Energy and electron transfer in β-alkynyl-linked porphyrin-[60] fullerene dyads

Sean A. Vail, David I. Schuster, Dirk M. Guldi, Marja Isosomppi, Nikolai Tkachenko, Helge Lemmetyinen, Amit Palkar, Luis Echegoyen, Xihua Chen, John Zhang

Research output: Contribution to journalArticle

Abstract

Three porphyrin-fullerene dyads, in which a diyne bridge links C 60 with a β-position on a tetraarylporphyrin, have been synthesized. The free-base dyad was prepared, as well as the corresponding Zn(II) and Ni(II) materials. These represent the first examples of a new class of conjugatively linked electron donor-acceptor systems in which π-conjugation extends from the porphyrin ring system directly to the fullerene surface. The processes that occur following photoexcitation of these dyads were examined using fluorescence and transient absorption techniques on the femtosecond, picosecond, and nanosecond time scales. In sharp contrast to the photodynamics associated with singlet excited-state decay of reference tetraphenylporphyrins (ZnTPP, NiTPP, and H2TPP), the diyne-linked dyads undergo ultrafast (<10 ps) singlet excited-state deactivation in toluene, tetrahydrofuran (THF), and benzonitrile (PhCN). Transient absorption techniques with the ZnP-C60 dyad clearly show that in toluene intramolecular energy transfer (EnT) to ultimately generate C60 triplet excited states is the dominant singlet decay mechanism, while intramolecular electron transfer (ET) dominates in THF and PhCN to give the ZnP.+/C60.- charge-separated radical ion pair (CSRP). Electrochemical studies indicate that there is no significant charge transfer in the ground states of these systems. The lifetime of ZnP .+/C60.- in PhCN was ∼40 ps, determined by two different types of transient absorption measurement in two different laboratories. Thus, in this system, the ratio of the rates for charge separation (kCS) to rates for charge recombination (kCR), k CS/kCR, is quite small, ∼7. The fact that charge separation (CS) rates increase with increasing solvent polarity is consistent with this process occurring in the normal region of the Marcus curve, while the slower charge recombination (CR) rates in less polar solvents indicate that the CR process occurs in the Marcus inverted region. While photoinduced ET occurs on a similar time scale in a related dyad 15 in which a diethynyl bridge connects C60 to the para position of a meso phenyl moiety of a tetrarylporphyrin, CR occurs much more slowly; i.e., kCS/k CR ≈ 7400. Thus, the position at which the conjugative linker is attached to the porphyrin moiety has a dramatic influence on kCR but not on kCS. On the basis of electron density calculations, we tentatively conclude that unfavorable orbital symmetries inhibit charge recombination in 15 vis a vis the β-linked dyads.

Original languageEnglish (US)
Pages (from-to)14155-14166
Number of pages12
JournalJournal of Physical Chemistry B
Volume110
Issue number29
DOIs
StatePublished - Jul 27 2006

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Porphyrins
Fullerenes
Excited states
porphyrins
fullerenes
electron transfer
polarization (charge separation)
energy transfer
Toluene
Electrons
tetrahydrofuran
toluene
Photoexcitation
excitation
Energy transfer
Ground state
Carrier concentration
Charge transfer
decay
Fluorescence

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Vail, S. A., Schuster, D. I., Guldi, D. M., Isosomppi, M., Tkachenko, N., Lemmetyinen, H., ... Zhang, J. (2006). Energy and electron transfer in β-alkynyl-linked porphyrin-[60] fullerene dyads. Journal of Physical Chemistry B, 110(29), 14155-14166. https://doi.org/10.1021/jp061844t

Energy and electron transfer in β-alkynyl-linked porphyrin-[60] fullerene dyads. / Vail, Sean A.; Schuster, David I.; Guldi, Dirk M.; Isosomppi, Marja; Tkachenko, Nikolai; Lemmetyinen, Helge; Palkar, Amit; Echegoyen, Luis; Chen, Xihua; Zhang, John.

