1. State Key Laboratory of Polymer Physics and Chemistry Beijing National Laboratory for Molecular Sciences CAS Research/Education Center for Excellence in Molecular Sciences Institute of Chemistry Chinese Academy of Sciences Beijing 100190 P. R. China
2. School of Chemistry and Biology Engineering University of Science and Technology Beijing Beijing 100083 P. R. China
3. University of Chinese Academy of Sciences Beijing 100049 P. R. China
4. School of Physics State Key Laboratory of Crystal Materials Shandong University Jinan Shandong 250100 P. R. China
5. State Key Laboratory for Mechanical Behavior of Materials Xi'an Jiaotong University Xi'an Shaanxi 710049 P. R. China