangles confirm the selective sharing of unpaired electrons among adjacent redox-active NDI subunit(s) within both molecules. The isosceles triangles have been employed as electrode-active materials in organic rechargeable lithium-ion batteries. The evaluation of the structure-performance relationships of this series of diimide-based triangles reveals that the increase in the number of NDI subunits, replacing PMDI ones, within the molecules improves the electrochemical cell performance of the batteries.

    View details for DOI 10.1021/jacs.6b02086

    View details for Web of Science ID 000375889100038

    View details for PubMedID 27070768

  • Supramolecular Gelation of Rigid Triangular Macrocycles through Rings of Multiple C-H center dot center dot center dot O Interactions Acting Cooperatively JOURNAL OF ORGANIC CHEMISTRY Liu, Z., Sun, J., Zhou, Y., Zhang, Y., Wu, Y., Nalluri, S., Wang, Y., Samanta, A., Mirkin, C. A., Schatz, G. C., Stoddart, J. 2016; 81 (6): 2581–88

    Abstract

    When equimolar solutions of the enantiomeric naphthalenediimide-based highly rigid triangles R-Δ and S-Δ in ClCH2CH2Cl are mixed, the racemate rac-Δ forms an organogel that is composed of interwoven fibers, resulting from the columnar stacking of the triangles in an alternating R-Δ/S-Δ fashion. Under identical conditions, the pure enantiomers do not form organogels. Density functional theory calculations reveal that the racemic RS dimer is more stable than the RR dimer as a result of the enantiomeric relationship between R-Δ and S-Δ, allowing them to act as two complementary rings comprised of 12 [C-H···O] interactions with an unprecedented and uninterrupted circular ADDAADDAADDA·DAADDAADDAAD alignment of hydrogen bond donors (D) and acceptors (A), in contrast with the square-wave manner in which the RR dimer forms a complementary yet interrupted ADADAD·DADADA circular sequence of six longer [C-H···O] hydrogen bonds. It follows that gelation is favored by weak interactions acting cooperatively in rings under precise stereoelectronic control.

    View details for DOI 10.1021/acs.joc.6b00281

    View details for Web of Science ID 000372664700036

    View details for PubMedID 26919158

  • Effects of Crystal Morphology on Singlet Exciton Fission in Diketopyrrolopyrrole Thin Films JOURNAL OF PHYSICAL CHEMISTRY B Hartnett, P. E., Margulies, E. A., Mauck, C. M., Miller, S. A., Wu, Y., Wu, Y., Marks, T. J., Wasielewski, M. R. 2016; 120 (7): 1357–66

    Abstract

    Singlet exciton fission (SF) is a promising strategy for increasing photovoltaic efficiency, but in order for SF to be useful in solar cells, it should take place in a chromophore that is air-stable, highly absorptive, solution processable, and inexpensive. Unlike many SF chromophores, diketopyrrolopyrrole (DPP) conforms to these criteria, and here we investigate SF in DPP for the first time. SF yields in thin films of DPP derivatives, which are widely used in organic electronics and photovoltaics, are shown to depend critically on crystal morphology. Time-resolved spectroscopy of three DPP derivatives with phenyl (3,6-diphenylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione, PhDPP), thienyl (3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione, TDPP), and phenylthienyl (3,6-di(5-phenylthiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione, PhTDPP) aromatic substituents in 100-200 nm thin films reveals that efficient SF occurs only in TDPP and PhTDPP (τSF = 220 ± 20 ps), despite the fact that SF is most exoergic in PhDPP. This result correlates well with the greater degree of π-overlap and closer π-stacking in TDPP (3.50 Å) and PhTDPP (3.59 Å) relative to PhDPP (3.90 Å) and demonstrates that SF in DPP is highly sensitive to the electronic coupling between adjacent chromophores. The triplet yield in PhTDPP films is determined to be 210 ± 35% by the singlet depletion method and 165 ± 30% by the energy transfer method, showing that SF is nearly quantitative in these films and that DPP derivatives are a promising class of SF chromophores for enhancing photovoltaic performance.

    View details for DOI 10.1021/acs.jpcb.5b10565

    View details for Web of Science ID 000371102800018

    View details for PubMedID 26820909

  • Oligorotaxane Radicals under Orders ACS CENTRAL SCIENCE Wang, Y., Frasconi, M., Liu, W., Sun, J., Wu, Y., Nassar, M. S., Botros, Y. Y., Goddard, W. A., Wasielewski, M. R., Stoddart, J. 2016; 2 (2): 89–98

    Abstract

    A strategy for creating foldameric oligorotaxanes composed of only positively charged components is reported. Threadlike components-namely oligoviologens-in which different numbers of 4,4'-bipyridinium (BIPY(2+)) subunits are linked by p-xylylene bridges, are shown to be capable of being threaded by cyclobis(paraquat-p-phenylene) (CBPQT(4+)) rings following the introduction of radical-pairing interactions under reducing conditions. UV/vis/NIR spectroscopic and electrochemical investigations suggest that the reduced oligopseudorotaxanes fold into highly ordered secondary structures as a result of the formation of BIPY(•+) radical cation pairs. Furthermore, by installing bulky stoppers at each end of the oligopseudorotaxanes by means of Cu-free alkyne-azide cycloadditions, their analogous oligorotaxanes, which retain the same stoichiometries as their progenitors, can be prepared. Solution-state studies of the oligorotaxanes indicate that their mechanically interlocked structures lead to the enforced interactions between the dumbbell and ring components, allowing them to fold (contract) in their reduced states and unfold (expand) in their fully oxidized states as a result of Coulombic repulsions. This electrochemically controlled reversible folding and unfolding process, during which the oligorotaxanes experience length contractions and expansions, is reminiscent of the mechanisms of actuation associated with muscle fibers.

