A near-infrared fluorescent probe with an improved Stokes shift achieved by tuning the donor-acceptor-donor character of the rhodamine skeleton and its applications.

In this paper, we report a novel near-infrared (NIR) mitochondrion-targeted fluorescent probe, RQS, with an improved Stokes shift (96 nm) for the specific detection of mitochondrial mercury ion (Hg(2+)) because mitochondrion is one of the main targeted organelles of Hg(2+). For the preparation of the probe, a novel asymmetrical fluorescent xanthene dye RQ was first synthesized by tuning the donor-acceptor-donor (D-A-D) character of the rhodamine skeleton, and then the probe RQS was constructed by the mechanism of mercury-promoted ring-opening reaction. As expected, RQS could be used for the specific detection of Hg(2+) with high selectivity, high sensitivity, and a detection limit down to the nanomolar range (2 nM). Importantly, RQS is capable of specifically distributing in mitochondria, and thus detect Hg(2+) in real-time and provided a potential tool for studying the cytotoxic mechanisms of Hg(2+).