Synthesis And Study On Fluorescent Properties Of Benzimidazole Derivatives

As a fluorophore,benzimidazole has a coplanar structure and unique linear and nonlinear optical properties.Its derivatives have strong coordination ability and electron and proton transfer ability,and can emit strong fluorescence in organic solvents and aqueous solutions.What’s more,the fluorescence quantum yield is high,and the Stokes shift is large,so it has been widely used in the field of fluorescence sensing and luminescent materials.Therefore,it is important that studying the influence of the structure of derivatives on their photophysical performance for the development of the application research of benzimidazole derivatives in the field of fluorescence sensing and luminescent materials.Firstly,change the structure of benzimidazole derivatives:Considering the number of benzimidazole groups,one or two benzimidazole groups are introduced from the ortho position of the phenolic hydroxyl group to synthesize compound 1-2;introducing different substituents on the para-position of the phenol,namely-CH₃,-Cl and-OCH₃,thereby synthesizing compound 2-4;introducing fluorine atoms at the 4,5 positions of the benzimidazole group,thereby synthesizing compound 5-7;A double bond was introduced between benzimidazole group and phenol to expand the degree of conjugation,thereby synthesizing compounds 8-10.Secondly,the photophysical properties of these 10 target compounds were studied by solvent effect test,F^-effect test,solid-state fluorescence spectrum test and fluorescence micrograph.The results show that expanding the number of benzimidazole groups,introducing fluorine atoms on the benzimidazole groups,and expanding the degree of conjugation can red-shift the emission wavelength,and with the enhancement of the electron-donating ability of the substituent on the para-position of phenol,the emission wavelength is also red-shifted accordingly.In addition,because benzimidazole derivatives 1-7 can undergo ESIPT process,they have luminescent properties.The solid luminescent color of compound 1-2 increases with the expansion of the number of benzimidazole groups,from blue to yellow.The solid luminescent color of compound 2-4 has a color reduction with the enhancement of substituent electron donating ability,from orange-yellow to yellow to yellow-green,while compound 5-7has a color-increasing effect,from green to yellow-green to yellow.Therefore,they are all expected to be designed as luminescent materials of different colors.Finally,both dibenzimidazole-phenols 2-4 and difluorobenzimidazole-phenols 5-7 can be designed as dual-response fluorescence sensors to achieve the sensing of Cu²⁺and Zn²⁺.Taking compound 4 as an example,it was tested in THF aqueous solution（30%Tris-HCl）and can be used as a colorimetric fluorescence sensor for Cu²⁺,and can also be used as a ratiometric fluorescence sensor for Zn².At last,it was successfully applied to actual water sample detection and fluorescence imaging in living cells.