1. Department of Chemistry and Pharmacy and Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, D-91058 Erlangen, Germany
2. Institute of Physics and Center for Nanotechnology, Westfälische Wilhelms-Universität Münster, Heisenbergstraße 11, D-48149 Münster, Germany