Photoredox chemistry of p-nitrophenylalanine and p-nitrophenethyl amine in basic aqueous solution: formation of an observable long-lived intermediate

Abstract

The photochemistry of p-nitrophenylalanine ( 1), an artificial amino acid, and p-nitrophenethyl amine ( 2) was studied in aqueous solution over a range of pH. Irradiation of these two compounds in basic solution results in the development of a highly visible orange—red colour which decays slowly over 24 h, indicative of the formation of a long-lived intermediate. Sunlight is effective in inducing this colour change with the more reactive p-nitrophenylalanine. From the structure of the final photolysis product ( p-aminobenzaldehyde ( 5)) and UV—visible and proton nuclear magnetic resonance ( 1H NMR) (360 MHz) studies of the photoreaction, a mechanism is proposed which involves initial electron transfer from the amino group of 1 and 2 to the nitrophenyl triplet excited state, followed by a complex reaction pathway resulting in overall intramolecular redox chemistry.