Intramolecular Electron Transfer in Biferrocene Monocation:  Evaluation of Franck−Condon Effects via a Time-Dependent Analysis of Resonance Raman Scattering in the Extended Near-Infrared

Franck−Condon effects associated with intramolecular electron transfer in the biferrocene monocation have been evaluated via time-dependent analyses of resonance Raman scattering intensities and the intervalence absorption line shape. Quantitative studies in the extended near-infrared (1320 and 1064 nm excitation) reveal that three vibrational modes are displaced in the electron-transfer process. The most significant of these, the symmetrical ring−Fe−ring stretch, has also been implicated in prior X-ray crystallographic studies. Mode or bond displacements obtained from the Raman analysis are slightly larger than estimates based on crystallographic displacements. These differences together with contributions from two additional modes identified by Raman appear to account for seemingly disparate estimates of vibrational reorganization energies provided by (a) the crystallographic method and (b) “Pekar plot” intercepts derived from intervalence absorption maxima. Implications for electron exchange kinetics are also discussed.