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  • The structures of the porphyrins I have studied here in osaka have 3 main components of interest, the first is the porphyrin macrocycle, where there are 4 substituents attatched to the meso position of the macrocycle. The second component is the metal which is incorporated in the center, and the third component is a quinoxaline group which is fused onto the macrocycle on the pyrolle ring. Gold porphyrins are of interest due to their ability to be easily reduced and have been used as electron acceptors in more complex systems. The site of electron transfer may either be on the metal itself, or on the porphyrin moiety. The site of electron transfer as well as the ease of electron transfer can be effected by the type of substituent on the porphyrin.
  • In the cyclic voltammogram of PQAu
  • In the cyclic voltammogram of PQAu
  • Esr showed radical anion
  • me10fc
  • No esr signal
  • Radical anion signal if you do the revers, they have diiferent resultant spectras, partially due to the interaction of scandium prior to reduction.
  • Radical signal for esr
  • No esr signal
  • No esr signal
  • No esr signal
  • Looks as if 2 sc is complexed to cpd
  • No esr signal, 2 electrons, do sc titration
  • Discussion slides 1

    1. 1. Investigated PorphyrinsNNNNt BuBu tBu tt Bu Bu tt But BuBu tMNNNNNNt BuBu tBu tt Bu Bu tt But BuBu tNNNNMM = Au (III) or Zn (II)How will the site of electron transfer be effected in thepresence of Sc3+?PQ QPQ
    2. 2. Electrochemistry: Titration with Sc(OTf)3NNNNt BuBu tBu tt Bu Bu tt But BuBu tMNNM = Au (III)+PF6-MM PP PP210 mV shiftNew processMM PPPP
    3. 3. Site of electron transfer: SpectroscopyNNNNt BuBu tBu tt Bu Bu tt But BuBu tMNNM = Au (III)+PF6-300 400 500 600 700 800 900Wavelength,nm(PQ)AuPF6inCH2Cl2a)1streductionEapp=-0.70V436409549 587b)2ndreductionEapp=-1.20V439409422549 587Metal centeredNo isobesticpoint, initiallyporphyrincentered, thengo toquinoxalineOu et al., Inorg Chem. 2004,43,2078-2086Resulting spectra resembles2ndreduction of (PQ)AuPF6
    4. 4. Absorbance plots for spectroscopic titrationsNNNNt BuBu tBu tt Bu Bu tt But BuBu tMNNM = Au (III)+PF6-Indicates it is a 1electron reductionIndicates 2 Sc3+ions arecomplexed
    5. 5. ESR signal of PQAuPF6 in the presence of Sc3+In the presence of excess scandium, the complex is reduced by 1 electronwith the site of electron transfer to the quinoxaline group of theporphyrin, which has an ESR signal of a radical anion.Ou et al., Inorg Chem. 2004,43,2078-2086300 Gg = 2.003020472048
    6. 6. M =Zn (II)Electrochemistry of PQZnNNNNt BuBu tBu tt Bu Bu tt But BuBu tMNN0.00.41.1Electrochemical titration of (PQ)Zn with Sc3+in PhCN, 0.1 MTBAPF6-1.27-1.27-0.17-0.17-1.27[Sc3+]/[PQM]0.00.41.1PP
    7. 7. M =Zn (II)Site of electron transfer: SpectroscopyNNNNt BuBu tBu tt Bu Bu tt But BuBu tMNN500 600 700 8000.10.30.50.7UV-visible spectral titration of 1.62 x 10-5M (PQ)Zn with Me10Fc(6.58 x 10-4M) in the presence of 8.02 x 10-4M Sc3+437460640radical anion
    8. 8. M =Zn (II)Stoichiometric Plots for PQZnNNNNt BuBu tBu tt Bu Bu tt But BuBu tMNN00.10.20.30.40.50.60.70.80.90 0.5 1 1.5 2 2.500.10.20.30.40.50.60 1 2 3 4 5 6 7Plot of 451 nm absorbance of neutral PQZn vs. [Sc3+]/[(PQ)Zn]Plot of 437 nm absorbance of (PQ)Zn vs.[Me10Fc]/[(PQ)Zn] with excess Sc3+[Sc3+]/[(PQ)Zn][Me10Fc]/[(PQ)Zn]1 electron transfer2 Sc3+ions1 or 2 Sc3+ions? 1[SC3+]/[(PQ)Zn] with excess Me10Fc[SC3+]/[(PQ)Zn]