    View details for DOI 10.1021/acscentsci.5b00377

    View details for Web of Science ID 000373182300008

    View details for PubMedID 27163033

    View details for PubMedCentralID PMC4827492

  • Photoinduced Charge and Energy Transfer within meta- and para-Linked Chlorophyll a-Perylene-3,4:9,10-bis(dicarboximide) Donor Acceptor Dyads JOURNAL OF PHYSICAL CHEMISTRY B Huang, G., Harris, M. A., Krzyaniak, M. D., Margulies, E. A., Dyar, S. M., Lindquist, R. J., Wu, Y., Roznyatovskiy, V. V., Wu, Y., Young, R. M., Wasielewski, M. R. 2016; 120 (4): 756–65

    Abstract

    Connecting electron donors and acceptors to a benzene ring in a meta or para relationship results in quantum interference effects that can strongly influence charge separation (CS) and charge recombination (CR) processes in these systems. We report on the energy and electron transfer behavior of chlorophyll-based para- and meta-linked donor-bridge-acceptor (D-B-A) dyads, where the semisynthetic chlorophyll a derivative, zinc methyl 3-ethyl-pyrochlorophyllide a (D), is covalently attached at its 20-position to the para position of one phenyl of diphenylacetylene (B). The meta or para position of the phenyl in B distal to the donor is in turn attached to perylene-3,4:9,10-bis(dicarboximide) (PDI) (A). Photoexcitation of the D-B-A dyads produces long-lived radical ion pairs D(•+)-B-A(•-), which recombine to the ground state and to both (3*)D-B-A and D-B-(3*)A. Time-resolved optical and electron paramagnetic resonance spectroscopies were used to monitor the charge transfer and triplet energy transfer (TEnT) processes. At longer times, TEnT occurs from (3*)D-B-A to D-B-(3*)A. Surprisingly, the D-B-A molecules linked via the meta linkage exhibit faster CS, CR, and TEnT rates than do those with the para linkage in contrast to most other meta/para-linked D-B-A molecules previously examined.

    View details for DOI 10.1021/acs.jpcb.5b10806

    View details for Web of Science ID 000369773100017

    View details for PubMedID 26731377

  • Ring-fusion as a perylenediimide dimer design concept for high-performance non-fullerene organic photovoltaic acceptors CHEMICAL SCIENCE Hartnett, P. E., Matte, H., Eastham, N. D., Jackson, N. E., Wu, Y., Chen, L. X., Ratner, M. A., Chang, R. H., Hersam, M. C., Wasielewski, M. R., Marks, T. J. 2016; 7 (6): 3543–55

    Abstract

    A series of perylenediimide (PDI) dimers are evaluated as acceptors for organic photovoltaic (OPV) cells. The materials are characterized using a wide variety of physical and computational techniques. These dimers are first linked at the bay position of each PDI molecule via an aromatic spacer; subsequent photocyclization affords ring-fused dimers. Thus, photocyclization of the thiophene-linked dimer 2,5-bis-[N,N'-bis-perylenediimide-1-yl]-thiophene (T1) affords the twisted acceptor [2,3-b:2',3'-d]-bis-[N,N'-bis-perylenediimide-1,12-yl]-thiophene (T2), while photocyclization of the thienothiophene-linked dimer, 2,5-bis-[N,N'-bis-perylenediimide-1-yl]-thienothiophene (TT1) affords the planar acceptor [2,3-b:2',3'-d]-bis-[N,N'-bis-perylenediimide-1,12-yl]-thienothiophene (TT2). Furthermore, a dimer linked by a phenylene group, 1,4-bis-[N,N'-bis-perylenediimide-1-yl]-benzene (Ph1), can be selectively photocyclized to form either the twisted dimer, [1,2:3,4]-bis-[N,N'-bis-perylenediimide-1,12-yl]-benzene (Ph1a) or the planar dimer [1,2:4,5]-bis-[N,N'-bis-perylenediimide-1,12-yl]-benzene (Ph2b). Ring-fusion results in increased electronic coupling between the PDI units, and increased space-charge limited thin film electron mobility. While charge transport is efficient in bulk-heterojunction blends of each dimer with the polymeric donor PBDTT-FTTE, in the case of the twisted dimers ring fusion leads to a significant decrease in geminate recombination, hence increased OPV photocurrent density and power conversion efficiency. This effect is not observed in planar dimers where ring fusion leads to increased crystallinity and excimer formation, decreased photocurrent density, and decreased power conversion efficiency. These results argue that ring fusion is an effective approach to increasing OPV bulk-heterojunction charge carrier generation efficiency in PDI dimers as long as they remain relatively amorphous, thereby suppressing excimer formation and coulombically trapped charge transfer states.

