Fluorescence of a ketocyanine dye in pure and mixed binary solvents at 77 K

Emission and excitation spectrum of a ketocyanine dye has been studied at 77 K in pure solvents (methanol, ethanol, 2-methyltetrahydrofuran (2MTHF)) and in several mixed solvents. In a pure solvent at 77 K a single fluorescence band appears. In protic solvents the band gets reduced in intensity on melting and a red shifted emission band is obtained. On the other hand a blue shifted band appears on melting for aprotic solvents. This has been explained as due to a geometry change on excitation. Two emitting species have been identified in a glass containing mixed protic + aprotic solvents at 77 K. Preferential solvation of the solute by ethanol over 2MTHF has been indicated in a mixed binary solvent containing these two solvents.