Synthesis And Photoelectric Properties Of Novel Bithiophene Imide Derivatives

In recent years,the application of organic semiconductor materials in organic field-effect transistors（OFETs）has made important progress.The hole mobility of p-type organic semiconductor materials has exceeded 20 cm²·V^-1·s^-1,while the development of n-type and bipolar organic semiconductor materials is relatively lagging,and their electron mobilities（μ_e）are generally lower than 5 cm²·V^-1·s^-1.In order to promote development of n-type and bipolar organic semiconductor materials,the development of novel acceptor units is still an important topic in the field of organic semiconductors.As a very important class of organic semiconductor materials,aromatic imide has excellent photochemical stability,high fluorescence quantum yields,rigid structure and strong electron-accepting capacity,so it is widely used in OFETs,organic light-emitting diodes（OLEDs）,organic solar cells（OSCs）and other fields.After decades of development,aromatic imide organic semiconductor materials have achieved tremendous development in OFETs.Among them,theμ_e of n-type polymer semiconductor materials based on naphthalene diimide has reached 8.5 cm²·V^-1·s^-1,and theμ_e of the n-type transistor based on dithiophenimide has been up to 3.71cm²·V^-1·s^-1.Recently,the application of small molecular aromatic imide in OLEDs has been developed rapidly.Currently,the external quantum efficiency（EQE）of naphthalimide-based doped devices has been up to 29.2%,and the EQE of biphenylimide-based undoped devices has been up to 24.7%.Therefore,the construction of new imide acceptor units has attracted more and more attention.Based on this,we designed and synthesized a new type of bithiophene imide acceptor unit（i BTI）,as well as a series of derivatives of four polymers and two small molecules based on i BTI,and systematically studied their photoelectric properties.The main work contents are as follows:1.Synthesis and photoelectric properties of four polymers based on i BTI.First,we designed a new acceptor unit i BTI with a wide band gap,and successfully achieved i BTI at the gram level through a series of reactions.Secondly,we prepared four series of polymers Pi BTI,Pi BTIE,Pi BTI2FT and Pi BTI2T by optimizing the conditions of Yamamoto and Stille coupling reactions.The DFT theoretical calculation results showed that the polymer backbone of Pi BTIE exhibited excellent coplanarity,the torsion angle was only about 0.002^o,and the other three polymer backbones displayed different degrees of distortion.In addition,the UV spectra and cyclic voltammetry analyses indicated that Pi BTI2FT and Pi BTI2T could be more inclined to form bipolar semiconductor materials,while Pi BTIE might be more prone to form unipolar n-type semiconductor materials.By copolymerizing i BTI with different donor or acceptor units,we have realized the regulation of the energy level and charge transport characteristics of semiconductor materials,which demonstrates that the new acceptor unit i BTI has huge application prospects in OFETs.2.Synthesis and photoelectric properties of two small molecules based on i BTI.We successfully synthesized two D-A-D-type small molecular emitters Cz Phi BTI and TPAi BTI with i BTI as the acceptor and phenylcarbazole or triphenylamine as the donor unit.The relationship between structure and photoelectric properties was systematically studied by DFT calculations,UV-vis and fluorescence spectra,cyclic voltammetries,and single crystal XRD analyses.Single crystal structure analyses showed that the seven-membered cyclic backbone of the imide in i BTI exhibied a certain twist angle,which is conductive to inhibiting the aggregation-caused quenching（ACQ）effect.Fluorescence spectra,theoretical calculations and natural transition orbit analyses of Cz Phi BTI and TPAi BTI showed that the two molecules attained a sufficiently small triplet-singlet energy gap difference in the high-lying excited states,ΔE_Tm-Sn,ensuring the fast reverse intersystem crossing（RISC）progress,and proving that Cz Phi BTI and TPAi BTI are the“hot exciton”materials based on the hybridized local and charge-transfer（HLCT）state.These reveal the huge application potential for Cz Phi BTI and TPAi BTI in OLEDs.