1. U.S. Naval Research Laboratory, Division of Optical Sciences, Washington, D.C. 20375, U.S. Naval Research Laboratory, Center for Bio/Molecular Science and Engineering, Washington, D.C. 20375, George Mason University, Manassas, Virginia 21220, Department of Chemistry, University of Albany, State University of New York, Albany, New York 12222, and Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742