Photophysical and thermophysical behavior of D-π-A-type fluorinated diphenylacetylenes bearing an alkoxy and an ethoxycarbonyl group at both longitudinal molecular terminals

Abstract

Fluorinated diphenylacetylenes have recently attracted significant attention because they exhibit intense photoluminescence (PL) in the crystalline state owing to their electron-density distribution and the formation of H···F hydrogen bonds. In this study, fluorinated diphenylacetylenes bearing alkoxy and ethoxycarbonyl (COOEt) groups at both longitudinal molecular terminals were synthesized, and their photophysical and thermophysical behavior were evaluated, along with their structure–property relationship. The COOEt-substituted fluorinated diphenylacetylenes exhibited blue PL in the solution and crystalline states. Both the fluorine atom and the COOEt substituent play a crucial role in forming a large electron-density distribution and restricting the molecular motion of diphenylacetylenes through H···F and O···H hydrogen bonds in the crystalline state. The alkoxy-chain length of the fluorinated diphenylacetylenes not only affected their PL behavior in the crystalline state, but also their thermophysical behavior. Notably, fluorinated diphenylacetylenes with long alkoxy chains, such as heptyloxy and octyloxy chains, displayed a nematic liquid-crystalline (LC) phase. These findings facilitate the development of promising multifunctional molecules possessing PL and LC characteristics.