PHOTOPHYSICS AND PHOTOCHEMISTRY OF SALICYLIC-ACID REVISITED

The spectral and photophysical properties of salicylic acid in various solvents have been studied by steady state and time resolved experime nts. Various emitting species have been identified. In alcohols, e.g. methanol, both the zwitterion and monoanion show emission. The additio n of a small amount of acid results only in zwitterionic emission, whe reas in the presence of a small amount of alkali, the monoanion is pro duced. Only the monoanion shows emission in water. In concentrated sul furic acid, emission from the cation is observed, whereas in concentra ted KOH solution, the dianion is the emitting species. In hydrogen bon ding solvents, e.g. diethyl ether, hydrogen bonded monomers are presen t. In polymer matrix poly(methyl methacrylate) only monomeric emission is observed. The deactivation of the cation is similar to that of the zwitterion, indicating that the presence of an extra proton in the ca rboxylic group increases the nonradiative process. Hydrogen bonding as well as viscosity/rigidity of the matrix have also been found to decr ease the deactivation rate in the zwitterion. (C) Elsevier Science S.A .