Evidence for comparable reactivity of alkanone excited singlet and triplet states toward hydrogen donors

Abstract

Studies of solvent effects on the relative fluorescence quantum yield (e (b) University of Rochester. (3) NSF Trainee, 1970-1971 ; NDEA Title IV Fellow, 1971-1978. (4) Alfred P. Sloan Fellow, 1966-1970. ( 5 ) P. J. Wagner, J . Amer. Chem. Soc., 88,5672 (1966). (6) P . J. Wagner, J . Amer. Chem. SOC., 89,2503 (1967). (7) R . Simonaitis, G. W. Cowell, and J. N. Pitts, Jr., Tetrahedron (8) P. J. Wagner, TetrahedronLett., 5385 (1968). (9) N . J. Turro and D. M. McDaniel, Mol. Photochem., 2,39 (1970). (10) For a recent review, see J. C. Dalton and N. J. Turro, Annu. Let t . , 3751 (1967). Reo. Phys. Chem.,21,499(1970). which the alkanone S1 and TI states have been shown to have comparable reactivity, l 1 We would like to present evidence from studies of solvent effects on the quantum yield and lifetimes of fluorescence from 2-adamantanone that demonstrate that several hydrogen donors quench the n,r* singlet and n,ri* triplet states a t equivalent rates. Our results suggest that alkanone SI and TI states have comparable reactivity (but not necessarily efficiency) toward intermolecular hydrogen abstraction. Experimental Section Solvents were at least spectral grade further purified by fractional distillation prior to use. 2-Adamantanone (Aldrich) was twice sublimed prior to use. Tributyltin hydride (TBTH) was prepared by reduction of tributyltin chloride. 2-Propanol-ds (Merck) was used as received. 2-Propanol-0-d was prepared by exchange with Fluorescence and phosphorescence lifetimes were measured using the single photon counting technique. The air spark lamp used had a half-width of 1.8 nsec. Phosphorescence lifetimes were measured on degassed solutions in acetonitrile. Fluorescence yield measurements were carried out using a Hitachi-Perkin-Elmer MPF-2A spectrofluorometer. Minor corrections were made for differences in absorbance at A,, (310 nm). Results and Discussion We have studied solvent effects on the fluorescence lifetime, T,, and relative fluorescence quantum yield, (11) See N. J. Turro, et ai., Accounts Chem. Res., 5 , 92 (1972), and DzO.