INTERACTION AND DYNAMICS OF NON-RIGID MOLECULES IN WEAK CRYSTALLINE COMPLEXES: SPECTROSCOPIC STUDIES OF 1:1 CRYSTALLINE COMPLEXES OF PERFLUOROBIPHENYL WITH NAPHTHALENE AND $BIPHENYL^{*}$

$^{1}$ D. G. Naae, Acta Cryst. B35, 2765 (1979). $^{*}$Supported by Air Force Office of Scientific Research, Contract \# F49620-79-C-0229. $^{\ast\ast}$Alfred P. Sloan Fellow.Author Institution:Biphenyl and perfluorobiphenyl molecules are non-rigid with respect to deformation between the two aromatic rings. The symmetries of these molecules are very much dependent on the crystalline interactions. For example biphenyl in pure crystal at room temperature is planar. On the other hand, a recent $report^{1}$ shows both biphenyl and perfluorobiphenyl to be non-planar in their 1:1 binary complex. No such structural information is available for the naphthalene: perfluorobiphenyl complex in which only one of the components, perfluorobiphenyl, is a typical non-rigid molecule. Raman spectroscopy, both in phonons nd internal vibration region, is used to investigate the interactions and dynamics of these complexes as well as for complexes involving isotopic Substitution with respect to the aromatic hydrocarbons. Results will also be presented from the singlet and the triplet electronic spectra of these complexes. The two complexes offer the possibilities of reversal of the energy order. In the naphthalene: perfluorobiphenyl complex the naphthalene (1st component) states are lower in energy, while in the biphenyl: perfluorobihenyl complex, the perfluorobiphenyl states are lower in energy compared to the first component (biphenyl). We investigate the interaction and dynamics by studying exciton interaction, intercomponent energy transfer and exciton-phonon coupling