New Organic Functional Materials Of Electron Donors And Field-effect Semiconductors: Design, Synthesis And Properties

Organic functional materials,which involve the fields of organic synthesis,physical chemistry and electronics,have attracted wide attention because of their potential use in photoelectric devices.In this dissertation,new organic electron donors and organic semiconductors were designed and synthesized.By studying and comparing their physical and chemical properties,as well as the theoretical calculation,we tried to understand the relationship between molecular structures and properties.The main contents and results are listed as follows:1.In the first part of this dissertation(Chapterâ…¡),twelve novel oligomeric electron donors(1a-b,2a-b,3a-b,4a,6',7,8,9a-b) containing two to six tetrathiafulvalene(TTF) units were synthesized.Their structures were assigned by NMR spectroscopy,infrared spectrometry and high resolution mass spectra.New precusors 19 and 23 were also developed in the synthetic route,which should be suitable for other synthetic transformations for the incorporation of TTF units.2.The configurations of novel donors were optimized by preliminary calcultion.TTF units in the linear oligomeric donors were found packing cross-vertically,while those in the macrocyclic donor arranged fan-shapedly around the symmetric center.The electrochemical properties were determined by cyclic voltammetry.All the linear or dendritic donors exhibited two pairs of nearly ideal reversible redox waves.This result could be well explained by the fact that they are non-conjugated oligomers linked byσ-bonds,and therefore little interactions occur among the TTF units.The redox potentials indicated that all of the new electron donors possessed similar electron-donating properties as BEDT-TTF.It was also found that the trisannulated macrocycle 8 exhibited a stepwise second oxidation process.The LB-film performance of pent-TTF and hex-TTF donor 2a and 4a was studied.Both molecules could form qualified monolayer,and their critical surface pressures were higher than former results.3.In the second part of this dissertation(Chapterâ…£),an analogue system of pentacene, 6-substituted-6H-Pyrrolo[3,2-b:4,5-b']bis[1,4]benzothiazine(PBBTZ),was applied as field-effect transistors for the first time.PBBTZ derivatives 1-3 and a related compound 4 were facilely synthesized and characterized.Their optical properties were studied by UV-Vis and fluorescence spectroscopy,and electrochemical properties were investigated by cyclic voltammetry(CV).Good thermal stability was observed by thermogravimetric analysis.X-ray analysis revealed a coplanar structure and a column stacking in the single-crystal of the N-unprotected PBBTZ 1,and a sandwich-herringbone arrangement of the molecules of compound 3.OTFT characterizations show that 1-4 were p-type organic semiconductors.The performance of these devices displayed good reproducibility at ambient conditions. When the devices of 1 were fabricated on OTS-treated SiO₂/Si substrate at 60℃,the best performance was achieved,with the average hole mobility as high as 0.34 cm² V^-1 s^-1 and the on/off ratio about 7×10⁶ - 3×10⁷.This performance was resulted from the well-ordered molecular packing as revealed by XRD and AFM analysis. When the substrate temperature was enhanced to 100℃,the mobility of the devices of 1 was still promising.The substitutes in 2 and 3 might retard the efficientÏ€-Ï€interacitons,resulting in decreased charge transport properties.Compound 3 was well soluble for low-cost fabrication with solution-processed technology,and it was also demonstrated the potential use in solar cell by photocurrent detection.4.Two fluoroalkyl substituted PBBTZ derivatives 5 and 6 were designed(Chapterâ…¤), synthesized and characterized.Their optical properties were studied by UV-Vis and fluorescence spectroscopy,electrochemical properties were investigated by cyclic voltammetry(CV),and thermal stabilities were evaluated by thermal gravimetric analysis(TGA).X-ray single-crystal analysis revealed a sandwich-herringbone arrangement of the molecules of compound 6.The energy gaps of 5 and 6 were taken directly from spectroscopic measurements.Their LUMO and HOMO energy levels were estimated by electrochemical performance.The introdution of trifluoromethyl decreased their energy levels effectively.Compound 5 exhibits higher thermal stability,while compound 6 exhibits better solubility in many common organic solvents.The low energy levels enable them to be environmentally highly stable,and render both of them to be protential n-type semiconductors.