Theoretical Study On The Design And Transport Properties Of Heteroatom-substituted Fused-ring Benzene Materials

Due to the fantastic properties, such as, low cost, easy chemical modification, and structural flexibility, organic semiconductor materials (OSCMs) are highly promising for organic light emitting diodes (OLEDs), organic photovoltaic cells (OPVCs) and organic field-effect transistors (OFETs) etc. However, most of the OSCMs couldn’t meet the needs of its application and air-stable OSCMs with high efficiency are very rare. Now considerable attention should be placed in designing of high-performance air-stable charge transport (CT) materials. Three main works related to the designation of high-performance air-stable CT materials and the prediction of the CT properties are discussed in this paper.First, the most common approaches for designing n-channel OSCMs are reviewed from two aspects. One is focus on the modification of the single molecule by introducing strong electronegative groups, such as-F,-Cl,-CN,-NO2,-C=O, etc. The other is focus on the modification of packing modes, including introducing polarity, increasing the C/H ratio, and adding hetero atoms to generate hydrogen bonds, halogen-halogen inter actions or chalcogen-chalcogen interactions.Then, we studied a serious of substituted DB-TTF derivatives by introducing N atoms to the aromatic molecular backbone and end substitution with fluoroalkyl. The packing structure is not only one of the key factors in determining the CT properties of the materials, but also the biggest challenges for the prediction of CT materials. In this paper, a new method SCM-DFT-D considering both the computational accuracy and the expense was proposed by us. It turned out by our tests, this method could not only give a good result to predict the crystal structures of this kind of TTF derivatives, but also be used for the searching of the polymorphs. Based on the predicted crystal packings of these designed molecules, we successfully calculated their electron mobilities, that is6.6×10-2cm2V-1S-1(5a),2.8×10-1cm2V-1S-1(5b),4.2×10-2cm2V-1S-1(6a),4.3×10-1cm2V-1S-1(6b),1.6×10-1cm2V-1S-11(7c) and7.8×10-2cm2V-1S-1(8a) respectively.In the last part, we investigated the charge transport properties of five bis-silylethynylated acenes in terms of their frontier molecular orbital energies, ionization energies (IP) reorganization energies (λ); transfer integrals, and CT mobilities. It turns out by our study that the packing structures are the main reason for their difference in CT properties. Tips-TBT exhibits high CT mobilities similar to the well-known OSCM Tips-PEN. Here, we successfully predicted the experimental and other possible packing modes of these two OSCMs with the assistance of SCM&DFT-D method. Our theoretical investigations will provide insight guidance for experimental design and synthesis of newly OSCMs.