Trimeric supramolecular liquid crystals induced by halogen bonds

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Abstract
This paper described a series of trimeric halogen bonded supramolecular thermotropic liquid crystals. The halogen bonding interaction was studied by infrared and X-ray photoelectron spectroscopy. It was observed that the aromatic skeleton infrared vibration of halogen bonded acceptor molecules had moved to higher frequencies relative to their corresponding unbonded counterparts. The halogen-bonded acceptors showed higher N 1s binding energies of 0.89–1.12 eV than those of unbonded components. In contrast, the halogen-bonded donors displayed lower I 3d binding energies than their corresponding unbonded species. The changes in binding energies and in infrared frequencies demonstrated the presence of effective halogen bonding interaction. The thermal behaviors of the halogen-bonded complexes were examined using differential scanning calorimetry and optical polarizing microscopy. Most of the trimeric complexes exhibited thermotropic liquid crystals with smectic A phases. The effect of length in spacers and terminal groups in halogen bond molecules on mesophase transition temperatures was investigated, revealing that there was little correlation between the length in spacers and terminal groups and phase transition temperatures.