Synthesis、Self-assembly And Photophysical Behaviors Of α-cyanostilbene-based Compounds With Multiple Alkyl Chains

Liquid crystals（LC）are most important soft materials,which show wide application prospect such as liquid crystal displays,photosensitive solar cells and organic photoelectric devices.Liquid crystal molecules could self-assemble into complex mesophases,such as smectic,columnar and cubic mesophases via weak intermolecular interactions including dipole-dipole interactions,π-πstacking,microsegregation,van der Waals forces and hydrogen bonding etc.Tiny changes in the molecular structure of liquid crystal structures,such as alkyl chain length,type of aromatic group,substituent or/and linking group,have tremendous influence on their self-assembly behavior and photoelectric properties.The traditional liquid crystal molecules often suffered aggregation induced fluorescence quenching（ACQ）effect due to the strongπ-πstacking among rigid skeletons.How to endow these liquid crystal molecules with complex self-assembly and aggregation induced luminescence（AIE）has aroused wide attention of scientists.In order to realize complex structure of self-assembly in nanometer scale and aggregation induced luminescence（AIE）,we have designed a class of polycatenar liquid crystal molecules with carbazole,fluorobenzene and tetraphenylethylene as the central core and theα-cyanostilbene as the arm.The structure of these intermediates and target products was confirmed by NMR and elemental analysis.The self-assembly behaviors of these compounds with multiple alkyl chain were studied by polarized optical microscopy（POM）,differential scanning calorimetry（DSC）,small angle X-ray scattering（SAXS）and scanning electron microscopy（SEM）.With the increase of peripheral alkyl chain length and temperature,the self-assembly structure of carbazole containing compounds BCA/n changed from rectangular columnar phase(Col_rec/p2mm)to hexagonal columnar phase(Col_hex/p6mm).The LC self-assembly behavior of the fluorinated liquid crystal compounds I/n、II/n、III/n and IV/n is greatly affected by the degree of fluorination.These compounds I/n、II/n and III/n with lower degree of fluorination can self-assemble into rectangular column phase(Col_rec/p2mm),whereas compounds IV/n with highest degree of fluorination are non-mesogens.TPE/10 can self-assemble into hexagonal columnar phase(Col_hex/p6mm)in a wide temperature range.Besides,I/n、II/n、III/n and IV/n can form organogels with complex morphologies in different solvents and the gelation abilities increase with the increase of degree of fluorination.The solvatochromic effect and aggregation induced emission（AIE）behaviors of these compounds were studied by UV-visible absorption spectra and fluorescence emission spectra.With the increase of solvent polarity,the UV-visible absorption spectra of BCA/n、TPE/10 and IV/n changed little,but the fluorescence emission spectra show a great change.Both UV-visible absorption spectra and fluorescence emission spectra of I/n、II/n、and III/n change slightly.The gaussian calculation demonstrate that these phenomena are caused by intramolecular charge transfer（ICT）.In addition,all of these compounds showed strong fluorescence in both solutions and aggregated states（AIE）.