High Solid-State Efficiency Fluorescent Main Chain Liquid Crystalline Polytriazoles with Aggregation-Induced Emission Characteristics

Fluorescent liquid crystals (LCs) have wide applications in optoelectronic devices. However, the synthesis of high solid-state emission efficiency LCs is difficult. On one hand, impeding the aggregation of traditional luminogens is the prerequisite for high efficiencies; on the other hand, self-organization is an inherent attribute for LCs in the mesomorphic states. Because of such irreconcilable conflict, new strategy toward efficient fluorescent LCs is highly desirable. Herein, a conceptually new approach toward high efficiency fluorescent LCs is developed. Through rational design and combination of biphenyl-containing diazides and diynes carrying tetraphenylethylene units, soluble, regioregular, and liquid crystalline polytriazoles with high solid-state emission efficiencies (up to 63.7%) are obtained. The photophysical properties of the polymers are sensitive to their molecular structures and their solid-state quantum yields decrease with increasing spacer length. The spacer length also impacts on the mesomorphic properties. While polymers with rigid main chains exhibit nematicity, those with longer spacer lengths show better mesogenic packing and hence form smetcic phases.