1. Department of Chemistry, State University of New York at Binghamton, Binghamton, New York 13902, Department of Chemistry, Washington University, St. Louis, Missouri 63130, Department of Biochemistry and Molecular Biology, Center for Fluorescence Spectroscopy, University of Maryland School of Medicine, Baltimore, Maryland 21201, and Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061