Design,Synthesis,Photochemical And Luminescent Properties Of Imidazole And Distyrylbenzene Derivatives

Imidazole as a five-member heterocyclic ring,the bipolar structure of pushing and pulling electrons in the molecule makes imidazole derivatives a more adjustable photophysical and electrical properties,and more applications in OLED,organic photovoltaic,luminescent electrochemical batteries,optical sensors,electronic transfer media,memory devices and other aspects.Distyrylbenzene derivatives are a kind of good?electron conjugated skeleton,the sp² hybridization of double bond carbon atoms and the benzene ring of?electron make it easily delocalization from the electronic structure.The distyrylbenzene derivatives can be used as a carrier molecule,linked on a variety of functional groups in the preparation of functional molecules,have been widely applied in organic electroluminescent devices,organic solar cells and field effect transistor.Based on the simple structure and excellent performance of imidazole and distyrylbenzene derivatives,in this paper,a series of novel imidazole molecules with different structure types and electronic properties were designed and synthesized,in order to obtain a selective ion radius imidazole probe and explore the affect of different group replaced to the luminescent of imidazole derivatives.At the same time,more studies on the photo-oxidation reaction of imidazole metal complexes were taken.Besides,distyrylbenzene derivatives with D-A structure were designed and synthesized to study the mechanism of the stable existence of cis-trans isomers under light condition.Thus,the research content of this paper is based on the following:1.In this paper,a fluorescent probe of imidazole derivatives 5 was reported with the replacement of imidazole ring on both side,which had the similar structure to tribipyridine.The effect on ion selectivity was study by introduction of the smaller five-member imidazole ring.Compared with the tribipyridine probe 6,imidazole probe 5 had a certain selectivity to the ionic radius with a response to larger ions such as Ag⁺?Cd²⁺?Cu²⁺?Zn²⁺and no ionic radius relatively with smaller ions like Fe³⁺?Mn²⁺?Ni²⁺.However,probe 6 can response to all of these.The introduction of imidazole ring could increase the distance between molecule rings,higher complexing ability was requried.Thus small radius of metal ion couldn't ligand with the imidazole probe 5.The experimental data showed that probe 5 had a good detection performance in a wide range of pH value from 4 to 9,forming a 1:1 type complex with Zn²⁺,and the minimum detection limit could be 1.11×10^-77 mol/L.Thus,the ring spacing of probe has influenced the selectivity and had a certain selectivity to ionic radius.2.In the third chapter,imidazole derivative luminescent materials with symmetrical structure were synthesized by modifying different kinds of group at each point of the imidazole ring to study the effects of different substituents,conjugation degree and other factors on the luminescent properties of the materials.Compared to the larger twisted imidazole derivatives?2CH3IM?of which the luminescence efficiency in solution was around 50%,the efficiency of imidazoles derivatives with symmetric structure was much high?around 90%?,P2IM,P2PI could be close to 100%.This was because the large conjugated structure with planar symmetry structure which could effectively improve the luminous efficiency of materials.In solid state,strong intermolecular force was an important factor affecting the luminescence of solid materials due to the seriously quenching of luminescence in solid state.At the same time,the import of heavy metal atom Pt made the metal complexes PtP2IM a long-life phosphorescence emission with a lifespan of about 12?s and an AIE properties with a luminous efficiency of 20%in film,which was different from the properties of ligand.Therefore,through the import of large conjugated structure with planar symmetry structure,materials with high luminous efficiency and AIE property were got.3.In chapter 4,by means of in situ NMR,in situ UV and DFT calculation,a photo-oxidation reaction occurred in imidazole metal complexes PtP2IM was studied in detail.The occurrence process and conditions of this reaction were further studied through comparative experiments,and a possible reaction mechanism was proposed at last.It was found that the reaction could take place simply by light irradiation in the air,and the product was simple and highly efficient with a good stability in the absence of oxygen.The specific reaction process was as follows:under the condition of light,the C=C double bond of imidazole ring was attacked by oxygen generating the complexes PtPIMO with benzoylimino and benzamide group.Meanwhile,different substituents and pH environment was observed to have an obvious influence on the reaction rate,which meant the structural rearrangement.In the presence of oxygen capture agent,the reaction was stopped,which proved the essential of singlet oxygen in the reaction.The further test showed that the yield of singlet oxygen in the solution of dichloromethane with metal complex PtP2IM was 0.21,while the yield in AIE state was significantly increased.In the end,the reaction could be summed as the self-sensitized oxidation reaction at photo-excitation state,and a possible reaction mechanism was obtained,including the energy transfer process of singlet oxygen generation and the structural rearrangement process.The experimental data also showed the possibility of PtP2IM as a photosensitizer.4.In chapter 5,based on the structure of distyrylbenzene derivatives,the D-A structure molecule TPNCF with two stable E/Z configurations was designed and synthesized.Through in situ NMR,in situ UV,DFT calculation and other methods,the mechanism of its stable existence was studied.TPNCF molecule could maintain a good stability in high polar solvent,while in low polar solvent,it could rapidly isomerization.The further solvation experiment and theoretical calculation results showed that TPNCF molecule in low polar solvent had HLCT emission characteristics and CT state in high polar solvent.Therefore,the mechanism of the stable E/Z configuration of TPNCF under light radiation was obtained:the lowest excited states of TPNCF in low polar solvent have the HLCT emission characteristics,the existence of LE states could promote the generation of single bond ion state to isomerization,but in high polar solvent,due to the influence of solvent,there was obviously decline in CT state energy,which occupied the lowest excited state to maintain a good stability.The AIE properties of TPNCF molecule were also determined by their CT excited state.This theory would make an important contribution to the study of basic E/Z isomerization reaction of photochemistry and could guide the design of stable E/Z isomer materials for organic photoelectron applications.