LASER-INDUCED FLUORESCENCE STUDY OF THE S-0-S-1 TRANSITION OF 1-PERFLUORONAPHTHOL AND 2-PERFLUORONAPHTHOL IN A SUPERSONIC JET

The S-0-S-1 transition of 1- and 2-perfluoronaphthol (1-FN and 2-FN) h as been studied by fluorescence excitation and dispersed emission in a continuous supersonic expansion. Each compound gives rise at the orig in to two dissimilar excitation systems which can be distinguished by their emission region, While the higher energy systems exhibit both in absorption and in emission the characteristic features of unsubstitut ed perfluoronaphthalene, the low-energy systems present a different co mplex pattern typical of a strongly distorted excited state. The dispe rsed fluorescence from 1-FN shows a resolved resonant structure for bo th systems, but the emission extends largely toward the red for the ex citation of the low-energy system excitation. The dispersed emission f rom 2-FN low-energy system is totally diffuse and red shifted, with a maximum at about 4500 cm(-1) from the excitation. The two absorption s pectra have been tentatively attributed to the presence of the ground state cis and trans rotamers corresponding to a different orientation of the OH group with respect to the naphthalene frame and involving di fferent weak hydrogen bonding of OH with the neighboring fluorine atom . The spectroscopic properties of each rotamer have been shown to be s trongly sensitive to the position of the weak internal hydrogen bond.