    View details for DOI 10.1039/c5sc04956c

    View details for Web of Science ID 000377262200008

    View details for PubMedID 29997846

    View details for PubMedCentralID PMC6007210

  • Energy and Electron Transfer Dynamics within a Series of Perylene Diimide/Cyclophane Systems JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Ryan, S. J., Young, R. M., Henkelis, J. J., Hafezi, N., Vermeulen, N. A., Hennig, A., Dale, E. J., Wu, Y., Krzyaniak, M. D., Fox, A., Nau, W. M., Wasielewski, M. R., Stoddart, J., Scherman, O. A. 2015; 137 (48): 15299–307

    Abstract

    Artificial photosynthetic systems for solar energy conversion exploit both covalent and supramolecular chemistry to produce favorable arrangements of light-harvesting and redox-active chromophores in space. An understanding of the interplay between key processes for photosynthesis, namely light-harvesting, energy transfer, and photoinduced charge separation and the design of novel, self-assembling components capable of these processes are imperative for the realization of multifunctional integrated systems. We report our investigations on the potential of extended tetracationic cyclophane/perylene diimide systems as components for artificial photosynthetic applications. We show how the selection of appropriate heterocycles, as extending units, allows for tuning of the electron accumulation and photophysical properties of the extended tetracationic cyclophanes. Spectroscopic techniques confirm energy transfer between the extended tetracationic cyclophanes and perylene diimide is ultrafast and quantitative, while the heterocycle specifically influences the energy transfer related parameters and the acceptor excited state.

    View details for DOI 10.1021/jacs.5b10329

    View details for Web of Science ID 000366339900032

    View details for PubMedID 26551041

  • An Electrochromic Instable Molecular Switch JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Sun, J., Wu, Y., Wang, Y., Liu, Z., Cheng, C., Hartlieb, K. J., Wasielewski, M. R., Stoddart, J. 2015; 137 (42): 13484–87

    Abstract

    A tristable [2]catenane, composed of a macrocyclic polyether incorporating 1,5-dioxynaphthalene (DNP) and tetrathiafulvalene (TTF) units along with a 4,4'-bipyridinium (BIPY(•+)) radical cation as three very different potential recognition sites, interlocked mechanically with the tetracationic cyclophane, cyclobis(paraquat-p-phenylene) (CBPQT(4+)), was synthesized by donor-acceptor templation, employing a "threading-followed-by-cyclization" approach. In this catenane, movement of the CBPQT(4+) ring in its different redox states among these three potential recognition sites, with corresponding color changes, is achieved by tuning external redox potentials. In the starting state, where no external potential is applied, the ring encircles the TTF unit and displays a green color. Upon oxidation of the TTF unit, the CBPQT(4+) ring moves to the DNP unit, producing a red color. Finally, if all the BIPY(2+) units are reduced to BIPY(•+) radical cations, the resulting CBPQT(2(•+)) diradical dication will migrate to the BIPY(•+) unit, resulting in a purple color. These readily switchable electrochromic properties render the [2]catenane attractive for use in electro-optical devices.

    View details for DOI 10.1021/jacs.5b09274

    View details for Web of Science ID 000363916600012

    View details for PubMedID 26439892

  • Ultrafast Photoinduced Symmetry-Breaking Charge Separation and Electron Sharing in Perylenediimide Molecular Triangles JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wu, Y., Young, R. M., Frasconi, M., Schneebeli, S. T., Spenst, P., Gardner, D. M., Brown, K. E., Wuerthner, F., Stoddart, J., Wasielewski, M. R. 2015; 137 (41): 13236–39

    Abstract

    We report on a visible-light-absorbing chiral molecular triangle composed of three covalently linked 1,6,7,12-tetra(phenoxy)perylene-3,4:9,10-bis(dicarboximide) (PDI) units. The rigid triangular architecture reduces the electronic coupling between the PDIs, so ultrafast symmetry-breaking charge separation is kinetically favored over intramolecular excimer formation, as revealed by femtosecond transient absorption spectroscopy. Photoexcitation of the PDI triangle dissolved in CH2Cl2 gives PDI(+•)-PDI(-•) in τCS = 12.0 ± 0.2 ps. Fast subsequent intramolecular electron/hole hopping can equilibrate the six possible energetically degenerate ion-pair states, as suggested by electron paramagnetic resonance/electron-nuclear double resonance spectroscopy, which shows that one-electron reduction of the PDI triangle results in complete electron sharing among the three PDIs. Charge recombination of PDI(+•)-PDI(-•) to the ground state occurs in τCR = 1.12 ± 0.01 ns with no evidence of triplet excited state formation.

