Influence of the Protonic State of an Imidazole-Containing Ligand on the Electrochemical and Photophysical Properties of a Ruthenium(II)–Polypyridine-Type Complex (original) (raw)
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Inorganic Chemistry, 2007
This paper presents the synthesis, MO calculations, and photochemical and photophysical properties of cis-[Ru-(bpy) 2 (3Amdpy 2 oxaNBE)](PF 6) 2 (2), where bpy is 2,2′-bipyridine and 3Amdpy 2 oxaNBE is the novel 5,6-bis(3amidopyridine)-7-oxanorbornene chelate-ligand (1). Complex 2 is considered in relation to the cis-[Ru(bpy) 2-(3Amnpy) 2 ](PF 6) 2 (3) analogous complex, where 3Amnpy is 3-aminopyridine. Complexes 2 and 3 exhibit absorptions near 350 nm and in the 420−500 nm region attributable to a contribution from MLCT transitions (d π f bpy and d π f L; L) 3Amdpy 2 oxaNBE or 3Amnpy). Whereas complex 3 is photochemically reactive, complex 2 shows luminescence either at 77 K or at room temperature in fluid solution. The emission of 2 assignable as an MLCT (Ru f bpy) emission is characterized by a long lifetime at room temperature (650 ns in CH 3 CN and 509 ns in H 2 O). It is independent of λ irr , but it is temperature dependent; i.e., it increases as the temperature is lowered. Considering the chelate ring of 1 contributes to the stability of the complex 2 under continuous light irradiation, the difference in the primary photoprocesses of 3 (loss of 3Amnpy) and 2 (luminescence) may be caused by a lowering of the lowest excited state from 3 to 2. The surface crossing to the lowest MC state value of 987 cm-1 (similar to that of [Ru(bpy) 3 ] 2+) will be prevented in the case of complex 2, and as a result, efficient 3Amdpy moiety loss cannot occur. The electronic depopulation of the {Ru(bpy) 2 } unit and population of a bpy* orbital upon excitation are evident by comparing the photophysical properties with those of a [Ru(bpy) 3 ] 2+ related complex. Moreover, a reduction of a bpy ligand in the MLCT excited state is indicated by time-resolved spectra that show features typical of bpy •-. The photocatalytic property of 2 is spectroscopically demonstrated by oxidative quenching using either methylviologen 2+ or [RuCl(NH 3) 5 ] +2 electron-acceptor ions.
2018
CHEMICAL AND PHYSICAL STUDIES OF CHARGE TRANSFER EXCITED STATES OF RUTHENIUM COMPLEXES WITH AROMATIC LIGANDS by MARIM KHALIFA ALNAED August 2018 Advisors: Dr. John F. Endicott and Dr. Wen Li Major: Chemistry (Analytical) Degree: Doctor of Philosophy The 3MLCT excited states generated from tris-bipyridineruthenium(II), [Ru(bpy)3]2+ and related complexes were ionized by 405 nm irradiation in ambient, acidic aqueous solutions. The photoionization product was Ru(bpy)3]3+ and an electron with a quantum yield of about 0.04±0.02 in 0.5 M acid. However, 532 nm radiation does not induce photoionization, but it generates the 3MLCT excited state that can be photoionized by 405 nm irradiation. Dramatic decreases in [Ru(bpy)3]2+ emission intensities were observed when dual laser irradiations were used for 10-30 min in 0.5 M H+. The proton is a very good electron scavenger, and the rate of phoionization of the 3MLCT excited state was determined to be acid dependent and it increased about ten-fold...
Chemistry - A European Journal, 2005
To mimic the electron-donor side of photosystem II (PSII), three trinuclear ruthenium complexes (2, 2a, 2b) were synthesized. In these complexes, a mixed-valent dinuclear Ru2(II,III) moiety with one phenoxy and two acetato bridges is covalently linked to a Ru(II) tris-bipyridine photosensitizer. The properties and photoinduced electron/energy transfer of these complexes were studied. The results show that the Ru2(II,III) moieties in the complexes readily undergo reversible one-electron reduction and one-electron oxidation to give the Ru2(II,III) and Ru2(III,III) states, respectively. This could allow for photooxidation of the sensitizer part with an external acceptor and subsequent electron transfer from the dinuclear ruthenium moiety to regenerate the sensitizer. However, all trinuclear ruthenium complexes have a very short excited-state lifetime, in the range of a few nanoseconds to less than 100 ps. Studies by femtosecond time-resolved techniques suggest that a mixture of intramolecular energy and electron transfer between the dinuclear ruthenium moiety and the excited [Ru(bpy)3]2+ photosensitizer is responsible for the short lifetimes. This problem is overcome by anchoring the complexes with ester- or carboxyl-substituted bipyridine ligands (2a, 2b) to nanocrystalline TiO2, and the desired electron transfer from the excited state of the [Ru(bpy)3]2+ moiety to the conduction band of TiO2 followed by intramolecular electron transfer from the dinuclear Ru2(II,III) moiety to photogenerated Ru(III) was observed. The resulting long-lived Ru2(III,III) state decays on the millisecond timescale.
