Tungsten Iodide Clusters as Singlet Oxygen Photosensitizers: Exploring the Domain of Resonant Energy Transfer at 1 eV

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The photophysics of selected tungsten iodide clusters was examined with respect to their role as a photosensitizer for the production of singlet oxygen, O 2 (a 1 Δ g ). We examined all-iodo octahedral clusters, [W 6 I 8 (I 6 )] 2- , and ligand-substituted octahedral clusters, [W 6 I 8 (L 6 )] 2- , in which the ligand, L, occupies the outer apical positions surrounding the cluster core. We also examined a square-pyramidal cluster, [W 5 I 8 (I 5 )] ? , in which the tungsten core was presumably more accessible to diffusional encounter with ground state oxygen, O 2 (X 3 Σ g - ). For the compounds examined, we find pronounced cluster-dependent changes in the yield of photosensitized O 2 (a 1 Δ g ) production. In particular, although the iodine-encased octahedral cluster, [W 6 I 8 (I 6 )] 2- , is an efficient O 2 (a 1 Δ g ) sensitizer, the pyramidal cluster, [W 5 I 8 (I 5 )] ? , does not make O 2 (a 1 Δ g ) at all. The latter provides fundamental insight into the important case where the sensitizer triplet state is nearly degenerate with the O 2 (X 3 Σ g - )-O 2 (a 1 Δ g ) transition energy at 1 eV. Our data indicate that even with near resonance, energy transfer to form O 2 (a 1 Δ g ) will not occur within the 3 sensitizer-O 2 (X 3 Σ g - ) encounter pair if other more efficient channels for energy dissipation are available.

OriginalsprogEngelsk
TidsskriftJournal of Physical Chemistry A
Vol/bind123
Nummer9
Sider (fra-til)1730-1739
Antal sider10
ISSN1089-5639
DOI
StatusUdgivet - feb. 2019

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