Activated radiationless decay of rhodamine-3B: nonequilibrium polarization effects in viscous solvents

Nonequilibrium polarization effects that arise in high viscous polar solvents are discussed as regards to the rhodamine-3B-activated radiationless process. Rate constants are interpreted using dipole isomerization theories which enable the recovery of a barrier top region wave number identical to that previously obtained in less viscous solvents [J. Phys Chem. A 104, 11909 (2000)]. The Onsager-frequency-dependent reaction field can model the friction effect on the rate constants that in glycerol were estimated also from an adiabatic charge-transfer model. The cusp barrier height is half the electronic coupling, as expected from the equality found for the frequencies of the reactant well and barrier top in this process. Coupling to solvent polarization modes can control the friction effect on the reactive mode. A two-dimensional reaction surface explains the photophysical features detected in the radiationless decay and a state energy diagram is proposed for rhodamine-3B.