Bio

Reaching out to Stanford’s diverse body of students and beyond to share the excitement of scientific discovery has been a growing passion for Dr. Jennifer Schwartz Poehlmann. In addition to coordinating and co-teaching Stanford’s freshmen chemistry sequence, she takes a leadership role in developing training programs for teaching assistants and enhancing classroom and lab experiences for undergraduates, while also providing STEM learning opportunities for incoming freshmen and local high school students.

Jennifer Schwartz Poehlmann studied chemistry at Washington University in Saint Louis Missouri (A.B. 2002) before coming to Stanford University as a graduate student (Ph.D. 2008). Her thesis work under Prof. Edward Solomon addressed structural contributions to reactivity in active sites of non-heme di-iron enzymes, including ferritins. She joined the Stanford Center (now Vice Provost) for Teaching and Learning as a Teaching Fellow in 2008. In 2009, she became Lecturer and Introductory Course Coordinator for the Department of Chemistry, and in 2011 was promoted to Senior Lecturer. She has received multiple awards for her teaching and training work, including the Walter J. Gores Award for Excellence in Teaching, Dean’s Award for Achievements in Teaching, Hoagland Award Fund for Innovations in Undergraduate Teaching, and Society of Latino Engineers and School of Engineering’s Professor of the Year Award.

Teaching
Dr. Schwartz coordinates and co-teaches the introductory course sequence of Chem31A, 31B, and 33 for about 450 students each year. She has also created a set of companion courses (Chem31A-C, 31B-C, and 33-C) designed to provide motivated students an opportunity to build stronger study habits and problem solving tools that help them persevere in the sciences regardless of prior science background. In parallel, she has been involved in the creation and teaching of the Leland Scholars Program, which facilitates the transition to college for incoming freshman intending to study in STEM or pre-health fields.

Instructor Training
Dr. Schwartz has always believed that well-prepared and enthusiastic teachers inspire and motivate learning, yet excellent teaching requires training, feedback, reflection and support. She has worked both within the department and more broadly to help ensure that teaching assistants throughout the university receive the training, practice and mentorship they need to grow and excel as educators. She previously directed the Department of Chemistry’s TA Training program and, with the Vice Provost for Teaching and Learning, co-founded and directs the Mentors in Teaching Program, MinT, which provides training and resources to teaching mentors from more than 15 departments on campus. Through MinT, advanced graduate students learn effective ways to mentor TAs, through mid-quarter feedback, classroom observation, establishment of teaching goals, and workshops that enable new TAs to better engage with students in the classroom.

Enhanced Learning Experiences
Dr. Schwartz has been heavily involved in the development of hands-on, guided-inquiry lab activities that are now fully integrated into lab/lecture courses throughout the introductory general and organic chemistry sequence. Through the “Inspiring Future Scientists in Chemistry” Outreach Program, she is also helping to bring the excitement of exploring real-world chemistry into local high schools. She works with local high school teachers to design lab experiences that reinforce and compliment the chemistry concepts in the California State curriculum. Stanford Chemistry students take these activities to local high schools, providing hundreds of students the opportunity to work with enthusiastic young scientists while getting hands-on experience in chemistry. The program aims to demonstrate how chemistry relates to the ‘real world’ and to promote an appreciation for both science and higher education.

Academic Appointments

Administrative Appointments

  • Senior Lecturer & Introductory Course Coordinator, Stanford University (2011 - Present)
  • Lecturer & Introductory Course Coordinator, Stanford University (2009 - 2011)
  • Teaching Fellow, Center for Teaching and Learning, Stanford University (2008 - Present)
  • Consultant, Center for Teaching and Learning, Stanford University (2005 - 2008)
  • Senior Development and Documentation Teaching Assistant, Stanford University (2004 - 2007)
  • Graduate Research Assistant, Stanford University (2003 - 2008)
  • Lab Safety Officer, Stanford University (2003 - 2008)
  • Outreach TA, Stanford University (2003 - 2005)
  • Research Assistant, Washington University in St. Louis (2001 - 2002)
  • Summer School Administrator, Elmbrook School District (2000 - 2001)
  • Board Member, Education for Employment Council Board, Elmbrook District (1998 - 1999)

