Photochemistry of substituted cyclic enones. Part 11.1 Synthesis and photophysics of 5-arylalkyl-3-phenylcyclopentenones

Abstract

The photophysical properties of 3-phenyl-5-[2-(1-naphthyl)ethyl]cyclopent-2-enone and 5-[2-(1-naphthyl)methyl]-3-phenylcyclopent-2-enone have been compared with those of their constituent alkylated chromophores 1-ethylnaphthalene, 3-phenyl-5-(2-phenylethyl)cyclopent-2-enone and 3-phenyl-5-benzylcyclopent-2-enone by means of UV absorption spectroscopy, steady state and time resolved low temperature emission spectroscopy and laser flash photolysis. In mixed solvent low temperature glasses such as ethanol–isopentane–diethyl ether (2∶5∶5, v/v) (EPA) phosphorescence decay of all the enones shows multiexponential behaviour consistent with different lifetimes at different solvent sites. The naphthalene derivatives also show a longer lived emission consistent with slow processes involving a naphthalene localised triplet excited state. By contrast in fluid solution flash photolysis experiments reveal that there is rapid equilibration between the enone- and naphthalene-localised states.