1. Contribution from the Department of Chemistry, Korea University, Jochiwon, Chungnam 339-700, Korea, Laboratory for Photonics and Interfaces, Station 6, Institute of Chemical Sciences and Engineering, School of Basic Sciences, Swiss Federal Institute of Technology, CH-1015 Lausanne, Switzerland, and Istituto CNR di Scienze e Tecnologie Molecolari (ISTM-CNR), c/o Dipartimento di Chimica, Università di Perugia, Via Elce di Sotto 8, I-06123 Perugia, Italy