CIDEP measurement of the electron spin-lattice relaxation time of triplet benzophenone in liquid solution

The relaxation of chemically induced electron polarization (CIDEP) in photoexcited triplet benzophenone is measured in competition with triplet quenching by 2,2′-azobis[isobutyronitrile] (AIBN). The spin polarization, transferred to the resulting 2-cyano-2-propyl radicals, is determined by time-resolved ESR spectroscopy for different AIBN concentrations. The rate constant for quenching is found to be kQ = 4.4 × 109 M−1 s−1, and 3T1 = 0.8 ns is obtained for the electron spin-lattice relaxation time of triplet benzophenone in 1,2-epoxypropane at room temperature.