1. Department of Chemistry, Graduate School of Science, Tohoku University, 6‐3 Aramaki‐Aza, Aoba‐ku, Sendai 980‐8578 (Japan) http://www.ykbsc.chem.tohoku.ac.jp
2. Present address: School of Chemistry, University of Lincoln, Brayford Pool, Lincoln LN6 7TS (UK)
3. Research and Analytical Center for Giant Molecules, Graduate School of Science, Tohoku University, Sendai 980‐8578 (Japan)
4. Present address: Faculty of Science, Ibaraki University, Ibaraki 310‐8512 (Japan)