1. Department of Physics, University of Ioannina, P.O. Box 1186, 451 10 Ioannina, Greece, and Foundation for Research and Technology-Hellas, Biomedical Research Institute (FORTH−BRI), Ioannina, Greece, Department of Chemistry, University of Athens, Zografou 15771, Athens, Greece, and Max-Planck Institut für Polymerforschung, Postfach 3148, 55021 Mainz, Germany