1. Center for Superfunctional Materials, Department of Chemistry, Pohang University of Science and Technology, San 31, Hyojadong, Namgu, Pohang 790-784, Korea, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo, n. 2. Praha 6 166 10, Czech Republic, and School of Computational Science, Korea Institute for Advanced Study, 207-43, Cheongyangni-2-dong, Dongdaemun-gu, Seoul 130-722, Korea