1. Beijing National Laboratory for Molecular Sciences CAS Key Laboratory of Organic Solids Institute of Chemistry Chinese Academy of Sciences Beijing 100190 China
2. School of Chemistry and Chemical Engineering University of Chinese Academy of Sciences Beijing 100049 China
3. Materials Sciences Division Lawrence Berkeley National Laboratory Berkeley CA 94720 USA
4. Department of Physics and Astronomy Shanghai Jiaotong University Shanghai 200240 China
5. Polymer Science and Engineering Department University of Massachusetts Amherst MA 01003 USA