Naphthoylnaphthvalene -> naphthoylnaphthalene valence isomerization via anintermediate generated form the lowest excited singlet state

At room temperature, sub-picosecond laser photolysis of naphthoylnaphthvale ne (NNV) and naphthoylnaphthalene (NN) reveals that their lowest excited si nglet states ((NNV)-N-1* and (NN)-N-1*, respectively) have an identical Lif etime (0.7 ps). In comparison with the results obtained by nanosecond laser photolysis and steady-state photolysis of NNV (cf. Nakayama et al., Chem. Phys. Lett. 266 (1997) 601), however, it is concluded that the decay channe ls of (NNV)-N-1* are intersystem crossing to the lowest excited triplet sta te and valence isomerization yielding ground-state NN; of course, the decay channel of (NN)-N-1* is only intersystem crossing to the lowest excited tr iplet state. Interestingly, steady-state photolysis of NNV at 77 K and then measurements of the absorption and fluorescence spectra really indicate th e existence of an intermediate (P-77) for (NNV)-N-1* --> NN valence isomeri zation. Although no clear solvent effects on the absorption and fluorescenc e spectra of P-77 are observed, it is proposed that P-77 is either a bond-c loven species or a valence isomer of NNV generated from (NNV)-N-1*. (C) 199 9 Elsevier Science S.A. All rights reserved.