Quantum chemical studies on the conformational behaviour of substituted banana‐shaped mesogens with a central 1,3‐phenylene unit

Abstract

Ab initio and DFT calculations on the HF/STO‐3G and B3LYP/6‐31G(d) level were performed on the conformational behaviour of isolated banana‐shaped molecules of 1,3‐phenylene bis[4‐(4‐n‐hexyloxyphenyliminomethyl)benzoate] systems (P‐6‐O‐PIMB). The influence of small substituents in both the central phenyl ring and the external phenyl rings on the shape, polarity and flexibility of these molecules was investigated by one‐ and two‐fold relaxed potential energy scans in a systematic way. The effect of substituents on the global polarity of banana‐shaped mesogens was analysed by the magnitude and direction of the dipole moment and its components in relation to the long axis of the molecules. Moreover, a simple model for the calculation of the bending angle was tested for banana‐shaped molecules with a central 1,3‐phenylene unit. The findings for the isolated banana‐shaped molecules are correlated with solid state X‐ray and liquid crystalline state NMR results. Banana‐shaped molecules with both hexyloxy (P‐6‐O‐PIMB) and hexyl (P‐6‐PIMB) terminal chains are included to study the effect of substituents in the external phenyl rings on the flexibility of these chains. An attempt will be made to correlate the results with experimental findings on banana‐shaped mesogens.