“Fastening” Porphyrin in Highly Cross-Linked Polyphosphazene Hybrid Nanoparticles: Powerful Red Fluorescent Probe for Detecting Mercury Ion

Abstract

It is a significant issue to overcome the concentration-quenching effect of the small fluorescent probes and maintain the high fluorescent efficiency at high concentration for sensitive and selective fluorescent mark or detection. We developed a new strategy to “isolate” and “fasten” porphyrin moieties in a highly cross-linked poly­(tetraphenylporphyrin-<i>co</i>-cyclotriphosphazene) (TPP–PZS) by the polycondensation of hexachlorocyclotriphosphazene (HCCP) and 5,10,15,20-tetrakis­(4-hydroxyphenyl)­porphyrin (TPP-(OH)₄) in a suitable solvent. The resulting TPP–PZS particles were characterized with transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), ³¹P nuclear magnetic resonance (NMR), and ultraviolet and visible (UV–vis) absorption spectra. Remarkably, TPP–PZS particles obtained in acetone emitted a bright red fluorescence both in powder state and in solution because the aggregation of porphyrin moieties in “H-type” (face-to-face) and “J-type” (edge-to-edge) was effectively blocked. The fluorescent TPP–PZS particles also showed superior resistance to photobleaching, and had a high sensitivity and selectivity for the detection of Hg²⁺ ions. The TPP–PZS particles were therefore used as an ideal material for preparing test strips to quickly detect/monitor the Hg²⁺ ions in a facile way