Evidence for Iodine Atoms as Intermediates in the Dye Sensitized Formation of I-I Bonds

Visible light excitation of [Ru(bPZ)(2)(deeb)](PF6)(2), where bpz is 2,2'-bipyrazine and deeb is 4,4'-(CO2Et)(2)-2,2'-bipyridine, in acetonitrile solutions with iodide is shown to initiate excited-state electron transfer reactions that yield iodine atoms. The iodine atoms subsequently react with iodide to form the I-I bond in I-2(-center dot). The resultant Ru(bpz(-))(bpz)(deeb)(+), I-2(-center dot) stores similar to 1.64 eV of free energy and returns cleanly to ground-state products with k(cr) = (2.1 +/- 0.3) x 10(10) M-1 s(-1).