Honors & Awards

  • Professor of the Year, Society of Latino Engineers (SOLE) and the School of Engineering (2014)
  • H&S Dean’s Award for Achievements in Teaching, Stanford University (2012)
  • Hoagland Award Fund for Innovations in Undergraduate Teaching, Stanford University (2011-2013)
  • Dr. St. Clair Drake Teaching Award, Stanford University (2011)
  • Honored as one of the “Heroes Among Us”, Blue Oak Elementary School (2010)
  • Walter J. Gores Award for Excellence in Teaching, Stanford University (2008)
  • Linus Pauling Teaching Award, Stanford University, Department of Chemistry (2007)
  • Centennial Teaching Award for excellence in teaching, Stanford University (2004)
  • Honor, Phi Beta Kappa (2002)

Boards, Advisory Committees, Professional Organizations

  • Operations Committee for The Science Teaching and Learning Center, Stanford School of Humanities and Sciences (2013 - Present)
  • Curriculum Committee, Stanford Chemistry Department (2012 - Present)
  • Leland Scholars Program Advisory Board Member, Stanford Vice Provost for Undergraduate Education (2012 - Present)
  • Old Chemistry Design team, Stanford School of Humanities and Sciences (2012 - Present)
  • Undergraduate Studies Committee, Stanford Chemistry Department (2010 - 2012)
  • Director of IFS, Inspiring Future Scientists in Chemistry (2009 - Present)
  • Admissions Interviewer, Alumni & Parents Admission Program for Washington University in St. Louis (2006 - 2007)
  • Member, American Chemical Society (2002 - Present)
  • Member, Alpha Chi Sigma (2001 - Present)
  • Vice President, Women in Science (2001 - 2002)
  • Secretary, Women in Science (2000 - 2001)
  • VP, Membership, Alpha Phi Omega (2000 - 2001)
  • Member, Alpha Phi Omega (1999 - Present)
  • VP, Service, Alpha Phi Omega (1999 - 2002)
  • Violist, Washington University Quartet (1999 - 2002)
  • Violist, Washington University Chamber and Symphony Orchestra (1999 - 2002)
  • VP, Fellowship, Alpha Phi Omega (1999 - 1999)
  • Member, National Forensics League (1997 - 1999)

Professional Education

  • PhD, Stanford University, Inorganic Chemistry (2008)
  • BA, Washington University, Chemistry (2002)

Contact

  • Academic
    jks425@stanford.edu
    University - Academic staff Department: Chemistry Position: Sr Lecturer
    • 333 Campus Drive
    • Mudd Building
    • Stanford,  California  94305 

Additional Info

  • Mail Code: 5080
  • Other Names:
    Jennifer Kathleen Schwartz

Links

2024-25 Courses

All Publications

  • CD/MCD/VTVH-MCD Studies of Escherichia coli Bacterioferritin Support a Binuclear Iron Cofactor Site BIOCHEMISTRY Kwak, Y., Schwartz, J. K., Huang, V. W., Boice, E., Kurtz, D. M., Solomon, E. I. 2015; 54 (47): 7010-7018

    Abstract

    Ferritins and bacterioferritins (Bfrs) utilize a binuclear non-heme iron binding site to catalyze oxidation of Fe(II), leading to formation of an iron mineral core within a protein shell. Unlike ferritins, in which the diiron site binds Fe(II) as a substrate, which then autoxidizes and migrates to the mineral core, the diiron site in Bfr has a 2-His/4-carboxylate ligand set that is commonly found in diiron cofactor enzymes. Bfrs could, therefore, utilize the diiron site as a cofactor rather than for substrate iron binding. In this study, we applied circular dichroism (CD), magnetic CD (MCD), and variable-temperature, variable-field MCD (VTVH-MCD) spectroscopies to define the geometric and electronic structures of the biferrous active site in Escherichia coli Bfr. For these studies, we used an engineered M52L variant, which is known to eliminate binding of a heme cofactor but to have very minor effects on either iron oxidation or mineral core formation. We also examined an H46A/D50A/M52L Bfr variant, which additionally disrupts a previously observed mononuclear non-heme iron binding site inside the protein shell. The spectral analyses define a binuclear and an additional mononuclear ferrous site. The biferrous site shows two different five-coordinate centers. After O2 oxidation and re-reduction, only the mononuclear ferrous signal is eliminated. The retention of the biferrous but not the mononuclear ferrous site upon O2 cycling supports a mechanism in which the binuclear site acts as a cofactor for the O2 reaction, while the mononuclear site binds the substrate Fe(II) that, after its oxidation to Fe(III), migrates to the mineral core.

