1. Max-Planck-Institute for Metals Research, Department New Materials and Biosystems, Heisenbergstrasse 3, D-70569 Stuttgart, Germany, and University of Heidelberg, Institute for Physical Chemistry, Department Biophysical Chemistry, D-69120 Heidelberg, Germany, and Technical University of Munich, Department Chemie, Lehrstuhl II für Organische Chemie, Lichtenbergstrasse 4, D-85747 Garching, Germany