1. Roger Adams Laboratory, Departments of Chemistry and Materials Science & Engineering, The Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801; Department of Chemistry, Macalester College, 1600 Grand Avenue, St. Paul, Minnesota 55105; and 3M Adhesive Technology Center, 3M Center, 201-3N-04, St. Paul, Minnesota 55144