Vibronic Characteristics and Spin-Density Distributions in Bacteriochlorins as Revealed by Spectroscopic Studies of 16 Isotopologues. Implications for Energy- and Electron-Transfer in Natural Photosynthesis and Artificial Solar-Energy Conversion.

Vibronic characteristics and spin-density distributions in the core bacteriochlorin macrocycle were revealed by spectroscopic and theoretical studies of 16 isotopologues. The vibrational modes in copper bacteriochlorin isotopologues were examined via resonance Raman and Fourier-transform infrared spectroscopy. The resonance Raman spectra exhibit an exceptional sparcity of vibronically active modes of the core macrocycle, in contrast with the rich spectra of the natural bacteriochlorophylls.

Effects of linker torsional constraints on the rate of ground-state hole transfer in porphyrin dyads.

Understanding hole/electron-transfer processes among interacting constituents of multicomponent molecular architectures is central to the fields of artificial photosynthesis and molecular electronics. Herein, we utilize a recently demonstrated (203)Tl/(205)Tl hyperfine "clocking" strategy to probe the rate of hole/electron transfer in the monocations of a series of three thallium-chelated porphyrin dyads, designated Tl(2)-U, Tl(2)-M, and Tl(2)-B, that are linked via diarylethynes wherein the number of ortho-dimethyl substituents on the aryl group of the linker systematically increases (none, one, and two, respectively). Variable-temperature (160-340 K) EPR studies on the monocations of the three dyads were used to examine the thermal activation behavior of the hole/electron-transfer process and reveal the following: (1) Hole/electron transfer at room temperature (295 K) slows as torsional constraints are added to the diarylethyne linker [k(Tl(2)-U) > k(Tl(2)-M) > k(Tl(2)-B)], with rate constants that correspond to time constants in the 2-5 ns regime.