Synthesis of two tetra-azolium salts and the recognition performance for guests

One open tetra-benzimidazolium salt (1) and one cyclic tetra-imidazolium salt (2) based on tetramethylbenzene were synthesized and characterized. The single crystal structure of 1 was determined by X-ray diffraction. The recognition performance of compounds 1 and 2 for guests (1 for o-phenylenediamine (OPD) and 2 for F-) was investigated via fluorescent spectra, UV/vis spectra, H-1 NMR, HRMS and IR spectra. In particular, a remarkable color change (from colorless to pale brown) was observed in the recognition process of 2 for F-, which indicated that this recognition can not only be carried out by using an instrument but also by the naked eye, and this had great convenience in practice.