Spectrofluorometric Studies. X. The Photochemistry of Pentafluorobenzene

The vapor phase photochemistry of pentafluorobenzene has been examined at a variety of exciting wavelengths starting at 2540 A and extending to 2780 A. Most of the studies were carried out at 2620, 2660, and 2700 A. Below 2600 A pentafluorobenzene does not exhibit any detectable fluoroscence, above 2600 A a very weak fluorescent emission was observed. Addition of biacetyl does not markedly reduce the fluorescent yield, while addition of cyclohexane, CO2, and cis-butene-2 causes an increase in the fluorescent yield. The triplet yield of pentafluorobenzene excited at 2620, 2660, and 2700 A, measured by the sensitized emission of biacteyl technique, is also very low and is increased by the addition of cyclohexane, CO2, and cis-butene-2. cis-Butene-2 is the most effective gas, of the three examined, in increasing the fluorescent and triplet yields of pentafluorobenzene. The fate of the majority of pentafluorobenzene molecules excited in the 2600 A region is unknown.