1. National Research Center for Molecular Sciences, Key Laboratory of Molecular Nanostructure and Nanotechnology, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China
2. School of Chemical Engineering and Technology, Tianjin University, Tianjin 300350, P. R. China
3. Institute of Physics, Chinese Academy of Sciences, Beijing 100190, P. R. China
4. Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic Systems, School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081, P. R. China
5. University of Chinese Academy of Sciences, Beijing 100049, P. R. China
6. Department of Chemistry, Duke University, Durham, North Carolina 27708, United States