Polymers with Aggregation-induced Emission Characteristics

Organic luminescent materials have played important roles in optoelectronic device, chemo-/biosensing, and biomedical applications. However, traditional luminescent materials always suffer from the aggregation-caused quenching (ACQ) effect: they are highly emissive in dilute solutions but their emission becomes weaker or totally quenched in the practical application forms, i.e. the aggregate, film and solid states. The ACQ effect has greatly limited the applications of these luminescent materials in many fields. Exactly opposite to the ACQ, the aggregation-induced emission (AIE) can actively utilize the natural aggregation process of a molecule to provide intense emission in the aggregate and solid states. In the AIE area, the research is focusing on the low mass molecules, and the polymers have been paid less attention although they possess the unique properties such as good film-forming ability, amplification effect of the signals, and multiple functionalization, which facilitates their practical applications. In this review, we first accounted the used polymerizations for the construction of AIE polymers, such as polycouplings, radical polymerization, and click polymerizations. Next, we discussed the structure-property relationship of the AIE polymers based on the systematically investigation of the effect of substituent groups, the link of TPE and fluorene groups on the triazole rings, the attachment of TPE-diethynyl groups on phenyl rings with o, m, and p-positions, and the side-chains on their photo-physical properties. Moreover, the interesting non-conjugated AIE polymers without aromatic rings were also discussed and cluster oluminescence was proposed as the cause for this unique emission. Finally, the applications of the AIE polymers in chemo- and biosensors, and tracing were reviewed and the advantages of AIE polymers over AIE low-mass molecules were also emphasized. It is expected that this review could serve as a trigger for future innovation in the AIE research area.