Central condensed ring changes for manipulating the self-assembly and photophysical behaviors of cyanostilbene-based hexacatenars

Two series of condensed ring hexacatenars consisting of a central naphthalene/anthracene and two cyanostilbene units as the π-conjugated rigid core were reported. The thermodynamics behaviors and liquid crystalline structures of these mesogens were investigated by the combination of POM, DSC and XRD. It is indicated that only higher naphthalene-based homologues exhibit hexagonal columnar phases, the other lower naphthalene-based homologues and all the anthracene-based homologues are non-mesogens. The results demonstrated that the steric effect provided by the larger central aromatic group hinders the ordered molecular stacking. The temperature-dependent fluorescence demonstrated that the fluorescence stability of these hexacatenars increased from central phenyl via naphthyl to anthryl due to the increased degree of molecular distortions induced by the central larger aromatic group. The solvatochromism and AIEE behaviors were also studied by UV–vis absorption, fluorescence emission and density functional theory (DFT) demonstrating that the anthracene-based compounds exhibit more distinct solvatochromism, higher fluorescence quantum yield than those of naphthalene-based compounds and more distinct ICT effect, and both series of compounds exhibited strong fluorescence in both solutions and aggregated state due to ICT effect and the long π-conjugated aromatic core with twisted conformations. Additionally, photoisomerization behaviors demonstrated both cis and trans conformations showed high stability in condensed and solution states.