Far-red to near-infrared fluorescent probes based on silicon-substituted xanthene dyes for sensing and imaging

Far-red to near-infrared (NIR) fluorescent probes with absorption and emission in the spectral region of 600–900 nm are of high interest because of their low autofluorescence interference, deep-tissue penetration, and minimal photodamage to biological samples. In recent years, the Si-substituted xanthenes have attracted considerable attention owing to their remarkable far-red to NIR photophysical properties and biocompatible characteristics. This paper reviews the synthetic methods of silicon-substituted xanthene dyes and the progress in the development of far-red to NIR fluorescent probes based on these dyes, and introduces representative chemosensors along with their fluorescent behavior toward specific analytes. The fluorescent probes in sensing various biological species, including metal ions and anions, intracellular pH changes, reactive oxygen species (ROS) and reactive nitrogen species (RNS), as well as enzymes and other related species, were summarized. The sensing mechanisms and applications of corresponding sensors are also discussed.