1. School of Materials Science and EngineeringHebei University of Technology Tianjin 300130 P. R. China
2. Key Laboratory of Hebei Province for Molecular BiophysicsInstitute of BiophysicsHebei University of Technology Tianjin 300401 P. R. China
3. Key Laboratory of Organic SolidsInstitute of ChemistryChinese Academy of Sciences Beijing 100190 P. R. China