Naked-Eye-Detectable Supramolecular Sensing System for Glutaric Acid and Isophthalic Acid

We report a molecular sensor, comprising a porphyrin core and four 2-aminoquinolyl groups at meso positions, for the naked-eye detection of glutaric acid and isophthalic acid, both featuring a C3 spacer between two CO2H groups. In the presence of the C3 dicarboxylic acids, solutions of the porphyrin sensor underwent significant changes in color and absorption spectra. NMR spectroscopy and X-ray crystallography revealed that the porphyrin derivative bound to two molecules of the C3 dicarboxylic acids selectively to form 1:2 complexes, which dimerized through strong π-stacking interactions. Magnetic circular dichroism (MCD) spectroscopy and density functional theory (DFT) calculations suggested that the red-shifting of the Q-bands in the absorption spectra of the porphyrin derivative arose from tilted quinolyl rings in the dimeric complexes. In addition, we found that a test strip containing the porphyrin sensor could also be used to efficiently detect glutaric acid and isophthalic acid.