Dual fluorescence of the lactone form of rhodamine B (LRB) in polar aprotic solvents has been ascribed to two forms of the dye: lactone and zwitterion, which is built up after the dissociation of the lactonic bond in the excited state. We have studied the kinetics of fluorescence in both bands in several aprotic solvents as a function of temperature by the SPC technique using global analysis of the decay curves. It has been found that under certain conditions (solvent, temperature) the decay kinetics of the zwitterion fluorescence cannot be described by monoexponential function. The two-exponential fits of zwitterionic fluorescence decays are discussed in terms of a quenching effect of the surroundings on the excited molecule. The possibility of diabatic (back-) closure of the lactone ring as a deactivation channel is also considered.
Volume 134, 2022
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