Progress on heterocycle-based luminogens with aggregation-induced emission characteristics

Abstract

Aggregation-induced emission (AIE), conceptually termed by Tang et al in 2001, refers to a unique phenomenon that a series of propeller-shaped conjugated molecules are weakly or non-emissive in solution state but highly luminescent in the aggregate state. Experimental and theoretical studies have rationalized the restriction of intramolecular motion (including rotation and vibration) as the main cause for the AIE effect. Exactly opposite to conventional fluorophores that suffer from the aggregation-caused quenching (ACQ) effect, the AIE luminogens (AIEgens) could perform best in the condensed phases and enable the molecule aggregation to play positive instead of negative roles in enhancing luminescence. Attracted by this intriguing phenomenon and the application implications, scientists worldwide have actively involved in this research and promoted the development of this area. As a result, tremendous AIEgens have been synthesized and applied in optoelectronic and biologic fields etc. The progresses on the AIE have been well summarized in several excellent reviews. However, the reviewed structures of AIEgens are mostly based on the hydrocarbon ones, such as tetraphenylethene (TPE), distyrylanthracene (DSA), triphenylethene, tetraphenyl-1,4-butadiene (TPBD). Herein, we mainly review the advance of heterocycle-based AIEgens containing silicon, nitrogen, sulfur, boron and phosphorus atoms etc. for the first time. The versatile properties, such as tunable emission color, good thermal and photo-stability, and the applications of these heterocycle-based AIEgens in organic light-emitting diodes, fluorescent sensors and cell imaging etc. were also briefly discussed.