Synthesis And Optoelectric Properties Of Polymeric Semiconductors Based On S-Indaceno[1,2-b:5,6-b’]dithiophene Derivatives

Polymeric semiconductor materials are widely used in organic field-effect transistors（OFETs）,organic solar cells（OSCs）,and other devices because of their simple preparation process,light weight,good flexibility,and convenient processing.The development of novel polymeric semiconductor materials has become a hot research topic in the field of organic electronics.In this thesis,two types of novel acceptors（FIDTO and s-IDT）are developed by using s-indaceno[1,2-b:5,6-b’]dithiophene-4,9-dione（IDTO）as an important intermediate via"fluorination strategy"and"quinonization strategy".Both FIDTO and s-IDT are used as the acceptor building blocks to synthesize four D-A polymers.In order to study the specific relationship between the structure and properties of polymer materials,we carried out the following research:1)IDTO is a class of acceptor units with good planarity,large skeleton conjugation,strong electron affinity,and fine-tunable structure,which is widely used to construct high-performance organic small-molecule electron-transport materials.However,high-performance electron-transport polymeric materials of IDTO are rarely reported.In this chapter,we report synthesis and application of a novel2-decylteradecyl-substituted FIDTO acceptor,which is found to possess good solubility,strong electron affinity,and low-lying LUMO energy level（–3.89 e V）.Based on the newly-developed FIDTO motif,two novel D-A conjugated polymers（PFIDTO-T and PFIDTO-Se）are further developed by copolymerizing with thiophene or selenophene units via the Stille coupling method.The thermal stability,photophysical properties,electrochemical properties,and field-effect transistor performance of the obtained materials are systematically studied.The reseaech shows that:1)PFIDTO-T and PFIDTO-Se possess excellent thermal stability with the thermal decomposition temperatures over 390℃;2)PFIDTO-T and PFIDTO-Se exhibit typical double-band absorption characteristics,whose maximum absorption sidebands are broadened to around 1000 nm;3)The HOMO/LUMO energy levels of PFIDTO-T and PFIDTO-Se are determined as–5.81/–3.81 e V and–5.75/–3.84 e V,respectively,which are similar to the classical n-type polymer N2200.Therefore,PFIDTO-T and PFIDTO-Se are a class of potential n-type polymer semiconductor materials.In order to study their carrier transport properties,we further fabricate the OFET devices based on PFIDTO-T and PFIDTO-Se thin films.Both PFIDTO-T and PFIDTO-Se display typical unipolar electron-transport properties with maximum electron mobilities of 0.23 and 0.73 cm²V^–1 s^–1.2)The introduction of the qunioid structure into the organic conjugated system can effectively reduce the optical band gap and frontier orbital energy level of the conjugated materials,which can endow the conjugated materials with strong elecetron affinity and unique optoelectrical and magnetic properities.Therefore,the research on quinoid organic conjugated systems has attracted much attention in recent years.In this chapter,IDTO is used as an important intermediate to develop a new class of quinoid conjugated acceptor unit（s-IDT）via"quinoneization strategy".It is found that s-IDT has good solubility,strong electron affinity,and good planarity.Alternative arrangement of s-IDT and comonomers（e.g,benzothiadiazole and bithiophene）in the conjugated backbone yields two novel D-A conjugated polymers（PsIDT-BT and PsIDT-TT）.The thermal stability,photophysical properties,electrochemical properties,and OFET device performance of the obtained materials are systematically studied.Thermogravimetric analysis shows that PsIDT-BT and PsIDT-TT had excellent thermal stability;their thermal decomposition temperatures are above 425℃.The maximum absorption tailor of PsIDT-TT film reaches about700 nm.Due to intramolecular strong charge transfer,the absorption spectrum of the PsIDT-BT film is broadened to the near-infrared absorption range,with the absorption tailor of up to 900 nm.Electrochemical test reveals that both polymers exhibit a weak reduction process,whereas their oxidation process is very obvious.The HOMO levels of PsIDT-BT and PsIDT-TT are determined as–5.36 and–5.24 e V,respectively.To study their carrier transport properties,we further fabricate the OFET devices based on PsIDT-BT and PsIDT-TT thin-films.The results show that PsIDT-BT exhibits unipolar hole transport properties with a maximum hole mobility of about 0.01 cm²V^–1 s^–1,while PsIDT-TT does not obtain transistor performance within the instrument accuracy.