1 research outputs found
Visible-Light-Driven Photosystems Using Heteroleptic Cu(I) Photosensitizers and Rh(III) Catalysts To Produce H<sub>2</sub>
The
synthesis of two new heteroleptic CuÂ(I) photosensitizers (PS), [CuÂ(Xantphos)Â(NN)]ÂPF<sub>6</sub> (NN = biq = 2,2′-biquinoline, dmebiq = 2,2′-biquinoline-4,4′-dimethyl
ester; Xantphos = 4,5-bisÂ(diphenylphosphino)-9,9-dimethylxanthene),
along with the associated structural, photophysical, and electrochemical
properties, are described. The biquinoline diimine ligand extends
the PS light absorbing properties into the visible with a maximum
absorption at 455 and 505 nm for NN = biq and dmebiq, respectively,
in CH<sub>2</sub>Cl<sub>2</sub> solvent. Following photoexcitation,
both CuÂ(I) PS are emissive at low energy, albeit displaying stark
differences in their excited state lifetimes (τ<sub>MLCT</sub> = 410 ± 5 (biq) and 44 ± 4 ns (dmebiq)). Cyclic voltammetry
indicates a Cu-based HOMO and NN-based LUMO for both complexes, whereby
the methyl ester substituents stabilize the LUMO within [CuÂ(Xantphos)Â(dmebiq)]<sup>+</sup> by ∼0.37 V compared to the unsubstituted analogue.
When combined with H<sub>2</sub>O, <i>N,N</i>-dimethylaniline
(DMA) electron donor, and <i>cis</i>-[RhÂ(NN)<sub>2</sub>Cl<sub>2</sub>]ÂPF<sub>6</sub> (NN = Me<sub>2</sub>bpy = 4,4′-dimethyl-2,2′-bipyridine,
bpy = 2,2′-bipyridine, dmebpy = 2,2′-bipyridine-4,4′-dimethyl
ester) water reduction catalysts (WRC), photocatalytic H<sub>2</sub> evolution is only observed using the [CuÂ(Xantphos)Â(biq)]<sup>+</sup> PS. Furthermore, the choice of <i>cis</i>-[RhÂ(NN)<sub>2</sub>Cl<sub>2</sub>]<sup>+</sup> WRC strongly affects the catalytic
activity with turnover numbers (TON<sub>Rh</sub> = mol H<sub>2</sub> per mol Rh catalyst) of 25 ± 3, 22 ± 1, and 43 ±
3 for NN = Me<sub>2</sub>bpy, bpy, and dmebpy, respectively. This
work illustrates how ligand modification to carefully tune the PS
light absorbing, excited state, and redox-active properties, along
with the WRC redox potentials, can have a profound impact on the photoinduced
intermolecular electron transfer between components and the subsequent
catalytic activity