@article{springer_faries_diers_muthiah_mass_kee_kirmaier_lindsey_bocian_holten_2012, title={Effects of Substituents on Synthetic Analogs of Chlorophylls. Part 3: The Distinctive Impact of Auxochromes at the 7-versus 3-Positions}, volume={88}, ISSN={["1751-1097"]}, DOI={10.1111/j.1751-1097.2012.01083.x}, abstractNote={Assessing the effects of substituents on the spectra of chlorophylls is essential for gaining a deep understanding of photosynthetic processes. Chlorophyll a and b differ solely in the nature of the 7‐substituent (methyl versus formyl), whereas chlorophyll a and d differ solely in the 3‐substituent (vinyl versus formyl), yet have distinct long‐wavelength absorption maxima: 665 (a) 646 (b) and 692 nm (d). Herein, the spectra, singlet excited‐state decay characteristics, and results from DFT calculations are examined for synthetic chlorins and 131‐oxophorbines that contain ethynyl, acetyl, formyl and other groups at the 3‐, 7‐ and/or 13‐positions. Substituent effects on the absorption spectra are well accounted for using Gouterman’s four‐orbital model. Key findings are that ( 1 ) the dramatic difference in auxochromic effects of a given substituent at the 7‐ versus3‐ or 13‐positions primarily derives from relative effects on the LUMO+1 and LUMO; (2) formyl at the 7‐ or 8‐position effectively “porphyrinizes” the chlorin and (3) the substituent effect increases in the order of vinyl < ethynyl < acetyl < formyl. Thus, the spectral properties are governed by an intricate interplay of electronic effects of substituents at particular sites on the four frontier MOs of the chlorin macrocycle.}, number={3}, journal={PHOTOCHEMISTRY AND PHOTOBIOLOGY}, author={Springer, Joseph W. and Faries, Kaitlyn M. and Diers, James R. and Muthiah, Chinnasamy and Mass, Olga and Kee, Hooi Ling and Kirmaier, Christine and Lindsey, Jonathan S. and Bocian, David F. and Holten, Dewey}, year={2012}, pages={651–674} }
 @article{ptaszek_lahaye_krayer_muthiah_lindsey_2010, title={De Novo Synthesis of Long-Wavelength Absorbing Chlorin-13,15-dicarboximides}, volume={75}, ISSN={["1520-6904"]}, DOI={10.1021/jo902649d}, abstractNote={Chlorins bearing a six-membered imide ring spanning positions 13-15, commonly referred to as purpurinimides, exhibit long-wavelength absorption yet have heretofore only been available via semisynthesis from naturally occurring chlorophylls. A concise route to synthetic chlorins, which bear a geminal dimethyl group in the pyrroline ring, has been extended to provide access to chlorin-13,15-dicarboximides. The new route entails (i) synthesis of a 13-bromochlorin, (ii) palladium-catalyzed carbamoylation at the 13-position, (iii) regioselective 15-bromination under acidic conditions, and (iv) one-flask palladium-mediated carbonylation and ring closure to form the imide. In some cases the ring closure reaction afforded the isomeric (and readily separable) chlorin-isoimide in addition to the chlorin-imide. The resulting chlorin-imides and chlorin-isoimides exhibit long-wavelength absorption (679-715 nm) and emission (683-720 nm) in the far-red and near-infrared spectral region. The absorption of the chlorin-(iso)imides fills the spectral window between that of analogous synthetic chlorins and 13(1)-oxophorbines (603-687 nm) and bacteriochlorins (707-792 nm). The synthetic versatility of the de novo route complements the existing semisynthetic route from chlorophylls and should enable fundamental spectroscopic studies and photochemical applications.}, number={5}, journal={JOURNAL OF ORGANIC CHEMISTRY}, author={Ptaszek, Marcin and Lahaye, Dorothee and Krayer, Michael and Muthiah, Chinnasamy and Lindsey, Jonathan S.}, year={2010}, month={Mar}, pages={1659–1673} }
 @article{kee_diers_ptaszek_muthiah_fan_lindsey_bocian_holten_2009, title={Chlorin-Bacteriochlorin Energy-transfer Dyads as Prototypes for Near-infrared Molecular Imaging Probes: Controlling Charge-transfer and Fluorescence Properties in Polar Media}, volume={85}, ISSN={["1751-1097"]}, DOI={10.1111/j.1751-1097.2008.00532.x}, abstractNote={The photophysical properties of two energy‐transfer dyads that are potential candidates for near‐infrared (NIR) imaging probes are investigated as a function of solvent polarity. The dyads (FbC‐FbB and ZnC‐FbB) contain either a free base (Fb) or zinc (Zn) chlorin (C) as the energy donor and a free base bacteriochlorin (B) as the energy acceptor. The dyads were studied in toluene, chlorobenzene, 1,2‐dichlorobenzene, acetone, acetonitrile and dimethylsulfoxide (DMSO). In both dyads, energy transfer from the chlorin to bacteriochlorin occurs with a rate constant of ∼(5–10 ps)−1 and a yield of >99% in nonpolar and polar media. In toluene, the fluorescence yields (Φf = 0.19) and singlet excited‐state lifetimes (τ∼5.5 ns) are comparable to those of the benchmark bacteriochlorin. The fluorescence yield and excited‐state lifetime decrease as the solvent polarity increases, with quenching by intramolecular electron (or hole) transfer being greater for FbC‐FbB than for ZnC‐FbB in a given solvent. For example, the Φf and τ values for FbC‐FbB in acetone are 0.055 and 1.5 ns and in DMSO are 0.019 and 0.28 ns, whereas those for ZnC‐FbB in acetone are 0.12 and 4.5 ns and in DMSO are 0.072 and 2.4 ns. The difference in fluorescence properties of the two dyads in a given polar solvent is due to the relative energies of the lowest energy charge‐transfer states, as assessed by ground‐state redox potentials and supported by molecular‐orbital energies derived from density functional theory calculations. Controlling the extent of excited‐state quenching in polar media will allow the favorable photophysical properties of the chlorin–bacteriochlorin dyads to be exploited in vivo. These properties include very large Stokes shifts (85 nm for FbC‐FbB, 110 nm for ZnC‐FbB) between the red‐region absorption of the chlorin and the NIR fluorescence of the bacteriochlorin (λf = 760 nm), long bacteriochlorin excited‐state lifetime (∼5.5 ns), and narrow (≤20 nm) absorption and fluorescence bands. The latter will facilitate selective excitation/detection and multiprobe applications using both intensity‐ and lifetime‐imaging techniques.}, number={4}, journal={PHOTOCHEMISTRY AND PHOTOBIOLOGY}, author={Kee, Hooi Ling and Diers, James R. and Ptaszek, Marcin and Muthiah, Chinnasamy and Fan, Dazhong and Lindsey, Jonathan S. and Bocian, David F. and Holten, Dewey}, year={2009}, pages={909–920} }
 @article{muthiah_lahaye_taniguchi_ptaszek_lindsey_2009, title={Regioselective Bromination Tactics in the de Novo Synthesis of Chlorophyll b Analogues}, volume={74}, ISSN={["0022-3263"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-66449131206&partnerID=MN8TOARS}, DOI={10.1021/jo9002954}, abstractNote={The ability to introduce substituents at designated sites about the perimeter of the chlorin or 13(1)-oxophorbine macrocycle is essential for fundamental studies related to chlorophylls. A chlorin is a dihydroporphyrin, whereas a 13(1)-oxophorbine is a chlorin containing an annulated oxopentano ring spanning positions 13 and 15. 13(1)-Oxophorbines bearing auxochromes at the 7-position of the macrocycle are valuable targets given their resemblance to chlorophyll a or b, which contains the 13(1)-oxophorbine skeleton and bears a 7-methyl or 7-formyl group, respectively. A rational route to 7-substituted 13(1)-oxophorbines was developed that relies on a new method for regioselective bromination. Under neutral conditions, a 13-acetyl-10-mesitylchlorin (FbC-M(10)A(13)) undergoes bromination (with 1 molar equiv of NBS in THF) both in ring B (7-position) and at the 15-position (42% versus 28% isolated yield), thereby thwarting installation of the isocyclic ring (ring E, spanning the 13-15 positions). Under acidic conditions (10% TFA in CH(2)Cl(2)), ring B is deactivated, and bromination occurs preferentially at the 15-position (87% yield). The capability for preferential 15-bromination is essential to install the isocyclic ring, after which bromination can be directed to the 7-position of ring B (neutral conditions, 86% yield). The ability to suppress bromination in ring B (under acidic media) has been exploited in syntheses of sparsely substituted analogues of chlorophyll b. The analogues contain a 7-substituent (acetyl, formyl, or TIPS-ethynyl), a 10-mesityl group, and the 18,18-dimethyl group as the only substituents in the 13(1)-oxophorbine skeleton. The three analogues exhibit absorption spectral features that closely resemble those of free base analogues of chlorophyll b. Taken together, the facile access to chlorins and 13(1)-oxophorbines bearing substituents at distinct sites should enable fundamental spectroscopic studies and diverse applications.}, number={9}, journal={JOURNAL OF ORGANIC CHEMISTRY}, publisher={American Chemical Society (ACS)}, author={Muthiah, Chinnasamy and Lahaye, Dorothee and Taniguchi, Masahiko and Ptaszek, Marcin and Lindsey, Jonathan S.}, year={2009}, month={May}, pages={3237–3247} }
 @article{borbas_chandrashaker_muthiah_kee_holten_lindsey_2008, title={Design, synthesis, and photophysical characterization of water-soluble chlorins}, volume={73}, ISSN={["1520-6904"]}, DOI={10.1021/jo7026728}, abstractNote={The use of chlorins as photosensitizers or fluorophores in a range of biological applications requires facile provisions for imparting high water solubility. Two free base chlorins have been prepared wherein each chlorin bears a geminal dimethyl group in the reduced ring and a water-solubilizing unit at the chlorin 10-position. In one design (FbC1-PO3H2), the water-solubilizing unit is a 1,5-diphosphonopent-3-yl ("swallowtail") unit, which has previously been used to good effect with porphyrins. In the other design (FbC2-PO3H2), the water-solubilizing unit is a 2,6-bis(phosphonomethoxy)phenyl unit. Two complementary routes were developed for preparing FbC2-PO3H2 that entail introduction of the protected phosphonate moieties either in the Eastern-half precursor to the chlorin or by derivatization of an intact chlorin. Water-solubilization is achieved in the last step of each synthesis upon removal of the phosphonate protecting groups. The chlorins FbC1-PO3H2 and FbC2-PO3H2 are highly water-soluble (>10 mM) as shown by 1H NMR spectroscopy (D2O) and UV-vis absorption spectroscopy. The photophysical properties of the water-soluble chlorins in phosphate-buffered saline solution (pH 7.4) at room temperature were investigated using static and time-resolved absorption and fluorescence spectroscopic techniques. Each chlorin exhibits dominant absorption bands in the blue and the red region (lambda = 398, 626 nm), a modest fluorescence yield (Phi f approximately 0.11), a long singlet excited-state lifetime (tau = 7.5 ns), and a high yield of intersystem crossing to give the triplet state (Phi isc = 0.9). The properties of the water-soluble chlorins in aqueous media are comparable to those of hydrophobic chlorins in toluene. The high aqueous solubility combined with the attractive photophysical properties make these compounds suitable for a wide range of biomedical applications.}, number={8}, journal={JOURNAL OF ORGANIC CHEMISTRY}, author={Borbas, K. Eszter and Chandrashaker, Vanampally and Muthiah, Chinnasamy and Kee, Hooi Ling and Holten, Dewey and Lindsey, Jonathan S.}, year={2008}, month={Apr}, pages={3145–3158} }
 @article{kee_nothdurft_muthiah_diers_fan_ptaszek_bocian_lindsey_culver_holten_2008, title={Examination of chlorin-bacteriochlorin energy-transfer dyads as prototypes for near-infrared molecular imaging probes}, volume={84}, ISSN={["1751-1097"]}, DOI={10.1111/j.1751-1097.2008.00409.x}, abstractNote={New classes of synthetic chlorin and bacteriochlorin macrocycles are characterized by narrow spectral widths, tunable absorption and fluorescence features across the red and near‐infrared (NIR) regions, tunable excited‐state lifetimes (<1 to >10 ns) and chemical stability. Such properties make dyad constructs based on synthetic chlorin and bacteriochlorin units intriguing candidates for the development of NIR molecular imaging probes. In this study, two such dyads (FbC‐FbB and ZnC‐FbB) were investigated. The dyads contain either a free base (Fb) or zinc (Zn) chlorin (C) as the energy donor and a free base bacteriochlorin (B) as the energy acceptor. In both constructs, energy transfer from the chlorin to bacteriochlorin occurs with a rate constant of ∼(5 ps)−1 and a yield of >99%. Thus, each dyad effectively behaves as a single chromophore with an exceptionally large Stokes shift (85 nm for FbC‐FbB and 110 nm for ZnC‐FbB) between the red‐region absorption of the chlorin and the NIR fluorescence of the bacteriochlorin (λf = 760 nm, Φf = 0.19, τ ∼ 5.5 ns in toluene). The long‐wavelength transitions (absorption, emission) of each constituent of each dyad exhibit narrow (≤20 nm) spectral widths. The narrow spectral widths enabled excellent selectivity in excitation and detection of one chlorin–bacteriochlorin energy‐transfer dyad in the presence of the other upon diffuse optical tomography of solution‐phase phantoms.}, number={5}, journal={PHOTOCHEMISTRY AND PHOTOBIOLOGY}, author={Kee, Hooi Ling and Nothdurft, Ralph and Muthiah, Chinnasamy and Diers, James R. and Fan, Dazhong and Ptaszek, Marcin and Bocian, David F. and Lindsey, Jonathan S. and Culver, Joseph P. and Holten, Dewey}, year={2008}, pages={1061–1072} }
 @article{muthiah_kee_diers_fan_ptaszek_bocian_holten_lindsey_2008, title={Synthesis and excited-state photodynamics of a chlorin-bacteriochlorin dyad-through-space versus through-bond energy transfer in tetrapyrrole arrays}, volume={84}, ISSN={["1751-1097"]}, DOI={10.1111/j.1751-1097.2007.00258.x}, abstractNote={Understanding energy transfer among hydroporphyrins is of fundamental interest and essential for a wide variety of photochemical applications. Toward this goal, a synthetic free base ethynylphenylchlorin has been coupled with a synthetic free base bromobacteriochlorin to give a phenylethyne‐linked chlorin–bacteriochlorin dyad (FbC‐pe‐FbB). The chlorin and bacteriochlorin are each stable toward adventitious oxidation because of the presence of a geminal dimethyl group in each reduced pyrrole ring. A combination of static and transient optical spectroscopic studies indicate that excitation into the Qy band of the chlorin constituent (675 nm) of FbC‐pe‐FbB in toluene results in rapid energy transfer to the bacteriochlorin constituent with a rate of ∼(5 ps)−1 and efficiency of >99%. The excited bacteriochlorin resulting from the energy‐transfer process in FbC‐pe‐FbB has essentially the same fluorescence characteristics as an isolated monomeric reference compound, namely a narrow (12 nm fwhm) fluorescence emission band at 760 nm and a long‐lived (5.4 ns) Qy excited state that exhibits a significant fluorescence quantum yield (Φf = 0.19). Förster calculations are consistent with energy transfer in FbC‐pe‐FbB occurring predominantly by a through‐space mechanism. The energy‐transfer characteristics of FbC‐pe‐FbB are compared with those previously obtained for analogous phenylethyne‐linked dyads consisting of two porphyrins or two oxochlorins. The comparisons among the sets of dyads are facilitated by density functional theory calculations that elucidate the molecular‐orbital characteristics of the energy donor and acceptor constituents. The electron‐density distributions in the frontier molecular orbitals provide insights into the through‐bond electronic interactions that can also contribute to the energy‐transfer process in the different types of dyads.}, number={3}, journal={PHOTOCHEMISTRY AND PHOTOBIOLOGY}, author={Muthiah, Chinnasamy and Kee, Hooi Ling and Diers, James R. and Fan, Dazhong and Ptaszek, Marcin and Bocian, David F. and Holten, Dewey and Lindsey, Jonathan S.}, year={2008}, pages={786–801} }
