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Posted: April 11, 2008

Studies shed new light on organic semiconductors

(Nanowerk News) Researchers at the Key Laboratory of Organic Solids, the Chinese Academy of Sciences (CAS) Institute of Chemistry (ICCAS), have made progress in designing and synthesis of n- and p-type organic semiconductors. The research findings were published recently in the Journal of American Chemical Society (JACS).
Organic semiconductor materials as the heart element of preparing photo-conducting devices are critical. Considering the study and application of molecular devices, it is significant and useful to design and synthesis organic semiconductor materials with high mobility, stability and malleability. Perylene-3,4:9,10-tetracarboxylic diimide (perylene bisimide, PBI) is a potential material for electron transporting and has been applied in a wide range of applications including organic light-emitting diode (LED), solar battery and organic field-effect transistors (OFETs). Therefore, the high performance n-type semiconductors with novel structures and special characters can be prepared using PBI unit. Starting from tetrachloro-PBI, ICCAS researchers synthesized a variety of PBI derivates doped with dithiophene by Stille Reaction. The self-assembly behaviour of these derivates in solid state can be modulated by guest molecules (see the paper: Chem. Comm., 2006, 4587-4589). Stimulated by this result, the researchers discovered a kind of transition metal system with highly active tetrachloro-PBI. The system might conduct homocoupling of 2 mole PBIs through short molecular axis to construct full extended conjugated di-PBI compounds as the potential electron transporting materials, which possess the broad absorption in the region of visible light and the strong electron-accepting ability characterized by electro-chemistry methods (see J. Am. Chem. Soc., 2007, 129, 10664-10665). A Chinese patent on the research is also been applying.
Co-funded by the National Natural Science Foundation of China, Chinese Ministry of Science and Technology and CAS, the researchers designed and synthesized a series of functional organic small molecules based on S-heterocyclic PBIs by the reaction of fused-ring aromatic compounds with thiophene. The thin-films of S-heterocyclic PBIs are expected to serve as the p-type organic semiconductors. Introducing thiophene unit into the functional molecules, its single-crystal micrometer wires have unique double-channel superstructure. The cooperative effects between the multi-layer molecular self-assembly result a mobility of the single-crystal micrometer wires up to 0.8 cm2 V-1 s-1 (see J. Am. Chem. Soc., 2007, 129, 1882-1883).
Source: Chinese Academy of Sciences
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