The systems with aggregation induced emission: compounds, emission mechanisms and their applications

Organic systems with aggregation induced emission (AIE) have received increasing interest in recent years, resulting in the accumulation of a wealth of information on molecular design of AIE luminogens and mechanistic understanding of the AIE processes. The studies on the AIE systems have opened a new route to develop solid-state highly-emissive organic materials, especially for the high performance organic electroluminescent (EL) materials, which usually suffer from the severe aggregation-caused quenching (ACQ) effect. This review summarizes the recent advances in this research field, including the typical AIE systems, the AIE mechanisms and their various applications. The organic AIE systems mainly include aryl-substituted heterocyclic compounds, aryl-substituted vinyl compounds, intramolecular charge transfer compounds, hydrogen-bonding compounds, polymers and so on. Investigations of their structure-property relationships reveal that these compounds may possess different AIE mechanisms. The AIE phenomenon can be caused by restriction of intramolecular rotation, prohibition of non-radiative deactivation, distortion of molecular configuration to prevent from the excimer formation, or some specific molecular packing modes such as the J-aggregation, the cross dipole stacking and some unique molecular aggregates induced by intermolecular C-H⋯ π interaction or some unusual hydrogen bonding. Finally, the various applications of these AIE compounds in chemical/biological sensing, bioimaging, organic electroluminescent and logic gate devices are described.