@article{balasubramanian_strachan_boyle_lindsey_2000, title={Rational synthesis of beta-substituted chlorin building blocks}, volume={65}, ISSN={["0022-3263"]}, DOI={10.1021/jo000913b}, abstractNote={Chlorins bearing synthetic handles at specific sites about the perimeter of the macrocycle constitute valuable building blocks. We previously developed methodology for preparing meso-substituted chlorin building blocks and now present methodology for preparing several complementary beta-substituted chlorin building blocks. The chlorins bear one or two beta substituents, one meso substituent, a geminal dimethyl group to lock in the chlorin hydrogenation level, and no flanking meso and beta substituents. The synthesis involves convergent joining of an Eastern half and a Western half. New routes have been developed to two beta-substituted bromo-dipyrromethane monocarbinols (Eastern halves). A new beta-substituted Western half was prepared following the method for preparing an unsubstituted Western half (3,3-dimethyl-2,3-dihydrodipyrrin). Chlorin formation is achieved by a two-flask process of acid-catalyzed condensation followed by metal-mediated oxidative cyclization. beta-Substituted chlorins have been prepared in 18-24% yield bearing a 4-iodophenyl group at the 8-position, a 4-iodophenyl group or a 4-[2-(trimethylsilyl)ethynyl]phenyl group at the 12-position, and a 4-iodophenyl group and a 4-[2-(trimethylsilyl)ethynyl]phenyl group at diametrically opposed beta-positions (2, 12). The latter building block makes possible the stepwise construction of linear multi-chlorin architectures. The chlorins exhibit typical absorption and fluorescence spectra. A systematic shift in the absorption maximum (637-655 nm for the free base chlorins, 606-628 nm for the zinc chlorins) and intensity of the chlorin Q(y)() band (epsilon up to 79 000 M(-)(1) cm(-)(1)) is observed depending on the location of the substituents. The characteristic spectral features and location of substituents in defined positions make these chlorins well suited for a variety of applications in biomimetic and materials chemistry.}, number={23}, journal={JOURNAL OF ORGANIC CHEMISTRY}, author={Balasubramanian, T and Strachan, JP and Boyle, PD and Lindsey, JS}, year={2000}, month={Nov}, pages={7919–7929} }
 @article{strachan_df o'shea_balasubramanian_lindsey_2000, title={Rational synthesis of meso-substituted chlorin building blocks}, volume={65}, ISSN={["1520-6904"]}, DOI={10.1021/jo991942t}, abstractNote={Chlorins provide the basis for plant photosynthesis, but synthetic model systems have generally employed porphyrins as surrogates due to the unavailability of suitable chlorin building blocks. We have adapted a route pioneered by Battersby to gain access to chlorins that bear two meso substituents, a geminal dimethyl group to lock in the chlorin hydrogenation level, and no flanking meso and beta substituents. The synthesis involves convergent joining of an Eastern half and a Western half. A 3,3-dimethyl-2,3-dihydrodipyrrin (Western half) was synthesized in four steps from pyrrole-2-carboxaldehyde. A bromodipyrromethane carbinol (Eastern half) was prepared by sequential acylation and bromination of a 5-substituted dipyrromethane followed by reduction. Chlorin formation is achieved by a two-flask process of acid-catalyzed condensation followed by metal-mediated oxidative cyclization. The latter reaction has heretofore been performed with copper templates. Investigation of conditions for this multistep process led to copper-free conditions (zinc acetate, AgIO(3), and piperidine in toluene at 80 degrees C for 2 h). The zinc chlorin was obtained in yields of approximately 10% and could be easily demetalated to give the corresponding free base chlorin. The synthetic process is compatible with a range of meso substituents (p-tolyl, mesityl, pentafluorophenyl, 4-[2-(trimethylsilyl)ethynyl]phenyl, 4-iodophenyl). Altogether four free base and four zinc chlorins have been prepared. The chlorins exhibit typical absorption spectra, fluorescence spectra, and fluorescence quantum yields. The ease of synthetic access, presence of appropriate substituents, and characteristic spectral features make these types of chlorins well suited for incorporation in synthetic model systems.}, number={10}, journal={JOURNAL OF ORGANIC CHEMISTRY}, author={Strachan, JP and DF O'Shea and Balasubramanian, T and Lindsey, JS}, year={2000}, month={May}, pages={3160–3172} }
