Novel fluorescent pH sensor based on 5-(4-carboxy-phenyl)-10,15,20-tris(phenyl)-porphyrin

•A porphyrin was proposed as indicator for fluorescence pH sensing in acid media.•The pH sensor was based on asymmetrical carboxyl functionalized porphyrin.•The proposed pH sensor revealed good selectivity toward transitional metal ions.•The influence of pH on the UV–vis absorption spectra was studied.•Preparation and fully characterization of porphyrin was performed. A novel fluorescent pH sensor based on 5-(4-carboxy-phenyl)-10,15,20-tris(phenyl)-porphyrin, as sensing agent, has been developed. The carboxyl functionalized asymmetric porphyrin has been synthesized and characterized by high performance liquid chromatography (HPLC), thin layer chromatography (TLC), proton nuclear magnetic resonance (1H NMR), Fourier transform infrared spectroscopy (FT-IR), ultraviolet–visible (UV–vis), emission, excitation and mass spectrometry (MS) spectra. Optical and fluorescence behaviors were investigated in relationship with variation of acid concentration in the range of acid pH from 1.5 to 5.5. Upon increasing the acidity of the solution, the decrease of the fluorescence intensity was noticed, as a linear function of pH. Different metal ions were tested to put into evidence the changes regarding the fluorescence intensity, but the fluorescence obtained results revealed no significant interference on pH determination. The conclusion is that the proposed fluorescent sensor can measure pH in acid range in the presence of different metal ions making this sensor a proper one for pH determinations in leaching solutions of the recyclable processes of valuable metals.