**Abstract**

4-(Dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4*H*-pyran (DCM) is, commonly known as red dye, an electron donor-acceptor molecule that exhibits very interesting photophysical properties such as high molar absorption coefficients, tunable electronic absorption and fluorescence emission energies, and high fluorescence quantum yields. Several DCM analogous have been synthesized and explored for various practical applications that include solid-state lasers, organic light-emitting diode (OLED), fluorescent sensors, logic gates, photovoltaics, nonlinear optics (NLO), and bioimaging of cells. In recent years, a significant amount of research work has been devoted for developing optical sensors based on DCM dye for detection of various guest analytes. The first part of this book chapter describes comprehensive photophysical properties of the DCM dye which include the results of steady-state and time-resolved absorption and fluorescence studies. The second part of the book chapter summarizes the recent developments of DCMbased optical sensors that exhibit colorimetric, ratiometric, and fluorosensing towards selective detection of metal cations, anions, and neutral species.

**Keywords:** red dye, electron donor-acceptor molecules, photophysical properties, optical sensors, NIR fluorescence, dicyanomethylene-4H-benzopyran, dicyanomethylene-4H-pyran, chemosensors
