Abstract
Abstract— A novel method for the determination of singlet oxygen reaction rate constants is described and applied to studies of cyclohexadiene in methanol and gelatins in H2O and D2O. The technique uses tris (2,2′‐bipyridine) ruthenium(II) dication (Ru(bipy)32+) as both singlet oxygen sensitizer and in situ oxygen concentration monitor during irradiation of sealed samples. Because of the high efficiency with which the luminescence of Ru(bipy)32+* can be detected, and the fact that emission lifetimes are used, the method offers some advantages over those previously described. The advantages and disadvantages of the method are discussed. A rate constant of 2.1 (±0.3) x 106 mol‐1 dm3 s‐1 has been determined for the reaction of 1O2 with cyclohexadiene in methanol. For two different photographic gelatins the sums of reaction and quenching rate constants are 2.0 (±0.4) x 106 and 3.1 (±2.0) x 105 mol‐1 dm3 s‐1; for swine skin gelatin this value is 3.9 (±2.4) × 105 mol‐1 dm3 s‐1. Chemical reaction, rather than physical quenching, is the dominant reaction route for gelatins and 1O2.
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