Photochemistry of substituted cyclic enones. Part 11. Synthesis and photophysics of 5-arylalkyl-3-phenylcyclopentenones

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.