1. Institut für Organische Chemie and Röntgen Research Center for Complex Material Systems, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany, Molecular Photonics Group, van't Hoff Institute for Molecular Sciences (HIMS), Universiteit van Amsterdam, Nieuwe Achtergracht 129, 1018 WV Amsterdam, The Netherlands, and Department of Physics and Astronomy, Vrije Universiteit, de Boelelaan 1081, 1081 HV Amsterdam, The Netherlands