 @article{stromberg_marton_kee_kirmaier_diers_muthiah_taniguchi_lindsey_bocian_meyer_et al._2007, title={Examination of tethered porphyrin, chlorin, and bacteriochlorin molecules in mesoporous metal-oxide solar cells}, volume={111}, ISSN={["1932-7447"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-35748969147&partnerID=MN8TOARS}, DOI={10.1021/jp0749928}, abstractNote={The performance of five tetrapyrrole molecules as sensitizers in regenerative solar cells was evaluated. The tetrapyrroles form two sets. One set contains three meso-substituted porphyrins that differ only in the nature of their surface-binding tether:  isophthalic acid, ethynylisophthalic acid, or cyanoacrylic acid. The other set includes the ethynylisophthalic acid tether attached to porphyrin, chlorin, and bacteriochlorin macrocycles, which contain zero, one, and two saturated pyrrole rings, respectively. Incident photon-to-current efficiency was measured for each sensitizer loaded onto a mesoporous TiO2 semitransparent electrode in a solar cell. The porphyrin bearing the cyanoacrylic acid tether gives the largest peak and integrated (350−900 nm) photocurrent density of the five tetrapyrrole molecules. For this sensitizer, a quasi-monochromatic power conversion efficiency of 21% was obtained at the Soret maximum (450 nm), along with a fill factor of 0.69. To elucidate the molecular origins of the effec...}, number={42}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, publisher={American Chemical Society (ACS)}, author={Stromberg, Jonathan R. and Marton, Andras and Kee, Hooi Ling and Kirmaier, Christine and Diers, James R. and Muthiah, Chinnasamy and Taniguchi, Masahiko and Lindsey, Jonathan S. and Bocian, David F. and Meyer, Gerald J. and et al.}, year={2007}, month={Oct}, pages={15464–15478} }
 @article{muthiah_taniguchi_kim_schmidt_kee_holten_bocian_lindsey_2007, title={Synthesis and photophysical characterization of porphyrin, chlorin and bacteriochlorin molecules bearing tethers for surface attachment}, volume={83}, ISSN={["0031-8655"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-36248978026&partnerID=MN8TOARS}, DOI={10.1111/j.1751-1097.2007.00195.x}, abstractNote={The ability to tailor synthetic porphyrin, chlorin and bacteriochlorin molecules holds promise for diverse studies in artificial photosynthesis. Toward this goal, the synthesis and photophysical characterization of five tetrapyrrole compounds is described. Each compound bears a surface attachment group. One set contains three meso‐substituted porphyrins that differ only in the nature of a surface‐binding tether—isophthalic acid, ethynylisophthalic acid or cyanoacrylic acid. The other set includes a porphyrin, chlorin and bacteriochlorin each of which bears an ethynylisophthalic acid tether. The ester derivative of each compound was prepared for solution photophysical characterization studies. The photophysical studies include determination (in toluene or acetonitrile) of the electronic absorption and fluorescence spectra, fluorescence yield and lifetime of the lowest excited singlet state. The excited‐state lifetimes range from 1 to 5.6 ns for the five compounds. The radiative rate constant for the excited‐state decay was estimated from the photophysical data (fluorescence yield and excited‐state lifetime) and from Strickler–Berg analysis of the absorption and fluorescence spectra. The synthesis and characterization of the tetrapyrrole compounds underpin their use as sensitizers in molecular‐based solar cells.}, number={6}, journal={PHOTOCHEMISTRY AND PHOTOBIOLOGY}, publisher={Wiley}, author={Muthiah, Chinnasamy and Taniguchi, Masahiko and Kim, Han-Je and Schmidt, Izabela and Kee, Hooi Ling and Holten, Dewey and Bocian, David F. and Lindsey, Jonathan S.}, year={2007}, pages={1513–1528} }