Molecular recognition of 2-alkylbenzimidazole: Photophysical and structural studies

2-Alkylbenzimidazole (L1–3) forms organic salt co-crystals with several electron-deficient aromatic as well as aliphatic polycarboxylic acids. Electron-rich benzimidazole shows dramatic quenching of fluorescence in presence of electron-deficient acidic guest molecules. Higher selectivity was found towards pyromellitic acid. Substituted benzimidazole forms organic salt co-crystals with different acids of general composition [LnH+·A−] (where, A is the acid molecule). The non-covalent interactions between carboxylic acids and L1–3 were investigated by UV–vis, fluorescence and 1H NMR spectroscopic methods in solution and by single crystal X-ray diffraction in solid state.