3 years ago

Photoinduced Charge Shifts and Electron Transfer in Viologen–Tetraphenylborate Complexes: Push–Pull Character of the Exciplex

Photoinduced Charge Shifts and Electron Transfer in Viologen–Tetraphenylborate Complexes: Push–Pull Character of the Exciplex
Willy G. Santos, Darya S. Budkina, Alexander N. Tarnovsky, Daniel R. Cardoso, Victor M. Deflon, Malcolm D. E. Forbes
Viologen–tetraarylborate ion-pair complexes were prepared and investigated by steady-state and time-resolved spectroscopic techniques such as fluorescence and femtosecond transient absorption. The results highlight a charge transfer transition that leads to changes in the viologen structure in the excited singlet state. Femtosecond transient absorption reveals the formation of excited-state absorption and stimulated emission bands assigned to the planar (kobs < 1012 s–1) and twisted (kobs ∼ 1010 s–1) structures between two pyridinium groups in the viologen ion. An efficient photoinduced electron transfer from the tetraphenylborate anionic moiety to the viologen dication was observed less than 1 μs after excitation. This is a consequence of the push–pull character of the electron donor twisted viologen structure, which helps formation of the borate triplet state. The borate triplet state is deactivated further via a second electron transfer process, generating viologen cation radical (V•+).

Publisher URL: http://dx.doi.org/10.1021/jacs.7b01946

DOI: 10.1021/jacs.7b01946

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