1. State Key Laboratory for Mesoscopic Physics and Department of Physics; Peking University; Beijing 100871 P. R. China
2. Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education; Department of Chemistry; Tsinghua University; Beijing 100084 P. R. China
3. Valiant Corporation; Shandong 264006 P. R. China
4. Beijing National Laboratory for Molecular Sciences; State Key Laboratory of Rare Earth Materials Chemistry and Applications; College of Chemistry and Molecular Engineering; Peking University; Beijing 100871 P. R. China
5. College of Physics and Electronics Engineering; Hengyang Normal University; Hengyang 421008 P. R. China