USE OF TRIS (2,2'-BIPYRIDINE) RUTHENIUM(II) DICATION IN A NOVEL METHOD FOR THE DETERMINATION OF SINGLET OXYGEN REACTION-RATES - APPLICATIONTO STUDIES OF GELATIN

A novel method for the determination of singlet oxygen reaction rate c onstants is described and applied to studies of cyclohexadiene in meth anol and gelatins in H2(O) and D2O. The technique uses tris (2,2'-bipy ridine) ruthenium(II) dication (Ru(bipy)(3)(2+)) as both singlet oxyge n sensitizer and in situ oxygen concentration monitor during irradiati on of sealed samples, Because of the high efficiency with which the lu minescence of Ru(bipy)(3)(2+) can be detected, and the fact that emis sion lifetimes are used, the method offers some advantages over those previously described. The advantages and disadvantages of the method a re discussed. A fate constant of 2.1 (+/- 0.3) x 10(6) mol(-1) dm(3) s (-1) has been determined for the reaction of O-2 with cyclohexadiene i n methanol. For two different photographic gelatins the sums of reacti on and quenching rate constants are 2.0 (+/- 0.4) x 10(6) and 3.1 (+/- 2.0) x 10(5) mol(-1) dm(3) s(-1); for swine skin gelatin this value i s 3.9 (+/- 2.4) x 10(5) mol(-1) dm(3) s(-1). Chemical reaction, rather than physical quenching, is the dominant reaction route for gelatins and O-2.