1. Department of Chemistry University of Michigan Ann Arbor MI 48109 USA
2. Center of Single‐Molecule Sciences Institute of Modern Optics College of Electronic Information and Optical Engineering Nankai University China
3. Macromolecular Science and Engineering University of Michigan Ann Arbor MI 48109 USA
4. Department of Materials Science and Engineering University of Michigan Ann Arbor MI 48109 USA
5. Department of Chemical Engineering University of Michigan Ann Arbor MI 48109 USA