1. Department of Chemistry Tsinghua University Beijing 100084 P. R. China
2. College of Chemistry Taiyuan University of Technology Taiyuan 030024 P. R. China
3. Department of Chemistry and Pharmacy and Interdisciplinary Center of Molecular Materials Friedrich-Alexander-Universität Erlangen-Nürnberg 91058 Erlangen Germany
4. State Key Laboratory of Environmental-Friendly Energy Materials School of Materials Science and Engineering Southwest University of Science and Technology Mianyang 621010 P. R. China
5. Laboratory of Theoretical and Computational Nanoscience National Center for Nanoscience and Technology Chinese Academy of Sciences Beijing 100190 P. R. China