Time-resolved CIDEP in the photoreduction of quinones. A study of the spin lattice relaxation time of semiquinone radicals in solution

Abstract

The application of time-resolved CIDEP observations to the measurements of T1 of transient radicals is examined in detail. The importance of proper treatment of the response time is considered theoretically and demonstrated experimentally. By taking into account the variation of response time at high power, a method is described on how to evaluate B1. At low power levels when the response time does not vary significantly, the extrapolation to zero power will provide a good estimate of T1. The method was applied to measure T1 for both the neutral radical and the radical anions of the benzoquinone, tetrachlorobenzoquinone, and duroquinone. It is confirmed that there is no significant difference in T1 between the neutral radical and the radical anions. The values of the estimated T1 are 2.2 μs for semibenzoquinone, 2.7 μs for semitetrachlorobenzoquinone, and 3.2 μs for semiduroquinone, all at 10 °C and in a 50% isopropanol/toluene solvent.