On the photophysical behaviour of 4-halo-5-phenylisoxazoles

Detailed spectral and photophysical properties of 4-halo-5-phenylisoxazoles in cyclohexane solutions are presented, including measurements of energies of lowest excited singlet and triplet states, fluorescence quantum yields, lifetimes, phosphorescence and triplet-singlet difference absorption spectra. Upon addition of ethanol, loss of vibrational structure is observed in fluorescence spectra and attributed to formation of isoxazole-ethanol aggregates. The relevance of these properties to the photochemical and thermal reactivity of these systems is discussed.