Synthesis and Fluorescence Property of 5-amino-2-(2-hydroxyphenyl)-2H-benzotriazole Derivatives

Abstract

2-(2-hydroxyphenyl)-2H-benzotriazole derivatives show excited state intramolecular proton transfer (ESIPT) due to the formation of intramolecular hydrogen bonding between the hydroxyl group and the nitrogen atom in the benzotriazole group. Therefore, they are known to cause efficient non-radiative deactivation and show no fluorescence, and they are widely used as ultraviolet absorbers. We synthesized 2-(2-hydroxyphenyl)-2H-benzotriazole derivatives having an amino group, a monobutylamino group or a dimethylamino group at 5 position and found that they showed fluorescence in spite of having molecular structure capable of causing ESIPT. Characteristic absorption at the long-wavelength ultraviolet area of these derivatives didn't show significant change in the solvent which has hydrogen bonding acceptor inhibiting intramolecular hydrogen bonding. It may show that these derivatives have relatively weak intramolecular hydrogen bonding and the efficiency of the ESIPT is low. In addition, the higher the electron-donating of the substituent at the 5-position, the stronger the fluorescence. The electron-donating property of these substituents may reduce the proton acceptability of the benzotriazole group in the excited state, suppress ESIPT, and develop fluorescence.