Optical absorption and fluorescence of PRODAN in solution: Quantum chemical study based on the symmetry-adapted cluster-configuration interaction method

The optical absorption and fluorescence properties of 6-propionyl-2-(N,N-dimethyl)aminonaphthalene (PRODAN), a biological probe, were investigated using the symmetry-adapted cluster-configuration interaction (SAC-CI) method. The solvent effects were included using the polarizable continuum model (PCM). The PCM SAC/SAC-CI calculations well reproduced the significant solvatochromic shifts, without assuming twisted charge-transfer conformations. The geometry relaxation in naphthalene ring was significant for the lowest excited state. The nonequilibrium solvation was important in explaining the large solvatochromic shifts of the fluorescence. The present SAC-CI calculation showed that the absorption maximum corresponds to the second π–π∗ state, not the lowest excited state.