1. Howard Hughes Medical Institute, David Geffen School of Medicine, Departments of Biological Chemistry and Physiology, University of California, Los Angeles, California 90095, United States
2. Center for Polymers and Organic Solids, Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States
3. Physics and Chemistry of Materials, Theoretical Division and Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
4. Skolkovo Institute of Science and Technology, 143026 Moscow, Russia