Dual fluorescence of 9-(N,N-dimethylamino)anthracene: Effect of solvent polarity and viscosity

Absorption and fluorescence spectra of 9-(N,N-dimethylamino)anthracene (9-DMA) have been studied in a series of organic solvents and water. The induced circular dichroic spectra of 9-DMA were measured in beta- and gamma-cyclodextrins to locate the position of the L-1(a) and L-1(b) transitions in the absorption spectrum. The fluorescence spectra of 9-DMA exhibit dual emission bands in the solvents employed. Absorption and fluorescence excitation spectra of 9-DMA exhibit a local and an underlying charge-transfer band. The effects of temperature, solvent polarity, and viscosity on these spectra have been studied. The steady-state fluorescence polarization spectra were used to examine the transitions involved. The fluorescence quantum yields and lifetimes of 9-DMA in neat solvents and solvent mixtures have been measured. The pK(a) value of nitrogen protonation was estimated in aqueous solution. Semiempirical AMI calculations were performed to calculate energies and dipole moments of various conformers of 9-DMA obtained by twisting the -N(CH3)(2) group around the C-N bond.