Binding of Scandium Ions to Metalloporphyrin-Flavin Complexes for Long-Lived Charge Separation

Takahiko Kojima, Ryosuke Kobayashi, Tomoya Ishizuka, Shinya Yamakawa, Hiroaki Kotani, Tatsuaki Nakanishi, Kei Ohkubo, Yoshihito Shiota, Kazunari Yoshizawa, Shunichi Fukuzumi

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Abstract

A porphyrin-flavin-linked dyad and its zinc and palladium complexes (MPor-Fl: 2-M, M=2 H, Zn, and Pd) were newly synthesized and the X-ray crystal structure of 2-Pd was determined. The photodynamics of 2-M were examined by femto- and nanosecond laser flash photolysis measurements. Photoinduced electron transfer (ET) in 2-H2 occurred from the singlet excited state of the porphyrin moiety (H2Por) to the flavin (Fl) moiety to produce the singlet charge-separated (CS) state 1(H2Por.+-Fl.-), which decayed through back ET (BET) to form 3[H2Por]∗-Fl with rate constants of 1.2×1010 and 1.2×109 s-1, respectively. Similarly, photoinduced ET in 2-Pd afforded the singlet CS state, which decayed through BET to form 3[PdPor]∗-Fl with rate constants of 2.1×1011 and 6.0×1010 s-1, respectively. The rate constant of photoinduced ET and BET of 2-M were related to the ET and BET driving forces by using the Marcus theory of ET. One and two Sc3+ ions bind to the flavin moiety to form the Fl-Sc3+ and Fl-(Sc3+)2 complexes with binding constants of K 1=2.2×105 M -1 and K 2=1.8×103 M -1, respectively. Other metal ions, such as Y3+, Zn2+, and Mg2+, form only 1:1 complexes with flavin. In contrast to 2-M and the 1:1 complexes with metal ions, which afforded the short-lived singlet CS state, photoinduced ET in 2-Pd Sc3+ complexes afforded the triplet CS state (3[PdPor.+-Fl.--(Sc3+)2]), which exhibited a remarkably long lifetime of τ=110 ms (k BET=9.1 s-1). More than transient: A porphyrin-flavin-linked dyad and its zinc and palladium complexes were synthesized and the X-ray crystal structure of the palladium complex was determined. The Pd-Sc3+ complex afforded a remarkably long lifetime of 110 ms of the charge-separated state (see figure).

Original languageEnglish
Pages (from-to)15518-15532
Number of pages15
JournalChemistry - A European Journal
Volume20
Issue number47
DOIs
Publication statusPublished - Nov 1 2014

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Organic Chemistry

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    Kojima, T., Kobayashi, R., Ishizuka, T., Yamakawa, S., Kotani, H., Nakanishi, T., Ohkubo, K., Shiota, Y., Yoshizawa, K., & Fukuzumi, S. (2014). Binding of Scandium Ions to Metalloporphyrin-Flavin Complexes for Long-Lived Charge Separation. Chemistry - A European Journal, 20(47), 15518-15532. https://doi.org/10.1002/chem.201403960