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-) hasbeen proposed based on the competitive-displacement strategy betweenmeso-tetraphenylporphyrin (TPP) and meso-tetraphenylporphyrin cobalt(II) (CoTPP). InTHF-water solution, TPP emits strong fluorescence at 651 nm; however, the fluorescence wasquenched 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 assemblysystem showed significant color change by the anion. Both the fluorescence and the colorchange of the system exhibits remarkably high selectivity to SCN- over a large series ofanions. The interaction mechanisms among TPP, CoTPP and SCN- were primarilyinvestigated by fluorescence lifetime. The quenching of TPP fluorescence is attributed to theformation of TPP/CoTPP aggregates, and the fluorescence restoration is due to the binding ofCoTPP with SCN-, releasing the free TPP. This simple system has the potential to be used asa latent fluorescent sensing approach for SCN- for environmental analysis.