Photophysical and Theoretical Studies of Ruthenium(II)-Acetylide and -Cyanide Complexes with Aromatic Diimine and Trithiacyclononane

Ruthenium(II)-chloride, -cyanide, and -phenylacetylide complexes bearing aromatic diimine (2,2'-bipyridine (bpy), 4,4'-dimethy1-2,2'-bipyridine (Me(2)bpy), or dipyrido-[3,2-f.2',3'-h]-quinoxaline (dpq)) and cyclic tridentate thioether 1,4,7-trithiacyclononane ([9]aneS3) have been prepared. The crystal structures of [Ru([9]aneS3)(bpy)(C N)](PF6) and [Ru([9]aneS3)(diimine)(C CPh)](PF6) (diimine = bpy and Me(2)bpy) reveal Ru-C distances of 2.024(4) and 2.030(3)-2.038(2) angstrom, respectively. The oxidation waves for the complexes are attributed to the removal of an electron from a [d(pi)(Ru) + L] hybrid orbital (L = -Cl, -C N, and -C CPh), whereas the reduction waves are assigned as reduction of the aromatic diimine. The lowest-energy dipole-allowed absorptions for the complexes (lambda(max) = 403-475 nm, epsilon(max) = (3-5) x 10(3) dm(3) mol(-1) cm(-1) are assigned as [d(pi)(Ru-II) + L] -> pi*(diimine) charge transfer transitions. All the acetylide complexes weakly emit at lambda(max) = 663-680 nm in CH3CN at 298 K with quantum yield = (5-8) x 10(-4) (lambda(cx) = 450 nm), and these emissions are described as [d(pi)(Ru) + L] -> pi*(diimine) triplet charge transfer in nature. Density functional theory (DFT) and time-dependent-DFT (TD-DFT) calculations have been employed to examine the composition of the frontier molecular orbitals and the nature of the electronic transitions associated with the complexes.