Heavy Atoms as Molecular Probes in Studying the Solvent Dependence of the Dynamics of Triplet Exciplexes

Electron transfer reactions between thiopyronine triplet (acceptor 3A+) and the electron donors (D), aniline, p-Br-aniline and p-I-aniline, are investigated by flash spectroscopy in solvents of different viscosity and polarity. Due to the heavy-atom effect the radical yield becomes very sensitive to the solvent influence, which can be explained by the dynamic properties of a triplet exciplex (3(AD+)) formed as a primary product in the reaction between acceptor triplet and donor. Whereas on variation of solvent viscosity the solvent cage effect on the dissociation of 3(AD+) is observed, a change in solvent polarity is suggested to affect the radiationless deactivation of 3(AD+) to the ground state of the components