Recently, SUSTech Associate Professor Xugang Guo’s group from the Department of Material Sciences and Engineering published their latest research results on ladder-type n-channel organic semiconductors (OSCs) in Angewandte Chemie International Edition, a top international journal in the field of chemistry (IF=11.994). Titled “Ladder-type Heteroarenes: Up to 15 Rings with Five Imide Groups”, this work received highly positive comments from both editor and referees and was selected as cover paper.

Figure 1. Cover picture for the ladder-type n-channel organic semiconductor paper.

Ladder-type OSCs is a very important class of semiconducting materials. Advantages of these materials include being intrinsically rigid and planar, having highly delocalized electronic structures etc., making them promising candidates to realize high-mobility organic field-effect transistor devices. Ladder-type OSCs is usually electron rich and used as p-type semiconductor in electronic devices. Due to the synthetic challenge and the steric hindrance created by typical electron-drawing groups, only very few electron deficient ladder-type n-channel OSCs are reported to date. Besides, they normally show lower carrier mobility and decreased device stability compared to their p-type counterparts. Imide-functionalized polymer semiconductor is one of the most important OSCs in the field of organic electronics. Utilizing the strong electron withdrawing capability of the imide group, most of the high-performance n-type OSCs are functionalized with imide or amide groups. Starting from his Ph.D. study at graduate school, Prof. Xugang Guo pioneered in systematic study on the imide-functionalized polymer semiconductors and their applications in organic field-effect transistors and organic solar cells, achieving remarkable device performances (Chem. Rev. 2014, 114, 8943-9021).  

Figure 2. Chemical structures of the Ladder-type n-channel organic semiconductor materials BTI-BTI5 and the representative device performance of the BTI5 organic field-effect transistor.

Bithiophene imide (BTI) is an important building block for OSCs. In previous works, Prof. Xugang Guo successfully developed a series of high-performance OSCs based on BTI (Nature Photonics, 2013, 7, 825-833; J. Am. Chem. Soc. 2011, 133, 1405-1418; J. Am. Chem. Soc. 2012, 134, 18427-18439; J. Am. Chem. Soc. 2015, 137, 12565-12579; Adv. Mater. 2012, 24, 2242-2248). Attracted by the advantages of ladder-type materials, Prof. Guo’s lab synthesized a series of ladder-type n-channel OSCs extending from bithiophene imide. These new materials have well-defined structures, good solubility, precisely controllable conjugation lengths, tunable optical-electrical properties and energy level structures, accompanied by their intrinsic high planarity and crystallinity. When tested in organic field-effect transistors, they show encouraging electron transporting performance, with electron mobility up to 0.05 cm2 V-1 s-1, thus providing a remarkable platform for fundamental study of the basic physical and chemical properties of ladder-type materials and opening up the opportunities for further development of high-performance OSCs with these new building blocks.

Postdoc Yingfeng Wang and Research Fellow Dr. Han Guo from Prof. Guo’s lab are the co-first authors of this paper, undergraduate Shaohua Ling participated in part of the material synthesis work. DFT calculation and optical spectrum study was conducted by Dr. Rocio Ponce Ortiz from the University of Málaga in Spain. This research was supported by NSFC, Shenzhen Peacock plan, Shenzhen key lab fund and several other research grants.     

Link to the paper：http://onlinelibrary.wiley.com/doi/10.1002/anie.201702225/full

Link to the paper：http://onlinelibrary.wiley.com/doi/10.1002/anie.201706480/full