1. Department of Chemistry, University of Washington, Seattle, Washington 98195-1700, United States
2. Department of Materials Science and Engineering, University of Washington, Seattle, Washington 98195-2120, United States
3. Department of Physics and Astronomy, Shanghai Jiaotong University, Shanghai 200240, China
4. Department of Chemistry and Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, Hong Kong