FLASH PHOTOLYSIS OF CAMPHORQUINONE AND BIACETYL

Flash photolysis of the solutions of camphorquinone in benzene, carbon tetrachloride, and isopropyl alcohol and of the solutions of biacetyl in carbon tetrachloride and isopropyl alcohol was studied. The irradiations were limited to the visible absorption bands of the two diketones. The absorption spectra of the transients formed were measured from 200 to 1125 mμ. The transient spectra in the benzene and the carbon tetrachloride solutions contain absorption bands at ∼320 and 630-1100 mμ that are unique to the triplet excited molecules of the diketones and are attributable to the (i) 3π* (3I) → 3oσ* and (ii) the 3π* (3I) → 3π* (3II) transitions, respectively. The camphorquinone triplet was photosensitized by benzophenone and quenched by anthracene and oxygen; the anthracene triplet was photosensitized by camphorquinone. Oxygen also quenched the biacetyl triplet. Both the diketones were photoreduced during flash photolysis of their isopropyl alcohol solutions. The spectra of the resulting hydrogen adduct free radicals were found to be very similar to those of the corresponding triplets in the ultraviolet region, but the free radicals were much longer lived.