Research ArticleChemistry

Distinct properties of the triplet pair state from singlet fission

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Science Advances  14 Jul 2017:
Vol. 3, no. 7, e1700241
DOI: 10.1126/sciadv.1700241
  • Fig. 1 The model systems for intramolecular singlet fission and triplet harvesting.

    (A) Schematics of BP0, BP1, [Fe8O4]-Pc, and [Fe8O4]-BP0. R = (triisopropylsilyl)ethynyl (TIPS) for [Fe8O4]-Pc and (n-octyldiisopropyl)silylethynyl (NODIPS) for [Fe8O4]-BP0 and [Fe8O4]-BP1. The inset shows estimated IP and EA (electron affinity) from electrochemical oxidation/reduction potentials of [Fe8O4] and TIPS-pentacene. (B and C) Optical absorption spectra of (B) TIPS-Pc, BP0, and BP1 in toluene and (C) [Fe8O4], [Fe8O4]-Pc, and [Fe8O4]-BP0 in dichloromethane solutions.

  • Fig. 2 TA in the near-IR and visible regions reveal singlet and triplet characters of 1(TT).

    TA spectra in (A) the near-IR and (B) the visible regions for BP0 at different pump-probe delays, Δt = 0.1 ps (red), 10 ps (purple), and 100 ps (blue), following excitation at time zero by hν1 = 2.1 eV. The triplet TA spectrum from sensitization (black) is also shown in (A) and (B). (C) Kinetic profiles from TA spectra for BP0 at the indicated probe photon energies. (D) TA spectra at Δt = 1 ps (red) and 100 ps (blue) for BP1 following excitation at time zero by hν1 = 2.1 eV. The corresponding triplet spectrum (black) from sensitization is also shown.

  • Fig. 3 TA spectra of BP0 for the S1 and 1(TT) states from global analysis.

    Red: Singlet state. Blue: Triplet pair state. Inset: 2D pseudocolor (intensity) plot of TA spectra following excitation at time zero by hν1 = 2.1 eV. The transitions, along with vibronic progressions, are shown on each spectrum.

  • Fig. 4 TA of the 1(TT) state in the near-IR region depends on electronic coupling.

    Near-IR TA spectra of BP-42 (top) and BP-57 (bottom). The 1(TT) spectra (blue) have been multiplied by factors of 2.5 and 4.6 for BP-42 and BP-57, respectively, to normalize the peak intensities of 1(TT) to those of S1 (red).

  • Fig. 5 Estimated PES for BP0 molecule.

    The barrier-less nature for the crossing from S1 (red) to 1(TT) (blue) facilitates the fast singlet fission for BP0. The near-IR transition for BP0 can be explained by the transition from 1(TT) to Sn, which is similar to the transition from S1 to Sn′.

  • Fig. 6 TA reveals the strong coupling of CT state to T1.

    (A) TA spectra at 1 ps for [Fe8O4]-Pc (green) and [Fe8O4]-BP0 (red) upon CT excitation of 1.65 eV. The gray curve is the triplet spectrum of [Fe8O4]-BP0 from triplet sensitization. (B) Triplet decay dynamics for [Fe8O4]-Pc (green) and [Fe8O4]-BP0 (red and blue for ESA and ground-state bleaching, respectively). The solid curves are single-exponential fits with the indicated lifetimes (τ = 16 ± 2 ps for [Fe8O4]-Pc and 28 ± 3 ps for [Fe8O4]-BP0).

  • Fig. 7 TA spectra and dynamics of [Fe8O4]-BP0 under 2.1 eV excitation.

    (A) 2D pseudocolor plot of TA (= −ΔT/T; T, transmission) as a function of pump-probe delay (Δt) and probe photon energy. (B) TA spectra at Δt = 0 ps (red), 10 ps (blue), and 100 ps (green), along with T1 spectrum from sensitization (gray). (C) Singlet fission dynamics, as represented by S1 decay at 2.07 eV (red) or 1(TT) buildup at 2.36 eV (blue). (D) Comparison of 1(TT) decay dynamics for [Fe8O4]-BP0 and BP0.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/7/e1700241/DC1

    Transient absorption

    Triplet-sensitizing experiments

    Compound synthesis

    fig. S1. Transient absorption (TA) spectra and dynamics of [Fe8O4]-Pc.

    fig S2. Transient absorption for Fe8O4pz12Cl4 cluster (pumped at 2.58 and 2.07 eV) and [Fe8O4]-Pc (pumped at 1.65 eV).

