Effect of solvent polarity and viscosity on the decay dynamics of an intramolecular charge-transfer complex: 4-Dicyanomethylene-1,2,3,4-tetrahydromethylquinoline

Abstract

The absorption and emission spectra of 4-dicyanomethylene-1,2,3,4-tetrahydromethylquinoline (DCQ) in a variety of solvents are reported. DCQ exhibits a strong intramolecular charge-transfer absorption in the visible region and a considerable change in polarity on electronic excitation. The influence of solvent viscosity and polarity on the flurescence quantum yields (φ f) and decay time (τ f) of DCQ are examined. Both φ f and τ f increase with increasing solvent viscosity and polarity. The increase of φ f and τ f is due to hindrance of the free rotation of the exocyclic methylene moiety. The rate and activation energy of this process depend on solvent polarity and viscosity. Implications of these observations regarding the applicability of the existing theories are discussed.