    View details for DOI 10.1021/jacs.5b08386

    View details for Web of Science ID 000363438600007

    View details for PubMedID 26418462

  • Charge and Spin Transport in an Organic Molecular Square ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Wu, Y., Nalluri, S., Young, R. M., Krzyaniak, M. D., Margulies, E. A., Stoddart, J., Wasielewski, M. R. 2015; 54 (41): 11971–77

    Abstract

    Understanding electronic communication among multiple chromophoric and redox units requires construction of well-defined molecular architectures. Herein, we report the modular synthesis of a shape-persistent chiral organic square composed of four naphthalene-1,8:4,5-bis(dicarboximide) (NDI) sides and four trans-1,2-cyclohexanediamine corners. Single crystal X-ray diffraction reveals some distortion of the cyclohexane chair conformation in the solid state. Analysis of the packing of the molecular squares reveals the formation of highly ordered, one-dimensional tubular superstructures, held together by means of multiple [CH⋅⋅⋅OC] hydrogen-bonding interactions. Steady-state and time-resolved electronic spectroscopies show strong excited-state interactions in both the singlet and triplet manifolds. Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopies on the monoreduced state reveal electron sharing between all four NDI subunits comprising the molecular square.

    View details for DOI 10.1002/anie.201504576

    View details for Web of Science ID 000363396000012

    View details for PubMedID 26296239

  • Redox Control of the Binding Modes of an Organic Receptor JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Frasconi, M., Fernando, I. R., Wu, Y., Liu, Z., Liu, W., Dyar, S. M., Barin, G., Wasielewski, M. R., Goddard, W. A., Stoddart, J. 2015; 137 (34): 11057–68

    Abstract

    The modulation of noncovalent bonding interactions by redox processes is a central theme in the fundamental understanding of biological systems as well as being ripe for exploitation in supramolecular science. In the context of host-guest systems, we demonstrate in this article how the formation of inclusion complexes can be controlled by manipulating the redox potential of a cyclophane. The four-electron reduction of cyclobis(paraquat-p-phenylene) to its neutral form results in altering its binding properties while heralding a significant change in its stereoelectronic behavior. Quantum mechanics calculations provide the energetics for the formation of the inclusion complexes between the cyclophane in its various redox states with a variety of guest molecules, ranging from electron-poor to electron-rich. The electron-donating properties displayed by the cyclophane were investigated by probing the interaction of this host with electron-poor guests, and the formation of inclusion complexes was confirmed by single-crystal X-ray diffraction analysis. The dramatic change in the binding mode depending on the redox state of the cyclophane leads to (i) aromatic donor-acceptor interactions in its fully oxidized form and (ii) van der Waals interactions when the cyclophane is fully reduced. These findings lay the foundation for the potential use of this class of cyclophane in various arenas, all the way from molecular electronics to catalysis, by virtue of its electronic properties. The extension of the concept presented herein into the realm of mechanically interlocked molecules will lead to the investigation of novel structures with redox control being expressed over the relative geometries of their components.

    View details for DOI 10.1021/jacs.5b05618

    View details for Web of Science ID 000360867000037

    View details for PubMedID 26237091

  • Visible Light-Driven Artificial Molecular Switch Actuated by Radical-Radical and Donor-Acceptor Interactions JOURNAL OF PHYSICAL CHEMISTRY A Sun, J., Wu, Y., Liu, Z., Cao, D., Wang, Y., Cheng, C., Chen, D., Wasielewski, M. R., Stoddart, J. 2015; 119 (24): 6317–25

    Abstract

    We describe a visible light-driven switchable [2]catenane, composed of a Ru(bpy)3(2+) tethered cyclobis(paraquat-p-phenylene) (CBPQT(4+)) ring that is interlocked mechanically with a macrocyclic polyether consisting of electron-rich 1,5-dioxynaphthalene (DNP) and electron-deficient 4,4'-bipyridinium (BIPY(2+)) units. In the oxidized state, the CBPQT(4+) ring encircles the DNP recognition site as a consequence of favorable donor-acceptor interactions. In the presence of an excess of triethanolamine (TEOA), visible light irradiation reduces the BIPY(2+) units to BIPY((•+)) radical cations under the influence of the photosensitizer Ru(bpy)3(2+), resulting in the movement of the CBPQT(2(•+)) ring from the DNP to the BIPY((•+)) recognition site as a consequence of the formation of the more energetically favorable trisradical complex, BIPY((•+)) ⊂ CBPQT(2(•+)). Upon introducing O2 in the dark, the BIPY((•+)) radical cations are oxidized back to BIPY(2+) dications, leading to the reinstatement of the CBPQT(4+) ring encircled around the DNP recognition site. Employing this strategy of redox control, we have demonstrated a prototypical molecular switch that can be manipulated photochemically and chemically by sequential reduction and oxidation.

