Tracy Schloemer

All Publications

• Spatially Controlled Uv Light Generation at Depth Using Upconversion Micelles. Advanced materials (Deerfield Beach, Fla.) Zhou, Q., Wirtz, B. M., Schloemer, T. H., Burroughs, M. C., Hu, M., Narayanan, P., Lyu, J., Gallegos, A. O., Layton, C., Mai, D. J., Congreve, D. N. 2023: e2301563

  Abstract

  Ultraviolet (UV) light can trigger a plethora of useful photochemical reactions for diverse applications, including photocatalysis, photopolymerization, and drug delivery. These applications typically require penetration of high energy photons deep into materials, yet delivering these photons beyond the surface is extremely challenging due to absorption and scattering effects. Triplet-triplet annihilation upconversion (TTA-UC) shows great promise to circumvent this issue by generating high energy photons from incident lower energy photons. However, molecules that facilitate TTA-UC usually have poor water solubility, limiting their deployment in aqueous environments. To address this challenge, a nanoencapsulation method is leveraged to fabricate water-compatible UC micelles, enabling on-demand UV photon generation deep into materials. Two iridium-based complexes are presented for use as TTA-UC sensitizers with increased solubilities that facilitate the formation of highly emissive UV-upconverting micelles. Furthermore, this encapsulation method is shown to be generalizable to nineteen UV-emitting UC systems, accessing a range of upconverted UV emission profiles with wavelengths as low as 350 nm. As a proof-of-principle demonstration of precision photochemistry at depth, UV-emitting UC micelles are used to photolyze a fluorophore at a focal point nearly a centimeter beyond the surface, revealing opportunities for spatially controlled manipulation deep into UV-responsive materials. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/adma.202301563

  View details for PubMedID 37548335

• Water additives improve the efficiency of violet perovskite light-emitting diodes MATTER Hu, M., Fernandez, S., Zhou, Q., Narayanan, P., Saini, B., Schloemer, T. H., Lyu, J., Gallegos, A. O., Ahmed, G. H., Congreve, D. N. 2023; 6 (7): 2356-2367

  View details for DOI 10.1016/j.matt.2023.05.018

  View details for Web of Science ID 001058067600001

• Gelation Dynamics during Photo-Cross-Linking of Polymer Nanocomposite Hydrogels. ACS polymers Au Burroughs, M. C., Schloemer, T. H., Congreve, D. N., Mai, D. J. 2023; 3 (2): 217-227

  Abstract

  Embedding nanomaterials into polymer hydrogels enables the design of functional materials with tailored chemical, mechanical, and optical properties. Nanocapsules that protect interior cargo and disperse readily through a polymeric matrix have drawn particular interest for their ability to integrate chemically incompatible systems and to further expand the parameter space for polymer nanocomposite hydrogels. The properties of polymer nanocomposite hydrogels depend on the material composition and processing route, which were explored systematically in this work. The gelation kinetics of network-forming polymer solutions with and without silica-coated nanocapsules bearing polyethylene glycol (PEG) surface ligands were investigated using in situ dynamic rheology measurements. Network-forming polymers comprised either 4-arm or 8-arm star PEG with terminal anthracene groups, which dimerize upon irradiation with ultraviolet (UV) light. The PEG-anthracene solutions exhibited rapid gel formation upon UV exposure (365 nm); gel formation was observed as a crossover from liquid-like to solid-like behavior during in situ small-amplitude oscillatory shear rheology. This crossover time was non-monotonic with polymer concentration. Far below the overlap concentration (c/c* ≪ 1), spatially separated PEG-anthracene molecules were subject to forming intramolecular loops over intermolecular cross-links, thereby slowing the gelation process. Near the polymer overlap concentration (c/c* ∼ 1), rapid gelation was attributed to the ideal proximity of anthracene end groups from neighboring polymer molecules. Above the overlap concentration (c/c* > 1), increased solution viscosities hindered molecular diffusion, thereby reducing the frequency of dimerization reactions. Adding nanocapsules to PEG-anthracene solutions resulted in faster gelation than nanocapsule-free PEG-anthracene solutions with equivalent effective polymer concentrations. The final elastic modulus of nanocomposite hydrogels increased with nanocapsule volume fraction, signifying synergistic mechanical reinforcement by nanocapsules despite not being cross-linked into the polymer network. Overall, these findings quantify the impact of nanocapsule addition on the gelation kinetics and mechanical properties of polymer nanocomposite hydrogels, which are promising materials for applications in optoelectronics, biotechnology, and additive manufacturing.

