Excited-state dynamics of naphthoylnaphthvalene: valence isomerization of the lowest excited singlet state and intermolecular hydrogen-atom abstraction of the lowest excited triplet state

By measurements of phosphorescence and transient absorption spectra as well as steady-state photolysis of the title compound (NNV), it is concluded as follows: (1) In benzene and ethanol, intersystem crossing from the lowest excited singlet (1NNV∗) to triplet (3NNV∗) states competes withvalence isomerization of 1NNV∗ yielding ground-state naphthoylnaphthalene (NN). (2) In ethanol, the NNV ketyl radical (generated by hydrogen-atom abstraction of 3NNV∗ from the solvent molecule) also undergoes rapid valence isomerization and recombination of two NN ketyl radicals thus formed yields 1,1,2,2-tetranaphthyl-1,2-ethanediol (naphthopinacol).