Advancements in the development of fluorescent chemosensors based on CN bond isomerization/modulation mechanistic approaches.

The CN bond isomerization/modulation as a fluorescence signalling mechanism was explored by studying the photophysical properties of conformationally restricted molecules. From the beginning, the CN bond isomerization method has attracted the attention of researchers owing to its simplicity, high selectivity, and sensitivity in fluorescence evaluation. Continuous developments in the field of sensing using CN bond-containing compounds have been achieved via the customization of the isomerization process around the CN bond in numerous ways, and the results were obtained in the form of specific discrete photophysical changes. CN isomerization causes significant fluorescence enhancement in response to detected metal cations and other reactive species (Cys, Hys, ClO- , etc. ) straightforwardly and effectively. This review sheds light on the process of CN bond isomerization/modulation as a signalling mechanism depending on fluorescence changes via conformational restriction. In addition, CN bond isomerization-based fluorescent sensors have yet to be well reviewed, although several fluorescent sensors based on this signalling mechanism have been reported. Therefore, CN-based fluorescent sensors are summarized in this review.