  View details for DOI 10.1021/acspolymersau.2c00051

  View details for PubMedID 37065714

  View details for PubMedCentralID PMC10103194

• Controlling the durability and optical properties of triplet-triplet annihilation upconversion nanocapsules. Nanoscale Schloemer, T. H., Sanders, S. N., Narayanan, P., Zhou, Q., Hu, M., Congreve, D. N. 2023

  Abstract

  Deep penetration of high energy photons by direct irradiation is often not feasible due to absorption and scattering losses, which are generally exacerbated as photon energy increases. Precise generation of high energy photons beneath a surface can circumvent these losses and significantly transform optically controlled processes like photocatalysis or 3D printing. Using triplet-triplet annihilation upconversion (TTA-UC), a nonlinear process, we can locally convert two transmissive low energy photons into one high energy photon. We recently demonstrated the use of nanocapsules for high energy photon generation at depth, with durability within a variety of chemical environments due to the formation of a dense, protective silica shell that prevents content leakage and nanocapsule aggregation. Here, we show the importance of the feed concentrations of the tetraethylorthosilicate (TEOS) monomer and the methoxy poly(ethyleneglycol) silane (PEG-silane) ligand used to synthesize these nanocapsules using spectroscopic and microscopy characterizations. At optimal TEOS and PEG-silane concentrations, minimal nanocapsule leakage can be obtained which maximizes UC photoluminescence. We also spectroscopically study the origin of inefficient upconversion from UCNCs made using sub-optimal conditions to probe how TEOS and PEG-silane concentrations impact the equilibrium between productive shell growth and side product formation, like amorphous silica. Furthermore, this optimized fabrication protocol can be applied to encapsulate multiple TTA-UC systems and other emissive dyes to generate anti-Stokes or Stokes shifted emission, respectively. These results show that simple synthetic controls can be tuned to obtain robust, well-dispersed, bright upconverting nanoparticles for subsequent integration in optically controlled technologies.

  View details for DOI 10.1039/d3nr00067b

  View details for PubMedID 37000152

• Nanoengineering Triplet-Triplet Annihilation Upconversion: From Materials to Real-World Applications. ACS nano Schloemer, T., Narayanan, P., Zhou, Q., Belliveau, E., Seitz, M., Congreve, D. N. 2023

  Abstract

  Using light to control matter has captured the imagination of scientists for generations, as there is an abundance of photons at our disposal. Yet delivering photons beyond the surface to many photoresponsive systems has proven challenging, particularly at scale, due to light attenuation via absorption and scattering losses. Triplet-triplet annihilation upconversion (TTA-UC), a process which allows for low energy photons to be converted to high energy photons, is poised to overcome these challenges by allowing for precise spatial generation of high energy photons due to its nonlinear nature. With a wide range of sensitizer and annihilator motifs available for TTA-UC, many researchers seek to integrate these materials in solution or solid-state applications. In this Review, we discuss nanoengineering deployment strategies and highlight their uses in recent state-of-the-art examples of TTA-UC integrated in both solution and solid-state applications. Considering both implementation tactics and application-specific requirements, we identify critical needs to push TTA-UC-based applications from an academic curiosity to a scalable technology.

  View details for DOI 10.1021/acsnano.3c00543

  View details for PubMedID 36800310

• Gelation Dynamics during Photo-Cross-Linking of Polymer Nanocomposite Hydrogels ACS POLYMERS AU Burroughs, M. C., Schloemer, T. H., Congreve, D. N., Mai, D. J. 2022

  View details for DOI 10.1021/acspolymersau.2c00051

  View details for Web of Science ID 000891894900001

• Triplet Fusion Upconversion Nanocapsule Synthesis. Journal of visualized experiments : JoVE Schloemer, T. H., Sanders, S. N., Zhou, Q., Narayanan, P., Hu, M., Gangishetty, M. K., Anderson, D., Seitz, M., Gallegos, A. O., Stokes, R. C., Congreve, D. N. 2022

  Abstract

  Triplet fusion upconversion (UC) allows for the generation of one high energy photon from two low energy input photons. This well-studied process has significant implications for producing high energy light beyond a material's surface. However, the deployment of UC materials has been stymied due to poor material solubility, high concentration requirements, and oxygen sensitivity, ultimately resulting in reduced light output. Toward this end, nanoencapsulation has been a popular motif to circumvent these challenges, but durability has remained elusive in organic solvents. Recently, a nanoencapsulation technique was engineered to tackle each of these challenges, whereupon an oleic acid nanodroplet containing upconversion materials was encapsulated with a silica shell. Ultimately, these nanocapsules (NCs) were durable enough to enable triplet fusion upconversion-facilitated volumetric three-dimensional (3D) printing. By encapsulating upconversion materials with silica and dispersing them in a 3D printing resin, photopatterning beyond the surface of the printing vat was made possible. Here, video protocols for the synthesis of upconversion NCs are presented for both small-scale and large-scale batches. The outlined protocols serve as a starting point for adapting this encapsulation scheme to multiple upconversion schemes for use in volumetric 3D printing applications.

