Synthesis And Application Of Bisbenzimidazole Derivative PMOs

Periodic mesoprous organosilica(PMO)is a kind of materials which embeded organic groups in the silica skeleton as a part of framework.In this material,the organic group as an entity is uniformly distributed without'blocking the mesoporous pores.It can impart more reactivity to materials while maintaining mesoporous properties.PMOs have the characteristics of regular and orderly pores,large specific surface area,adjustable pore size and controllable morphology.They are widely used in catalysis,adsorption,drug delivery,photoelectric devices and sensing.Fluorescent probes have been used for metal ion detection due to their easy operation and fast response,which are used as metal ion detection.Compounds featured by aggregation-induced fluorescence emission(AIE)and excited-state intramolecular proton transfer(ESIPT)could be used to design ratiometric fluorescent probes that reduce environmental impact and avoid self-absorption during analytical testing.By embedding an organic fluorophore in a PMO material,a solid-state fluorescence sensor can be constructed,which has improved stability compared to a simple organic compound and can be recycled many times.In this paper,a novel compound,bisbenzimidazole derivative BBM,was synthesized,which is a fluorescent compound with both AIE and ESIPT features.It can detect metal ions in aqueous solution.The precursor BBM-Si was prepared by silanization of BBM,the bridged BBM-PMO was synthesized by using cetyltrimethylammonium bromide(CTAB)as the structure directing agent.A series of technique were used to characterize the materials and the result demonstrated that BBM is successfully embedded in the mesoporous materials.These materials maintain their mesoporous structure and at the same time,show good sensing ability to Cu2+.The main research contents are as follows:(1)A novel compound bisbenzimidazole derivative(BBM)and the bridged organosilicon precursor(BBM-Si)were synthesized,explored the effect of solvent on the aggregation-induced fluorescence effect(AIE)and the intramolecular proton transfer effect(ESEPT)of BBM,have been tested.The mixture of THF and H2O at THF:H2O=3:7(v/v)are chosen as the medium for the metal ion sensing.BBM has high selectivity to Cu2+ iin this medium,its detection limit is as low as 6.9×10-7 M.The detection has not been interfered by other coexisting metal ions,such as Ba2+,Ca2+,Cd2,,Co2+,Fe+,Hg2+,Mg2+,Mn2+,Ni2+,Pb2+,Zn2d+,Ag+,K+,Na+,Al3+,Cr3+and Fe3+.BBM can detect Cu2+ in solution at a wide pH range and is not affected by the surrounding environment.It is found that BBM and Cu2+ are coordinated in a ratio of 1:2.(2)The bridged BBM-PMOs were synthesized using BBM-Si and TEOS as the mixed silicon source and CTAB as the structure-directing agent.By small angle X-ray scattering(SAXS),infrared spectroscopy(FTIR),solid state 29Si nuclear magnetic analysis,differential-scan calorimetry analysis(TGA/DSC),scanning electron microscopy(SEM),high resolution transmission electron microscopy(HR-TEM),nitrogen adsorption/desorption isotherm,and so on.It was demonstrated that BBM is successfully embedded in the mesoporous material.BBM is a molecule with aggregation-induced fluorescence enhancement,and the fluorescence intensity of BBM-PMOs with increasing the organic content embedded in the materials.The silica framework in the material limits the intramolecular rotation of the BBM molecule,forming a more rigid structure that promotes the fluorescence emission of fluorophore in the material.In addition,the material has the characteristics of excited intramolecular proton transfer(ESIPT).The fluorescence emission spectrum shows a single excitation result in double emissions.After addition of Cu2+,the enol fluorescence emission remains unchanged but the keto fluorescence emission was quenched by Cu2+.So Cu2+ could be detected sensitively by raliometric fluorescence method.Compared to BBM molecules,the detection limit is as low as nmol and can be recycled multiple times.The coordination structure of BBM-PMOs/Cu2+ and the detection mechanism were proved by X-ray absorption technique.