International Journal of Innovative Research in Science, Engineering and Technology, 2013
The present work involves an attempt to prepare two Ruthenium(II) complexes [Ru(bpy)3]2+ (I) and [Ru(phen)3]2+ (II) by simple and effective one-pot synthesis in a greener way and we have succeeded in achieving the target compounds in very good yields. Furthermore, we have studied extensively the photochemical reduction of complex I and II , *[Ru(NN)3]2+ in their excited states with various aromatic amines in the absence and presence of oxygen molecules by the luminescence quenching technique. The quenching rate constants, kq for each photoredox reactions have been determined using Stern - Volmer analysis. The results exhibit an interesting trend which depends on the nature of the quencher. In particular, the result proves the efficient interacting mechanism of oxygen with the excited state of *[Ru(NN)3]2+.
Role of Ruthenium Oxidation States in Ligand-to-Ligand Charge Transfer Processes
Inorganic Chemistry, 2012
We describe in this paper the properties of [Ru II/III (bpy) 2 ClL] +1/+2 and [Ru II/III (bpy) 2 L 2 ] +2/+3. L = ditolyl-3-pyridylamine (dt3pya) is a redox active ligand related to triarylamines, which is very similar to 3-aminopyridine except for the reversible redox behavior. The monosubstituted complex shows a metal-to-ligand charge-transfer (MLCT) at 502 nm, and reversible waves in acetonitrile at E 0 (Ru III/II) = 1.07 V, E 0 (L +/0) = 1.46 V (NHE). The disubstituted complex shows an MLCT at 461 nm, a photorelease of dt3pya with quantum yield of 0.11 at 473 nm, and two reversible one-electron overlapped waves at 1.39 V associated with one of the ligands (1.37 V) and Ru III/II (1.41 V). Further oxidation of the second ligand at 1.80 V forms a 2,2′-bipiridine derivative, in an irreversible reaction similar to dimerization of triphenylamine to yield tetraphenylbenzidine. In the dioxidized state, the spectroelectrochemistry of the disubstituted complex shows a ligand-to-ligand charge transfer at 1425 nm, with a transition moment of 1.25 Å and an effective two-state coupling of 1200 cm −1. No charge transfer between ligands was observed when Ru was in a 2+ oxidation state. We propose that a superexchange process would be involved in ligand−metal−ligand charge transfer, when ligands and metals are engaged in complementary π interactions, as in metal−ligand−metal complexes. Best orbital matching occurs when metallic donor fragments are combined with acceptor ligands and vice versa. In our case, Ru III bridge (an acceptor) and two dt3pya (donors, one of them being oxidized) made the complex a Robin−Day Class II system, while the Ru II bridge (a donor, reduced) was not able to couple two dt3pya (also donors, one oxidized).
Inorganic Chemistry, 1996
A series of mono-and dinuclear Ru(bpy) 2 complexes (bpy) 2,2′-bipyridine) containing 2,2′-bis(benzimidazol-2-yl)-4,4′-bipyridine (bbbpyH 2) were prepared. The mononuclear complex [Ru(bpy) 2 (bbbpyH 2)](ClO 4) 2 ‚CH 3-OH‚4H 2 O was characterized by an X-ray structure determination. Crystal data are as follows: triclinic, space group P1 h, a) 14.443(4) Å, b) 15.392(4) Å, c) 11.675(2)Å, R) 101.44(2)°,) 107.85(2)°, γ) 96.36(2)°, V) 2380(1) Å 3 , Z) 2. The coordination geometry of the ruthenium(II) ion is approximately octahedral. The dihedral angle between the two pyridyl rings in bbbpyH 2 is 9.4(3)°, which is close to coplanar, in the complex. Mono-and dinuclear complexes exhibit broad charge-transfer absorption bands at 420-520 nm and emission at 660-720 nm in CH 3 CN solution with lifetimes of 200-800 ns at room temperature. Transient difference absorption spectra and resonance Raman (rR) spectra were used to assign the charge-transfer bands in the 420-520 nm region and to identify the lowest excited states. Both absorption and emission spectra are sensitive to solvent and solution pH. Deprotonation of the dinuclear complex raises the energies of the π* orbitals of the bbbpyH 2 ligand, so that they become closer in energy to the π* orbitals of bpy. The intervalence band of [(bpy) 2 Ru-(bbbpyH 2)Ru(bpy) 2 ] 5+ is observed at 1200 nm () 170 M-1 cm-1) in CH 3 CN. The value of the electronic coupling matrix element, H AB , was determined as 120 cm-1. Upon deprotonation, the IT band was not observed. It is therefore concluded that a superexchange pathway occurs predominantly via the Ru(II) dπ-bbbpyH 2 π* interaction, since deprotonation decreases the interaction. The role of the intervening fragments in the bridging ligand is discussed from the viewpoint of orbital energies and their orbital mixing with Ru dπ orbitals.