    View details for DOI 10.1021/acs.jpca.5b04570

    View details for Web of Science ID 000356753600019

    View details for PubMedID 25984816

  • Complexation of Polyoxometalates with Cyclodextrins JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wu, Y., Shi, R., Wu, Y., Holcroft, J. M., Liu, Z., Frasconi, M., Wasielewski, M. R., Li, H., Stoddart, J. 2015; 137 (12): 4111–18

    Abstract

    Although complexation of hydrophilic guests inside the cavities of hydrophobic hosts is considered to be unlikely, we demonstrate herein the complexation between γ- and β-cyclodextrins (γ- and β-CDs) with an archetypal polyoxometalate (POM)--namely, the [PMo12O40](3-) trianion--which has led to the formation of two organic-inorganic hybrid 2:1 complexes, namely [La(H2O)9]{[PMo12O40]⊂[γ-CD]2} (CD-POM-1) and [La(H2O)9] {[PMo12O40]⊂[β-CD]2} (CD-POM-2), in the solid state. The extent to which these complexes assemble in solution has been investigated by (i) (1)H, (13)C, and (31)P NMR spectroscopies and (ii) small- and wide-angle X-ray scattering, as well as (iii) mass spectrometry. Single-crystal X-ray diffraction reveals that both complexes have a sandwich-like structure, wherein one [PMo12O40](3-) trianion is encapsulated by the primary faces of two CD tori through intermolecular [C-H···O═Mo] interactions. X-ray crystal superstructures of CD-POM-1 and CD-POM-2 show also that both of these 2:1 complexes are lined up longitudinally in a one-dimensional columnar fashion by means of [O-H···O] interactions. A beneficial nanoconfinement-induced stabilizing effect is supported by the observation of slow color changes for these supermolecules in aqueous solution phase. Electrochemical studies show that the redox properties of [PMo12O40](3-) trianions encapsulated by CDs in the complexes are largely preserved in solution. The supramolecular complementarity between the CDs and the [PMo12O40](3-) trianion provides yet another opportunity for the functionalization of POMs under mild conditions by using host-guest chemistry.

    View details for DOI 10.1021/ja511713c

    View details for Web of Science ID 000352244800024

    View details for PubMedID 25757159

  • Thiophene-based dyes for probing membranes ORGANIC & BIOMOLECULAR CHEMISTRY Lopez-Duarte, I., Chairatana, P., Wu, Y., Perez-Moreno, J., Bennett, P. M., Reeve, J. E., Boczarow, I., Kaluza, W., Hosny, N. A., Stranks, S. D., Nicholas, R. J., Clays, K., Kuimova, M. K., Anderson, H. L. 2015; 13 (12): 3792–3802

    Abstract

    We report the synthesis of four new cationic dipolar push–pull dyes, together with an evaluation of their photophysical and photobiological characteristics pertinent to imaging membranes by fluorescence and second harmonic generation (SHG). All four dyes consist of an N,N-diethylaniline electron-donor conjugated to a pyridinium electron-acceptor via a thiophene bridge, with either vinylene (–CH=CH–) or ethynylene (–C≡C–) linking groups, and with either singly-charged or doubly-charged pyridinium terminals. The absorption and fluorescence behavior of these dyes were compared to a commercially available fluorescent membrane stain, the styryl dye FM4-64. The hyperpolarizabilities of all dyes were compared using hyper-Rayleigh scattering at 800 nm. Cellular uptake, localization, toxicity and phototoxicity were evaluated using tissue cell cultures (HeLa, SK-OV-3 and MDA-231). Replacing the central alkene bridge of FM4-64 with a thiophene does not substantially change the absorption, fluorescence or hyperpolarizability, whereas changing the vinylene-links to ethynylenes shifts the absorption and fluorescence to shorter wavelengths, and reduces the hyperpolarizability by about a factor of two. SHG and fluorescence imaging experiments in live cells showed that the doubly-charged thiophene dyes localize in plasma membranes, and exhibit lower internalization rates compared to FM4-64, resulting in less signal from the cell cytosol. At a typical imaging concentration of 1 μM, the doubly-charged dyes showed no significant light or dark toxicity, whereas the singly-charged dyes are phototoxic even at 0.5 μM. The doubly-charged dyes showed phototoxicity at concentrations greater than 10 μM, although they do not generate singlet oxygen, indicating that the phototoxicity is type I rather than type II. The doubly-charged thiophene dyes are more effective than FM4-64 as SHG dyes for live cells.

    View details for DOI 10.1039/c4ob02507e

    View details for Web of Science ID 000351352100033

    View details for PubMedID 25703541

  • Sugar and pH dual-responsive mesoporous silica nanocontainers based on competitive binding mechanisms NANOSCALE Yilmaz, M., Xue, M., Ambrogio, M. W., Buyukcakir, O., Wu, Y., Frasconi, M., Chen, X., Nassar, M. S., Stoddart, J., Zink, J. I. 2015; 7 (3): 1067–72

    Abstract

    A sugar and pH dual-responsive controlled release system, which is highly specific towards molecular stimuli, has been developed based on the binding between catechol and boronic acid on a platform of mesoporous silica nanoparticles (MSNs). By grafting phenylboronic acid stalks onto the silica surface, catechol-containing β-cyclodextrins can be attached to the orifices of the MSNs' nanopores through formation of boronate esters which block access to the nanopores. These esters are stable enough to prevent cargo molecules from escaping. The boronate esters disassociate in the presence of sugars, enabling the molecule-specific controlled-release feature of this hybrid system. The rate of release has been found to be tunable by varying both the structures and the concentrations of sugars, as a result of the competitive binding nature associated with the mechanism of its operation. Acidification also induces the release of cargo molecules. Further investigations show that the presence of both a low pH and sugar molecules provides cooperative effects which together control the rate of release.

