1. Research and Analytical Center for Giant Molecules, Graduate School of Science, Tohoku University, Aramaki, Aoba‐ku, Sendai 980‐8578 (Japan)
2. Department of Chemistry, Graduate School of Science, Tohoku University, Aramaki, Aoba‐ku, Sendai 980‐8578 (Japan)
3. Process Technology Research Laboratories, Daiichi Sankyo Co., Ltd, Edogawa‐ku, Tokyo 134‐8630 (Japan)