Design, Synthesis Of Indolo[3, 2-b] Carbazole Derivatives And Performance Of Thin-film Field-effect Transistors

Organic thin-film transistor(OTFT) is a transistor in which the active layer is based on organic materials.OTFTs have been widely applied to many field and obtained greatly success.The reason is that OTFTs possess many merits that inorganic field-effect can not be compared with.For example:the origin of organic materials is wide and the OTFTs' performance can be improved by modifying the molecular structures.OTFTs can also be fabricated easily with large device by simple fabrication technologies,and can be made into different fugures because of their good machine processing capability.Among materials of OTFTs,indolo[3,2-b]carbazole arose many people's attention for studies because it has a relatively large and planar molecular structure that is similar with pentacene to enable facile establishment of higher structural order for charge transport and have good environmental stability.Moreover many new compounds can be gained by modifying molecular structure,and have good soluble capability.We have designed and synthesized a series of new organic semiconductor materials based on indolo[3,2-b]carbazole by classic Vilsmeier,Wittig,Suzuki Reaction and characterized by nuclear magnetic resonance,mass spectrum and elemental analysis. Crystals of ICZB,ICZF and 28TICZ were grown by using solvent evaporation and crystals of 2TICZ was gained by theoretical calculation.By studying the electrical, optical and other properties,the relationships between molecular structure and charge transport were discussed in detail,and were confirmed by OTFTs.The primary results are as follows:(1) A series of new organic thin-film transistor materials based on indolo[3,2-b]carbazole have designed and synthesized.The introduction of long alkyl chains to N-5 and N-11 positions of indolo[3,2-b]carbazole can not only improve the solubility of the compounds in common solvents but also promote the molecular self-organization of indolo[3,2-b]carbazole derivatives to form films with high orientations during vacuum deposition,then improve the charge transport performance.(2) Crystal structures of ICZB,ICZF,28TICZ were determined by single crystal X-ray diffraction method and crystal structures of 2TICZ was gained by theoretical calculation.By studying the substituent effect on molecular conformation and packing characteristics,it can be found that indolo[3,2-b]carbazole derivatives display good planar structure.Although very small dihedral angles exist between each rings and indolo[3,2-b]carbazole,there are still strong intermolecular interactions,which will facilitate charge transport.(3) UV-visible absorption and emission spectra of the compounds were measured in toluene solution(concentration 1×10^-6 mol L^-1) and the thin films deposited at substrate temperature of about 25℃.The PL spectra of 6TICZ,ICZF,ICZ3F,ICZN and ICZB show blue shifts in the film state compared to that of the solution,suggesting H aggregations occur in the film and two interacting molecules form a dimmer.The PL spectra of 28TICZ and 2TICZ in the film state are red shifted as compared to that in the solution,indicating J aggregation instead,and more effective conjugation length and planar in the film state.Band gaps of compounds were obtained according to the experience formula of Eg =1240/λ,showing larger band gap between HOMO-LUMO energy levels and lower HOMO energy levels,which indicated that they possessed excellent environmental stabilities.(4) OTFTs using indolo[3,2-b]carbazole-based organic semiconductors were fabricated.All the compounds exhibit p-type organic semiconductor characteristics with high mobility and high on/off ratio.The mobility of 6TICZ and ICZB are 0.039,0.023 cm² V^-1 s^-1,and on/off ratio are 10⁵,5×10⁴,respectively.