Synthesis Of D-A Conjugated Small Molecules And Research On The Performance Of Solution-Processed Field Effect Devices

It is considered feasible to design high-performance organic semiconductor materials for organic field-effect transistors through the donor（D）-acceptor（A）strategy,and many related literatures have reported on it.Owing to the polydispersity of the polymers,D-A polymers are restricted in large-scale applications despite the excellent solution-processed performance.D-A small molecules with precise structure and molecular weight can effectively reduce the impact of batch differences.In addition,the relatively high molecular weight and adjustable side chain structure endow D-A small molecules with good solution processability.In this paper,several D-A small molecular organic semiconductor materials based on indacenodithieno[3,2-b]thiophene（IDTT）were designed and synthesized for the study of solution-processed OFET.The experiment content and results are as follows:（1）Two small molecules（M1 and M2）were designed which were based on IDTT as donor unit,the electron-withdrawing malononitrile derivative as the acceptor unit and combined with the N substitution strategy.The cyano unit with electron-withdrawing ability can effectively lower the LUMO energy level and is suitable for the electron-transporting n-type materials.In addition,the substitution of N atoms not only further lowers the LUMO energy level,but also enhances the intramolecular interaction which provided a planar conjugated skeleton（decreased dihedral angle）.The performance of field-effect transistors based on two small molecules are as follows:M1showed the maximum electron mobility of 1.0×10^-3cm²V^-1s^-1and the average mobility of 7.0×10^-4cm²V^–1s^–1,and M2 showed the maximum electron mobility of 3.4×10^-3cm²V^-1s^-1and the average mobility of 1.0×10^-3cm²V^–1s^–1.（2）Two small molecules（IDTT-MI and IDTT-T-MI）based on IDTT as donor unit and semi-indigo as acceptor unit were designed.The introduction of a thiophene bridge between IDTT and the semi-isoindigo unit extends the conjugated length of the main chain.Meanwhile,the S···O interaction also allows IDTT-T-MI to maintain excellent planarity and enhance the ability of molecular stacking.The performance of IDTT-T-MI organic field-effect transistors based on chloroform solvent spin-coating have been greatly improved,with the highest hole mobility of 0.8 cm²V^–1s^–1.IDTT-T-MI also showed the excellent mobility of 0.34 cm²V^–1s^–1when the non-halogen solvent tetrahydrofuran used as the solvent.