trans→cis Photoisomerization of 1-styrylnaphthalene and its 4′-bromo- and 4′-chloro-derivatives. A fluorimetric and laser flash photolytic study

Abstract

The trans→cis photoisomerization of 1-styrylnaphthalene (1-StN) and two para-halogen-substituted derivatives (Cl- and Br-1-StN) have been studied in solution by laser flash photolysis and by fluorimetric and photochemical methods. Measurements of the fluorescence lifetime (τ_F) and quantum yield (ϕ_F), the corresponding triplet data (τ_T, ϕ_T), and the trans→cis photoisomerization quantum yield (ϕ_t→c) in a large temperature range are reported as well as the effects of solvents, quenchers and sensitizers. The temperature dependences of these parameters suggest that twisting around the central double bond in the lowest excited singlet state competes successfully with fluorescence and intersystem crossing for the three 1-StNs at elevated temperatures. At room temperature, twisting in the lowest triplet state contributes to a minor degree for 1-StN but markedly for Br-1-StN while at lower temperatures this because the only pathway for trans→ cis photoisomerization of the three 1-StNs.