1. Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials; Key Laboratory of Cluster Science; Ministry of Education of China; School of Chemistry; Beijing Institute of Technology; Beijing 100081 P. R. China
2. Center of Advanced Science and Engineering for Carbon (Case 4Carbon); Department of Macromolecular Science and Engineering; Case School of Engineering; Case Western Reserve University; Cleveland OH 44106 USA
3. Department of Chemistry; Renmin University of China; Beijing 100872 P. R. China