Assemblies of Luminescent Ruthenium(II)- and Osmium(II)-polypyridyl Complexes Based on Hydrogen Bonding

Abstract The spectroscopic properties of complexes denoted as Ru(tBu2bpy)2(bpy-X)2+ (RuX) and Os(tBu2bpy)2(bpy-Y)2+ (OsY) are reported (bpy is 2,2′-bipyridine and tBu2bpy 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 1H NMR or luminescence spectroscopy. The adenine/thymine couple is responsible for a low association constant for the RuA · TOs associate, KA∼ 102 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 (∼10−4M) By contrast, the hydrogen bonding interaction for the couple RuC/OsG results in KA ⩾ 5 × 103 M−1 in dichloromethane at 22 °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 ken = 9.3 × 107 s−1.