Effects Of Solvent Effect And Substituent Effect On Proton Transfer Of 2-(2-Hydroxyphenyl) Benzimidazole

In this paper,the effect of solvent effect and substituent basis on proton transfer is studied by combining theory with experiment.1.Combined with previous synthesis methods,2-(2-hydroxyphenyl)benzimidazole(HPBI)and its five derivatives were designed and synthesized.2.The influence of solvent effect and para-substituent of hydroxyl on the proton transfer of HPBI excited state has been studied theoretically and experimentally in two aspects.The experiment showed that HPBI showed the double fluorescence emission peaks of enol type(normal)and ketone type(tautomer)near 350 nm and 460 nm,respectively.The fluorescence spectra showed that the proton type solvent inhibited the transfer of the endoplasmic reticulum in the excited state of HPBI,while the non proton solvent promoted the transfer of the endoplasmic reticulum in the excited state.The very large solvent has hindered the ESIPT.The theoretical calculation of TD B3LYP/6-311++G(d)shows that,according to the PCM solvent model,the experimental value of the maximum absorption wavelength of the absorption spectrum of HPBI in each solvent is close to the theoretical calculation of the enol configuration,indicating that the enol configuration is the dominant configuration of the base state of HPBI.The theoretical value of the fluorescence emission wavelength of the keto configuration is slightly lower than the experimental value,but the enol configuration is higher than the experimental value,but the emission wavelength varies with the polarity of the solvent,and the experimental values are basically the same as the theoretical values.The experimental results of the HPBI Stokes displacement theory are basically consistent.In addition,with the increase of solution alkalinity,the fluorescence spectra of HPBI in aqueous solution will also change correspondingly.When the alkali reaches a certain concentration,the fluorescence emission peaks at 350 nm and 460 nm will disappear,and a new fluorescence peak,which is produced by the benzimidazole phenoxy anion from HPBI and alkali,is produced at 415 nm.TD The theoretical prediction of B3LYP/6-311++G(d)indicates that the emission peak wavelength is 409.44 nm.The fluorescence spectra show that the HPBI and its hydroxyl groups have different substituent derivatives,which show the double fluorescence emission peaks of the Enol and Keto in the vicinity of 350 nm and 460 nm,respectively.Through the study of the bond length,bond angle and front-line orbit of HPBI and its derivatives,it is shown that the hydroxyl group of HPBI has a hindering effect on its ESIPT when the group is connected with the electron donor group.Even if the group has the electron absorbing group,it can promote its ESIPT.The phenomenon of molecular frontier orbital and surface electrostatic potential of HPBI and its derivatives is further illustrated.3.The influence of HPBI hydroxyl meta-substituents on proton transfer is studied by theoretical calculation.The calculation shows that the substituents of the hydroxyl interposition can cause a certain degree of torsion of the benzimidazole ring and the benzene ring of the HPBI molecule,and weaken the hydrogen bond between the hydroxyl hydrogen atom and the adjacent nitrogen atom,which makes the energy barrier of the proton transfer rise and is not conducive to the proton transfer.Even the electron withdrawing group has the opposite effect on proton transfer.