Meso-substituented pyronine: colorful emission and versatile platform for the rational design of fluorescent probes

•The specific spectra properties of 9- and 10-position-substituted pyronines (meso-substituted pyronines) are reviewed.•The chemosensing and bioimaging applications of meso-substituted pyronines in living cells are presented.•The challenges and opportunities for design of pyronine-based fluorescent probes are discussed. Pyronine dyes have attracted lots of attention and have been applied as extremely powerful fluorescence imaging tools in the complex biosystems in recent years owing to their satisfactory and tunable photophysical properties. Versatile and multifunctional pyronine-based fluorescent probes can be obtained via rationally modifying this platform by introducing various groups in the meso-position (both 9- and 10-position), resulting in the enormous changes of photophysical properties, such as the larger Stokes shifts and redshifts of absorption and emission bands, which leads novel pyronine dyes more suitable for tracking and bioimaging both in vivo and in vitro. This review dedicates to discussing the design strategies of various meso-substituted pyronines, and summarizes the meso-substituted pyronine based fluorescent probes for the detection of reactive biological species and micro-/macro-environments.