Abstract: Flavonoid dyes have a series of advantages such as high fluorescence brightness, good photostability, easy chemical modification and wavelength regulation. At present, they have been widely used in cutting-edge research such as biological imaging and phototherapy. However, flavonoid dyes still face challenges in long-wavelength window diagnosis and treatment as well as targeting. By adjusting the absorption and emission wavelengths, as well as the photothermal and photodynamic properties of dyes through the heavy atom effect, the application of organic dyes in the field of clinical diagnosis and treatment has been enriched, providing new tools for pathological and biomedical research. Therefore, taking the easily modified flavonoid dye skeleton as the parent body, aiming at the bottleneck problems of wavelength limitation and insufficient targeting, a new type of flavonoid dye was developed by focusing on the heavy atom effect. The oxygen atoms in the dye parent body were replaced with selenium atoms, and a new type of long-wavelength dye was developed which maximum absorption wavelength when bound to RNA can reach 760 nm. Taking advantage of the obvious wavelength change of this dye before and after binding to RNA, it can achieve the effect of long-wavelength photothermal therapy with RNA activation.