1. Institute of Advanced Materials, Physicochemical Processes, Nanotechnology and Microsystems, Terma Patr. Gregoriou, Aghia Paraskevi Attikis, 15310 (Greece), Fax: (+30) 210‐6511766
2. Laboratory of Photochemistry, Department of Drug Sciences, University of Catania, Viale Andrea Doria 6, I‐95125 Catania (Italy)