    View details for DOI 10.1021/acs.biochem.5b01033

    View details for Web of Science ID 000365930700005

    View details for PubMedID 26551523

  • Spectroscopic Studies of Single and Double Variants of M Ferritin: Lack of Conversion of a Biferrous Substrate Site into a Cofactor Site for O-2 Activation BIOCHEMISTRY Kwak, Y., Schwartz, J. K., Haldar, S., Behera, R. K., Tosha, T., Theil, E. C., Solomon, E. I. 2014; 53 (3): 473-482

    Abstract

    Ferritin has a binuclear non-heme iron active site that functions to oxidize iron as a substrate for formation of an iron mineral core. Other enzymes of this class have tightly bound diiron cofactor sites that activate O2 to react with substrate. Ferritin has an active site ligand set with 1-His/4-carboxylate/1-Gln rather than the 2-His/4-carboxylate set of the cofactor site. This ligand variation has been thought to make a major contribution to this biferrous substrate rather than cofactor site reactivity. However, the Q137E/D140H double variant of M ferritin, has a ligand set that is equivalent to most of the diiron cofactor sites, yet did not rapidly react with O2 or generate the peroxy intermediate observed in the cofactor sites. Therefore, in this study, a combined spectroscopic methodology of circular dichroism (CD)/magnetic CD (MCD)/variable temperature, variable field (VTVH) MCD has been applied to evaluate the factors required for the rapid O2 activation observed in cofactor sites. This methodology defines the coordination environment of each iron and the bridging ligation of the biferrous active sites in the double and corresponding single variants of frog M ferritin. Based on spectral changes, the D140H single variant has the new His ligand binding, and the Q137E variant has the new carboxylate forming a μ-1,3 bridge. The spectra for the Q137E/D140H double variant, which has the cofactor ligand set, however, reflects a site that is more coordinately saturated than the cofactor sites in other enzymes including ribonucleotide reductase, indicating the presence of additional water ligation. Correlation of this double variant and the cofactor sites to their O2 reactivities indicates that electrostatic and steric changes in the active site and, in particular, the hydrophobic nature of a cofactor site associated with its second sphere protein environment, make important contributions to the activation of O2 by the binuclear non-heme iron enzymes.

    View details for DOI 10.1021/bi4013726

    View details for Web of Science ID 000330543100004

    View details for PubMedID 24397299

    View details for PubMedCentralID PMC3985457

  • Structural and Spectroscopic Properties of the Peroxodiferric Intermediate of Ricinus communis Soluble Delta(9) Desaturase INORGANIC CHEMISTRY Srnec, M., Rokob, T. A., Schwartz, J. K., Kwak, Y., Rulisek, L., Solomon, E. I. 2012; 51 (5): 2806-2820

    Abstract

    Large-scale quantum and molecular mechanical methods (QM/MM) and QM calculations were carried out on the soluble Δ(9) desaturase (Δ(9)D) to investigate various structural models of the spectroscopically defined peroxodiferric (P) intermediate. This allowed us to formulate a consistent mechanistic picture for the initial stages of the reaction mechanism of Δ(9)D, an important diferrous nonheme iron enzyme that cleaves the C-H bonds in alkane chains resulting in the highly specific insertion of double bonds. The methods (density functional theory (DFT), time-dependent DFT (TD-DFT), QM(DFT)/MM, and TD-DFT with electrostatic embedding) were benchmarked by demonstrating that the known spectroscopic effects and structural perturbation caused by substrate binding to diferrous Δ(9)D can be qualitatively reproduced. We show that structural models whose spectroscopic (absorption, circular dichroism (CD), vibrational and Mössbauer) characteristics correlate best with experimental data for the P intermediate correspond to the μ-1,2-O(2)(2-) binding mode. Coordination of Glu196 to one of the iron centers (Fe(B)) is demonstrated to be flexible, with the monodentate binding providing better agreement with spectroscopic data, and the bidentate structure being slightly favored energetically (1-10 kJ mol(-1)). Further possible structures, containing an additional proton or water molecule are also evaluated in connection with the possible activation of the P intermediate. Specifically, we suggest that protonation of the peroxide moiety, possibly preceded by water binding in the Fe(A) coordination sphere, could be responsible for the conversion of the P intermediate in Δ(9)D into a form capable of hydrogen abstraction. Finally, results are compared with recent findings on the related ribonucleotide reductase and toluene/methane monooxygenase enzymes.

