1. Department of Polymer Science and Engineering; School of Chemistry and Chemical Engineering; Key Laboratory of High Performance Polymer Materials and Technology; MOE, State Key Laboratory of Co-ordination Chemistry; Nanjing University; Nanjing 210093 P. R. China
2. Institute of Physics; University of Rostock; 18051 Rostock Germany
3. School of Physical Science and Technology; Xinjiang Laboratory of Phase Transitions and Microstructures in Condensed Matters; Yili Normal University; Yining 835000 P. R. China