Study On Photophysical Behavior And Energy Transfer Of 2-(2’-hydroxyphenyl)benzimidazole And Its BODIPY Dyad Compound

Based on the synthesis of 2-（2’-hydroxy-5’-aminophenyl）benzimidazole（HABI）,1,3,5,7-tetramethyl dipyrrometheneboron difluoride（BODIPY OR BDP）,1,3,5,7-tetramethyl-8-p-aminophenyl dipyrrometheneboron difluoride（BODIPY-NH₂ OR BDP-NH₂）as well as 2-（2’-hydroxyphenyl）benzimidazole bridged with BOP（HBI-BDP）dyad compound,the effects of solvents and substituent groups on the spectroscopic properties and excited state intramolecular proton transfer（ESIPT）of HABI were studied by using spectroscopy and density functional theory.The fluorescence resonance energy transfer between HABI and BPD or BDP-NH₂ were investigated.The spectroscopic properties,intramolecular energy transfer and effect of p H value on the stability for dyad HBI-BDP were researched.The main results and conclusions are as follows:1.Proton transfer compound HABI was synthesized.The UV-absorption spectra and fluorescence emission spectra of HABI were measured in the five solvents,i.e.toluene,1-4dioxane,DMF,methanol and H₂O.The electronic spectra and the ESIPT behaviour of HABI were theoretically simulated and analysed by density functional theory at the TD PBE1PBE D3/TZVP.The results indicated that the wavelength of maximum absorption peak of HABI are about 300nm in the used solvents and have a certain red shift with the increase of solvent polarity.The fluorescence spectra of HABI appeared dual emission peaks which the wavelength about 315nm and 530nm respectivitely correspond to the enol and keto configuration in the solvents.The fluorescence of enol is partially quenched due to the form of hydrogen-bond complex between HABI and CH₃OH or H₂O in methanol or water.The ESIPT reaction for HABI can take place in the all solvents.The electronic spectra and the ESIPT behaviour of HABI are obviously affected by the electron effect of substituents,the electron-donating substituent can prompt the absorption and emission peaks red shift and the ESIPT proceeding.2.Compounds BDP and BDP-NH₂ were synthesized.The intermolecular interaction between HABI and BPD or BDP-NH₂ were investigated by spectroscopy according to fluorescence resonance energy transfer（FRET）theory.The results showed that HABI as the energy donator can generate photoinduced energy transfer with the energy acceptor BPD or BDP-NH₂.The fluorescence intensity of acceptor is enhanced,but quenched partially for the donator in this FRET process.3.Dyad compound HBI-BDP with dual fluorophore was synthesized.The absorption spectrum and fluorescence emission spectrum of HBI-BDPI were measured in the organic solvents,such as dichloromethane,THF,1-4 Dioxane,and DMSO.The optimized molecular structure and frontier molecular orbital energy were calculated by DFT B3LYP/6-31G（d）method.The research revealed that absorption and emission peak of HBI-BDP is separately located in 502nm and 513nm in used solvents.The fluorescence intensity of the dyad are enhanced with the increase of solvent polarity.The fluorescence intensity of HBI-BDP are remained stable under acidic conditions（p H=1-7）,but decreased gradually with the increase of alkalinity.It was indicated that the structure of the compound may be damaged in the strong alkaline environment,the amide bond of the bridging group breaks.The fluorescence spectra are only emerged the characteristic of BODIPY fluorophore.It was suggested that the intramolecular FRET is happened between HABI fluorophore and BDP-NH₂fluorophore in the dyad compound.