1. College of Physics and Optoelectronics Faculty of Science Beijing University of Technology Beijing 100124 P. R. China
2. Institute of Chemistry Chinese Academy of Sciences Beijing 100190 P. R. China
3. Key Laboratory of Organic Optoelectronics and Molecular Engineering Department of Chemistry Tsinghua University Beijing 100084 P. R. China
4. Key Laboratory of Luminescence and Optical Information Ministry of Education School of Science Beijing Jiaotong University Beijing 100044 P. R. China
5. Department of Chemistry and Energy Institute Hong Kong University of Science and Technology Clear Water Bay, Kowloon 999077 Hong Kong