  View details for DOI 10.3791/64374

  View details for PubMedID 36155426

• Triplet fusion upconversion nanocapsules for volumetric 3D printing. Nature Sanders, S. N., Schloemer, T. H., Gangishetty, M. K., Anderson, D., Seitz, M., Gallegos, A. O., Stokes, R. C., Congreve, D. N. 2022; 604 (7906): 474-478

  Abstract

  Three-dimensional (3D) printing has exploded in interest as new technologies have opened up a multitude of applications1-6, with stereolithography a particularly successful approach4,7-9. However, owing to the linear absorption of light, this technique requires photopolymerization to occur at the surface of the printing volume, imparting fundamental limitations on resin choice and shape gamut. One promising way to circumvent this interfacial paradigm is to move beyond linear processes, with many groups using two-photon absorption to print in a truly volumetric fashion3,7-9. Using two-photon absorption, many groups and companies have been able to create remarkable nanoscale structures4,5, but the laser powerrequired to drive this process has limited print size and speed, preventing widespread application beyond the nanoscale. Here we use triplet fusion upconversion10-13 to print volumetrically with less than 4milliwatt continuous-wave excitation. Upconversion is introduced to the resin by means of encapsulation with a silica shell and solubilizing ligands. We further introduce an excitonic strategy to systematically control the upconversion threshold to support either monovoxel or parallelized printing schemes, printing at power densities several orders of magnitude lower than the power densities required for two-photon-based 3D printing.

  View details for DOI 10.1038/s41586-022-04485-8

  View details for PubMedID 35444324

• Managing big data NATURE ENERGY Schloemer, T. H. 2022

  View details for DOI 10.1038/s41560-021-00972-w

  View details for Web of Science ID 000746760500001

• Reflections on hosting summer undergraduate researchers in the midst of a pandemic. Matter Gallegos, A. O., Ahmed, G. H., Schloemer, T. H., Congreve, D. N. 2021; 4 (10): 3074-3077

  Abstract

  The COVID-19 pandemic continues to impact nearly every aspect of our lives, including academic research. In this Matter of Opinion, we reflect on hosting both in-person and virtual undergraduate students during these challenging times.

  View details for DOI 10.1016/j.matt.2021.09.013

  View details for PubMedID 34632371

• The Molybdenum Oxide Interface Limits the High-Temperature Operational Stability of Unencapsulated Perovskite Solar Cells ACS ENERGY LETTERS Schloemer, T. H., Raiford, J. A., Gehan, T. S., Moot, T., Nanayakkara, S., Harvey, S. P., Bramante, R. C., Dunfield, S., Louks, A. E., Maughan, A. E., Bliss, L., McGehee, M. D., van Hest, M. M., Reese, M. O., Bent, S. F., Berry, J. J., Luther, J. M., Sellinger, A. 2020; 5 (7): 2349–60

  View details for DOI 10.1021/acsenergylett.0c01023

  View details for Web of Science ID 000552668000030

• CsI-Antisolvent Adduct Formation in All-Inorganic Metal Halide Perovskites ADVANCED ENERGY MATERIALS Moot, T., Marshall, A. R., Wheeler, L. M., Habisreutinger, S. N., Schloemer, T. H., Boyd, C. C., Dikova, D. R., Pach, G. F., Hazarika, A., McGehee, M. D., Snaith, H. J., Luther, J. M. 2020

  View details for DOI 10.1002/aenm.201903365

  View details for Web of Science ID 000510251700001

• Doping strategies for small molecule organic hole-transport materials: impacts on perovskite solar cell performance and stability. Chemical science Schloemer, T. H., Christians, J. A., Luther, J. M., Sellinger, A. 2019; 10 (7): 1904-1935

  Abstract

  Hybrid organic/inorganic perovskite solar cells (PSCs) have dramatically changed the landscape of the solar research community over the past decade, but >25 year stability is likely required if they are to make the same impact in commercial photovoltaics and power generation more broadly. While every layer of a PSC has been shown to impact its durability in power output, the hole-transport layer (HTL) is critical for several reasons: (1) it is in direct contact with the perovskite layer, (2) it often contains mobile ions, like Li+ - which in this case are hygroscopic, and (3) it usually has the lowest thermal stability of all layers in the stack. Therefore, HTL engineering is one method with a high return on investment for PSC stability and lifetime. Research has progressed in understanding design rules for small organic molecule hole-transport materials, yet, when implemented into devices, the same dopants, bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) and tris(2-(1H-pyrazol-1-yl)-4-tert-butylpyridine)cobalt(iii) tri[bis(trifluoromethane)sulfonimide] (FK209), are nearly always required for improved charge-transport properties (e.g., increased hole mobility and conductivity). The dopants are notable because they too have been shown to negatively impact PSC stability and lifetime. In response, new research has targeted alternative dopants to bypass these negative effects and provide greater functionality. In this review, we focus on dopant fundamentals, alternative doping strategies for organic small molecule HTL in PSC, and imminent research needs with regard to dopant development for the realization of reliable, long-lasting electricity generation via PSCs.

  View details for DOI 10.1039/c8sc05284k

  View details for PubMedID 30881622

  View details for PubMedCentralID PMC6390699