1. Department of Chemistry, Nanoscience Center, University of Jyväskylä, P.O. Box 35, 40014 Finland, Department of Chemical Physics, Chemical Center, Lund University, Box 124, SE-22100 Lund, Sweden, Kekulé-Institut für Organische Chemie und Biochemie der Rheinischen, Friedrich-Wilhelms-Universität Bonn, Gerhard-Domagk Strasse 1, 53121 Bonn, Germany, and Department of Chemistry “G. Ciamician”, University of Bologna, V.F. Selmi 2, 40126 Bologna, Italy