| In recent years,the performance of organic thin film transistors(OTFTs)has improved significantly,but the development of high-performance n-type organic semiconductors has lagged far behind compared to p-type counterparts.In comparison to polymers,small molecules have advantages of precise structures,easy purification,facile functionalization and excellent reproducibility.Solution processing has relatively low costs and processing temperatures.Therefore,it is very important to develop high-performance solution-processed n-type small molecule semiconductors.Diketopyrrolopyrrole(DPP)has a rigid skeleton with strong electron-withdrawing properties,which is conductive to the formation of strong?-?interactions between molecules.Acceptor–donor–acceptor(A-D-A)molecules with 3-(dicyanomethylidene)-indan-1-one(IC)and its derivatives as end groups,with indacenodithiophene(IDT)and other aromatic fused ring units as cores have the advantages of low lowest unoccupied molecular orbital(LUMO)energy levels and strong?-?interaction.Based on these considerations,in the current thesis,a series of A-D-A molecules were synthesized with thiophene(selenophene)-flanked DPP as the central unit and IC or its derivative as the terminals.Their photophysical and electrochemical properties and OTFTs performance were studied in details.The main results include:(1)Four A-D-A molecules DPP1012,DPP1012-4Cl,DPP1012-4F and DPP68-4F were synthesized with thiophene-flanked DPP as the central unit,IC and its derivatives as terminals.Single crystal structure analysis of DPP68-4F indicated that these molecules were arranged in a slipped one dimensional?-stacking structure.All four molecules had a strong near-infrared(NIR)absorption band and the LUMO levels were lower than-4.1 e V.The introduction of F or Cl atoms in the terminal units caused the decrease of frontier orbital energy levels and an obvious bathochromic-shift of absorption.Four molecules were n-type semiconductor materials with electron mobilities of spin-coated OTFTs over 0.1 cm2 V-1 s-1.DPP1012-4F had the highest film order and the best film morphology,and achieved electron mobilities up to 1.05 cm2 V-1 s-1 in N2 atmosphere and 0.88 cm2 V-1 s-1 in air.(2)A-D-A molecules Se DPP1012-4F and Se DPP68-4F were synthesized with selenophene-flanked DPP as the central unit and 2F-IC as terminals.The two molecules were arranged in a slipped one dimensional?-stacking structure with better planarity and shorter?-?stacking distance.The LUMO energy level of Se DPP1012-4F and Se DPP68-4F displayed about 0.1 e V lower than that of DPP1012-4F and DPP68-4F,and the low energy absorption maxima were remarkably red-shifted by 30 nm.Spin-coated OTFTs based on Se DPP1012-4F exhibited the highest electron mobility of 0.84 cm2 V-1 s-1 in air.However,compared to DPP68-4F,the performance of OTFTs based on Se DPP68-4F decreased as a result of the decrease in molecular solubility and poor film quality. |
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