Competitive Energy and Electron Transfer in β-Functionalized Free-Base Porphyrin-Zinc Porphyrin Dimer Axially Coordinated to C 60 : Synthesis, Supramolecular Formation and Excited-State Processes

Hu, Yi; Thomas, Michael B.; Jinadasa, R. G.  Waruna; Wang, Hong; D'Souza, Francis

doi:10.1002/chem.201702178

Title: Competitive Energy and Electron Transfer in β-Functionalized Free-Base Porphyrin-Zinc Porphyrin Dimer Axially Coordinated to C ₆₀ : Synthesis, Supramolecular Formation and Excited-State Processes

Journal Article · Wed Jun 07 00:00:00 EDT 2017 · Chemistry - A European Journal

DOI:https://doi.org/10.1002/chem.201702178· OSTI ID:1533141

Hu, Yi ^[1]; Thomas, Michael B. ^[1]; Jinadasa, R. G. Waruna ^[1]; Wang, Hong ^[1];

^[1]

Univ. of North Texas, Denton, TX (United States)

Abstract Simultaneous occurrence of energy and electron transfer events involving different acceptor sites in a newly assembled supramolecular triad comprised of covalently linked free‐base porphyrin–zinc porphyrin dyad, H ₂ P−ZnP axially coordinated to electron acceptor fullerene, has been successfully demonstrated. The dyad was connected through the β‐pyrrole positions of the porphyrin macrocycle instead of the traditionally used meso ‐positions for better electronic communication. Interestingly, the β‐pyrrole functionalization modulated the optical properties to such an extent that it was possible to almost exclusively excite the zinc porphyrin entity in the supramolecular triad. The measured binding constant for the complex with 1:1 molecular stoichiometry was in the order of 10 ⁴ m ⁻¹ revealing moderately stable complex formation. An energy level diagram constructed using optical, electrochemical and computational results suggested that both the anticipated energy and electron events are thermodynamically feasible in the triad. Consequently, it was possible to demonstrate occurrence of excited state energy transfer to the covalently linked H ₂ P, and electron transfer to the coordinated ImC ₆₀ from studies involving steady‐state and time‐resolved emission, and femto‐ and nanosecond transient absorption studies. The estimated energy transfer was around 67 % in the dyad with a rate constant of 1.1×10 ⁹ s ⁻¹ . In the supramolecular triad, the charge separated state was rather long‐lived although it was difficult to arrive the exact lifetime of charge separated state from nanosecond transient spectral studies due to overlap of strong triplet excited signals of porphyrin in the monitoring wavelength window. Nevertheless, simultaneous occurrence of energy and electron transfer in the appropriately positioned energy and electron acceptor entities in a supramolecular triad was possible to demonstrate in the present study, a step forward to unraveling the complex photochemical events occurring in natural photosynthesis and its implications in building light energy harvesting devices.

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Research Organization:: Miami Univ., Oxford, OH (United States)

Sponsoring Organization:: USDOE Office of Science (SC)

Grant/Contract Number:: SC0010800; FG02-13ER46976

OSTI ID:: 1533141

Alternate ID(s):: OSTI ID: 1392178

Journal Information:: Chemistry - A European Journal, Vol. 23, Issue 52; ISSN 0947-6539

Publisher:: ChemPubSoc EuropeCopyright Statement

Country of Publication:: United States

Language:: English

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Cited by: 10 works

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Title: Competitive Energy and Electron Transfer in β-Functionalized Free-Base Porphyrin-Zinc Porphyrin Dimer Axially Coordinated to C 60 : Synthesis, Supramolecular Formation and Excited-State Processes

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Title: Competitive Energy and Electron Transfer in β-Functionalized Free-Base Porphyrin-Zinc Porphyrin Dimer Axially Coordinated to C ₆₀ : Synthesis, Supramolecular Formation and Excited-State Processes