    View details for DOI 10.1021/ic2018067

    View details for Web of Science ID 000301007100014

    View details for PubMedID 22332845

  • Developing Graduate Student Teaching Consultants and Mentors at Stanford: The TA Consultant (TAC) and Mentors in Teaching (MinT) Programs Practically speaking: A sourcebook for instructional consultants in higher education Dunbar, R. W., Schwartz, J. K., Marincovich, M. Stillwater, OK: New Forums Press.. 2012
  • Hybrid Genetic Algorithm with an Adaptive Penalty Function for Fitting Multimodal Experimental Data: Application to Exchange-Coupled Non-Kramers Binuclear Iron Active Sites JOURNAL OF CHEMICAL INFORMATION AND MODELING Beaser, E., Schwartz, J. K., Bell, C. B., Solomon, E. I. 2011; 51 (9): 2164-2173

    Abstract

    A Genetic Algorithm (GA) is a stochastic optimization technique based on the mechanisms of biological evolution. These algorithms have been successfully applied in many fields to solve a variety of complex nonlinear problems. While they have been used with some success in chemical problems such as fitting spectroscopic and kinetic data, many have avoided their use due to the unconstrained nature of the fitting process. In engineering, this problem is now being addressed through incorporation of adaptive penalty functions, but their transfer to other fields has been slow. This study updates the Nanakorrn Adaptive Penalty function theory, expanding its validity beyond maximization problems to minimization as well. The expanded theory, using a hybrid genetic algorithm with an adaptive penalty function, was applied to analyze variable temperature variable field magnetic circular dichroism (VTVH MCD) spectroscopic data collected on exchange coupled Fe(II)Fe(II) enzyme active sites. The data obtained are described by a complex nonlinear multimodal solution space with at least 6 to 13 interdependent variables and are costly to search efficiently. The use of the hybrid GA is shown to improve the probability of detecting the global optimum. It also provides large gains in computational and user efficiency. This method allows a full search of a multimodal solution space, greatly improving the quality and confidence in the final solution obtained, and can be applied to other complex systems such as fitting of other spectroscopic or kinetics data.

    View details for DOI 10.1021/ci2001296

    View details for Web of Science ID 000295114700016

    View details for PubMedID 21819138

  • CD and MCD Spectroscopic Studies of the Two Dps Miniferritin Proteins from Bacillus anthracis: Role of O-2 and H2O2 Substrates in Reactivity of the Diiron Catalytic Centers BIOCHEMISTRY Schwartz, J. K., Liu, X. S., Tosha, T., Diebold, A., Theil, E. C., Solomon, E. I. 2010; 49 (49): 10516-10525

    Abstract

    DNA protection during starvation (Dps) proteins are miniferritins found in bacteria and archaea that provide protection from uncontrolled Fe(II)/O radical chemistry; thus the catalytic sites are targets for antibiotics against pathogens, such as anthrax. Ferritin protein cages synthesize ferric oxymineral from Fe(II) and O(2)/H(2)O(2), which accumulates in the large central cavity; for Dps, H(2)O(2) is the more common Fe(II) oxidant contrasting with eukaryotic maxiferritins that often prefer dioxygen. To better understand the differences in the catalytic sites of maxi- versus miniferritins, we used a combination of NIR circular dichroism (CD), magnetic circular dichroism (MCD), and variable-temperature, variable-field MCD (VTVH MCD) to study Fe(II) binding to the catalytic sites of the two Bacillus anthracis miniferritins: one in which two Fe(II) react with O(2) exclusively (Dps1) and a second in which both O(2) or H(2)O(2) can react with two Fe(II) (Dps2). Both result in the formation of iron oxybiomineral. The data show a single 5- or 6-coordinate Fe(II) in the absence of oxidant; Fe(II) binding to Dps2 is 30× more stable than Dps1; and the lower limit of K(D) for binding a second Fe(II), in the absence of oxidant, is 2-3 orders of magnitude weaker than for the binding of the single Fe(II). The data fit an equilibrium model where binding of oxidant facilitates formation of the catalytic site, in sharp contrast to eukaryotic M-ferritins where the binuclear Fe(II) centers are preformed before binding of O(2). The two different binding sequences illustrate the mechanistic range possible for catalytic sites of the family of ferritins.

