Light Driven Electron Transfer in Methylbipyridine/Phenol Complexes Is Not Proton Coupled

The pursuit of systems that undergo optical electron proton transfer (photo-EPT) is very attractive, due to the wealth of information contained in the absorption spectra of such complexes. However, separating photo-EPT transitions from conventional charge transfer states remains a major challenge. In this study, we show that optical charge transfer in a complex between 4-methoxyphenol and N-methyl-4,4'-bipyridyl, previously assigned to occur through photo-EPT involving a hydrogen bond between the reactants (GagliardiC. J.; WangL.; DongareP.; BrennamanM. K.; PapanikolasJ. M.; MeyerT. J.; ThompsonD. W. Proc. Natl. Acad. Sci. U.S.A. 2016, 113, 11106-11109), does not lead to protonation of the acceptor molecule. Additionally, we propose that association of the complex is likely due to donor-acceptor interactions rather than hydrogen bonding.