1. Institute of Physical Science and Information Technology Anhui University Hefei Anhui 230601 P. R. China
2. Department of Organic Chemistry Arrhenius Laboratory Stockholm University SE-10691 Stockholm Sweden
3. School of Materials Science and Engineering Jiangsu University of Science and Technology Zhenjiang 212003 P. R. China
4. Department of Natural Sciences Mid Sweden University SE-85170 Sundsvall Sweden