    View details for DOI 10.1021/bi101346c

    View details for Web of Science ID 000284975000017

    View details for PubMedID 21028901

    View details for PubMedCentralID PMC3075618

  • CD and MCD studies of the effects of component B variant binding on the biferrous active site of methane monooxygenase BIOCHEMISTRY Mitic, N., Schwartz, J. K., Brazeau, B. J., Lipscomb, J. D., Solomon, E. I. 2008; 47 (32): 8386-8397

    Abstract

    The multicomponent soluble form of methane monooxygenase (sMMO) catalyzes the oxidation of methane through the activation of O 2 at a nonheme biferrous center in the hydroxylase component, MMOH. Reactivity is limited without binding of the sMMO effector protein, MMOB. Past studies show that mutations of specific MMOB surface residues cause large changes in the rates of individual steps in the MMOH reaction cycle. To define the structural and mechanistic bases for these observations, CD, MCD, and VTVH MCD spectroscopies coupled with ligand-field (LF) calculations are used to elucidate changes occurring near and at the MMOH biferrous cluster upon binding of MMOB and the MMOB variants. Perturbations to both the CD and MCD are observed upon binding wild-type MMOB and the MMOB variant that similarly increases O 2 reactivity. MMOB variants that do not greatly increase O 2 reactivity fail to cause one or both of these changes. LF calculations indicate that reorientation of the terminal glutamate on Fe2 reproduces the spectral perturbations in MCD. Although this structural change allows O 2 to bridge the diiron site and shifts the redox active orbitals for good overlap, it is not sufficient for enhanced O 2 reactivity of the enzyme. Binding of the T111Y-MMOB variant to MMOH induces the MCD, but not CD changes, and causes only a small increase in reactivity. Thus, both the geometric rearrangement at Fe2 (observed in MCD) coupled with a more global conformational change that may control O 2 access (probed by CD), induced by MMOB binding, are critical factors in the reactivity of sMMO.

    View details for DOI 10.1021/bi800818w

    View details for Web of Science ID 000258225600017

    View details for PubMedID 18627173

    View details for PubMedCentralID PMC2614212

  • Spectroscopic definition of the ferroxidase site in M ferritin: Comparison of binuclear substrate vs cofactor active sites JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Schwartz, J. K., Liu, X. S., Tosha, T., Theil, E. C., Solomon, E. I. 2008; 130 (29): 9441-9450

    Abstract

    Maxi ferritins, 24 subunit protein nanocages, are essential in humans, plants, bacteria, and other animals for the concentration and storage of iron as hydrated ferric oxide, while minimizing free radical generation or use by pathogens. Formation of the precursors to these ferric oxides is catalyzed at a nonheme biferrous substrate site, which has some parallels with the cofactor sites in other biferrous enzymes. A combination of circular dichroism (CD), magnetic circular dichroism (MCD), and variable-temperature, variable-field MCD (VTVH MCD) has been used to probe Fe(II) binding to the substrate active site in frog M ferritin. These data determined that the active site within each subunit consists of two inequivalent five-coordinate (5C) ferrous centers that are weakly antiferromagnetically coupled, consistent with a mu-1,3 carboxylate bridge. The active site ligand set is unusual and likely includes a terminal water bound to each Fe(II) center. The Fe(II) ions bind to the active sites in a concerted manner, and cooperativity among the sites in each subunit is observed, potentially providing a mechanism for the control of ferritin iron loading. Differences in geometric and electronic structure--including a weak ligand field, availability of two water ligands at the biferrous substrate site, and the single carboxylate bridge in ferritin--coincide with the divergent reaction pathways observed between this substrate site and the previously studied cofactor active sites.

    View details for DOI 10.1021/ja801251q

    View details for Web of Science ID 000257796500058

    View details for PubMedID 18576633

    View details for PubMedCentralID PMC2531225

  • Geometric and electronic structure studies of the binuclear nonheme ferrous active site of Toluene-4-monooxygenase: Parallels with methane monooxygenase and insight into the role of the effector proteins in O-2 activation JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Schwartz, J. K., Wei, P., Mitchell, K. H., Fox, B. G., Solomon, E. I. 2008; 130 (22): 7098-7109

    Abstract

    Multicomponent monooxygenases, which carry out a variety of highly specific hydroxylation reactions, are of great interest as potential biocatalysts in a number of applications. These proteins share many similarities in structure and show a marked increase in O2 reactivity upon addition of an effector component. In this study, circular dichroism (CD), magnetic circular dichroism (MCD), and variable-temperature, variable-field (VTVH) MCD have been used to gain spectroscopic insight into the Fe(II)Fe(II) active site in the hydroxylase component of Toluene-4 monoxygenase (T4moH) and the complex of T4moH bound by its effector protein, T4moD. These results have been correlated to spectroscopic data and density functional theory (DFT) calculations on MmoH and its interaction with MmoB. Together, these data provide further insight into the geometric and electronic structure of these biferrous active sites and, in particular, the perturbation associated with component B/D binding. It is found that binding of the effector protein changes the geometry of one iron center and orientation of its redox active orbital to accommodate the binding of O2 in a bridged structure for efficient 2-electron transfer that can form a peroxo intermediate.

