One- and Two-Photon Turn-on Fluorescent Probe for Cysteine and Homocysteine with Large Emission Shift

A novel dendritic chromophore with efficient intramolecular charge transfer (ICT) and strong two-photon absorption (TPA) was designed as a turn-on fluorescent probe for cysteine (Cys) and homocysteine (Hcy). The probe exhibited greatly enhanced fluorescence intensity as well as a very large emission peak shift (165 nm) upon addition of Cys/Hcy due to ICT switch off. The sensing process was also monitored by two-photon excited fluorescence (TPEF).