Through-bond energy transfer cassette based on spirobifluorene–tetrrhodamine for the colorimetric and ratiometric investigation towards trace Hg2+

We have designed and synthesized a spirobifluorene–tetrrhodamine fluorescent probe 2 based on the through-bond energy transfer (TBET) system for the “off–on” detection of Hg2+. As compared with fluorescence resonance energy transfer (FRET) strategy, the TBET system did not need spectral overlap between the donor emission and the acceptor absorption, therefore, the choice of dye pairs for the probe design was wide. The Stokes shift was larger and the energy transfer efficiency was higher than that of the FRET system. The probe 2 showed exclusive response toward Hg2+ by the fluorescence enhancement and the color changed from colorless to pink. Other metal ions showed no significant variation to Hg2+. The energy-transfer efficiency was calculated to be 99.6%, and the detection limit was determined to be 3 ppb. Thus, probe 2 could be used as a fluorescent and colorimetric chemosensor for the detection of Hg2+.