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.

In this study, we synthesized a molecularly chiral [3]­rotaxane comprising a calix-bis-crown ether (as the macrocyclic component) and two unsymmetrical dialkylammonium salts (as dumbbell-shaped components) without any chirality in any of the individual components. Chiral high-performance liquid chromatography was used to separate the enantiomers, which were characterized by circular dichroism spectroscopy. Density functional theory calculations gave an insight into the absolute configuration of each [3]­rotaxane.