 @article{yang_seth_strachan_gentemann_kim_holten_lindsey_bocian_1999, title={Ground and excited state electronic properties of halogenated tetraarylporphyrins. Tuning the building blocks for porphyrin- based photonic devices}, volume={3}, DOI={10.1002/(SICI)1099-1409(199902)3:2<117::AID-JPP110>3.0.CO;2-X}, abstractNote={The rational design of molecular photonic devices relies on the ability to select components with predictable electronic structure, excited state lifetimes and redox chemistry. Electronic communication in multiporphyrin arrays depends critically on the relative energies and electron density distributions of the frontier molecular orbitals, especially the energetically close highest occupied molecular orbitals (a 2u and a 1u ). To explore how these ground and excited state properties can be modulated, we have synthesized and characterized 40 free base ( Fb ), magnesium and zinc tetraarylporphyrins. The porphyrins bear meso-substituents with the following substitution patterns: (1) four identical substituents (phenyl, o-chlorophenyl, p-chlorophenyl, o,o'-difluorophenyl, pentafluorophenyl, mesityl); (2) one, two, three or four o,o'-dichlorophenyl substituents; (3) one p-ethynylphenyl group and three mesityl or pentafluorophenyl groups; (4) one p-ethynyl-o,o″-dichlorophenyl or p-ethynyl-o,o″-dimethylphenyl and three phenyl groups. For each neutral complex the ground state electronic properties were investigated using electrochemical methods and optical absorption spectroscopy. Similarly the absorption, emission, and relaxation properties of the lowest singlet excited state were probed by time-resolved absorption and fluorescence methods. Each oxidized complex was investigated by static absorption and liquid and frozen solution EPR spectroscopy. The collective results of these investigations have provided insights into the direct (orbital overlap) and indirect (inductive/conjugative) mechanisms by which halogenated phenyl rings influence the static and dynamic electronic properties of neutral and oxidized porphyrinic chromophores. Three key findings are as follows. (1) The effective electron-withdrawing strength of halogenated phenyl rings required to reverse the ordering of the a 2u and a 1u HOMOs in Mg versus Zn tetraarylporphyrins has been elucidated. (2) Appropriate halogenation can significantly increase the excited state lifetime of a Zn porphyrin relative to the unsubstituted complex. (3) Halogenation can be used to modulate redox potentials in a manner that complements the enhancement of other electronic properties. The insights gained from study of this library of porphyrins provide a foundation for tuning the electronic properties of monomeric porphyrins as building blocks for multichromophoric assemblies in optoelectronics and other applications.}, number={2}, journal={Journal of Porphyrins and Phthalocyanines}, author={Yang, S. I. and Seth, J. and Strachan, J. P. and Gentemann, S. and Kim, D. and Holten, D. and Lindsey, Jonathan and Bocian, D. F.}, year={1999}, pages={117–147} }
 @article{strachan_gentemann_seth_kalsbeck_lindsey_holten_bocian_1998, title={Synthesis and characterization of tetrachlorodiarylethyne-linked porphyrin dimers. Effects of linker architecture on intradimer electronic communication}, volume={37}, ISSN={["0020-1669"]}, DOI={10.1021/ic970967c}, abstractNote={The effects of incorporating chloro groups at all ortho positions of a diphenylethyne linker that bridges the zinc and free base (Fb) components of a porphyrin dimer (ZnFbB(Cl(4))) have been investigated in detail via various static and time-resolved spectroscopic methods. The excited-state energy-transfer rate in ZnFbB(Cl(4)) ((134 ps)(-)(1)) is 5-fold slower than that in the corresponding dimer having an unsubstituted linker (ZnFbU, (24 ps)(-)(1)) but is only modestly slower than that in the dimer having o-methyl groups on the linker (ZnFbB(CH(3))(4), (115 ps)(-)(1)). The ground-state hole/electron-hopping rates in the oxidized bis-Zn analogues of all three dimers are much slower than the excited-state energy-transfer rates. There is no discernible difference between the hole/electron-hopping rates in the o-chloro- and o-methyl-substituted arrays. The similar ground- and excited-state dynamics observed for the o-chloro- and o-methyl-substituted arrays is attributed to the dominance of torsional constraints in mediating the extent of through-bond electronic communication. These constraints attenuate intradimer communication by restricting the rotation toward coplanarity of the phenyl rings of the linker and the porphyrin rings. Thus, the o-chloro groups on the linker decrease electronic communication via a steric, rather than purely electronic, mechanism.}, number={6}, journal={INORGANIC CHEMISTRY}, author={Strachan, JP and Gentemann, S and Seth, J and Kalsbeck, WA and Lindsey, JS and Holten, D and Bocian, DF}, year={1998}, month={Mar}, pages={1191–1201} }
