Synthesis and characterization of AIE-active and photo-active α-cyanostilbene-containing carbazole-based hexacatenars

Abstract

This study describes the synthesis, liquid crystal and photophysical properties of fluorescent biscyanovinyl diphenylcarbazole-based hexacatenars. The mesomorphic and thermodynamic properties were investigated by using polarized optical microscopy (POM), differential scanning calorimetry (DSC), and small-angle X-ray scattering (SAXS), revealing that these compounds self-assemble into different columnar phase with extremely wide mesophase range. Upon terminal chain elongation and temperature increment, a mesophase transition from Colrec/p2mm to Colhex/p6mm could be observed. The UV–vis absorption, fluorescence emission, fluorescence quantum yields and fluorescence lifetimes were studied in various organic solvents with different polarities, solid state, LC state as well as in THF-water mixtures, indicating that these compounds display significant solvatochromism, large Stokes shifts and extremely bright fluorescence in both solution and aggregated states (AIEE). The density function theory calculations indicate that ICT effect and the twisted geometries are responsible for the large solvent effect and AIEE characteristic, respectively. Additionally, these hexacatenars also showed reversible photoinduced mesophase and fluorescence transition behaviours. The design strategies here provide a new avenue for fabricating functionalized AIE-active luminescent LCs with complex self-assembly structures and photo-responsive behaviours.