One- and two-photon processes in the photochemistry of 1.3-bis(1-naphthyl)-2-propanone: an example of a "reluctant" Norrish type I reaction

Abstract

Photoexcitation of 1,3-bis(1-naphthyl)-2-propanone in the carbonyl or naphthalene chromophore leads to the formation of a carbonyl-localized singlet state in the subnanosecond time scale. This singlet decays (tau/sub s/ = 1.4 ns in isooctane), presumably to yield the carbonyl triplet, which rapidly populates the naphthalene-localized triplet state. This intermediate can be readily detected by laser flash photolysis and shows typical naphthalene-like characteristics (TT absorption, lambda/sub max/ = 430 nm). Product and quenching studies indicate that the Norrish Type I cleavage occurs from the singlet state with Phi approx. = 0.002. Excitation of the triplet state with the pulses from a dye laser (430 nm) leads to cleavage of the CH/sub 2/-CO bond to yield 1-naphthylmethyl radicals in a process that the authors describe as a reluctant Norrish Type I reaction. The quantum yield for this process is approx.0.06. The structural features required for this type of process to occur are discussed.