**2.2 Fluorescent dyes**

Fluorescence is a photophysical process which involves the emission of light by the substance as a consequence of the absorption of electromagnetic radiation. In most of the cases, the emitted light radiation has a longer wavelength (λem) than the absorbed light radiation (λabs). Likewise, fluorescent dyes, also known as '*fluorophores'* or '*reactive dyes'* remit light radiation upon absorption. Earlier, fluorescent dyes were extensively used in the textile industries to color fibers, cotton, yarns, and silk. Eventually, the use of fluorescent dyes has become a key technique for the detection and elucidation of biological structures by fluorescence emission technology. Because of their high photostability, and intense brightness, fluorescent dyes have been significantly used in fluorescent labeling (staining) of biomolecules. Fluorescent quenching studies have helped to detect DNA and proteins in biological systems. Techniques such as immunofluorescence, fluorescence microscopy, and flow cytometry rely upon fluorescent dyes. Currently, the requirement of fluorescent dyes insisted greatly because of their ample applications which could be substantiated through microwave-assisted synthesis. The advantages of microwave applications for the synthesis of fluorescent dyes have been intensively discussed [29].