 @article{ravikanth_strachan_li_lindsey_1998, title={Trans-substituted porphyrin building blocks bearing iodo and ethynyl groups for applications in bioorganic and materials chemistry}, volume={54}, ISSN={["0040-4020"]}, DOI={10.1016/S0040-4020(98)00408-6}, abstractNote={The modular synthesis of linear or cyclic multiporphyrin arrays relies on the availability of trans-substituted porphyrin building blocks with high solubility in organic solvents. Eleven porphyrin building blocks were synthesized bearing iodo, ethynyl, and 2-(trimethylsilyl)ethynyl groups at the 4-, 3-, or 3,5-positions of two meso-aryl units, and mesityl groups at the other two meso-positions. The synthesis involves condensation of 5-mesityldipyrromethane with one or two aryl aldehydes. Combinations of functional groups include di-iodo, tetra-iodo, bis[(2-(trimethylsilyl)ethynyl], iodo and 2-(trimethylsilyl)ethynyl, and ethynyl and 2-(trimethylsilyl)ethynyl. In addition, a porphyrin bearing one 4-iodophenyl group and one 3,5-bis(boron-dipyrrin)phenyl group was synthesized for applications in molecular photonic devices. The iodo and ethynyl groups are ideally-suited for Pd-mediated coupling reactions, allowing the porphyrin building blocks to be joined in the systematic construction of soluble multiporphyrin arrays.}, number={27}, journal={TETRAHEDRON}, author={Ravikanth, M and Strachan, JP and Li, FR and Lindsey, JS}, year={1998}, month={Jul}, pages={7721–7734} }
 @article{strachan_gentemann_seth_kalsbeck_lindsey_holten_bocian_1997, title={Effects of orbital ordering on electronic communication in multiporphyrin arrays}, volume={119}, ISSN={["0002-7863"]}, DOI={10.1021/ja971678q}, abstractNote={The rational design of molecular photonic devices requires a thorough understanding of all factors affecting electronic communication among the various constituents. To explore how electronic factors mediate both excited- and ground-state electronic communication in multiporphyrin arrays, we have conducted a detailed static spectroscopic (absorption, fluorescence, resonance Raman, electron paramagnetic resonance), time-resolved spectroscopic (absorption, fluorescence), and electrochemical (cyclic and square-wave voltammetry, coulometry) study of tetraarylporphyrin dimers. The complexes investigated include both zinc-free base (ZnFb) and bis-Zn dimers in which the porphyrin constituents are linked via diphenylethyne groups at the meso positions. Comparison of dimeric arrays containing pentafluorophenyl groups at all nonlinking meso positions (F30ZnFbU and F30Zn2U) with nonfluorinated analogs (ZnFbU and Zn2U) directly probes the effects of electronic factors on intradimer communication. The major findings of the study are as follows: (1) Energy transfer from the photoexcited Zn porphyrin to the Fb porphyrin is the predominant excited-state reaction in F30ZnFbU, as is also the case for ZnFbU. Energy transfer primarily proceeds via a through-bond process mediated by the diarylethyne linker. Remarkably, the energy-transfer rate is 10 times slower in F30ZnFbU ((240 ps)-1) than in ZnFbU ((24 ps)-1), despite the fact that each has the same diphenylethyne linker. The attenuated energy-transfer rate in the former dimer is attributed to reduced Q-excited-state electronic coupling between the Zn and Fb porphyrins. (2) The rate of hole/electron hopping in the monooxidized bis-Zn complex, [F30Zn2U]+, is ∼10-fold slower than that for [Zn2U]+. The slower hole/electron hopping rate in the former dimer reflects strongly attenuated ground-state electronic coupling. The large attenuation in excited- and ground-state electronic communication observed for the fluorine-containing dimers is attributed to a diminution in the electron-exchange matrix elements that stems from stabilization of the a2u porphyrin orbital combined with changes in the electron-density distribution in this orbital. Stabilization of the porphyrin a2u orbital results in a switch in the HOMO from a2u in ZnFbU to a1u in F30ZnFbU. This orbital reversal diminishes the electron density at the peripheral positions where the linker is appended. Collectively, our studies clarify the origin of the different energy-transfer rates observed among various multiporphyrin arrays and exemplify the interconnected critical roles of a1u/a2u orbital ordering and linker position in the design of efficient molecular photonic devices.}, number={46}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Strachan, JP and Gentemann, S and Seth, J and Kalsbeck, WA and Lindsey, JS and Holten, D and Bocian, DF}, year={1997}, month={Nov}, pages={11191–11201} }