Regulation of conjugate rigid plane structures for achieving transformation of fluorescence recognition properties

Abstract

Bisbenzimidazole is an important class of fluorescence molecular probe materials with applications in environmental, clinical, and biological systems. Moreover, different bisbenzimidazole derivatives, due to excellent coordination properties and fluorescence characteristics, were widely studied for cation recognition. In this study, the relationship between three bisbenzimidazole derivatives (B₁, B₂ and B₃) with respect to the increase of the phenyl group conjugate systems and fluorescence sensing properties for the detection of toxic heavy metal ions such as Hg²⁺ is explored and analyzed. B₁ contains a bisbenzimidazole unit without an appendage, while B₂ and B₃ have different phenyl appendages between two benzimidazole rings; with the extension of the conjugated system, the selectivity of cation recognition increases but the stability decreases significantly. Simultaneously, their limits of detections (LODs) and recognition mechanism for Hg²⁺ were investigated via various methods such as fluorescence spectroscopy, ¹H NMR spectroscopy, ICP analysis, and DFT calculations. Inspiringly, B₂ shows high adsorption and separation efficiency, which provides a reference for the development of mercury ion absorption/removal materials.