Colorimetric and Fluorescent Sensing of SCN(-) Based on meso-Tetraphenylporphyrin/meso-Tetraphenylporphyrin Cobalt(II) System

An approach for colorimetric and fluorescent sensing of thiocyanate (SCN(-)) has been proposed based on the competitive-displacement strategy between meso-tetraphenylporphyrin (TPP) and meso-tetraphenylporphyrin cobalt(II) (CoTPP). In THF-water solution, TPP emits strong fluorescence at 651 nm; however, the fluorescence was quenched stepwise by CoTPP, and then restored by SCN(-), the detection limit is 6.0 × 10(-4) M. The recognition of SCN(-) could also be easily achieved by visual way since the assembly system showed significant color change by the anion. Both the fluorescence and the color change of the system exhibits remarkably high selectivity to SCN(-) over a large series of anions. The interaction mechanisms among TPP, CoTPP and SCN(-) were primarily investigated by fluorescence lifetime. The quenching of TPP fluorescence is attributed to the formation of TPP/CoTPP aggregates, and the fluorescence restoration is due to the binding of CoTPP with SCN(-), releasing the free TPP. This simple system has the potential to be used as a latent fluorescent sensing approach for SCN(-) for environmental analysis.