Columnar self-assembly, electrochemical and luminescence properties of basket-shaped liquid crystalline derivatives of Schiff-base-moulded p-tert-butyl-calix[4]arene

Abstract

A new family of supramolecular liquid crystalline compounds with a calix[4]arene core and two linking groups appended on four sides, exhibiting a wide range of hexagonal columnar phases, has been synthesised and well characterised. The liquid crystal behaviour of the novel materials was studied by using polarising optical microscopy (POM), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), and was further confirmed using high-temperature powder X-ray diffraction (XRD). An electrochemical study was carried out using cyclic voltammetry (CV) and the results were compared with theoretical values obtained from a DFT study. These compounds showed light sky-blue luminescence in solution and as a thin film under long-wavelength UV light. It was observed that all the prepared target compounds exhibited enantiotropic mesophases with good thermal stability. The structural and conformational characterisation of these new compounds was achieved using various spectroscopic techniques, including FT-IR, ¹H NMR, ¹³C NMR and MALDI-TOF. The relationship between the structure and the mesomorphic behaviour of the compounds containing an ethyl bridge with linked ester groups (5a–5d) is discussed. This new class of supramolecular derivatives is promising, especially considering the emissive nature and stabilisation of their columnar hexagonal mesophases, and their high range of thermal stability.