    9. 9. ESR of PQZn + Sc3++ (BNA)2 in PhCN300 Gg = 2.003620472048Indicates a radical anion
    10. 10. M =Zn (II)Electrochemistry of QPQZnNNNNt BuBu tBu tt Bu Bu tt But BuBu tNNNNM-1.13-1.46-0.19-0.15-1.14-1.28-1.11-0.44-0.65[Sc3+][Sc3+]/[PQZn]PPPP0.00.31.13 new processes
    11. 11. M =Zn (II)Site of electron transfer: SpectroscopyNNNNt BuBu tBu tt Bu Bu tt But BuBu tNNNNM(PQ)Zn, 1st step undersame conditions, 2 Sc3+ions after both processes3 or 4 Sc3+ions
    12. 12. 00.10.20.30.40.50.60.70.80 0.5 1 1.5 2 2.5 3 3.5M =Zn (II)Stoichiometric Plots for QPQZnNNNNt BuBu tBu tt Bu Bu tt But BuBu tNNNNMPlot of 441 nm absorbance of (QPQ)Zn vs. [Me10Fc ]/[(QPQ)Zn in the presence of excess Sc3400UV-visible titration of (QPQ)Zn with Me10Fc in the presence of excess Sc3+4411st step2st step500 600 700 8004604415355114605432 electrons
    13. 13. ESR of QPQZn + Sc3++ (BNA)2 in PhCN300 Gg = 2.003620472048Indicates a radical anion, like PQZn
    14. 14. 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0-0.28 -0.790.310.310.310.31-0.05-0.05-0.05-0.77-0.26-0.56-1.37-1.62-0.91-1.40-0.56-0.95-1.45-0.99-1.554.713.632.551.340.00Figure. Electrochemical titration of 7.42 x 10-4M (QPQ)AuPF6with Sc3+(2.85 x 10-3M) 0.1 M TBAPF6, PhCNNNNNt BuBu tBu tt Bu Bu tt But BuBu tNNNNMM = Au (III)+PF6-Electrochemistry of QPQAuPF6[Sc3+][Sc3+]/[QPQAuPF6]
    15. 15. NNNNt BuBu tBu tt Bu Bu tt But BuBu tNNNNMM = Au (III)+PF6-Site of electron transfer: Spectroscopy300 400 500 600 700 900800515650455416600Figure y. The UV-Visible spectral titration of (QPQ)AuPF6 + 203+UV-visible spectral changes of (QPQ)Au upon addingMe10Fc with excess Sc3+Indicates is a porphyrinradical-type reduction,similar to PQAuPF6Spectral changes upon the addition of Me10Fc in the presence ofexcess Sc3+,PhCn600400 500 700 800 900515439418UV-visible spectral changes of (PQ)AuPF6 upon the addition of Me10Fc in the presenceof Sc3+595
    16. 16. NNNNt BuBu tBu tt Bu Bu tt But BuBu tNNNNMM = Au (III)+PF6-Stoichiometric plots for QPQAuPF600.10.20.30.40.50.60.70.80.910 0.5 1 1.5 2 2.5 3Plot of 455 nm absorbance vs. [Me10Fc]/[QPQAuPF6] in excess Sc3+, PhCN[Me10Fc]/[QPQAuPF6]2 electrons
    17. 17. DFT calculation of QPQAuPF6QuickTime™ and adecompressorare needed to see this picture.(QPQ)AuLUMO OrbitalsQuickTime™ and adecompressorare needed to see this picture.(QPQ)Au + H+Basis set: B3LYP/Lanl2dz
    18. 18. -0.004-0.00200.0020.004400 500 600 700 800∆ΑβσΩαϖελενγτη, νµΝΝΝ ΝΑρΑρΑρ ΑρΖνΝΝΝΝΝΝΑρ ΑρΑρΑρΑυΝΝ[ΖνΠΘ−ΑυΠΘ+] = 1.0 ξ 10−5 Μ[Σχ(ΟΤφ)3] = 5.0 ξ 10–3 Μιν ΠηΧΝεξχιτατιον: 430 νµΖνΠΘ−ΑυΠΘ+00.0010.0020.0030.0040 1 2 3 4ΔAbs at 600-800 nmTime, μsC S Lifetime: 430 nsInthe absence ofSc3+: τcs = 250 psOhkubo, K. etal. C hem. Phys. 2006, 326, 3CS lifetime of 2 bound PQM:
    19. 19. SummaryZn and AuPF6 (PQ)-type compounds undergo 1-electronreduction at the porphyrin-quinoxaline π-conjugated systemin the presence of Sc3+, where 2 Sc3+ions are complexed tothe compound.Zn and AuPF6 (QPQ)-type compounds undergo 2-electronreduction at the porphyrin-quinoxaline π-conjugated systemin the presence of Sc3+, where 3 or 4 Sc3+ions are complexedin the case of (QPQ)Zn.(QPQ)AuPF6 titration with Sc3+in the presence of Me10Fcneeds to be performed as well as Sc3+ion reactivity studiestoward the PQZn-PQAu complex

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