Nature of 2-Aminoxanthone Fluorescence

Absorption and fluorescence spectra of 2-aminoxanthone in solutions of different types at 77-350 K were studied. The existence of three bands (λ_{1 max} = 417 nm, τ₁ = 14 ns; λ_{2 max} = 528 nm, τ₂ = 13 ns; and λ_{3 max} = 565 nm, τ₃ = 6 ns) in fluorescence of 2-aminoxanthone solutions has been established. It was shown that the first short-wave band was determined by deactivation of singlet excitation of an aminoxanthone molecule. The band with λ_{3 max} = 565 nm (depending on the concentration) is connected with excimer-type aggregates, which are formed by aminoxanthone molecules grouped with the help of dipole molecules of solvent or by weak hydrogen bonds between aminoxanthone molecules. The emission in band λ_{2 max} = 528 nm is caused by reversible changes in the 2-aminoxanthone molecule and probably is connected with an intramolecular proton transfer.