Issue 20, 1999

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

Abstract

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-[RuII(NH3)4(LD)(LA)][PF6]3 [LD = NH3 and LA = Medap+ 1, PymQ+ 2, Mebpe+ 3 or Phbpe+ 4; LD = pyridine (py) and LA = Medap+ 8, PymQ+ 9, Mebpe+ 10 or Phbpe+ 11; LD = 1-methylimidazole (mim) and LA = Medap+ 12, PymQ+ 13, Mebpe+ 14 or Phbpe+ 15]. The salt trans-[RuII(NH3)4(py)(4,4 ′-bpy)][PF6]2 (4,4 ′-bpy = 4,4 ′-bipyridine) 16 has also been prepared. The dipolar complexes in 1–4 and 8–15 exhibit intense dπ(RuII)→π*(LA) metal-to-ligand charge-transfer (MLCT) absorptions in the region 560–700 nm. For a given LA, the MLCT energy decreases as the donor strength of LD increases, in the order py < NH3 < 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 LA 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 LA. 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 8·4MeCN and 16·2MeCN have been determined. Molecular first hyperpolarizabilities β 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 β0 derived by using the two-level model are also very large, with 13 having the largest at 336 × 10–30 esu. In general, β0 increases as the absorption energy decreases, in keeping with the two-level model.

Supplementary files

Article information

Article type
Paper

J. Chem. Soc., Dalton Trans., 1999, 3617-3625

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

B. J. Coe, J. A. Harris, I. Asselberghs, A. Persoons, J. C. Jeffery, L. H. Rees, T. Gelbrich and M. B. Hursthouse, J. Chem. Soc., Dalton Trans., 1999, 3617 DOI: 10.1039/A905652A

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