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 l g ( I 655 / I 477 ) = 0.2750 ( p H ) − 2.2989 $lg(I_{655}/I_{477})=0.2750(pH)-2.2989$ (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 Cu 2+ and nitrogen in porphyrin , NCPs@PEI-1 was used as sensor for detecting Cu 2+ with a function of y = − 0.0074 x + 0.5990 $y=-0.0074x+0.5990$ (R 2  = 0.999) and the limit of detection was calculated to be 136 nM based on 3σ/κ. These NCPs with tunable emission, excellent fluorescence, and “two in one” characteristic for Cu 2+ and pH sensing highlights NCPs@PEI as a potential fluorescent probe for multi-target analysis.