1. State Key Laboratory of Precision Measuring Technology and Instruments School of Precision Instrument and Optoelectronics Engineering Tianjin University Tianjin 300072 P. R. China
2. Department of Chemistry University of British Columbia Vancouver V6T 1Z1 Canada
3. Department of Chemistry School of Science Tianjin University Tianjin 300072 P. R. China
4. School of Chemistry and Chemical Engineering Huazhong University of Science and Technology Wuhan 430074 P. R. China