1. Department of Chemistry, Center for Biophysics and Quantitative Biology, Materials Research Laboratory, and the Beckman Institute for Advanced Science and Technology, University of Illinois Urbana−Champaign, 600 S. Mathews Ave., Urbana, Illinois 61801, United States
2. Beckman Institute for Advanced Science and Technology, Center for Biophysics and Quantitative Biology, and Department of Physics, University of Illinois Urbana−Champaign, Urbana, Illinois 61801, United States
3. Department of Chemistry, University of Michigan, 930 N. University Ave., Ann Arbor, Michigan 48109, United States
4. Department of Chemistry, Indiana University, 800 E. Kirkwood Ave., Bloomington, Indiana 47405, United States