1. Beijing National Laboratory for Molecular Sciences State Key Laboratory of Polymer Physics and Chemistry CAS Research/Education Center for Excellence in Molecular Sciences Institute of Chemistry Chinese Academy of Sciences Beijing 100190 P. R. China
2. University of Chinese Academy of Sciences Beijing 100049 P. R. China
3. School of Materials Science and Engineering Tianjin Key Laboratory of Molecular Optoelectronic Science Tianjin University Tianjin 300350 P. R. China