Effect of fluoroalkyl-substituent in bistolane-based photoluminescence liquid crystals on their physical behavior

Abstract

Photoluminescentliquid crystals (PLLCs) have attracted significant attention owing to their broad applicabilityin thermosensing and PL switching. Extensive efforts have been madeto develop bistolane-based PLLCs containing flexible units at both molecular terminals, and it has been revealed that their PL behavior can switch with the phase transition between the crystallineand LC phases. Although slight modulation of the flexible unit structure dramatically alters the LC and PL behaviors, few studies into modification of the flexible units have been conducted. With the aim of achieving dynamic changes in their physical behaviors, we developed a family of bistolane derivatives containing a simple alkyl or a fluoroalkyl flexible chain, and carried out a detailed systematic evaluationof their physical behaviors. Bistolanes containing a simple alkyl chain showed a nematic LC phase, whereas switching the flexible chain in the bistolane to a fluoroalkyl moiety significantly altered the phase to generate a smectic phase. The fluoroalkyl-containing bistolanes displayed a stronger deep blue PL than their corresponding non-fluorinated counterparts, even in the crystalline phase, which was attributed to the construction of rigid molecular aggregates through intermolecular F···H and F···F interactions to suppress non-radiative deactivation.