Phosphorescence of Phenylcarboxylic Acids and Their Salts

The phosphorescence spectra and lifetimes of a series of carboxylic acids, phenyl–(CH2)n–COOH, and their salts have been measured. It is shown, contrary to accepted attitudes, that the lowest triplet state of benzoic acid is not an excitation localized on the benzene ring but involves considerable delocalization onto the carboxyl group. The lowest triplet energy of the carboxyl group and its radiative lifetime are estimated as 29.7 kK and 4 sec, respectively.