1. Laboratory for Photonics and Interfaces, Institute of Chemical Sciences and Engineering, School of Basic Sciences, Swiss Federal Institute of Technology, CH - 1015 Lausanne, Switzerland, Istituto CNR di Scienze e Tecnologie Molecolari and Dipartimento di Chimica, Università di Perugia, I-06123, Perugia, Italy, and Department of New Material Chemistry, Korea University, Jochiwon, Chungnam 339-700, Korea