1. Department of Physics, The Chinese University of Hong Kong, New Territories, Hong Kong
2. Department of Chemistry, Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, Hong Kong
3. Hong Kong Institute for Advanced Study, City University of Hong Kong, Hong Kong
4. State Key Laboratory of Silicon Materials, MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, P. R. China
5. Center for Chemistry of High-Performance & Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou 310027, Zhejiang, China
6. Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, SE-58183, Sweden
7. The Institute for Advanced Studies, Wuhan University, Wuhan 430072, China
8. Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
9. Department of Chemistry and Biochemistry, The University of Arizona, Tucson, Arizona 85721-0088, USA