Luminescent Iridium Complexes with a Sulfurated Bipyridine Ligand: PCET Thermochemistry of the Disulfide Unit and Photophysical Properties

Oelschlegel, Manuel and Hua, Shao-An and Schmid, Lucius and Marquetand, Philipp and Bäck, Anna and Borter, Jan-Hendrik. and Lücken, Jana and Dechert, Sebastian and Wenger, Oliver S. and Siewert, Inke and Schwarzer, Dirk and González, Leticia and Meyer, Franc. (2022) Luminescent Iridium Complexes with a Sulfurated Bipyridine Ligand: PCET Thermochemistry of the Disulfide Unit and Photophysical Properties. Inorganic Chemistry, 61 (35). pp. 13944-13955.

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Official URL: https://edoc.unibas.ch/89950/

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Molecular systems combining light harvesting and charge storage are receiving great attention in the context of, for example, artificial photosynthesis and solar fuel generation. As part of ongoing efforts to develop new concepts for photoinduced proton-coupled electron transfer (PCET) reactivities, we report a cyclometallated iridium(III) complex [Ir(ppy)2(S–Sbpy)](PF6) ([1]PF6) equipped with our previously developed sulfurated bipyridine ligand S–Sbpy. A new one-step synthetic protocol for S–Sbpy is developed, starting from commercially available 2,2′-bipyridine, which significantly facilitates the use of this ligand. [1]+ features a two-electron reduction with potential inversion (|E1| > |E2|) at moderate potentials (E1 = −1.12, E2 = −1.11 V versus. Fc+/0 at 253 K), leading to a dithiolate species [1]–. Protonation with weak acids allows for determination of pKa = 23.5 in MeCN for the S–H···S– unit of [1H]. The driving forces for both the H atom and the hydride transfer are calculated to be ∼60 kcal mol–1 and verified experimentally by reaction with a suitable H atom and a hydride acceptor, demonstrating the ability of [1]+ to serve as a versatile PCET reagent, albeit with limited thermal stability. In MeCN solution, an orange emission for [1]PF6 from a triplet-excited state was found. Density functional calculations and ultrafast absorption spectroscopy are used to give insight into the excited-state dynamics of the complex and suggest a significantly stretched S–S bond for the lowest triplet-state T1. The structural responsiveness of the disulfide unit is proposed to open an effective relaxation channel toward the ground state, explaining the unexpectedly short lifetime of [1]+. These insights as well as the quantitative ground-state thermochemistry data provide valuable information for the use of S–Sbpy-functionalized complexes and their disulfide-/dithiol-directed PCET reactivity.
Faculties and Departments:05 Faculty of Science > Departement Chemie > Chemie > Anorganische Chemie (Wenger)
UniBasel Contributors:Wenger, Oliver and Schmid, Lucius
Item Type:Article, refereed
Article Subtype:Research Article
Publisher:American Chemical Society
Note:Publication type according to Uni Basel Research Database: Journal article
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Last Modified:24 Aug 2023 01:30
Deposited On:28 Sep 2022 06:32

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