Naphthoylnaphthvalene → naphthoylnaphthalene valence isomerization via an intermediate generated form the lowest excited singlet state

Abstract

At room temperature, sub-picosecond laser photolysis of naphthoylnaphthvalene (NNV) and naphthoylnaphthalene (NN) reveals that their lowest excited singlet states ( 1 NNV ∗ and 1 NN ∗ , respectively) have an identical lifetime (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 channels of 1 NNV ∗ are intersystem crossing to the lowest excited triplet state and valence isomerization yielding ground-state NN; of course, the decay channel of 1 NN ∗ is only intersystem crossing to the lowest excited triplet state. Interestingly, steady-state photolysis of NNV at 77 K and then measurements of the absorption and fluorescence spectra really indicate the existence of an intermediate (P-77) for 1 NNV ∗→ NN valence isomerization. Although no clear solvent effects on the absorption and fluorescence spectra of P-77 are observed, it is proposed that P-77 is either a bond-cloven species or a valence isomer of NNV generated from 1 NNV ∗ .