1. Institute of Functional Material Chemistry; Faculty of Chemistry; Northeast Normal University; Renmin Street No. 5268 Changchun 130024 P. R. China
2. Physics Department; Durham University; Durham DH1 3LE UK
3. State Key Laboratory of Polymer Physics and Chemistry; Changchun Institute of Applied Chemistry; Chinese Academy of Sciences; Changchun 130022 P. R. China
4. Chemistry Department; Durham University; Durham DH1 3LE UK