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

Abstract

Spin-correlated radical pairs (SCRP) of radical anions formed by photoreduction of anthraquinone-9,lOdisulfonic acid, disodium salt (AQ) by sodium sulfite in solution of Aerosol OT (AOT) reverse micelles in isooctane have been studied by time resolved electron spin resonance (TR ESR) and nanosecond laser flash photolysis employing optical absorption. 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 2 20. The value of exchange interaction in such micelles was determined and found to be on the order of a few tenths of a gauss. The photoreduction of AQ is accompanied by strong emissive ESR spectra of the radicals AQ'- and S03'-. The hyperfine coupling in AQ'- is fully resolved at the relatively long time of several microseconds after the laser flash. The initial SCRP spectra are succeeded in time by an WA ESR pattern due to a radical pair mechanism. The rate constants of radical recombination within micelles and radical pair exit from the micelles were determined by laser flash photolysis. The results are consistent with the formation of associates such as AQ'-/Na+/ SO3'- triads in reverse micelles; Le., the radical anions are held together by a bridging sodium ion.