Design,Synthesis And Application Of Solution-solid Dual-state Emission Organic Luminescent Materials Based On Intramolecular Charge Transfer

Dual state emission（DSE）materials refer to the organic fluorescent materials that can emit fluorescence in both dilute solutions and the solid state.It combines the advantageous emission properties of aggregation caused quenching（ACQ）materials and aggregation induced emission（AIE）materials,overcoming the limitations that many organic fluorescent materials can only emit efficiently in a single state.Thus,they have attracted a lot of research interests,and been widely applied in chemical sensors,bio-imaging,organic light-emitting diodes（OLEDs）,and etc.Compared with the widely investigated ACQ and AIE materials,the study of DSE materials lags behind.So far,researchers have developed several strategies to obtain DSE materials,i.e.,structure modification of ACQ materials,suitable intramolecular charge transfer（ICT）,self isolation（SI）,namely introducing steric hindering groups to the rigid molecular backbone,excited state intramolecular proton transfer,etc.Among these strategies,utilization of electron donor（D）and acceptor（A）units to construct molecules owning suitable ICT characteristics is an important method to have DSE materials.In this thesis,on the basis of the thorough literature review of the progress of the development of DSE materials,a series of D-A molecules with carefully screened D/A unites have been investigated.In combination with the engineering of molecular conformation,the ICT process of these molecules can be adjusted,and the DSE emission can be realized from non-emission,ACQ or AIE materials.The influence of the conjugation degree of molecular backbone,electronic effect of substituents,molecular conformation to the DSE properties have been studied,and their application in chemical sensors,bio-imaging,data encryption has been investigated.The main contents are as below:1.Utilizing non-emissive coumarin as acceptor,TPE,N,N-diethylamino,and TPE-phenyl as donor,three Coumarin-TPE molecules with D-A,D-A-D and D-A-D structure（CT,NCT,NCPT）are designed and synthesized.TPE is a star AIE molecules,the introduction of TPE can effectively reduce theπ-πinteraction of coumarin,which makes CT show typical AIE property.Different with CT,various substituents,i.e.,N,N-diethylamino and phenyl group are introduced to the 7-position of CT,or between the TPE and coumarin,respectively.Thus,the conjugation length and electronic delocalization degree of the molecules have been strengthened,and the ICT properties are adjusted.NCT and NCPT both exhibit DSE properties(ФNCT,_THF=0.22,ФNCT,_solid=0.35;ФNCPT,_THF=0.44,ФNCPT,_solid=0.36).Compared with NCT,NCPT has stronger emission in solution,which can be explained by the lower energy consumption of TPE as phenyl group is introduced.The strong emission in solution of NCT and NCPT make them have potential application in bio-imaging,and the strong solid-state emission brings them good MFC properties.2.In the basis of the study of NCPT,TPE was replaced by a planar unit pyrene to get a novel D-A coumarin-pyrene derivative HPPE.After that,F,N,N-diethylamino groups are introduced to the 7-position of coumarin to prepare a D-A molecule FPPE and a D-A-D molecule NPPE.The different substituents can adjust the ICT process in different aspects.The results indicate that F atom can help the ICT from pyrene to coumarin,while N,N-diethylamino group enhances the ICT from coumarin to pyrene.These materials all show DSE properties(Ф_HPPE,THF=0.42,ФHPPE,solid=0.21;ФFPPE,THF=0.60,ФFPPE,solid=0.31;ФNPPE,THF=0.53,ФNPPE,solid=0.14).They also have MFC properties,and can be used for rewritable test papers.In solution,they can selectively detect PA through energy transfer and photo-induced electron transfer process.In addition,the molecules can be absorbed by living cells,therefore,they can be used for cell imaging.3.Utilizing TPA as donor unit,and benzaldehyde as acceptor,a new D-A-D type TPA derivative 2TPACHO is designed and synthesized.It has strong fluorescence in both solution and the solid state.The ICT between TPA and benzaldehyde will be favor for the strong emission of the molecule in solution(Ф_THF=0.43).On the other hand,the twisted molecular conformation of TPA can reduce the intermolecularπ-πstacking,realize strong emission in the solid state(Ф_solid=0.62).2TPACHO has reversible MFC property,after grinding,the emission peak red shifts from 480 nm to 497 nm,but the quantum yield decreases from 0.66 to 0.22.X-ray diffraction experiments prove that the MFC properties of the materials are resulting from the transformation of crystalline to non-crystalline state.In solution,2TPACHO can sensitively detect the trace amount of water in common organic solvents,i.e.,1,4-dioxne,THF,acetone,DMF and DMSO,the detection limit is 0.0065%,0.0074%,0.0026%,0.0284%,0.0282%.4.With pyrene and TPA as donor,and cyanostyrene/cyanostilbene as acceptor,two D-A-D molecules（PETPA and PEPHTPA）with DSE properties are synthesized.Compared with PETPA,the extra benzene ring in PEPHTPA adapts the ICT process,increased the twist of molecular backbone,show stronger dual state emission(ΦPETPA,_THF=0.49,ΦPEPHTPA,_THF=0.77,Φ_PETPA,solid=0.95,Φ_{PEPHTPA,solid}=0.97).In the solid state,PETPA and PEPHTPA both show high contrast MFC properties(Δλ_PETPA=50 nm,Δλ_PEPHTPA=55 nm).After grinding,the fluorescence of PETPA and PEPHTPA change from yellow and green to red and yellow,respectively.In solution,the molecules realize living cell-imaging,as they have large Stokes shift and high quantum yields.5.Based on the previous study about PEPHTPA,utilizing electron-withdrawing moietynaphthalimide to replace TPA,and in the meantime change the position of the cyano group,two D-A-A molecules（NIPEαand NIPEβ）are prepared.The twisted molecular conformation and suitable ICT effect result in the DSE characteristics of the two molecules(Φ_NIPEα,cy=0.15,ΦNIPEβ,_cy=0.45,ΦNIPEα,_solid=0.46,ΦNIPEβ,_solid=0.45).The position of the cyano group can affect the ICT process,thus changing the quantum yields of the molecules in dilute solution.NIPEβhas a stronger ICT effect,and its emission is solution is stronger.NIPEαand NIPEβboth can detect the trace amount of water in THF and Diox,and the detection limits are（0.2402%（Diox/NIPEα）、0.1071%（THF/NIPEα）、0.0608%（Diox/NIPEβ）and 0.0677%（THF/NIPEβ））.In the solid state,they both have reversible MFC properties(Δλ_NIPEα=13 nm,Δλ_NIPEβ=10nm).