1. Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland
2. Department of Chemistry and Physics of Materials, University of Salzburg, Jakob-Haringer-Str. 2A, A-5020 Salzburg, Austria
3. Institute of Applied Physics, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland