Spectral properties and modeling of knightletin, a novel aminocoumarin with intramolecular hydrogen bonding

Knightletin is a novel, high quantum-yield, substituted coumarin in the group of fluorescent 7-aminocoumarins. The molecule reveals the influence of a vicinal hydroxyl group on the aminocoumarin structure through its absorbance-fluorescence properties and interaction with several initial solvents. The substitution on the benzene ring of the coumarin affects electronic states, the molecular dipole moment and involves both intramolecular and intermolecular hydrogen bonding. This report describes the synthesis of knightletin, its absorbance-fluorescence characteristics in three solvents of varying polarity and hydrogen-bonding ability, and insights on its confor-mation from density functional theory modeling. The quantum yield of 0.81 in methanol is remarkable. The modeling indicates a ground state geometry with a pyramidal NH2 group interacting with the OH in an NH-donor hydrogen bond and predicts spectroscopic characteristics consistent with the experimental observations.