1. 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
2. Department of Materials Science and Engineering City University of Hong Kong Kowloon 999077 Hong Kong
3. Guangdong Provincial Key Laboratory of Luminescence from Molecular Aggregates (South China University of Technology) Guangzhou 510640 P. R. China
4. Department of Chemistry City University of Hong Kong Kowloon 999077 Hong Kong
5. School of Energy and Environment City University of Hong Kong Kowloon 999077 Hong Kong