1. Department of Chemistry, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010-2899, United States
2. University of Electronic Science and Technology of China, Chengdu, China 610054
3. Department of Physics, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010-2899, United States
4. Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States
5. Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0358, United States