Controlling AIE and ACQ properties of conjugated carbazole-tetraphenylethene copolymers by ethynylene spacer

Aggregation-induced emission (AIE) polymers have been widely investigated by introducing various AIEgens into the polymer chains. In the research program of developing new polymer nanoparticles or polymer dots (Pdots) with excellent fluorescence properties, we synthesized conjugated copolymers based on carbazole (Cz) and one of the most common AIEgens, namely, tetraphenylethene (TPE). When the Cz unit was directly copolymerized with TPE by Suzuki coupling, the resulting polymers showed AIE properties. However, when an ethynylene spacer was inserted between the Cz and TPE units, the copolymers displayed aggregation-caused quenching (ACQ) properties. Although the connectivity patterns of the Cz unit, namely, 1,8-, 2,7-, and 3,6-substituted Cz structures, slightly affected the degree of the AIE or ACQ behavior, the ethynylene spacer mainly determined the fluorescent properties in the solid states. Detailed photophysical characterization of these two series of copolymers suggested that the inactive AIE properties are caused by the subtle difference in the structural twisting and intra- or inter-molecular interactions of the conjugated copolymers resulting from the ethynylene spacers. The AIE polymer-based Pdots were fabricated and exhibited an excellent water-dispersion stability, which can be potentially used as bioimaging probes. Our results revealed structure-property relationships and provided a new insight into the AIE polymers.