A phthalocyanine-porphyrin triad for ratiometric fluorescent detection of Lead(II) ions

A phthalocyanine-porphyrin hetero-triad H2Pc-beta-(ZnPor)(2) (1) was designed for the ratiometric fluorescent detection of lead(II) ions. The triad 1 features a high efficient intramolecular fluorescence resonance energy transfer (FRET) process from the two zinc-porphyrin (ZnPor) units to the metal-free phthalocyanine (H2Pc) unit. The selective binding of Pb2+ to H2Pc can effectively quench the emission of phthalocyanine unit, also recover the emission of ZnPor units by suppressing the intramolecular FRET process, thus leading to remarkable ratiometric fluorescent responses. The emission intensity ratio of ZnPor and H2Pc (F-605/F-700) experiences an 82-fold enhancement upon the addition of Pb2+ (0-3 equiv) to a solution of 1 (2.0 mu M in THF/CH3OH, 4:1 in v/v), and displays a good linear relationship to Pb2+ concentration in the range of 0-2.0 mu M, resulting in a limit of detection (LOD) value down to 4.1 nM (0.86 ppb).