Evidence for iodine atoms as intermediates in the dye sensitized formation of I-I bonds.

Visible light excitation of [Ru(bpz)(2)(deeb)](PF(6))(2), where bpz is 2,2'-bipyrazine and deeb is 4,4'-(CO(2)Et)(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)(-*). The resultant Ru(bpz(-))(bpz)(deeb)(+), I(2)(-*) stores approximately 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).