    View details for DOI 10.1039/c4nr04796f

    View details for Web of Science ID 000347373500029

    View details for PubMedID 25475070

  • Assembly of Supramolecular Nanotubes from Molecular Triangles and 1,2-Dihalohydrocarbons JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Liu, Z., Liu, G., Wu, Y., Cao, D., Sun, J., Schneebeli, S. T., Nassar, M. S., Mirkin, C. A., Stoddart, J. 2014; 136 (47): 16651–60

    Abstract

    Precise control of molecular assembly is a challenging goal facing supramolecular chemists. Herein, we report the highly specific assembly of a range of supramolecular nanotubes from the enantiomeric triangular naphthalenediimide-based macrocycles (RRRRRR)- and (SSSSSS)-NDI-Δ and a class of similar solvents, namely, the 1,2-dihalo-ethanes and -ethenes (DXEs). Three kinds of supramolecular nanotubes are formed from the columnar stacking of NDI-Δ units with a 60° mutual rotation angle as a result of cooperative [C-H···O] interactions, directing interactions of the [X···X]-bonded DXE chains inside the nanotubes and lateral [X···π] or [π···π] interactions. They include (i) semiflexible infinite nanotubes formed in the gel state from NDI-Δ and (E)-1,2-dichloroethene, (ii) rigid infinite nonhelical nanotubes produced in the solid state from NDI-Δ and BrCH2CH2Br, ClCH2CH2Br, and ClCH2CH2I, and (iii) a pair of rigid tetrameric, enantiomeric single-handed (P)- and (M)-helical nanotubes formed in the solid state from the corresponding (RRRRRR)- and (SSSSSS)-NDI-Δ with ClCH2CH2Cl. In case (i), only the electron-rich C═C double bond of (E)-1,2-dichloroethene facilitates the gelation of NDI-Δ. In cases (ii) and (iii), the lengths of anti-DXEs determine the translation of the chirality of NDI-Δ into the helicity of nanotubes. Only ClCH2CH2Cl induces single-handed helicity into the nanotubes. The subtle interplay of noncovalent bonding interactions, resulting from the tiny structural variations involving the DXE guests, is responsible for the diverse and highly specific assembly of NDI-Δ. This research highlights the critical role that guests play in constructing assembled superstructures of hosts and offers a novel approach to creating supramolecular nanotubes.

    View details for DOI 10.1021/ja509480u

    View details for Web of Science ID 000345720500028

    View details for PubMedID 25357152

  • Electron Delocalization in a Rigid Cofacial Naphthalene-1,8:4,5-bis(dicarboximide) Dimer ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Wu, Y., Frasconi, M., Gardner, D. M., McGonigal, P. R., Schneebeli, S. T., Wasielewski, M. R., Stoddart, J. 2014; 53 (36): 9476–81

    Abstract

    Investigating through-space electronic communication between discrete cofacially oriented aromatic π-systems is fundamental to understanding assemblies as diverse as double-stranded DNA, organic photovoltaics and thin-film transistors. A detailed understanding of the electronic interactions involved rests on making the appropriate molecular compounds with rigid covalent scaffolds and π-π distances in the range of ca. 3.5 Å. Reported herein is an enantiomeric pair of doubly-bridged naphthalene-1,8:4,5-bis(dicarboximide) (NDI) cyclophanes and the characterization of four of their electronic states, namely 1) the ground state, 2) the exciton coupled singlet excited state, 3) the radical anion with strong through-space interactions between the redox-active NDI molecules, and 4) the diamagnetic diradical dianion using UV/Vis/NIR, EPR and ENDOR spectroscopies in addition to X-ray crystallography. Despite the unfavorable Coulombic repulsion, the singlet diradical dianion dimer of NDI shows a more pronounced intramolecular π-π stacking interaction when compared with its neutral analog.

    View details for DOI 10.1002/anie.201403816

    View details for Web of Science ID 000342677000009

    View details for PubMedID 25044761

  • Template-directed approach to large yet monodisperse multi-redox n-n stacked ladder structures Wu, Y., Avestro, A., Wasielewski, M., Stoddart, J. AMER CHEMICAL SOC. 2014
  • Mechanical Bonds and Topological Effects in Radical Dimer Stabilization JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Frasconi, M., Kikuchi, T., Cao, D., Wu, Y., Liu, W., Dyar, S. M., Barin, G., Sarjeant, A. A., Stern, C. L., Carmieli, R., Wang, C., Wasielewski, M. R., Goddard, W. A., Stoddart, J. 2014; 136 (31): 11011–26

