Infrared and UV–visible absorption spectra of hexafluoroacetylacetone in a low-temperature argon matrix. II. Detection of the nπ* transition by monitoring IR spectral changes due to photoisomerization

The chelated enol-type isomer was found to isomerize to a non-chelated enol isomer by UV irradiation between 260 and 300 nm, while backward isomerization was observed by that between 320 and 340 nm although no electronic absorption band was detectable in this region. Wavelength dependence of the isomerization rate constants, measured by monitoring the infrared spectral changes, shows that the isomerization by UV radiation is caused by the ππ* transition for the chelated enol located around 280 nm and by the ππ* and nπ* transitions for the non-chelated enol around 260 and 340 nm, respectively.