Assemblies of luminescent ruthenium(II)- and osmium(II)-polypyridyl complexes based on hydrogen bonding

The spectroscopic properties of complexes denoted as Ru((t)Bu(2)bpy)(2)(bpy-X)(2+) (Ru-X) and Os((t)Bu(2)bpy)(2)(bpy-Y)(2+) (Os-Y) are reported (bpy is 2,2'-bipyridine and (t)Bu(2) bpy is 4,4'-bis-(tert-butyl)-2,2'-bpy). X and Y are pairs of functional groups containing bases known to be capable of hydrogen bonding; X/Y = adenine/thymine (A/T) form double hydrogen bonds, and cytosine/guanine (C/G) can form triple hydrogen bonds. The association processes for the Ru-X/Os-Y couples bearing complementary base pairs in dichloromethane have been investigated by using (1)H NMR or luminescence spectroscopy. The adenine/thymine couple is responsible for a low association constant for the Ru-A T-Os associate, K(A) similar to 10(2) M(-1), and mixtures of Ru-A and Os-T complexes do not give significant amounts of associate in solution at the highest concentrations used for spectroscopic studies (similar to 10(-4) M). By contrast, the hydrogen bonding interaction for the couple Ru-C/Os-G results in K(A) greater than or equal to 5 x 10(3) M(-1) in dichloromethane at 22 degrees C, as evaluated by using luminescence results before and after addition of ethanol. The photoinduced Ru --> Os energy transfer within the Ru-C.G-Os associate (exothermicity ca. 0.3 eV) could be monitored with the use of time-resolved luminescence spectroscopy and was found to occur with a rate constant k(en) = 9.3 x 10(7) s(-1). (C) 1998 Elsevier Science S.A.