A phenothiazine–rhodamine ratiometric fluorescent probe for Hg2+ based on FRET and ICT

Rhodamine B and phenothiazine building blocks have been used to synthesize a novel ratiometric fluorescent probe 1 for Hg2+. Based on fluorescence resonance energy transfer (FRET) and internal charge transfer (ICT) mechanisms, a low detection limit for Hg2+ of 1.8 ppb has been achieved. The intensity ratio (F580 nm/F520 nm) of fluorescent probe 1 increased on going from 0.1 to 1.0 equiv of Hg2+. In the FRET process, energy is transferred from the phenothiazine moiety to the rhodamine B moiety. Probe 1 shows a selective response to Hg2+ by color and fluorescence changes.