Intramolecular charge transfer of coumarin dyes confined in methanol-in-oil reverse micelles

Abstract

The reverse micelles (RMs) of bis(2-ethylhexyl)sulfosuccinate sodium salt (AOT) are considered as a model system for the molecular dynamics investigation of small chromophores, where the micelle-size-dependent dynamics are interpreted as the unique solvent properties in the core of RMs. The sizes of RMs are practically proportional to the molar ratio between polar solvent and surfactant. However, the formation of RMs with nonaqueous polar solvents methanol or acetonitrile is not clearly understood yet. In this work, we have shown that the formation of RMs with methanol core depends strongly on the concentration of surfactant AOT by the experimental evidence of the absorption, emission, and Raman spectroscopic measurements. In addition, the intramolecular charge transfer dynamics of coumarin 481 (C481) and coumarin 153 in methanol RMs were investigated by steady-state and time-resolved electronic spectroscopy, where the differences of the excited-state dynamics in the RMs are understood as the effect of the molecular rotation of diethylamino group of C481.