1. George & Josephine Butler Polymer Research Laboratory Center for Macromolecular Science & Engineering Department of Chemistry University of Florida Gainesville FL 32611 USA
2. Faculty of Materials Science and Engineering South China University of Technology Guangzhou 510640 China
3. Present address: Laboratory of Nano Biomedicine & International Joint Cancer Institute Naval Medical University Shanghai 200433 China
4. Guangdong Provincial Key Laboratory of Luminescence from Molecular Aggregates South China University of Technology) Guangzhou 510640 China