Key Mechanisms That Generate New Spectroscopic Properties of Aggregates
During the past decade, luminophores have become an important research field of supramolecular chemistry and have attracted great attention because of their simplicity, high selectivity, and sensitivity in fluorescent assays. In the design of new luminophores, the exploration of new sensing mechanisms between recognition and signal reporting units is of interest. In recent years, great efforts have been devoted to developing new fluorescent materials with various sensing mechanisms for the detection of analytes in order to achieve super-sensitivity, ultra-selectivity, as well as fast response time. Based on various photophysical processes of aggregation, various sensing mechanisms have been investigated and reviewed extensively in the literature. This chapter focuses on the key mechanisms that generate new spectroscopic properties of aggregates. Conventional sensing mechanisms including photo-induced electron transfer (PET), resonance energy transfer (RET), electron exchange or dexter interactions, intramolecular charge transfer (ICT), Excited-state intramolecular proton transfer (ESIPT), restriction of intramolecular rotation (RIR), restriction of intramolecular vibrations (RIV), restriction of intramolecular motions (RIM) and C=N isomerization have been explained through relevant examples as well as those that elucidate interesting aspects of the aggregation process or its potential applications. Finally, conclusions and future outlook are presented and discussed.