1. State Key Laboratory of Information Photonic and Optical Communications and School of Science, Beijing University of Posts and Telecommunications (BUPT), Beijing 100876, P. R. China
2. Department of Molecular and Macromolecular Chemistry, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
3. College of Chemistry, Beijing Normal University, Beijing 100875, P. R. China