Component Analysis of Dyads Designed for Light-Driven
Water Oxidation
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Abstract
A series of seven dyad molecules
have been prepared utilizing a [Ru(tpy)(NN)I]<sup>+</sup> type oxidation
catalyst (NN = 2,5-di(pyrid-2′-yl) pyrazine (<b>1</b>), 2,5-di-(1′,8′-dinaphthyrid-2′-yl) pyrazine
(<b>2</b>), or 4,6-di-(1′,8′-dinaphthyrid-2′-yl)
pyrimidine (<b>3</b>). The other bidentate site of the bridging
ligand was coordinated with 2,2′-bipyridine (bpy), 1,10-phenanthroline
(phen), or a substituted derivative. These dinuclear complexes were
characterized by their <sup>1</sup>H NMR spectra paying special attention
to protons held in the vicinity of the electronegative iodide. In
one case, <b>10a</b>, the complex was also analyzed by single
crystal X-ray analysis. The electronic absorption spectra of all the
complexes were measured and reported as well as emission properties
for the sensitizers. Oxidation and reduction potentials were measured
and excited state redox properties were calculated from this data.
Turnover numbers, initial rates, and induction periods for oxygen
production in the presence of a blue LED light and sodium persulfate
as a sacrificial oxidant were measured. Similar experiments were run
without irradiation. Dyad performance correlated well with the difference
between the excited state reduction potential of the photosensitizer
and the ground state oxidation potential of the water oxidation dyad.
The most active system was one having 5,6-dibromophen as the auxiliary
ligand, and the least active system was the one having 4,4′-dimethylbpy
as the auxiliary ligand