Spectral properties of a high quantum yield, novel aminocoumarin with a vicinal hydroxyl group

Knightletin is a novel, high quantum-yield, substituted coumarin in the group of fluorescent aminocoumarins. The molecule reveals the influence of a hydroxyl group on the aminocoumarin structure through its absorbance-fluorescence properties and interaction with several solvents. The substitution on the benzene ring of the coumarin affects electronic states, the molecular dipole moment and hydrogen bonding between vicinal groups as well as hydrogen bonding with solvents. This report describes the synthesis of knightletin, its absorbance-fluorescence characteristics in three solvents of varying polarity, and insights on its conformation 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.