Exploiting the Disulfide/Thiol Switch for Photoinduced Proton-Coupled Multielectron Transfer Reactivity

by Manuel Oelschlegel
Doctoral thesis
Date of Examination:2024-02-29
Date of issue:2024-03-27
Advisor:Prof. Dr. Franc Meyer
Referee:Prof. Dr. Franc Meyer
Referee:Prof. Dr. Inke Siewert
Referee:Prof. Dr. Dirk Schwarzer
Referee:Prof. Dr. Oliver Wenger
Referee:Prof. Dr. Anna Krawczuk
Referee:Prof. Dr. Johannes C. L. Walker
Persistent Address: http://dx.doi.org/10.53846/goediss-10422

 

 

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Abstract

English

Energy storage and efficient release has become a pivotal issue for our society relying progressively on renewable energy sources. The dichotomy between harvesting the sun’s energy in daylight hours, and requiring it the most during nighttime, produces the need for prolonged energy storage. Herein, molecular systems capable of performing a reversible single-photon triggered proton-coupled multi-electron transfer (PCET) are established. To achieve accumulation of two electrons from their photo-excited states and their decoupled release in the absence of light, the potential inversion of a disulfide/thiol redox switch is exploited. Assembly of the light harvesting and charge relay unit in one molecular system is accomplished by the combination of a transition-metal photosensitizer and a redox-active disulfide ligand directly coordinated to the metal center. A cyclometalated iridium-, as well as an organometallic rhenium photosensitizer decorated with a disulfide functionality on the bipyridyl ligand periphery, capable of storing two electrons and one proton, are presented. The photophysics of these complexes are investigated using a combination of (ultrafast) spectroscopy and non-adiabatic dynamics simulations, revealing a major influence of disulfide functionalization on the excited-state processes. Uptake of two electrons and one proton from the photo-excited state is achieved on the disulfide, forming a stable thiol-thiolate complex, and the underlying mechanism is investigated. Release of the stored redox equivalents can occur in the form of protons, H atoms, or formal hydride ions, as demonstrated by substrate reactivity and thermodynamic cycles. A comparatively low bond-dissociation free energy is found for the S−H bond of these complexes. This thesis sheds light on the use of disulfides as redox switch in molecular artificial photosynthetic systems and provides valuable insights into their photochemistry, as well as ground-state PCET chemistry.
Keywords: photochemistry; photophysics; disulfide; PCET; hydrogen atom transfer; hydride transfer; redox-active ligand; artificial photosynthesis; photosensitizer
 
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