Synthesis And OFET Properties Of Organic Hybrid Conjugative Materials

In these years, organic field-effect transistors (OFETs) have attracted considerable attention, due to their low cost, processibility and structure flexibility. They show potential uses in electronic papers, complementary integrated circuits, active-matrix display and chemical sensors. The performance of OFETs is mainly determined by the carrier mobility of the organic semiconductor layers. Therefore, exploring new organic semiconductor materials and study the relationship between the molecular structure, film morphology and the property are still the major challenges. In this thesis, we synthesized two kinds of hybrid organic semiconductors and studied their optical and electronic properties.1. The structures, optical properties, thin-film and single-crystal field-effect transistor performance of three thiophene-based hybrid materials, 5-(9-butyl-3-carbazolyl)terthiophene (BCTT),2,5-bis(9-butyl-3-carbazolyl)thiophene (BBCT) and 2-(9-butyl-3-carbazolyl)-5-(2-dibenzothienyl)thiophene (BCDT), are reported. The structural modifications at one side of thiophene have significant effects on the intermolecular interaction, morphology and carrier-transport properties. The adjacent molecules in the solid state of BCTT have H aggregation and show strong intermolecular interaction. While both compound BBCT and BCDT exhibit the formation of J aggregation, as showed by the optical propertis and XRD analyses. In BCTT, the crystal structure features are herringbone motifs. The BCTT molecules easily assemble into 1D microribbons and the vacuum-deposited film shows high crystalline microstructure. In contrast, the precipitations of BBCT and BCDT from solution form flexible microribbons and the vacuum-deposited films of BBCT and BCDT show amorphous characteristics. The morphology difference of these films would exert great influence on the OFET performance.All the OFETs of the three materials are p-type. The film transistors of BCTT display moderate hole-transport property. While the hole mobility for the single-crystal field-effect transistor based on BCTT reaches 0.094 cm2/V-s, which is much higher than those of BBCT and BCDT. The BCTT single-crystal transistors also show good stability. These results would be beneficial to understanding the structure-property relationships and related studies on the intrinsic transport properties of hybrid materials.2. The optical and electronic properties of six symmetrical distyrylarylene derivatives are studied.4,4'-Bis(2-thienylvinyl)biphenyl (BTVBP), 4,4'-bis(2-bithienylvinyl)biphenyl (BBTVBP),4,4'-bis(2-thienothienylvinyl)biphenyl (BTTVBP),4,4'-bis(2-dibenzothienylvinyl)biphenyl (BDTVBP), 4,4'-bis[2-(3-N-butylcarbazolyl)-vinyl]biphenyl (BBCVBP) and 4,4'-bis(2-anthracenylvinyl)biphenyl (BAVBP) were easily synthesized with good yields by Horner-Emmons reaction. The difference in the end substitution results in great variations in optical and electronic properties.Both the film absorption spectra of BTTVBP and BDTVBP show blue shift compared with those of solution, which suggests H aggregation of adjacent molecules having their long axes parallel to each other. In the case of compound BTVBP and BBTVBP, their solid state absorption spectra are drastically broadened. This broadness implies that different types of intermolecular interaction coexist in the film. In contrast, the solid state absorption spectrum of BBCVBP is essentially identical to the solution spectrum with a slight broadening of the absorption band, indicating the weak intermolecular interaction in the solid state. Different from other distyrylarylene derivatives, the BAVBP shows aggregation-induced emission behavior, which shows highly luminescent in the solid state than in solution.The vapor-deposited film morphology was investigated by XRD and AFM analyses. All these compounds show high crystalline except BTVBP and BBCVBP. A new crystal structure or polymorph appears in the deposited film of BTTVBP, and this new gas phase is the main ingredient in the OTS-pretreated substrate. In the high substrate temperature, the OTS-pretreation is helpful for the molecules of BTTVBP to adopt much more perpendicular mode in the substrate. The OFET properties of these materials vary with substrate temperature, due to the change in grain size and continuity. The performance fabricated on OTS-pretreated SiO2 is higher than that on bare SiO2 for improved crystallinity. The film transistors of BTVBP display moderate hole-transport property mainly due to the low crystalline nature in the film. The hole mobilities of BBTVBP and BTTVBP are more than 10-2 cm2/V·s with on/off current ratio over 105. The hole mobility of BDTVBP reaches 5.2×10-2 cm/V·s with on/off current ratio of 107. No obvious decrease in mobility as well as on/off ratio was found in air. The good environmental stability is extremely valuable for realizing long-lived organic electronic devices. This result may provide a new promising choice for organic semiconductors based on DSA derivatives, and these stable organic semiconductors will be valuable for the future commercialization of organic electronic devices.