1. Key Laboratory of Functional Polymer Materials, Ministry of Education, College of Chemistry and College of Physics, Nankai University, Tianjin, 300071, P. R. China, Department of Polymer Science and Engineering, The School of Chemistry and Chemical Engineering, State Key Laboratory of Co-ordination Chemistry, Nanjing University, Nanjing 210093, P. R. China, and Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada