Crystal Structures of the Room-Temperature Phase of 4,4″-Difluoro-p-terphenyl and 4,4″′-Difluoro-p-quaterphenyl

Abstract 4,4″-Difluoro-p-terphenyl and 4,4″′-difluoro-p-quaterphenyl were synthesized and their crystal structures were determined at room temperature. These are isostructural to p-terphenyl and p-quaterphenyl, respectively. Some “disorder” in the inner benzene ring orientation was detected and resolved by the split-atom method. A rigid-body librational analysis of each benzene ring around the long molecular axis was performed. A rough estimate of the barrier height of the planar conformation for 4,4″-difluoro-p-terphenyl was obtained as being about 1 kJ mol−1. The results are compared with the properties of p-terphenyl and p-quaterphenyl, and the effect of fluorine-substitution on the molecular properties is discussed in relation to the low-temperature phase transitions.