Photophysical Phenomenon of Aggregation
The supramolecular aggregates have been the focus of many investigations, and its significance has been highlighted throughout the years. The principal characteristic of aggregation is certainly its influence on the photophysical properties of luminophores. Conventional spectroscopic techniques, such as absorption and fluorescence, are particularly appropriate for exploring aggregation in solution since molecular aggregates have distinct optical properties compared to individual molecules. Strong spectral shifts or splitting of the absorption band are typical aggregation characteristics. These spectroscopic changes are a consequence of exciton interactions between the individual molecules forming the aggregate. In this chapter, the spectroscopic nature of molecular aggregates is described by theoretical models. Next, photophysical phenomenon of aggregation i.e., aggregation induced quenching (AIQ) and aggregation induced emission phenomenon (AIE), aggregation induced emission enhancement (AIEE), aggregation induced phosphorescence (AIP), aggregation induced electrochemiluminescence (AIECL), aggregation induced delayed fluorescence (AIDF), aggregation-induced energy transfer, aggregation induced photon upconversion (iPUC) and aggregation-induced resonance Raman optical activity (AIRROA) is illustrated through relevant examples as well as those that elucidate interesting aspects of the aggregation process or its potential applications. Finally, conclusions and future scope are presented and discussed.