1. School of Materials Science and Engineering, Changchun University of Science and Technology, Changchun 130022, P. R. China, Fax: +86‐431‐85583015
2. School of Chemistry & Environmental Engineering, Changchun University of Science and Technology, Changchun 130022, P. R. China
3. Institute of Organic Chemistry & Biochemistry, Czech Academy of Science, 16610 Praha 6, Czech Republic