1. Department of Materials Science and Engineering University of Washington Seattle WA 98195‐2120 USA
2. Institute of Polymer Optoelectronic Materials and Devices State Key Laboratory of Luminescent Materials and Devices South China University of Technology Guangzhou 510640 P. R. China
3. Department of Chemistry City University of Hong Kong Kowloon Hong Kong
4. Department of Materials Science & Engineering City University of Hong Kong Kowloon Hong Kong