"Fastening" porphyrin in highly cross-linked polyphosphazene hybrid nanoparticles: Powerful red fluorescent probe for detecting mercury ion

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-co- 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.