Evidence For Iodine Atoms As Intermediates In The Dye Sensitized Formationof I-i Bonds

摘要

Photoinitiated reactions that form chemical bonds are of considerable importance for the conversion and storage of solar energy. While the O-O bond formation necessary for solar water splitting continues to be the "holy grail" in this area, there is also considerable interest in the formation of bonds between other elements such as halogens. For example, iodide oxidation to form I-I bonds is key to sensitizer regeneration in champion dye-sensitized solar cells. Mechanistic details of how iodide oxidation yields the I-I bonds present in I_2~(-·) and I_3~- reaction products are under active investigation but remain speculative. Here we provide the first direct evidence that electron transfer sensitized to visible light with metal-to-ligand charge transfer (MLCT) excited states can directly yield iodine atoms that subsequently react to form an I-I chemical bond.