Development of a benzothiazole-functionalized red-emission pyronin dye and its dihydro derivative for imaging lysosomal viscosity and tracking endogenous peroxynitrite

Although strategies based on -conjugation expansion and one-atom replacement have routinely been used to extend the emission wavelengths of rhodamine dyes from the visible region to the biologically more favorable red to near-infrared (NIR) region, the strategy of introducing electron-withdrawing groups to the meso -position of pyronin dyes for the same goal is still in its infant phase. In this work, we present a benzothiazole-functionalized pyronin dye BTP as a red-emission fluorescent dye platform for bioimaging applications. Due to the electron-withdrawing nature of the meso -substituted benzothiazole unit, BTP exhibited a large red-shift in absorption and emission wavelengths compared to classic rhodamines. Interestingly, BTP could not only behave like a molecular rotor to fluorescently respond to viscosity changes, but also specifically target lysosomes and light up them assisted by a lysosomal viscous microenvironment. Furthermore, based on the BTP platform, we developed its dihydro derivative, i.e. , HBTP , and evaluated its sensing performance to reactive oxygen species (ROS). The obtained results showed that HBTP is a highly selective fluorescent probe for sensing endogenous peroxynitrite (ONOO ) with quite rapid fluorescence offon response and high sensitivity. It is greatly expected that the present study could stimulate research interest in exploiting various rhodamine-inspired fluorescent dyes or probes for bioimaging applications. Based on the pyronin dye platform, a red-emission molecular rotor BTP and its dihydro derivative HBTP were developed for imaging lysosomal viscosity and endogenous ONOO , respectively.