In: Journal of Physical Chemistry B, Vol. 110, No. 29, 27.07.2006, p. 14155-14166.

Research output: Contribution to journalArticle

Vail, SA, Schuster, DI, Guldi, DM, Isosomppi, M, Tkachenko, N, Lemmetyinen, H, Palkar, A, Echegoyen, L, Chen, X & Zhang, J 2006, 'Energy and electron transfer in β-alkynyl-linked porphyrin-[60] fullerene dyads', Journal of Physical Chemistry B, vol. 110, no. 29, pp. 14155-14166. https://doi.org/10.1021/jp061844t
Vail SA, Schuster DI, Guldi DM, Isosomppi M, Tkachenko N, Lemmetyinen H et al. Energy and electron transfer in β-alkynyl-linked porphyrin-[60] fullerene dyads. Journal of Physical Chemistry B. 2006 Jul 27;110(29):14155-14166. https://doi.org/10.1021/jp061844t
Vail, Sean A. ; Schuster, David I. ; Guldi, Dirk M. ; Isosomppi, Marja ; Tkachenko, Nikolai ; Lemmetyinen, Helge ; Palkar, Amit ; Echegoyen, Luis ; Chen, Xihua ; Zhang, John. / Energy and electron transfer in β-alkynyl-linked porphyrin-[60] fullerene dyads. In: Journal of Physical Chemistry B. 2006 ; Vol. 110, No. 29. pp. 14155-14166.
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AU - Vail, Sean A.

AU - Schuster, David I.

AU - Guldi, Dirk M.

AU - Isosomppi, Marja

AU - Tkachenko, Nikolai

AU - Lemmetyinen, Helge

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N2 - Three porphyrin-fullerene dyads, in which a diyne bridge links C 60 with a β-position on a tetraarylporphyrin, have been synthesized. The free-base dyad was prepared, as well as the corresponding Zn(II) and Ni(II) materials. These represent the first examples of a new class of conjugatively linked electron donor-acceptor systems in which π-conjugation extends from the porphyrin ring system directly to the fullerene surface. The processes that occur following photoexcitation of these dyads were examined using fluorescence and transient absorption techniques on the femtosecond, picosecond, and nanosecond time scales. In sharp contrast to the photodynamics associated with singlet excited-state decay of reference tetraphenylporphyrins (ZnTPP, NiTPP, and H2TPP), the diyne-linked dyads undergo ultrafast (<10 ps) singlet excited-state deactivation in toluene, tetrahydrofuran (THF), and benzonitrile (PhCN). Transient absorption techniques with the ZnP-C60 dyad clearly show that in toluene intramolecular energy transfer (EnT) to ultimately generate C60 triplet excited states is the dominant singlet decay mechanism, while intramolecular electron transfer (ET) dominates in THF and PhCN to give the ZnP.+/C60.- charge-separated radical ion pair (CSRP). Electrochemical studies indicate that there is no significant charge transfer in the ground states of these systems. The lifetime of ZnP .+/C60.- in PhCN was ∼40 ps, determined by two different types of transient absorption measurement in two different laboratories. Thus, in this system, the ratio of the rates for charge separation (kCS) to rates for charge recombination (kCR), k CS/kCR, is quite small, ∼7. The fact that charge separation (CS) rates increase with increasing solvent polarity is consistent with this process occurring in the normal region of the Marcus curve, while the slower charge recombination (CR) rates in less polar solvents indicate that the CR process occurs in the Marcus inverted region. While photoinduced ET occurs on a similar time scale in a related dyad 15 in which a diethynyl bridge connects C60 to the para position of a meso phenyl moiety of a tetrarylporphyrin, CR occurs much more slowly; i.e., kCS/k CR ≈ 7400. Thus, the position at which the conjugative linker is attached to the porphyrin moiety has a dramatic influence on kCR but not on kCS. On the basis of electron density calculations, we tentatively conclude that unfavorable orbital symmetries inhibit charge recombination in 15 vis a vis the β-linked dyads.

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