Biphotonic photodissociation of phenylalanine in aqueous solution at 20°C

The photophysical processes leading to the photochemical changes in the aromatic amino acid phenylalanine were examined as a function of pH in aqueous solutions at 20°C, using the technique of flash photolysis. The photodissociation reaction to form the benzyl (φCH₂) radical was found to occur via a biphotonic process at pH 5.9 and pH 0.45, and via a monophotonic process at pH 11.0. Using characteristics quenches, the precursor of the photodissociation of phenylalanine at all pH values was shown to be a long-lived (triplet) excited state.