1. School of Optoelectronic Engineering, Guangdong Polytechnic Normal University, Guangzhou 510665, P. R. China
2. Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong 999077, P. R. China
3. School of Chemistry and Chemical Engineering, Henan Institute of Science and Technology, Xinxiang 453003, P. R. China
4. 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