Utilizing sunlight to make chemical bonds is one promising route to store solar energy. Optimally, the light to bond conversion reaction should operate quantitatively. The design and fine tuning of supramolecular assemblies that promote covalent bond formation when illuminated are therefore of utmost importance. Herein, we report on the excited-state electron transfer (ET) between iodide and seven ruthenium complexes. These complexes shared one common ligand, specifically designed to promote ion-pairing with iodide, while the ancillary ligands tuned the driving force for ET. The complexes formed 1:2 Ru:I ion-paired adducts, as demonstrated through <sup>1</sup>H NMR and UV-Vis titrations. Interestingly, the ET mechanism in the termolecular system was shown to depend strongly on the driving force, as evidenced by a combination of Stern-Volmer experiments and transient absorption spectroscopy. Indeed, with large driving force for iodide oxidation, a stepwise mechanism was shown to occur with rates close to the diffusion limit. When the thermodynamic driving force for iodide photo-oxidation was close to zero, the quenching rate constant became iodide independent at high concentrations. An explanation for this observation is that the excited-state electron transfer occurred solely within the ion-paired assembly and did not involve the free iodide. This work shows that by rational design of complexes and by careful tuning of the thermodynamic driving force, the mechanism and functionality of photoinduced bond formation reactions can be controlled.

Driving force dependence of iodide oxidation in termolecular {Ru:2I<sup>-</sup>} ruthenium excited-states

256th National Meeting (2018)

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Driving force dependence of iodide oxidation in termolecular {Ru:2I-} ruthenium excited-states

Driving force dependence of iodide oxidation in termolecular {Ru:2I^-} ruthenium excited-states