Bidirectional concerted proton-electron transfer (CPET) involves the transfer of a proton and electron simultaneously to and from quantum mechanically different orbitals. We are investigating base-appended radical cations. These systems are designed to undergo bidirectional CPET, with the proton-accepting and electron-accepting sites spatially separated. Computational work revealed a kinetically unfavorable conformational shift in the reaction of 10-(2-pyridinyl)-10H-phenothiazine radical cation (PPT•+) with 2,4,6-tri-t-butylphenol. This shift is believed to be responsible for the higher experimental activation barrier for this reaction relative to that for a similar molecule, 10-methyl-3-(2-pyridinyl)-10H-phenothiazine radical cation, with the same donor. Hence, the conformational shift affects the intrinsic barrier for CPET, in parallel to the same effect in electron transfer. We hypothesize that altering the geometry of the central ring of the phenothiazine will further change the dynamics of this conformational shift. Current work is focused on 3,6-dimethoxy-10-(2-pyridinyl)-10H-carbazole radical cation, in which a five-membered ring replaces the central six-membered ring of the phenothiazine of PPT•+. Calculations indicate the molecule will remain planar throughout the reaction. Preliminary experimental work will also be presented.

Probing the effects of conformation on concerted proton-electron transfer

249th National Meeting (2015)

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