FACTORS GOVERNING THE EFFICIENCY OF SINGLET OXYGEN PRODUCTION DURING OXYGEN QUENCHING OF SINGLET AND TRIPLET-STATES OF ANTHRACENE-DERIVATIVES IN CYCLOHEXANE SOLUTION

The efficiencies of singlet oxygen production from the first excited s inglet and triplet states of a range of substituted anthracenes in cyc lohexane are reported. For all of the anthracene derivatives in this s olvent, the efficiency of singlet oxygen production from the triplet s tate, f(DELTA)T, is found to be unity. In contrast, however, the effic iency of singlet oxygen production from the first excited singlet stat e, f(DELTA)S, varies from zero for anthracene to unity for 9,10-dicyan oanthracene. It is established that the magnitude of f(DELTA)S is dete rmined by the same factors which govern intersystem crossing yields fo r anthracene derivatives, i.e., the activation energy for intersystem crossing to higher triplet states. In addition it is confirmed that ox ygen quenching of the excited singlet states of four anthracene deriva tives in cyclohexane proceeds exclusively via enhanced intersystem cro ssing yielding triplet states. Some previously unavailable photophysic al data are also reported for these substituted anthracenes, i.e., tri plet energies, triplet yields, and rate constants for oxygen quenching of triplet states.