Photoinduced Electron Transfer in Bianthryl and Cyanobianthryl in Solution:  The Case for a High-Frequency Intramolecular Reaction Coordinate

Photoinduced intramolecular electron transfer (ET) in symmetric 9,9‘-bianthryl (BA) was studied by femtosecond pump-supercontinuum-probe spectroscopy in solvents covering the whole polarity scale. Results are compared with those obtained for the nonsymmetric 10-cyano derivative (CBA). The behavior exhibited by both compounds is qualitatively the same, which suggests that symmetry plays no essential role. Our measurements provide novel aspects: (i) electron-transfer proceeds in CBA within a time on the order of 10 fs and therefore along a high-frequency coordinate, (ii) the observation of both educt and product bands allows an estimate of the ET equilibrium, which shifts through solvent relaxation. We find no evidence of dynamics along the intramolecular twist coordinate before ET.