Chain-Length-Dependent Phase Behavior and Photoluminescence in Imidazole-Substituted Fluorinated Tolane Liquid Crystals.

Multifunctional materials that exhibit both photoluminescence (PL) and liquid-crystalline (LC) properties, referred to as photoluminescent liquid crystals (PLLCs), have garnered considerable interest for applications in fluorescent thermometers and thermosensors. This interest is attributable to their reversible fluorescence switching behavior, driven by aggregated structural changes associated with phase transitions upon heating and cooling. The research group has developed various PLLCs by incorporating fluorescent π-conjugated mesogens into donor-π-acceptor (D-π-A)-type fluorinated tolanes, functionalized with a range of electron-donating and electron-withdrawing groups (EWGs) at the molecular terminal positions. This article introduces a novel class of D-π-A-type fluorinated tolanes featuring an imidazole ring, which functions as an EWG with both steric and electronic effects. These compounds exhibit distinct phase transition behaviors and photophysical properties depending on the chain length of the flexible alkoxy units. Furthermore, for compounds exhibiting any LC phase, the PL behavior in the mesophase is evaluated. The results reveal that phase transitions lead to changes in both the fluorescence wavelength and intensity. These findings demonstrate that nitrogen-containing heterocycles, such as imidazole, are effective EWG units with both steric and electronic contributions. As such, they hold promise for the design of PLLCs for use in PL sensing materials.