1. Department of Chemistry; South China University of Technology; Guangzhou 510640 PR China
2. Department of Applied Physics; South China University of Technology; Guangzhou 510640 PR China
3. Department of Biochemistry and Molecular Biology; Guang Dong Medical University; Zhanjiang 524023 PR China
4. State Key Laboratory of Optoelectronics Materials and Technologies; Sun-Yat Sen University; Guangzhou 510275 China
5. Department of Chemistry; Michigan State University; E. Lansing MI 48824 USA