THE DEACTIVATION OF SINGLET EXCITED ALL-TRANS-1,6-DIPHENYLHEXA-1,3,5-TRIENE BY INTERMOLECULAR CHARGE-TRANSFER PROCESSES .1. MECHANISMS OF FLUORESCENCE QUENCHING AND OF TRIPLET AND CATION FORMATION

The photophysical and fluorescence quenching properties of all-trans-1 ,6-diphenylhexa-1,3,5-triene (DPH) were investigated in toluene and ac etonitrile solution and the influences of the external heavy-atom effe ct (HAE) and of charge transfer (CT) processes on the fluorescence que nching mechanism were characterized. Particular emphasis was placed up on the elucidation of the electron transfer reactions in the quenching of DPH fluorescence by p-dicyanobenzene (p-DCB) in acetonitrile. It w as shown that the combination of stationary and time-resolved fluoresc ence measurements, laser flash photolysis and CIDNP experiments allows a comprehensive description of the primary and secondary electron tra nsfer reactions in the fluorescence quenching process. In particular, the characterization of the kinetics of genuine charge recombination ( CR) reactions of the DPH/p-DCB singlet and tripler ion pairs, of the s pin evolution process and of the degenerate electron transfer between neutral and cationic DPH was achieved.