The influence of alkyl lengths on circularly polarized luminescence for non-liquid crystalline binaphthol-based cyanostilbene

Abstract

In previous studies, the increasing alkyl length of liquid crystalline molecules enhanced the chiral transfer and resulted in better CPL performance. But no work concerned the influence of alkyl lengths on CPL properties for non-liquid crystalline systems. In this research, three R-binaphthol-based cyanostilbene derivatives with various alkyl chains (BC-5, BC-8 and BC-12) were prepared in yields of 60–69%. They did not exhibit liquid crystalline behavior but were seen as soft materials at room temperature. They displayed excellent AIE fluorescence in aggregated states. Chiroptical investigations suggested good CD and CPL properties for their cyanostilbene units, indicating the successful chiral transfer from the binaphthol moieties to cyanostilbene units. Moreover, the values of g_abs for CD signals and g_lum for CPL signals displayed the changing order of BC-5 > BC-8 > BC-12. These results suggested that the shorter alkyl chains for non-liquid crystalline systems led to stronger CPL emission, which was opposite to the results of the liquid crystalline molecules. This work provided a new strategy for the design and synthesis of chiroptical materials with good CPL properties based on non-liquid crystalline molecules.