High Efficiency Luminescent Liquid Crystalline Polymers Based on Aggregation-Induced Emission and "Jacketing" Effect: Design, Synthesis, Photophysical Property, and Phase Structure

A series of high efficiency luminescent liquid crystalline polymers (LLCPs) based on aggregation-induced emission (AIE) and the "Jacketing" effect, namely, poly{2,5-bis{[2-(4-oxytetraphenylethylene)-n-alkyl] oxycarbonyl}styrene} (denoted as Pm, m = 2, 4, 6, 8, 10, 12), were successfully designed and synthesized via introducing tetraphenylethylene to the side group with different length spacers. Because of the AIE effect, the resultant LLCPs are completely free of aggregation caused quenching. The photophysical properties and phase behavior were studied via various techniques such as UV-vis absorption spectra, photoluminescence spectra (PL), polarized light microscopy (PLM), differential scanning calorimetry (DSC), and variable temperature one-dimensional wide-angle X-ray diffraction (1D WAXD). The results revealed that the resultant monomers showed typical ATE behavior and the polymers exhibited aggregation enhanced emission (AEE) behavior. Moreover, due to the "Jacketing" effect, the polymers showed high efficiency luminescence in the liquid crystalline state, which was significantly dependent on the spacer length (the solid-state quantum yields decreased from 52% to 18% with increasing spacer length). Meanwhile, the glass transition temperatures (T-g) decreased with increasing the length of spacers. With increasing the spacer length, the phase structure transformed from smectic A (SmA) (Pms, m = 2, 4, 6) to hexagonal columnar phase (Col(H)) (Pms, m = 8, 10, 12). All the polymers presented good film forming property and processing performance, which made them be promising materials for the luminescent devices.