Design, synthesis and performance control of dendritic fluorescent liquid crystal polymers with aggregation-induced emission properties

Abstract

A series of dendritic fluorescent liquid crystal polymers, in which the tetraphenylethylene was linked to the styrene main-chain via flexible spacer with different lengths: poly{3,4,5-tri{[2-(4-oxytetraphenylethylene)-alkoxy]styrene} (denoted as 3P-n, n stands for the length of alkyl spacer and n = 2, 4, 6, 8, 10) were rationally designed and synthesized. The self-assembly behaviors and photophysical properties of 3P-n were investigated in detail by a combination of techniques including differential scanning calorimetry (DSC), polarizing optical microscopy (POM), small-angle X-ray scattering (SAXS), UV–vis absorption spectra (UV–vis spectra) and photoluminescence spectra (PL spectra). Because of the “space volume effect” of side groups and the aggregation-induced emission characteristics of tetraphenylethylene molecule, all of 3P-n are liquid crystal materials with excellent solid-state fluorescence emission performance. Moreover, the self-assembly behaviors and solid-state fluorescence emission efficiency of 3P-n could be effectively regulated by adjusting the flexible spacer length. On one hand, 3P-n could self-assemble into stable columnar nematic phase before decomposition when the flexible spacer was shorter (n = 2, 4, 6, 8). And when the flexible spacer increased to 10, 3P-10 was isotropic at low temperature and formed hexagonal columnar phase at high temperatures, showing typical phase reentrant properties. And the other, the flexible spacer length also made a significant influence on the solid-state fluorescence emission capacity of 3P-n. The solid fluorescence quantum yield of 3P-n first increased with the growth of flexible spacer length (n < 6), and then the solid fluorescence quantum yield of 3P-n would remain unchanged when the flexible spacer increased to a certain length (n≥6).