New symmetric/unsymmetrical self-assembling salicylaldimine-chalcones: Synthesis, photophysical study and DFT approach

To understand the impact of chalcone unit, lateral hydroxy group and different alkoxy chain length on the overall mesomorphic properties, new symmetric/unsymmetrical salicylaldimine-chalcone mesogens were synthesized with different alkoxy chains on both terminals of the compound. From the study of mesomorphic behaviour of CHRS-(6-18) series it has been observed that compounds with shorter alkyl chain at both the ends showed nematic behaviour which diminished as the number of carbons increases. The middle members of the series with (n = 12, 14, & 16) displayed enantiotropic smectic C mesophase except the compound with (n = 18) chain which was found to be nonmesogenic. The compounds with a fixed dodecyloxy chain on the chalcone end and a variable alkoxy chain length at the Schiff base end 12-CHRS-(6-18), (n = 6, 8, 10, 14, 16, 18) showed an enantiotropic smectic C mesophase. Higher homologue (n = 18) of both the series were found to be non-mesogenic. All the salicylaldiine-chalcones were also studied for their photophysical properties in solid and solution phase. AIE (aggregation-induced emission) was exhibited by all the compounds. While in solution phase emission property diminished for all the compounds except for CHRS-NO2. To support the experimental findings about the mesomorphic behaviour, DFT calculations were used. Additionally, a comparison of dipole moment, polarizability, molecular electrostatic potentials, frontier molecular orbitals, and thermodynamic variables was given.