    Abstract

    While mechanical bonding stabilizes tetrathiafulvalene (TTF) radical dimers, the question arises: what role does topology play in catenanes containing TTF units? Here, we report how topology, together with mechanical bonding, in isomeric [3]- and doubly interlocked [2]catenanes controls the formation of TTF radical dimers within their structural frameworks, including a ring-in-ring complex (formed between an organoplatinum square and a {2+2} macrocyclic polyether containing two 1,5-dioxynaphthalene (DNP) and two TTF units) that is topologically isomeric with the doubly interlocked [2]catenane. The separate TTF units in the two {1+1} macrocycles (each containing also one DNP unit) of the isomeric [3]catenane exhibit slightly different redox properties compared with those in the {2+2} macrocycle present in the [2]catenane, while comparison with its topological isomer reveals substantially different redox behavior. Although the stabilities of the mixed-valence (TTF2)(•+) dimers are similar in the two catenanes, the radical cationic (TTF(•+))2 dimer in the [2]catenane occurs only fleetingly compared with its prominent existence in the [3]catenane, while both dimers are absent altogether in the ring-in-ring complex. The electrochemical behavior of these three radically configurable isomers demonstrates that a fundamental relationship exists between topology and redox properties.

    View details for DOI 10.1021/ja504662a

    View details for Web of Science ID 000340079800037

    View details for PubMedID 25010890

  • Electron Sharing and Anion-pi Recognition in Molecular Triangular Prisms ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Schneebeli, S. T., Frasconi, M., Liu, Z., Wu, Y., Gardner, D. M., Strutt, N. L., Cheng, C., Carmieli, R., Wasielewski, M. R., Stoddart, J. 2013; 52 (49): 13100–13104

    Abstract

    Stacking on a full belly: Triangular molecular prisms display electron sharing among their triangularly arranged naphthalenediimide (NDI) redox centers. Their electron-deficient cavities encapsulate linear triiodide anions, leading to the formation of supramolecular helices in the solid state. Chirality transfer is observed from the six chiral centers of the filled prisms to the single-handed helices.

    View details for DOI 10.1002/anie.201307984

    View details for Web of Science ID 000327410300065

    View details for PubMedID 24227594

  • Assembly of rigid macrocycles into functional covalent nanotubes Schneebeli, S. T., Stoddart, F., Frasconi, M., Wu, Y., Cheng, C., Strutt, N. L., Holcroft, J., Vermeulen, N., Hartlieb, K. J. AMER CHEMICAL SOC. 2013
  • Light-induced release of a surface grafted ruthenium(II) complex from mesoporous silica nanoparticles Frasconi, M., Liu, Z., Lei, J., Wu, Y., Sauvage, J., Stoddart, F. J. AMER CHEMICAL SOC. 2013
  • Photoexpulsion of Surface-Grafted Ruthenium Complexes and Subsequent Release of Cytotoxic Cargos to Cancer Cells from Mesoporous Silica Nanoparticles JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Frasconi, M., Liu, Z., Lei, J., Wu, Y., Strekalova, E., Malin, D., Ambrogio, M. W., Chen, X., Botros, Y. Y., Cryns, V. L., Sauvage, J., Stoddart, J. 2013; 135 (31): 11603–13

    Abstract

    Ruthenium(II) polypyridyl complexes have emerged both as promising probes of DNA structure and as anticancer agents because of their unique photophysical and cytotoxic properties. A key consideration in the administration of those therapeutic agents is the optimization of their chemical reactivities to allow facile attack on the target sites, yet avoid unwanted side effects. Here, we present a drug delivery platform technology, obtained by grafting the surface of mesoporous silica nanoparticles (MSNPs) with ruthenium(II) dipyridophenazine (dppz) complexes. This hybrid nanomaterial displays enhanced luminescent properties relative to that of the ruthenium(II) dppz complex in a homogeneous phase. Since the coordination between the ruthenium(II) complex and a monodentate ligand linked covalently to the nanoparticles can be cleaved under irradiation with visible light, the ruthenium complex can be released from the surface of the nanoparticles by selective substitution of this ligand with a water molecule. Indeed, the modified MSNPs undergo rapid cellular uptake, and after activation with light, the release of an aqua ruthenium(II) complex is observed. We have delivered, in combination, the ruthenium(II) complex and paclitaxel, loaded in the mesoporous structure, to breast cancer cells. This hybrid material represents a promising candidate as one of the so-called theranostic agents that possess both diagnostic and therapeutic functions.

    View details for DOI 10.1021/ja405058y

    View details for Web of Science ID 000323019400040

    View details for PubMedID 23815127

    View details for PubMedCentralID PMC4086662

  • Mapping microbubble viscosity using fluorescence lifetime imaging of molecular rotors PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Hosny, N. A., Mohamedi, G., Rademeyer, P., Owen, J., Wu, Y., Tang, M., Eckersley, R. J., Stride, E., Kuimova, M. K. 2013; 110 (23): 9225–30

    Abstract

    Encapsulated microbubbles are well established as highly effective contrast agents for ultrasound imaging. There remain, however, some significant challenges to fully realize the potential of microbubbles in advanced applications such as perfusion mapping, targeted drug delivery, and gene therapy. A key requirement is accurate characterization of the viscoelastic surface properties of the microbubbles, but methods for independent, nondestructive quantification and mapping of these properties are currently lacking. We present here a strategy for performing these measurements that uses a small fluorophore termed a "molecular rotor" embedded in the microbubble surface, whose fluorescence lifetime is directly related to the viscosity of its surroundings. We apply fluorescence lifetime imaging to show that shell viscosities vary widely across the population of the microbubbles and are influenced by the shell composition and the manufacturing process. We also demonstrate that heterogeneous viscosity distributions exist within individual microbubble shells even with a single surfactant component.

