TIME-RESOLVED ELECTRON-SPIN-RESONANCE AND LASER FLASH SPECTROSCOPY INVESTIGATION OF THE PHOTOREDUCTION OF ANTHRAQUINONE-2,6-DISULFONIC ACID, DISODIUM SALT BY SODIUM-SULFITE IN AEROSOL OT REVERSE MICELLES

Spin-correlated radical pairs (SCRP) of radical anions formed by photo reduction of anthraquinone-9,10-disulfonic acid, disodium salt (AQ) by sodium sulfite in solution of Aerosol OT (AOT) reverse micelles in is ooctane have been studied by time resolved electron spin resonance (TR ESR) and nanosecond laser flash photolysis employing optical absorpti on. The molar ratio of water to AOT w was varied from 5 to 50, and the spectra of SCRP were observed in micelles with w greater than or equa l to 20. The value of exchange interaction in such micelles was determ ined and found to be on the order of a few tenths of a gauss. The phot oreduction of AQ is accompanied by strong emissive ESR spectra of the radicals AQ(.-) and SO3.-. The hyperfine coupling in AQ(.-) is fully r esolved at the relatively long time of several microseconds after the laser flash. The initial. SCRP spectra are succeeded in time by an E/A ESR pattern due to a radical pair mechanism. The rate constants of ra dical recombination within micelles and radical pair exit from the mic elles were determined by laser flash photolysis. The results are consi stent with the formation of associates such as AQ(.-)/Na+/SO3.- triads in reverse micelles; i.e., the radical anions are held together by a bridging sodium ion.