Circularly polarized organic room temperature phosphorescence activated by liquid crystalline polymer networks

Abstract

Circularly polarized luminescent (CPL) materials have attracted much attention due to their potential applications in 3D imaging, anti-counterfeiting, etc. However, it is still a great challenge to achieve circularly polarized room temperature phosphorescence (CPRTP). In this work, a series of chiral compounds (denoted as (R/S)-B-n-CzO, n = 4, 8 and 12) are successfully designed and synthesized combining binaphthol and carbazole–dibenzofuran for the fabrication of CPRTP materials. The resultant compounds show excellent luminescence behaviour in both solution and the solid state with absolute fluorescence quantum yields of up to 52.97%. Due to the existence of a chiral group, these compounds show circular dichroism (CD) in solution, but no CPL behaviour is observed. Furthermore, this kind of compound is doped into a commercial liquid crystalline monomer (2-methyl-1,4-phenylene bis (4-(((4-(acryloyloxy) butoxy) carbonyl) oxy) benzoate, LC-242)) to fabricate CPRTP materials through liquid crystal (LC) self-assembly and a confined phosphorescent moiety by UV light cross-linking the monomer. As a result, the obtained liquid crystalline polymer network shows CPRTP behaviour with the largest luminescence dissymmetry (g_lum) value of +0.098. This provides a meaningful design idea for the preparation of CPRTP materials.