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Effect Of Functionalization Of Benzene On Molecular Packing Mode And Carrier Transport Properties

Posted on:2016-01-31Degree:MasterType:Thesis
Country:ChinaCandidate:L GuanFull Text:PDF
GTID:2271330473462226Subject:Physical chemistry
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In recent decades, organic semiconductor materials have got more and more attentions. In contrast to conventional silicon-based transistors, they have many advantages, for instance, low-cost, convenient large-area fabrication, and flexible adjustion of properties. Among the current organic materials, acenes and their derivatives are one of the most widely used materials for their prominent (opto)electronic properties. In this thesis, based upon the systematical study of the acenes and their derivatives containing nitrogen heteroatoms, halogen and Triisopropylsilylethynyl(TIPS), we have analyzed in detail the geometries, molecular stacking character, electronic and charge transport properties of studied molecules. In addition, the relationship between intermolecular interactions and the molecular packing character in organic crystals have also been discussed by binding energy calculation. Our study is expected to provide some valuable theoretical supports for designing and synthesizing new OFET materials with both the high carrier mobility and air stability. The work mainly includes two parts as follows:1. In this section, three air-stable heptacene derivatives i.e., 1.18,4.5,9.10,13.14-tetrabenzoheptacene(TTBH), 6,8,15,17-tetraaza-tetrabenzoheptacene(TTH), and 6,8,15,17-tetraphenyl-tetrabenzoheptacene(Ph-TTBH) have been investigated by means of density functional theory(DFT) calculations and incoherent charge hopping model. Based on parent TTBH, we discuss the effect of nitrogen doping and phenyl substitution on geometries, electronic properties, molecular stacking character and charge transport properties. The relationship between intermolecular interactions and the molecular packing in crystals are best illustrated by the contour maps of binding energies calculated at the B3LYP-D3. Our results indicate that the nitrogen doping (TTH) at the 6,8,15,17 positions improves its stability in air and the ability of electron injection and in the meantime slightly changes the molecular stacking due to the C-H…N interaction. For both TTBH and TTH, large hole transport mobility(μh) and electron transport mobility(μe) that are in the same order of magnitude, are given rise by their dense displaced π-stacking in crystal. Comparatively, the phenyl substitution(Ph-TTBH) at the 6,8,15,17 positions adopts a non-planar conformation, adverse to closely packing and therefore leads to the smaller electron/hole transport mobility(μ) than those of TTBH and TTH. The calculations suggest TTBH and TTH are promising candidates for excellent ambipolar OFET materials.2. In present study, the optimized structure, reorganization energy, frontier orbitals, ionization potential and electron affinity of a series of TIPS-tetracene and its derivatives have been studied by density functional theory(DFT) with B3LYP/6-31G++(d,p) //B3LYP/6-31G(d). We computed the charge transfer integrals at the PW91PW91/6-31G(d) level and predicted the hole and electron mobilities by using Marcus-Hush theory. The results show that the introduction of TIPS and heteroatoms in parent molecular maintain their plane conjugate structure. Although the substitution of TIPS increases the reorganization energy and the centroid distance of dimer and is bad for charge transfer, the introduction of both TIPS and N (TIPS and Cl) atoms can significantly reduce the FMO energy level, increase the ability of electron injection, make the crystal packing in a more beneficial way(brick-walk), and then result to enhanced orbital coupling of adjacent molecular. As a result, the introduction of TIPS is an effective means to change the crystal packing, making them to be high performance and stability organic materials.
Keywords/Search Tags:Density functional theory, Charge transport, Acene, Mobility, Organic semiconductor, Triisopropylsilylethynyl
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