Exciton Coupling and Dipolar Correlations in a Columnar Liquid Crystal:  Photophysics of a Bent-Rod Hexacatenar Mesogen

Abstract

A novel bent-rod hexacatenar liquid crystal is reported that displays a hexagonal columnar (Col h ) phase. The organization of conjugated hexacatenar mesogens in the columnar phase is of interest for their anisotropic electronic properties. The emissive nature of the mesogens varies over the temperature range of the Col h phase and the spectral shifts were analyzed in terms of an exciton-coupling model. The variation of the emission band in this phase is consistent with varying degrees of rotational disorder between the mesogens. The bent-rod shape and highly dipolar nature of the liquid crystal core (mesogen) promotes (as suggested by computation, X-ray diffraction, and photophysical studies) a high degree of antiparallel intermolecular correlations between nearest neighbors. The antiparallel organization is novel and differs from structures previously identified in other polycatenars. These studies illustrate the utility of the exciton-coupling model to probe the nature and degree of intermolecular correlations in highly dipolar liquid crystals.