Enhancement of Luminescence Lifetimes of Mononuclear Ruthenium(II)−Terpyridine Complexes by Manipulation of the σ-Donor Strength of Ligands

Abstract

The synthesis and characterization of mixed ligand 2,2';6',2' '-terpyridine (tpy) ruthenium complexes with 2,6-bis([1,2,4]triazol-3-yl)pyridine, 2,6-bis(5-phenyl-[1,2,4]triazol-3-yl)pyridine, and 2,6-bis([1,2,3,4]tetrazol-5-yl)pyridine are reported. The species are characterized by HPLC, 1H NMR, UV/vis, and emission spectroscopy. The photophysical properties of the complexes are investigated as a function of temperature over the range 80-320 K. The emission lifetime observed for the fully deprotonated compounds at room temperature is about 80 ns. This increase by 2 orders of magnitude with respect to the parent "[Ru(tpy)2](2+)" complex is rationalized by an increase in the energy of the metal based dsigma orbital, rather than by manipulation of the pi* orbitals on the ligands. The acid-base and electrochemical properties of the compounds are reported also.

Multielectron Storage and Photo‐Induced Electron Transfer in Oligonuclear Complexes Containing Ruthenium(II) Terpyridine and Ferrocene Building Blocks

“…Protonation of the amino group renders the tpy-NH 3 + ligand a weaker σ donor, thus decreasing the electron density at the metal centre and lowering the occupied metal-based orbitals. [12,40] Deprotonation of the COOH group of [2] 2+ shifts the unoccupied orbitals of the tpy-COO -ligand to higher energies. Further deprotonation (of the NH 2 group) renders the tpy-NH -ligand a better donor, increasing the energy of the occupied ruthenium orbitals and thus shifting the 1 MLCT absorption to lower energy.…”

Metal derivatives of tetrazoles

“…(m-Cl)Cl(CO) 6 ], which represent (according to X-ray diffraction data) unusual examples of metal ± metal interaction; the tetrazolate anions in these complexes are bound in the tridentate bridging mode. 76 Similarly, the substitution of 5-(2-pyridyl)tetrazole and 2,6-bis(tetrazol-5-yl)pyridine for chlorine in the complexes RuL 2 Cl 2 (L is 2,2 H -bipyridine, 4,4 H -dimethyl-2,2 H -bipyridine) 51 and Ru(tpy)Cl 3 (tpy is 2,2 H : 6 H ,2 HH -terpyridine) 78 gave ruthenium-containing tetrazoles 62 and 63 in 55% ± 84% yields. The UVspectroscopic and electrochemical studies have shown that the introduction of a tetrazolyl group having strong s-donor properties into the Ru(tpy)Cl 3 complex results in destabilisation of the ground energy state and decreases the metal oxidation potential.…”

“…This is also accompanied by a decrease in the emission energy and an increase in the luminescence time from 1 to 80 ns. 78 The 5-R-tetrazolate anion replaces the acetoxy group in 2-and 4-mercuriomethylquinolinium salts. The 1 H NMR characteristics of compounds 64 prepared in this way in 76% ± 96% yields indicate that only one N-isomer is formed in each case; however, the available data are insufficient for assigning the reaction products to either N(1)-or N(2)-isomeric tetrazoles.…”

Enhanced DNA photocleavage properties of Ru(II) terpyridine complexes upon incorporation of methylphenyl substituted terpyridine and/or the polyazine bridging ligand dpp (2,3-bis(2-pyridyl)pyrazine)

“…The photophysical properties of molecules can be tuned by the introduction of various substituents on the terpyridine ligand [7][8][9][10][11][12][13][14]. Electron-withdrawing groups stabilize the lowest unoccupied molecular orbital (LUMO), while electron-donating groups destabilize the highest occupied molecular orbital (HOMO) [15].…”