    View details for DOI 10.1021/ja800654d

    View details for Web of Science ID 000256301200046

    View details for PubMedID 18479085

  • Effects of multiple pathways on excited-state energy flow in self-assembled wheel-and-spoke light-harvesting architectures JOURNAL OF PHYSICAL CHEMISTRY B Song, H., Kirmaier, C., Schwartz, J. K., Hindin, E., Yu, L., Bocian, D. F., Lindsey, J. S., Holten, D. 2006; 110 (39): 19131-19139

    Abstract

    Static and time-resolved optical measurements are reported for three cyclic hexameric porphyrin arrays and their self-assembled complexes with guest chromophores. The hexameric hosts contain zinc porphyrins and 0, 1, or 2 free base (Fb) porphyrins (denoted Zn(6), Zn(5)Fb, or Zn(4)Fb(2), respectively). The guest is a core-modified (O replacing one of the four N atoms) dipyridyl-substituted Fb porphyrin (DPFbO) that coordinates to zinc porphyrins of a host via pyridyl-zinc dative bonding. Each architecture is designed to have a gradient of excited-state energies for excitation funneling among the weakly coupled constituents of the host to the guest. Energy transfer to the lowest-energy chromophore(s) (coordinated zinc porphyrins or Fb porphyrins) within a hexameric host occurs primarily via a through-bond (TB) mechanism, is rapid ( approximately 40 ps), and is essentially quantitative (>or=98%). Energy transfer from a pyridyl-coordinated zinc porphyrin of the host to the guest in the Zn(6)*DPFbO complex has a yield of approximately 75%, a rate constant of approximately (0.7 ns)(-1), and significant Förster through-space (TS) character. In the case of Zn(5)Fb*DPFbO, which has an additional TS route via the Fb porphyrin with a rate constant of approximately (20 ns)(-1), the yield of energy transfer to the guest is somewhat lower ( approximately 50%) than that for Zn(6)*DPFbO. Complex Zn(4)Fb(2)*DPFbO has an identical TS pathway via the Fb porphyrin plus an additional TS pathway involving the second Fb porphyrin (closer to the guest) with a rate constant of approximately (0.5 ns)(-1). This complex exhibits an energy-transfer yield to the guest that is significantly enhanced over that for Zn(5)Fb*DPFbO and comparable to that for Zn(6)*DPFbO. Collectively, the results for the various arrays suggest designs for similar host-guest complexes that are expected to exhibit much more efficient light harvesting and excitation trapping at the central guest chromophore.

    View details for DOI 10.1021/jp064001a

    View details for Web of Science ID 000240825900011

    View details for PubMedID 17004760

  • Mechanisms, pathways, and dynamics of excited-state energy flow in self-assembled wheel-and-spoke light-harvesting architectures JOURNAL OF PHYSICAL CHEMISTRY B Song, H., Kirmaier, C., Schwartz, J. K., Hindin, E., Yu, L., Bocian, D. F., Lindsey, J. S., Holten, D. 2006; 110 (39): 19121-19130

    Abstract

    Static and time-resolved optical measurements are reported for two cyclic hexameric porphyrin arrays and their self-assembled complexes with guest chromophores. The hexameric hosts contain zinc porphyrins and 0 or 3 free base (Fb) porphyrins (denoted Zn(6) or Zn(3)Fb(3), respectively). The guests are a tripyridyl arene (TP) and a dipyridyl-substituted free base porphyrin (DPFb), each of which coordinates to zinc porphyrins of a host via pyridyl-zinc dative bonding. Each architecture is designed to have an overall gradient of excited-state energies that affords excitation funneling within the host and ultimately to the guest. Collectively, the studies delineate the various pathways, mechanisms, and rate constants of energy flow among the weakly coupled constituents of the host-guest complexes. The pathways include downhill unidirectional energy transfer between adjacent chromophores, bidirectional energy migration between identical chromophores, and energy transfer between nonadjacent chromophores. The energy transfer to the lowest-energy chromophore(s) within the backbone of a hexameric host (Fb porphyrins in Zn(3)Fb(3) or pyridyl-coordinated zinc porphyrins in Zn(6)*TP and Zn(6)*DPFb) proceeds primarily via a through-bond mechanism; the transfer is rapid (approximately 40 ps depending on the array) and essentially quantitative (>or=98%). The energy transfer from a pyridyl-coordinated zinc porphyrin of the host to the Fb porphyrin guest in the Zn(6)*DPFb complex is almost exclusively Förster through-space in nature; this process is much slower ( approximately 1 ns) and has a lower yield (65%). These studies highlight the utility of cyclic architectures for efficient light harvesting and energy transfer to a designated trapping site.

