1. Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, Institut Européen de Chimie et Biologie, Université de Bordeaux, CNRS UMR5248, 2 rue Robert Escarpit, 33607 Pessac Cedex, France, and Molecular Photonics Group, Van’t Hoff Institute for Molecular Sciences, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands