1. Laboratory for Chemistry of Novel Materials, Center for Research on Molecular Electronics and Photonics, University of Mons-Hainaut, Place du Parc 20, B-7000 Mons Belgium, Lash-Miller Chemical Laboratories, Institute for Optical Sciences and Centre for Quantum Information and Quantum Control, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6 Canada, and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139