Influence of the solvent on the emission of 3-( N,N-dimethylamino)-2H-1-benzopyran-2-one

Abstract

3-( N,N-dimethylamino)-2H-1-benzopyran-2-one (DMAC) exhibits a relatively strong shortlived emission (λ max ≈ 460 nm; lifetime, 0.2 ns) in non-polar solvents with a Stokes' shift of about 8000 cm −1. In more polar solvents, the emission shifts bathochromically (Stokes' shift up to 10 000 cm −1 and lifetime of 0.5 ns). Polar protic solvents quench the fluorescence and the quenching can be quantitatively described by a Stern—Volmer dependence. The bimolecular quenching rate constants are lower than those controlled by diffusion. The monomethyl derivative 3-( N-methylamino)-2H-1-benzopyran-2-one (MAC) exhibits emission in non-polar and polar solvents which is hypsochromically shifted with respect to DMAC (λ max ≈ 400 nm; Stokes' shift around 4000 cm −1) and is short-lived (less than 0.1 ns). The fluorescence of DMAC and MAC originates in the intramolecular charge-transfer state.