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

J Am Chem Soc. 2017 Jun 14;139(23):7681-7684. doi: 10.1021/jacs.7b01946. Epub 2017 May 30.

Abstract

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•+).

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, Non-U.S. Gov't