    View details for DOI 10.1021/jp064000i

    View details for Web of Science ID 000240825900010

    View details for PubMedID 17004759

  • Comparison of excited-state energy transfer in arrays of hydroporphyrins (chlorins, oxochlorins) versus porphyrins: Rates, mechanisms, and design criteria JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Taniguchi, M., Ra, D., Kirmaier, C., Hindin, E., Schwartz, J. K., Diers, J. R., Knox, R. S., Bocian, D. F., Lindsey, J. S., Holten, D. 2003; 125 (44): 13461-13470

    Abstract

    A set of chlorin-chlorin and oxochlorin-oxochlorin dyads has been prepared with components in the same or different metalation states. In each case a 4,4'-diphenylethyne linker spans the respective 10-position of each macrocycle. The dyads have been studied using static and time-resolved absorption and emission spectroscopy, resonance Raman spectroscopy, and electrochemical techniques. Excited-state energy transfer from a zinc chlorin to a free-base (Fb) chlorin occurs with a rate constant of (110 ps)(-1) and an efficiency of 93%; similar values of (140 ps)(-1) and 83% are found for the corresponding oxochlorin dyad. Energy transfer in both dyads is slower and less efficient than found previously for the analogous porphyrin dyad, which displays a rate of (24 ps)(-1) and a yield of 99%. The slower rates and diminished efficiencies in the ZnFb chlorin and oxochlorin dyads versus the ZnFb porphyrin dyad are attributed to substantially weaker linker-mediated through-bond (TB) electron-exchange coupling (as indicated by resonance Raman data). Although the through-space (TS, i.e., dipole-dipole) coupling in the ZnFb-chlorin and -oxochlorin dyads is enhanced relative to the ZnFb porphyrin dyad (as indicated by Förster calculations), this enhancement is insufficient to compensate for the greatly diminished TB coupling. Taken together, the chlorin and oxochlorin dyads examined herein serve as benchmarks for elucidating the energy-transfer, electrochemical, and other properties of light-harvesting arrays containing multiple chlorins or oxochlorins.

    View details for DOI 10.1021/ja035987u

    View details for Web of Science ID 000186289300047

    View details for PubMedID 14583042

  • Synthesis and excited-state photodynamics of a perylene-monoimide-oxochlorin dyad. A light-harvesting array JOURNAL OF PHYSICAL CHEMISTRY B Muthukumaran, K., Loewe, R. S., Kirmaier, C., Hindin, E., Schwartz, J. K., Sazanovich, I. V., Diers, J. R., Bocian, D. F., HOLTEN, D., Lindsey, J. S. 2003; 107 (15): 3431-3442

    View details for DOI 10.1021/jp026941a

    View details for Web of Science ID 000182167500015

  • Synthesis and electronic properties of regioisomerically pure oxochlorins JOURNAL OF ORGANIC CHEMISTRY Taniguchi, M., Kim, H. J., Ra, D. Y., Schwartz, J. K., Kirmaier, C., Hindin, E., Diers, J. R., Prathapan, S., Bocian, D. F., HOLTEN, D., Lindsey, J. S. 2002; 67 (21): 7329-7342

