INTRAMOLECULAR CHARGE-TRANSFER IN AMINOBENZONITRILES - REQUIREMENTS FOR DUAL FLUORESCENCE

Dual fluorescence and intramolecular charge transfer (ICT) are observe d with aminobenzonitriles when two excited state levels (S1 and S2(CT) in DMABN) have an energy gap sufficiently small for vibronic coupling : a solvent-induced pseudo-Jahn-Teller effect. It is argued that the N -inversion of the amino group acts as a promoting mode. These conclusi ons are based on a comparison of absorption spectra and photostationar y and time-resolved fluorescence data. Dual fluorescence is also obser ved with MMD, in which the dimethylamino group is twisted towards a pe rpendicular configuration with respect to the phenyl ring.