Aggregation induced phosphorescence of metal complexes: From principles to applications

Metal complexes are the prototypes of phosphorescent materials, widely used in a range of optoelectronic and sensing applications. This review reports the most recent and tutorial results in the area of aggregation induced phosphorescence (AIP) of metal complexes, i.e. molecules that are weakly or non-phosphorescent in deaerated fluid solution and whose room temperature phosphorescence is switched on upon aggregation. The examples are divided into two main classes according to the AIP mechanism: (i) rigidification that causes a restriction of intramolecular motions as well as of structural distortion of the phosphorescent excited state and (ii) metallophilic interaction that brings about new electronic transitions compared to the isolated chromophores. The last section is devoted to a special class of molecules and supramolecular systems, in which metal complexation turns on phosphorescence of nearby organic chromophores, so that the metal complex is not directly involved in the phosphorescence process.