Linearly polarized photoluminescence from an asymmetric cyclophane showing thermo- and mechanoresponsive luminescence

Abstract

The first cyclophane to exhibit linearly polarized photoluminescence in the liquid-crystalline and crystalline states is described. An asymmetric cyclophane featuring a 4,7-bis(phenylethynyl)-2,1,3-benzothiadiazole group forms a thermodynamically metastable nematic liquid-crystalline phase at room temperature. The compound sandwiched between two glass substrates coated with rubbed polyimide thin layers exhibits homogeneous alignment after shearing. The transition dipole moments of the luminophores align along the rubbing direction. As a result, linearly polarized photoluminescence is achieved at room temperature without any other host materials. Furthermore, the polarized emission is retained after the transition to the crystalline phase, which is induced by annealing at 60 °C for 1 h. The cyclophane also shows a thermal and mechanical stimuli-induced change in the photoluminescence colors.