Reversible photodimerization of coumarin-modified Wells–Dawson anions

Abstract

Organo-modified photo-sensitive polyoxometalates (POMs) are a unique class of functional molecular materials. Here we show how the light-driven dimerization in organo-functionalized POMs can be achieved. To this end, the vanadium-substituted Wells–Dawson cluster [P₂V₃W₁₅O₆₂]⁹⁻ was modified with a coumarin-based derivative to give the new organic–inorganic hybrid (nBu₄N)₄H₂[C₁₂H₉O₄NHC(CH₂O)₃P₂W₁₅V₃O₅₉]. Upon photo-irradiation, the compound undergoes photodimerization which was characterized using various spectroscopic methods including FT-IR, UV-vis, DLS (dynamic light scattering), ¹H NMR, COSY NMR and ESI-MS. These results are in good agreement with the formation of dimer species. In addition, XPS and EPR analyses of the photo-irradiation product indicate that V⁵⁺ is partially reduced to V⁴⁺, while W⁶⁺ is not affected, suggesting that the coupled photo-dimerization and selective redox-switching might become possible.