Novel Heteroleptic Ruthenium(II) Complexes with 2,2′- Bipyridines Containing a Series of Electron-Donor and Electron-Acceptor Substituents in 4,4′-Positions: Syntheses, Characterization, and Application as Sensitizers for ZnO Nanowire-Based Solar Cells

Abstract

A novel series of complexes of the formula [Ru­(4,4′-X2-bpy)2(Mebpy-CN)]­(PF6)2 (X −CH3, −OCH3, −N­(CH3)2; Mebpy-CN = 4-methyl-2,2′-bipyridine-4′-carbonitrile) have been synthesized and characterized by spectroscopic, electrochemical, and photophysical techniques. Inclusion of the electron-withdrawing substituent −CN at one bpy ligand and different electron-donor groups −X at the 4,4′-positions of the other two bpy ligands produce a fine tuning of physicochemical properties. Redox potentials, electronic absorption maxima, and emission maxima correlate well with Hammett’s σp parameters of X. Quantum mechanical calculations are consistent with experimental data. All the complexes can be anchored through the nitrile moiety of Mebpy-CN over ZnO nanowires in dye-sensitized solar cells that exhibit an improvement of light to electrical energy conversion efficiency as the electronic asymmetry increases in the series.

New ruthenium polypyridyl complexes as potential sensors of acetonitrile and catalysts for water oxidation

“…Mixing between MOs centered in the metal center and 4,4′-(N(CH 3 ) 2 ) 2 -bpy ligands has been recently reported for heteroleptic Ru bipyridyl complexes. 35 On the other hand, this stabilization of the HOMOs increases in the series when going from 1 to 3 and correlates with the trend observed in the maximum absorption of the lowest energy MLCT bands, as described in the UV-vis spectroscopy section. In complex 1, the LUMO is delocalized over the ligands with a main contribution of (bpy-OMe) and equal contributions from the pyridyl rings of trpy, while in complexes 2 and 3 the LUMOs are mainly centred in the trpy rings with a concomitant energy stabilization respect to 1.…”

Coupling of photoactive transition metal complexes to a functional polymer matrix**

“…Second, the regular periodic structure of the PPV−Ru system illustrated in Figure 2b certainly represents an idealization with respect to the periodicity of the attached photosensitizer, the assumption of a straight polymer, the exact length of the linker between polymer and photosensitizer and the representation of the aqueous environment by a finite number of explicit water molecules in just one structure. Still, our DFT calculations yield a HOMO‐LUMO gap of the Ru photosensitizer that is by roughly 1 eV larger than the experimentally derived value which has also been found in similar systems [64,65] …”

“…Still, our DFT calculations yield a HOMO-LUMO gap of the Ru photosensitizer that is by roughly 1 eV larger than the experimentally derived value which has also been found in similar systems. [64,65] Time-dependent density functional theory, on the other hand, is well established to access and predict the light-driven processes in transition metal complexes [44,66] and soft matter embedded light-harvesting units. [67] Through TDDFT, individual excited states and their properties such as oscillator strength and electron density become accessible, which allows fundamental insights into the mechanisms of light-driven processes such as electron or hole injection.…”

Coupling of photoactive transition metal complexes to a functional polymer matrix

“…Still, our DFT calculations yield a HOMO-LUMO gap of the Ru photosensitizer that is by roughly 1 eV larger than the experimentally derived value which has also been found in similar systems. 64,65 Time-dependent density functional theory, on the other hand, is well established to access and predict the light-driven processes in transition metal complexes 44,66 and soft matter embedded light-harvesting units . 67 Through TDDFT, individual excited states and their properties such as oscillator strength and electron density become accessible, which allows fundamental insights into the mechanisms of light-driven processes such as electron or hole injection.…”