    Abstract

    We describe a two-step conversion of C-alkylated zinc chlorins to zinc oxochlorins wherein the keto group is located in the reduced ring (17-position) of the macrocycle. The transformation proceeds by hydroxylation upon exposure to alumina followed by dehydrogenation with DDQ. The reactions are compatible with ethyne, iodo, ester, trimethylsilyl, and pentafluorophenyl groups. A route to a spirohexyl-substituted chlorin/oxochlorin has also been developed. Representative chlorins and oxochlorins were characterized by static and time-resolved absorption spectroscopy and fluorescence spectroscopy, resonance Raman spectroscopy, and electrochemistry. The fluorescence quantum yields of the zinc oxochlorins (Phi(f) = 0.030-0.047) or free base (Fb) oxochlorins (Phi(f) = 0.13-0.16) are comparable to those of zinc tetraphenylporphyrin (ZnTPP) or free base tetraphenylporphyrin (FbTPP), respectively. The excited-state lifetimes of the zinc oxochlorins (tau = 0.5-0.7 ns) are on average 4-fold lower than that of ZnTPP, and the lifetimes of the Fb oxochlorins (tau = 7.4-8.9 ns) are approximately 40% shorter than that of FbTPP. Time-resolved absorption spectroscopy of a zinc oxochlorin indicates the yield of intersystem crossing is >70%. Resonance Raman spectroscopy of copper oxochlorins show strong resonance enhancement of the keto group upon Soret excitation but not with Q(y)()-band excitation, which is attributed to the location of the keto group in the reduced ring (rather than in the isocyclic ring as occurs in chlorophylls). The one-electron oxidation potential of the zinc oxochlorins is shifted to more positive potentials by approximately 240 mV compared with that of the zinc chlorin. Collectively, the fluorescence yields, excited-state lifetimes, oxidation potentials, and various spectral characteristics of the chlorin and oxochlorin building blocks provide the foundation for studies of photochemical processes in larger architectures based on these chromophores.

    View details for DOI 10.1021/jo025843i

    View details for Web of Science ID 000178598600021

    View details for PubMedID 12375962

  • Synthesis and photophysical properties of light-harvesting arrays comprised of a porphyrin bearing multiple perylene-monoimide accessory pigments JOURNAL OF ORGANIC CHEMISTRY Tomizaki, K., Loewe, R. S., Kirmaier, C., Schwartz, J. K., Retsek, J. L., Bocian, D. F., HOLTEN, D., Lindsey, J. S. 2002; 67 (18): 6519-6534

    Abstract

    We present the synthesis and characterization of new light-harvesting arrays containing two, four, or eight perylene-monoimide accessory pigments attached to a zinc porphyrin. Each perylene is substituted with one or three 4-tert-butylphenoxy substituents. A 4,3'- or 4,2'-diarylethyne linker joins the perylene N-imide position and the porphyrin meso-position, affording divergent or convergent architectures, respectively. The architectures are designed to provide high solubility in organic media and facile perylene-to-porphyrin energy transfer, while avoiding charge-transfer quenching of the excited porphyrin product. For the array containing four perylenes per porphyrin in both nonpolar (toluene) and polar (benzonitrile) media and for the array containing eight perylenes per porphyrin in toluene, the photoexcited perylene-monoimide dye (PMI) decays rapidly ( approximately 3.5 ps) and predominantly (>or=90%) by energy transfer to the zinc porphyrin to form the excited zinc porphyrin (Zn), which has excited-state characteristics (lifetime, fluorescence yield) comparable (within approximately 10%) to those of the isolated chromophore. For the array containing eight perylenes in benzonitrile, PMI decays approximately 80% by energy transfer (forming Zn) and approximately 20% by hole transfer (forming PMI- Zn+); Zn subsequently decays approximately 20% by electron transfer (also forming PMI- Zn+) and approximately 80% by the normal routes open to the porphyrin monomer (intersystem crossing, internal conversion, fluorescence). In addition to rapid and efficient perylene-to-porphyrin energy transfer, the broad blue-green to yellow absorption of the perylene dyes complements the blue absorption of the porphyrin, resulting in excellent light harvesting across a significant spectral region. Collectively, the work described herein identifies multiperylene-porphyrin arrays that exhibit suitable photochemical properties for use as motifs in larger light-harvesting systems.

    View details for DOI 10.1021/jo0258002

    View details for Web of Science ID 000177880900032

    View details for PubMedID 12201776

  • Synthesis and Photophysical Properties of Light-Harvesting Arrays Comprised of a Porphyrin Bearing Multiple Perylene-Monoimide Accessory Pigments J. Org. Chem Tomizaki, K., Loewe, R. S., Kirmaier, C., Schwartz, J. K., Retsek, J. L., Bocian, D. F., Holten, D., Lindsey, J. S. 2002; 67 (18): 6519-6534

    View details for DOI 10.1021/jo0258002