Tuning of charge-transfer absorption and molecular quadratic non-linear optical properties in ruthenium(II) ammine complexes

摘要

The ligands N-methyl-2, 7-diazapyrenium (Medap~+), N-(2-pyrimidyl)-4, 4'-bipyridinium (PymQ~+), N-methyl-4-[trans-2-(4-pyridyl)ethenyl]pyridinium (Mebpe~+)and N-phenyl-4-[trans-2-(4-pyridyl)ethenyl]pyridinium (Phbpe~+) have been used to prepare a series of complex salts trans-[Ru~(II)(NH_3)_4(L~D)(L~A)][PF_6]_3 [L~D = NH_3 and L~A = Medap~+ 1, PymQ~+ 2, Mebpe~+ 3 or Phbpe~+ 4; L~D=pyridine (py) and L~A = Medap~+ 8, PymQ~+ 9, Mebpe~+ 10 or Phbpe~+ 11; L~D = 1-methylimidazole (mim) and L~A = Medap~+ 12, PymQ~+ 13, Mebpe~+ 14 or Phbpe~+ 15]. The salt trans-[Ru~(II)(NH_3)_4(py)(4, 4'-bpy)][PF_6]_2 (4, 4'-bpy = 4, 4'-bipyridine) 16 has also been prepared. the dipolar complexes in 1-4 and 8-15 exhibit intense d_(#pi#)(Ru~(II)) -> #pi#~*(L~A) metal-to-ligand charge-transfer (MLCT) absorptions in the region 560-700 nm. For a given L~A, the MLCT energy decreases as the donor strength of L~D increases, in the order py < NH_3 < mim. Within the pairs of Medap~+/PymQ~+ complexes, the energy of the Ru-based HOMO is constant and the MLCT energy decreases by ca. 0.3 eV as the acceptor strength of L~A increases on going from Medap~+ to PymQ~+. The complexes of Mebpe~+ or Phbpe~+ also have similar HOMO energies which are lower than those of their Medap~+/PymQ~+ counterparts due to the increased basicity of L~A. Replacement of Mebpe~+ by Phbpe~+ decreases the MLCT energy by ca. 0.1 eV due to the greater electron-withdrawing ability of Phbpe~+. Single-crystal structures of 8 centre dot 4MeCN and 16 centre dot 2MeCN have been determined. Molecular first hyperpolarizabilities #beta# of 1-4 and 8-15, obtained from hyper-Rayleigh scattering measurements at 1064 nm, are in the range (579-1068) * 10~(-30) esu. Static hyperpolarizabilities #beta#_0 derived by using the two-level model are also very large, with 13 having the largest at 336 * 10~(-30) esu. In general, #beta#_0 increases as the absorption energy decreases, in keeping with the two-level model.