Design,synthesis And Application Of Organic Dual-State Luminescent Materials With Solvatochromism

Since Tang group proposed the concept of aggregation-induced emission(AIE)in 2001,the research on AIE has attracted widespread attention.Traditional dye molecules usually appear to disaggregation-induced emission phenomena.They exhibit bright fluorescence in the disoved state,but in the aggregated state,because of the ?-? stacking interaction,the excited state of such aggregates often relaxe back to the ground state via non-radiative channels,resulting in the emission quenching of the luminophores.The property of aggregation-induced quenching phenomenon of tranditional dyes can also be called disaggregation-induced emission(DIE).Thus their utilization in the solid state has met great challenges.Instead,AIEgens can overcome the shortcomings of traditional DIEgens,because they emit intense fluorescence in solid or the aggregated state.However,both DIEgens and AIEgens can only exhibit bright fluorescence in a single state(solution or solid state).There is a growing interest in organic dual-state emission emitters(DSEgens),intensely emitting in both the solution and solid states.However,only a few examples demonstrated DSE behaviours.There is no valid design strategy for designing DSEgens with solvatochromism because of the lack of an investigation into the relationship between structure and DSE property.And there are few practical applications of DSEgens.In this paper,we synthesized a new class of organic dual-state emission luminogens(DSEgens)by changing the donors and acceptors.First,the general design strategy for dual-state emssion molecules were proposed: by combining the partially shared donor-acceptor pattern and twisted structures,we introduced different electron-withdrawing group and designed three dual-state triphenylamine derivatives with remarkable solvatochromism properties that can be used for encryption and anti-counterfeiting;in addition,based on the above rules,by introducing malononitrile as an acceptor into different donors such as dimethylamino,tetraphenylethylene,triphenylamine and carbazole,and altering the molecular dipole moment,we realized the change of molecules from aggregation-induced emission(AIE)to molecular rotor(TICT)and dual-state emission(DSE).The following are the main contents in this thesis:(1)Three electron-withdrawing groups were introduced into a steric triphenylamine molecule,respectively,by Friedel Crafts acylation reactions.The obtained products are brightly emissive in both the solution and solid state,with solvatochromism behavior depending on solvent polarity.Based on theoretical analysis and experimental data,a design strategy for fluorescent molecules with dual-state emission(DSE)and solvatochromism properties is reported.A twisted intramolecular charge transfer(TICT)mechanism may be responsible for solvatochromism behaviours of these DSEgens,similar to traditional TICT molecules for viscosity measurement.A variable-temperature experiment was performed to explore the relation between structural conformation and emission location.The unique solvatochromism behaviour depending on solvent polarity and large Stokes shift,thus they can be applied to anti-counterfeiting.This work clearly demonstrates a general design strategy for dual-state emission luminogens by the construction of a partially shared donor-acceptor pattern and the introduction of nonplanar structures,and also provides a rational explanation for the solvatochromism of these DSEgens.(2)All synthesized fluorophores contain the structures of di-cyano(DCN)group,and malononitrile was introduced into different donors through Knoevenagel condensation.Four kinds of organic emission materials with different properties were abtained.Some of them show the traditional TICT phenomenon,and they emit neither in solution nor in solid state,but emit bright fluorescence by increasing environmental viscosity(eg.DMABM).Some show the properties of aggregation-induced emission(AIE),and these AIEgens emit intense fluorescence in the aggregated or solid state,but become weakly emissive in the dissolved state(eg.TPVBM).The others show dual-state emission(DSE)properties,intensely emitting in both the solution and solid states(eg.DPABM and CBM).Through natural bond orbital(NBO)analysis,we found that the different luminescence properties were caused by changes in dipole moment between donors and acceptors.Alteration in molecular dipole moments is a key parameter for the conversion of AIEgens to DSEgens and TICTgens.The variable-temperature experiment and viscosity-depending fluorescence enhancement data have verified the cause of solvatochromism of dual-state emission molecules.This work not only reports the new dual-state emission molecules with long wavelength and high quantum efficiency,but also explains the causes of different emissin phenomena with different donors from the perspective of molecular polarity,which can be expanded to the development of different kinds of organic emission luminogens.In summary,we have designed and synthesized a class of dual-state emitters(DSEgens)and their anti-counterfeiting applications were further demonstrated.First,three electron-withdrawing groups were introduced into a steric triphenylamine molecule,respectively.The abtained luminogens possess dual-state emission(DSE)and solvatochromism properties,which can be used for anti-counterfeiting applications.In addition,the malononitrile moiety was used as an acceptor,and a group of dual-state emission molecules with large Stokes shifts and high quantum yields were synthesized by changing the electron-donating group,and its different emission behaviour is discussed from the perspective of molecular polarity.