Modifications of the small molecule maltol and photoactivity when coordinated to transition metals.




Bruner, Britain C.

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The family of hetero-substituted maltol chelators, thiomaltol (Htma), dithiomaltol (Httma), and 3-hydroxypyridine-4-thione (Hopto) have been used to generate complexes with Ru(II), Pt(II), Ti(IV), and P(III) that exhibit unique photochemical and photophysical properties. Photo-excitation into ligand-based absorption bands of complexes [Ru(bpy)₂(ttma)] ⁺ and Zn(ttma)₂ engendered electron transfer reactions. Both complexes exhibit long-lived triplet emissions in the near IR spectral region. Photochemical experiments with [Ru(bpy)₂(ttma)] ⁺ formed alcohol and aldehyde products upon photolysis in presence of mild oxidants that do not oxidize in the dark, such as methyl viologen, [Ru(NH₃) ₆] ³⁺ and [Co(NH₃)₅Cl]²⁺. A family of new Pt(II) bipyridyl complexes are reported using the maltol-derived ligands as electron-donors. The [Pt(bpy)L]⁺ complexes display intense and long-lived luminescences due to Ligand-to-Ligand Charge Transfer (LLCT) states; these luminescences are quenched by electron acceptors such as methylviologen and O₂. These compounds are also efficient at singlet oxygen (¹O₂) generation and quenching. Likewise, a family of Ti(IV) complexes with maltol-derived chelators has been synthesized to model the use in dye-sensitized solar cell applications. Lastly, several novel six-coordinate phosphorous complexes with the chelators of the formula P(L)₂X₂were synthesized, which also exhibit room temperature emissions. These several families of photo-active complexes represent a useful palette of dyes for photochemical applications.