1. Department of Chemistry, Chungnam National University, Taejon 305-764, Korea, and Center for Molecular Science, 373-1 Kusung-dong, Yusung-gu, Taejon 305-701, Korea, and Department of Material Science, Himeji Institute of Technology, 1479-1 Kanaji, Kamigohri, Hyogo 678-12, Japan