Spectrofluorometric studies. III. Ortho- and para-difluorobenzene

Spectrofluorometric techniques have been used to determine gas phase singlet and triplet yields in ortho- and para-difluorobenzene as a function of exciting wavelength and pressure. The importance of the "around the corner effect" in such measurements as the cause of large errors is briefly discussed.In the case of ortho-difluorobenzene, maxima in fluorescent yield are produced by the exciting wavelengths 2490, 2580, and 2700 Å; minima at 2540 and 2660 Å. Triplet yields, using the sensitized biacetyl emission technique, have been determined at 2500, 2580, 2660, and 2700 Å. The sums of the singlet and triplet yields at these wavelengths are 0.34, 0.52, 0.75, and 0.97 respectively.Para-difluorobenzene has the largest quantum yield of fluorescence of any fluorinated benzene yet examined. The fluorescent yield shows only one definite minimum at 2740 Å. Triplet yields have been determined at 2660, 2740, and 2760 Å. The sums of the singlet and triplet yields at these wavelengths are 0.5, 0.5, and 0.7 respectively.