Torsional barriers and correlations between dihedrals in p-polyphenyls

The torsional energy curves for biphenyl, p-terphenyl, and p-quaterphenyl are calculated using the B3LYP density functional with a triple-zeta polarized basis set. In agreement with recent accurate literature data, barriers of similar height are found at 0degrees and 90degrees for biphenyl. For the higher members, the torsional energy curves show an increasing tendency to lower the barrier of the coplanar conformations. The correlation effects between different dihedrals are reasonably small and discussed extensively. In addition, torsional potential functions at different levels of accuracy, suitable for computer simulations, are proposed for all the members of the series up to p-quinquephenyl.