Basic Science

New Organic Semiconductor Materials Patented

Researchers from the Laboratory of Material Chemistry, Shanghai Institute of Organic Chemistry, CAS have developed a new class of solution-processable n-type organic semiconductors based on core-expanded naphthalene diimides fused with 2-(1,3-dithiol-2-ylidene) malonitrile groups (see Figure 1, R is long branched alkyl), through fusing electron-deficient aromatic nuclear with electron-rich sulfur-containing heterocyclic compounds (to improve the mobility) and using electron-withdrawing malonitrile end-group (to improve the stability). Though cooperation with researchers from the Key Laboratory of Organic Solids, Institute of Chemistry, CAS, they successfully fabricated the OTFT (organic thin film transistor) devices of this class of molecular material by means of solution processing. The devices exhibit high electron mobility of up to 0.51 cm2V-1s-1, with current on/off ratios of 105 and threshold voltages below 10V. Moreover, they have excellent air and operating stability. The devices have best mobility and stability among solution-processable n-type organic micro-molecular materials reported so far. A Chinese patent has been applied for relevant work, some results of which were published by the Journal of the American Chemical Society（J. Am. Chem. Soc. 2010, 132, 3697-3699).

Series Progress in Fullerene Derivatives Research

Exohedral functionalization of fullerenes and metal fullerenes to regular the electronic structure and performance of this type functional molecules is one of key research fields in fullerene chemistry. Recently, researchers from the Key Lab of Molecular Nanostructure ＆ Nanotechnology, CAS, through cooperation with scientists from the Xiamen University, achieved series of new research results in the derivatization of fullerenes and endohedral metallofullerenes. For the functionalization of endohedra fullerenes, researchers selected a kind of carbide endohedral metallofullerene Sc3C2@C80 to carry out exohedral functionalization. This is a molecule with novel paramagnetism. It has an unpaired electron distributed at the endohedral Sc3C2 cluster. They found that Sc3C2 cluster rotated freely at high speed before chemical reaction due to high symmetry (Ih) of C80 cage, resulting in identical chemical environment of three Scandium (Sc) ions and formation of a twin-conical structure with D3h symmetry between those three Sc ions and C2. If a pyrrolidine group was added to C80 cage through chemical reaction, the electric field distribution inside C80 would be sure to lose homogeneity when the high symmetry of fullerene cage was broken, which greatly limited the movement of Sc3C2 cluster. This directly resulted in decrease of the symmetry of Sc3C2 cluster from D3h to C2v and strongly affected its electronic properties due to the alteration of its molecular structure. Significant change of its paramagnetism before and after chemical reaction was clearly observed in the experiment (Angew. Chem., Int. Ed. 2010, 49, 1786–1789). This approach of altering the structure of endohedral Sc3C2 cluster and then regulating the molecular magnetism through exohedral functionalization provides foundation for the construction of fullerene molecular device and fullerene-based quantum computer research. Relevant research results were published in Angew. Chem., Int. Ed. 2010, 49, 962-966 and Angew. Chem., Int. Ed. 2010, 49, 1786 –1789 and highlighted in the Nature China.