A dual-emission porphyrin coordination polymer for ratiometric fluorescent sensing of pH and copper ion

Synthesis of nano coordination polymers (NCPs) with dual fluorescence emission is highly desirable, but is still a challenge for further ratiometric sensing applications. In this work, porphyrin-based NCPs with dual fluorescence emission were prepared via a solvothermal process using branched polyethyleneimine (PEI) as passivation agent for ratiometric fluorescent sensing of pH and copper ion. Two NCPs@PEI can be obtained with different fluorescence emissions due to regulation of reaction time. NCPs@PEI-1 exhibited a good fluorescence response to pH with a calibration function of lg(I-655 /I-477) = 0.2750 (pH) -2.2989 (R-2 = 0.977), derived from protonation and deprotonation of pyrrolic nitrogen and amino groups in the NCPs@PEI. Moreover, by exploiting the electron transfer between Cu2+ and nitrogen in porphyrin, NCPs@PEI-1 was used as sensor for detecting Cu2+ with a function of y =-0.0074x + 0.5990 (R-2 = 0.999) and the limit of detection was calculated to be 136 nM based on 3 sigma/kappa. These NCPs with tunable emission, excellent fluorescence, and "two in one " characteristic for Cu2+ and pH sensing highlights NCPs@PEI as a potential fluorescent probe for multi-target analysis.