Synthesis,Aggregation Structure And Optoelectronic Properties Of Aromatic Imide Molecules

Organic conjugated semiconductors have been widely applied in organic light emitting diodes（OLEDs）,organic field effect transistors（OFETs）,organic photovoltaics（OPVs）because of their advantages of light-weight,flexibility,low-cost,and tunable optoelectronic properties.Based on a large number of materials,the electronic properties and intermolecular interaction of materials could be regulated and controlled by changing the molecular structures,substituents or molecular configuration.Usually,the optoelectronic performance of device strongly depends on the condensed state of materials,which was affected by the molecular structures and intermolecular interaction types of conjugated semiconductors.Therefore,it is very important and meaningful to investigate the relationship between molecular structure,aggregation behavior and their optoelectronic performance,which could give full play to these materials.As typical aromatic conjugated molecules,perylene bisimide derivatives（PBIs）have been extensively applied in OPVs and OFET area owing to their fantastic advantages such as photo-,thermo-and chemical stability,high quantum efficiency and charge transport et al.However,some challenge still exist for their optoelectronic application.This is mainly attributed to the large conjugated planar skeleton of PBIs,which leads to strong aggregation and poor solubility in common solvents.The aggregation will lead PBIs to form large aggregates in their solid state,causing fluorescence quenched and hampering their application in OLEDs.Besides,large aggregates made against to exciton dissociation in OPV devices.So it should be paid attention that designing special PBI molecular structures and investigating their aggregation behavior and optoelectronic properties.In this thesis,we design and synthesize new PBI molecules with different aggregation behaviors,and investigate the molecular structures,aggregation and optoelectronic properties through controlling the intermolecularπ-πstacking,hydrogen bonding and inter/intra-molecular charge transfer interaction.We applied them to different areas including OPVs,OLEDs and organic thermoelectric conversion devices（TEs）,respectively.The detailed research progress is listed as follows:InChapter 2,we designed and synthesized two PBI molecules with similar structures:with/without CH3 substituent at ortho-position of phenoxyl substituents in the bay area.The research showed no effects on photophysical properties of monomers in solution state after introduction of the methyl substituent.While obvious difference in aggregation styles could be observed in their solid films.With CH3,PBI 3a showed good solubility and typical J-aggregation behavior in solid state.Whereas PBI 3b,without CH3,showed face to face H-aggregation.In addition,we changed the N-substituent from butyl to simple H atom and got a new molecule PBI-H,which could form intermolecular H-bonding.We could obtain different nano-morphologies of PBI-H via controlling theπ-πstacking and H-bonding supramolecular interactions.Ultraviolet photoelectron spectrometer showed the different extent of decrease of ITO work function by two kinds of nano-structured PBI-H films.Besides,the charge transfer process between C60 and ITO/PBI composite electrode could be observed.So,we applied PBI-H as interlayer in inverted OPV device,the P3HT:PC61BM device modified with nanofibers showed a PCE of 3.69%,much higher than that modified by nanoparticles.The improved OPV performance could be caused by the low work function of ITO and good charge transport inside the nanofibers.When applied in PTB7:PC71BM OPV system,the PCE could be as high as 9.11%,which was highest efficiency reported at that time.The excellent performance showed a great potential of n-typed PBI derivatives with tunable aggregation behavior in application in OPV area.In Chapter 3,in order to study the imide materials in application of light emitting area,we designed and synthesized several D-A twisted molecules utilizing naphthalene imides as acceptor unit.We could obtained materials with different colors by introducing suitable donors.The experimental and theoretical analysis revealed that the enlarged energy gap between the lowest singlet state（S1）and lowest triplet state（T1）,and the mismatched electronic configuration of these two states can effectively suppress the ISC process in D-A type NMI derivatives and enhance their luminescent properties.The doped OLED performance showed that TPA-NMI with triphenylamine as donor could achieved a maximum luminous efficiency of 15.5 cd/A and a maximum external quantum efficiency of 5.96%,which is the best device performance ever achieved based on the naphthalimide derivatives.The exciton utilization efficiency could be up to 44%,exceeding 25%exciton utilization.However,it might be not beneficial to light emitting if the intramolecular charge transfer is too strong.Here,we found a new D-A molecule based on PBI derivative POI.The structure was ambiguously confirmed by two-dimensional NMR,mass spectrum and infrared spectrum and we also proposed the mechanism of new reaction.The electron withdrawing of four chlorine atoms at bay area played a key role in the reaction.POI showed no fluorescence.Interestingly,in DMF solvent,the absorption of POI could red-shifted to infrared region,which was caused by the strong intramolecular charge transfer,forming a PBI anion state or zwitterion structure.The discovery of new D-A PBI derivative was rather meaningful to the chemistry of perylene bisimides.In previous chapter,the absorption characters of PBI anions were observed.As we know,some negative charges would located on the skeleton of PBI anions,which could enhance solubility by the electrostatic repulsion interaction.Inspired by this,in Chapter4,we dissolved insoluble PBI-1 derivative by forming PBI dianions in hydrazine hydrate under solvothermal treatment.The uniform films could be fabricated by drop-casting and the chemical composition of each film could be confirmed by UV/vis,ESR,and Raman spectra characterization.The film formed in air was defined as PBI neutral state film;the film formed in N2 was mainly composed of dianions and a little bit of radical anions,so-called PBI^2-/PBI^·-film;when PBI^2-/PBI^·-film exposed to air for hours,the composition of film could be PBI neutral state as main components and radical anion as a bit of dopants,so-called PBI/PBI^·-film.Except PBI neutral film,both PBI^2-/PBI^·-film and PBI/PBI^·-film showed regular nanorods in the film and exhibited high conductivities.Most Interestingly,PBI^2-/PBI^·-film exhibited a p-type semiconductor characters when used in thermoelectric conversion device,while PBI/PBI^·-film still showed typical n-typed characters.According to the theory of molecular orbitals,we proposed the innovative model of conversion of n-type/p-type semiconductor in PBI system.Based on the model,we designed a 4Cl-PBI derivative and found it undergoing a dechlorination processes in the solvothermal condition.The fabricated anionic film exhibited an excellent p-type thermoelectric performance with ZT=0.96,which is much higher than that ever achieved of organic semiconductors（ZT=0.42）.Ultilizing PBI dianion species to fabricate anionic films to realize polarity conversion could provide a novel design thought for the development of high performance organic thermoelectric materials.