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 Chemistry and Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong 999077, P. R. China
3. School of Materials Science and Engineering, Tianjin University, Tianjin 300350, P. R. China
4. Department of Physics, Organic and Carbon Electronics Laboratory (ORaCEL), North Carolina State University, Raleigh, North Carolina 27695, United States
5. Beijing National Laboratory for Molecular Sciences, Beijing 100190, P. R. China