Synthesis of Bisimidazole Derivatives for Selective Sensing of Fluoride Ion.

Liang Zhang,Fang Liu

doi:10.3390/molecules22091519

Abstract

Rapid and efficient analysis of fluoride ion is crucial to providing key information for fluoride ion hazard assessment and pollution management. In this study, we synthesized one symmetrical structure called 1,4-bis(4,5-diphenyl-1H-imidazol-2-yl)benzene (1a) and two asymmetrical structures, namely 2-(4-(4,5-diphenyl-1H-imidazol-2-yl)phenyl)-1H-phenanthro(9,10-d)imidazole (1b) and 2-(4-(4,5-diphenyl-1H-imidazol-2-yl)phenyl)-1H-imidazo(4,5-f)(1,10)phenanthroline (1c), which served as an efficient anion sensor for fluoride ion over a wide range of other anions (Cl−, Br−, I−, NO3−, ClO4−, HSO4−, BF4−, and PF6−) owing to imidazole group in the main backbone. The absorption intensity of compound 1a at λmax 358 nm slightly decreased; however, a new band at λmax 414 nm appeared upon the addition of fluoride ion, while no evident change occurred upon the addition of eight other anions. The photoluminescence intensity of compound 1a at λmax 426 nm was nearly quenched and fluorescence emission spectra were broadened when fluoride ion was added into dimethyl sulfoxide (DMSO) solution of compound 1a. Compared with the optical behaviors of the DMSO solution of compound 1a in the presence of Bu4N+F−, compounds 1b and 1c exhibited considerable sensitivity to fluoride ion due to the increase in coplanarity. Furthermore, compared with the fluorescence emission behaviors of the DMSO solutions of compounds 1a and 1b in the presence of Bu4N+F−, compound 1c exhibited the most significant sensitivity to fluoride ion due to the charge transfer enhancement. Consequently, the detection limits of compounds 1a–1c increased from 5.47 × 10−6 M to 4.21 × 10−6 M to 9.12 × 10−7 M. Furthermore, the largest red shift (75 nm) of the DMSO solution compound 1c in the presence of fluoride ion can be observed. Our results suggest that the increase in coplanarity and the introduction of electron-withdrawing groups to the imidazole backbone can improve the performance in detecting fluoride ion.

Highlights

The field of anion recognition and sensing has attracted considerable attention in the past decades because different anions play different functions in biological and environmental processes and either inadequate or excessive anions would be harmful [1–12]
Our results suggest that the increase in coplanarity and the introduction of electron-withdrawing groups to the imidazole backbone can improve the performance in detecting fluoride ion
An efficient analysis of fluoride ion is crucial to providing key information for fluoride ion hazard assessment and pollution management

Summary

Introduction

The field of anion recognition and sensing has attracted considerable attention in the past decades because different anions play different functions in biological and environmental processes and either inadequate or excessive anions would be harmful [1–12]. Many groups have made substantial efforts to design and synthesize optical sensors of fluoride ion in recent years [26–32]. Among these optical sensors, imidazole-based optical sensors have been extensively investigated because these sensors are obtained and exhibit distinctive fluorescence property and strong interaction between. The relationship between molecular structures and optical properties for the used as optical sensors for fluoride ion. Phenanthrene group was used as an electron donor in compound 1b and charge transfer occur from phenanthrene group (acceptor). DMSO solution for the of fluoride ion influenced by and the electronic molecular solution for the analysis of fluoride ionanalysis influenced by the molecular structures structures and electronic properties of substitute groups are investigated in detail.

Synthesis

N presence

Conclusions