1. State Key Laboratory of Luminescent Materials and Devices Institute of Polymer Optoelectronic Materials and Devices South China University of Technology Guangzhou 510640 P. R. China
2. Department of Organic Materials Science Graduate School of Organic Materials Science Yamagata University Yonezawa 992‐8510 Japan
3. Research Center for Organic Electronics (ROEL) Frontier Center for Organic Materials (FROM) Yamagata University Yonezawa 992‐8510 Japan