1. Department of Chemistry, School of Molecular Science BK21 and Center for Molecular Design and Synthesis, KAIST, 373‐1 Guseong‐dong, Yuseong‐gu, Daejeon 305‐701, Korea
2. Department of Chemistry, Kongju National University, 182 Shinkwan, Kongju, Chungnam 314‐701, Korea, Fax: + 82‐41‐850‐8479