    View details for DOI 10.1073/pnas.1301479110

    View details for Web of Science ID 000320503000022

    View details for PubMedID 23690599

    View details for PubMedCentralID PMC3677502

  • Molecular rheometry: direct determination of viscosity in L-o and L-d lipid phases via fluorescence lifetime imaging PHYSICAL CHEMISTRY CHEMICAL PHYSICS Wu, Y., Stefl, M., Olzynska, A., Hof, M., Yahioglu, G., Yip, P., Casey, D. R., Ces, O., Humpolickova, J., Kuimova, M. K. 2013; 15 (36): 14986–93

    Abstract

    Understanding of cellular regulatory pathways that involve lipid membranes requires the detailed knowledge of their physical state and structure. However, mapping the viscosity and diffusion in the membranes of complex composition is currently a non-trivial technical challenge. We report fluorescence lifetime spectroscopy and imaging (FLIM) of a meso-substituted BODIPY molecular rotor localised in the leaflet of model membranes of various lipid compositions. We prepare large and giant unilamellar vesicles (LUVs and GUVs) containing phosphatidylcholine (PC) lipids and demonstrate that recording the fluorescence lifetime of the rotor allows us to directly detect the viscosity of the membrane leaflet and to monitor the influence of cholesterol on membrane viscosity in binary and ternary lipid mixtures. In phase-separated 1,2-dioleoyl-sn-glycero-3-phosphocholine-cholesterol-sphingomyelin GUVs we visualise individual liquid ordered (Lo) and liquid disordered (Ld) domains using FLIM and assign specific microscopic viscosities to each domain. Our study showcases the power of FLIM with molecular rotors to image microviscosity of heterogeneous microenvironments in complex biological systems, including membrane-localised lipid rafts.

    View details for DOI 10.1039/c3cp51953h

    View details for Web of Science ID 000323520600019

    View details for PubMedID 23912893

  • A Cyclometallated Platinum Complex as a Selective Optical Switch for Quadruplex DNA CHEMISTRY-A EUROPEAN JOURNAL Suntharalingam, K., Leczkowska, A., Furrer, M. A., Wu, Y., Kuimova, M. K., Therrien, B., White, A. P., Vilar, R. 2012; 18 (51): 16277–82

    Abstract

    Hits the spot: A cyclometalled platinum(II) complex with a substituted phenanthroline ligand is reported. The complex has high in vitro affinity for quadruplex DNA and upon binding its emission is switched on. The complex can be easily delivered to the cell by using a metallo-cage as a carrier (see illustration). By means of confocal microscopy, it is shown that the complex is released inside the cell, penetrates the nucleus and localises in the nucleoli.

    View details for DOI 10.1002/chem.201202990

    View details for Web of Science ID 000312275200003

    View details for PubMedID 23165895

  • Closing the Ring to Bring Up the Light: Synthesis of a Hexacyclic Acridinium Cyanine Dye CHEMISTRY-A EUROPEAN JOURNAL Mahmood, T., Wu, Y., Loriot, D., Kuimova, M., Ladame, S. 2012; 18 (39): 12349–56

    Abstract

    The synthesis of a geometrically constrained and near-planar hexacyclic acridinium cyanine dye 9 is reported. When compared to its unlocked and non-fluorescent monomethine cyanine dye analogue 3, this photostable dye emits in the green area of the spectrum with a remarkable quantum yield close to unity in organic solvents and above 0.5 in water. A detailed steady-state and time-resolved spectroscopic study revealed that dye 9 forms emissive aggregates in water, which are responsible for a red-shifted and broadened emission band and longer emission lifetime, τ≈33 compared to 6.5-7.0 ns for the monomeric dye. Dye 9 also binds strongly to DNA (both duplex and quadruplex) in its monomeric form and is very efficiently taken up by cells, in which it accumulates primarily into the nucleus.

    View details for DOI 10.1002/chem.201200802

    View details for Web of Science ID 000308879000024

    View details for PubMedID 22907584

  • Photoinduced electron transfer in a clicked fullerene-porphyrin conjugate JOURNAL OF MATERIALS CHEMISTRY Iehl, J., Vartanian, M., Holler, M., Nierengarten, J., Delavaux-Nicot, B., Strub, J., Van Dorsselaer, A., Wu, Y., Mohanraj, J., Yoosaf, K., Armaroli, N. 2011; 21 (5): 1562–73

    View details for DOI 10.1039/c0jm02310h

    View details for Web of Science ID 000286332000035