1. Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, 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, and Department of Chemistry, The University of Arizona, Tucson, Arizona 85721-0041