1. Key Laboratory of Cluster Science Ministry of Education of China Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials School of Chemistry and Chemical Engineering Beijing Institute of Technology Beijing 100081 P. R. China
2. State Key Laboratory of Nonlinear Mechanics Institute of Mechanics Chinese Academy of Sciences Beijing 100190 P. R. China
3. Key Laboratory of Organic Optoelectronics & Molecular Engineering Ministry of Education Department of Chemistry Tsinghua University Beijing 100084 China