Fluorescence of chloropentafluoroacetone

The fluorescence of chloropentafluoroacetone in the gaseous state at room temperature is reported. The fluorescence extends from 337 nm to greater than 560 nm with a maximum intensity at 420 nm and is unaffected by low pressures of oxygen. The energy of the first excited singlet state is estimated as about 83 kcal and the fluorescence data for 313 and "290" nm excitation indicate that fluorescence enhancement occurs as the pressure increases. The fluorescent yield at high pressures [Formula: see text] is independent of the nature of the gas used to attain the high pressure. The lifetime of the fluorescent state is 35.1 ± 0.3 ns.A simple mechanism correlates the experimental observations and the values of the rate constants are considered. The reciprocal of the natural radiative lifetime is calculated to be 6.6 × 105 s−1 and the rate constant assigned to intersystem crossing to the triplet is 2.8 × 107 s−1. A comparison with the data in the literature for hexafluoroacetone shows the effect of substitution by a heavy atom in the fluorinated ketone. It about doubles the value of the rate constant associated with intersystem crossing from the first excited singlet state in the gas phase.