1. Department of Chemistry, Korea Advanced Institute of Science and Technology, Taejon 305-701, Korea
2. Chemistry Division, Kyungil University, Kyungsan, Kyungsangbuk-do 712-701, Korea
3. Department of Chemistry, School of Education, Pusan National University, Pusan 609-735, Korea
4. Department of Polymer Science and Engineering, Hannam University, 133 Ojung-dong, Daeduck-gu, Taejon 306-791, Korea