    fig. S3. Triplet-sensitizing experiments.

    fig. S4. Synthetic route for compound 2.

    fig. S5. Synthetic route for compound 3.

    fig. S6. Synthetic route for compound Pc-Phenol.

    fig. S7. Synthetic route for compound BP0-Phenol.

    fig. S8. Synthetic route for compound BP1-Phenol.

    fig. S9. Synthetic route for compound [Fe8O4]-Pc, [Fe8O4]-BP0, and [Fe8O4]-BP1.

    fig. S10. Infrared spectra.

    fig. S11. Absorption spectra.

    fig. S12. Normalized absorption spectra.

    fig. S13. Normalized absorption spectra.

    fig. S14. NMR spectrum (0–9.5 ppm), compound 2.

    fig. S15. NMR spectrum (0–145 ppm), compound 2.

    fig. S16. NMR spectrum (0–9.5 ppm), compound 3.

    fig. S17. NMR spectrum (0–145 ppm), compound 3.

    fig. S18. NMR spectrum (0–9.5 ppm), Pc-Phenol.

    fig. S19. NMR spectrum (0–155 ppm), Pc-Phenol.

    fig. S20. NMR spectrum (0–9.5 ppm), BP0-Phenol.

    fig. S21. NMR spectrum (0–155 ppm), BP0-Phenol.

    fig. S22. NMR spectrum (0–9.5 ppm), BP1-Phenol.

    fig. S23. NMR spectrum (0–160 ppm), BP1-Phenol.

    fig. S24. NMR spectrum (−40 to 55 ppm), [Fe8O4]-Pc, before solvent addition.

    fig. S25. NMR spectrum (−40 to 55 ppm), [Fe8O4]-Pc, after solvent addition.

    fig. S26. Negative and positive mode NMR spectra (1000 to 5000 m/z), [Fe8O4]-BP0.

    fig. S27. Negative and positive mode NMR spectra (1000 to 5000 m/z), [Fe8O4]-BP1.

  • Supplementary Materials

    This PDF file includes:

    • Transient absorption
    • Triplet-sensitizing experiments
    • Compound synthesis
    • fig. S1. Transient absorption (TA) spectra and dynamics of Fe8O4-Pc.
    • fig S2. Transient absorption for Fe8O4pz12Cl4 cluster (pumped at 2.58 and 2.07 eV) and Fe8O4-Pc (pumped at 1.65 eV).
    • fig. S3. Triplet-sensitizing experiments.
    • fig. S4. Synthetic route for compound 2.
    • fig. S5. Synthetic route for compound 3.
    • fig. S6. Synthetic route for compound Pc-Phenol.
    • fig. S7. Synthetic route for compound BP0-Phenol.
    • fig. S8. Synthetic route for compound BP1-Phenol.
    • fig. S9. Synthetic route for compound Fe8O4-Pc, Fe8O4-BP0, and Fe8O4-BP1.
    • fig. S10. Infrared spectra.
    • fig. S11. Absorption spectra.
    • fig. S12. Normalized absorption spectra.
    • fig. S13. Normalized absorption spectra.
    • fig. S14. NMR spectrum (0–9.5 ppm), compound 2.
    • fig. S15. NMR spectrum (0–145 ppm), compound 2.
    • fig. S16. NMR spectrum (0–9.5 ppm), compound 3.
    • fig. S17. NMR spectrum (0–145 ppm), compound 3.
    • fig. S18. NMR spectrum (0–9.5 ppm), Pc-Phenol.
    • fig. S19. NMR spectrum (0–155 ppm), Pc-Phenol.
    • fig. S20. NMR spectrum (0–9.5 ppm), BP0-Phenol.
    • fig. S21. NMR spectrum (0–155 ppm), BP0-Phenol.fig. S22. NMR spectrum (0–9.5 ppm), BP1-Phenol.
    • fig. S23. NMR spectrum (0–160 ppm), BP1-Phenol.
    • fig. S24. NMR spectrum (–40 to 55 ppm), Fe8O4-Pc, before solvent addition.
    • fig. S25. NMR spectrum (–40 to 55 ppm), Fe8O4-Pc, after solvent addition.
    • fig. S26. Negative and positive mode NMR spectra (1000 to 5000 m/z), Fe8O4-BP0.
    • fig. S27. Negative and positive mode NMR spectra (1000 to 5000 m/z), Fe8O4-BP1.

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