Design And Synthesis Of Thiophene-based Organic Semiconductors For Optoelectronic Applications

With the rapid development of the internet of things and artificial intelligence,organic electronic devices are gaining popularity due to their unique photoelectric performance and low manufacturing cost.Small molecule semiconductors play an important role in theoretical analysis and applied exploration for their determining molecular structure and quality,good repeatability,batch efficient purification process,high carrier mobility and many other advantages.In this paper,a variety of thiophene-based organic semiconductors are designed and synthesized,and their optoelectronic properties are regulated from three levels: molecular conformation,exciton dynamics and charge concentration.New materials with memory,photothermal cooperative detection and high conductivity are obtained,and multifunctional field effect transistor devices are constructed.The main contents of this thesis are as below:(1)Reversible molecular conformational change in an organic semiconductor crystal for memory applications.In chapter 2,we report a novel organic semiconductor,3,6-DATT,and it has two crystalline phases(room temperature phase and high temperature phase),which share almost identical packing arrangement but tiny difference in molecular conformation induced by the small torsion angle variation between two aromatic planes.Remarkably,the electric field and ultraviolet irradiation can induce the reversible molecular conformational change(i.e.,phase change)in 3,6-DATT crystals,based on which organic memory transistor(OMT)with novel working principle is constructed.Significantly,OMT exhibits high performance including very quick response(3 s),recovery rate(3 s),long conformational retention time(>2 h).This work presents a new molecule design concept for OSCs with reversible molecular conformational change,and opens a novel avenue for memory devices and other functional applications.(2)Thermally-enhanced photo-electric response of an organic semiconductor with low exciton binding energy for simultaneous and distinguishable detection of light and temperature.In chapter 3,we designed and synthesized a narrow band gap organic small molecule semiconductor DPP-T-TPA with low exciton binding energy(about 37±1.6 me V)and small activation energy(about 61±1.6me V)for distinct thermal-dependence of charge carrier and exciton.As a result,the photo-electronic response of OPT devices based on DPP-T-TPA are very susceptible to the temperature of the environment,and the enhanced photo-electronic response(9.2*105,4.0 A W-1,4.4*1012 Jones)can be realized at heated temperature of 90 o C,which is significantly higher than that(7.2,2.5*10-5 A W-1,2.7*107 Jones)at RT under the irradiation power of 0.5 m W cm-2.The results indicated that organic photo-electronic functional materials with both low exciton binding energy and small activation energy have great potential to realize the simultaneous and distinguishable detection of light and temperature,which may significantly extend the functions and application fields of OPTs.(3)Synthesis and formation mechanism of organic free radical semiconductor materials with high charge density.In chapter 4.By introducing highly electronegative F atoms into different positions of 2,6-diphenyldithiophene[3,2-B:2’,3’-d] thiophene,we synthesize a novel organic small molecule semiconductor o F-DP-DTT and the contrast molecules of DP-DTT and m FDP-DTT.The experimental results show that the intermolecular distance of semiconductor materials can be well adjusted by substituting F atoms at different positions,(o F-DP-DTT(2.832 (?))/DP-DTT(3.738 (?))/ m F-DP-DTT(3.758 (?))),and the intermolecular interaction is greatly increased.In addition,OF-DP-DTT has typical closed shell singlet double radical properties,which have been verified by variable temperature NMR and variable temperature ESR,and it is concluded that oxygen is responsible for the free-radical properties of o F-DP-DTT.Single crystal OFET are prepared based on DPDTT and m F-DP-DTT,which show typical FET modulation characteristics,while o F-DP-DTT shows weak gate voltage dependence and high charge density,which can reach 7.5×1017 cm-3.The design idea of this kind material provides reference and support for the design and functional application of semiconductor materials with high charge concentration.