ChemInform Abstract: Dielectric Relaxation in Some Fluoro-Substituted Diphenyl Derivatives

Dielectric relaxation measurements have been performed on the four isomers 2,2′ -, 2,3′ -, 3.3′ - and 2,4′ -difluorodiphenyl (DFDP) in p -xylene in the frequency and temperature ranges of 1.5–10 GHz and 293–323 K respectively. It has been found that symmetrically substituted derivatives (2,2′ - and 3,3′ -difluorodiphenyls) show a Debye-like pattern and that for non-symmetrically substituted derivatives (2,3′ - and 2,4′ -DFDP) the dielectric absorption differs strongly from this type of pattern. According to the model, this behaviour indicates that in the symmetrical compounds the contribution of the intramolecular rotation can be neglected and that in the case of non-symmetrically substituted derivatives there are two dielectric relaxations connected with internal rotation and overall molecular reorientation respectively. The analysis of the dielectric relaxation times together with moments of inertia is used to obtain further information about the molecular dynamics.