Dinuclear bis(terpyridine)ruthenium(II) complexes by amide coupling of ruthenium amino acids: Synthesis and properties

Breivogel, Aaron; Hempel, Klaus; Heinze, Katja

doi:10.1016/j.ica.2011.03.046

Cited by 21 publications

(51 citation statements)

References 54 publications

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“…The Ru II / Ru III oxidation is shifted by 0.6−0.7 V to lower potentials compared to bis(terpyridine)ruthenium complexes bearing the same functional groups. 89 This illustrates the strong σ-donor character of the cyclometalating ligand that greatly increases the electron density at the metal center. The NHCOMe group at the cyclometalating ligand in 1(PF 6 ) indeed leads to a further shift of the ruthenium-based oxidation by 0.10 V to lower values as compared to [Ru(tpy)(dpb)] + , while the COOEt substitution of the dpb ligand in 2(PF 6 ) slightly increases this redox potential by 0.02 V.…”

Section: Inorganic Chemistrymentioning

confidence: 95%

Understanding the Excited State Behavior of Cyclometalated Bis(tridentate)ruthenium(II) Complexes: A Combined Experimental and Theoretical Study

et al. 2015

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The synthesis and characterization of the donor-acceptor substituted cyclometalated ruthenium(II) polypyridine complex isomers [Ru(dpb-NHCOMe)(tpy-COOEt)](PF6) 1(PF6) and [Ru(dpb-COOEt)(tpy-NHCOMe)](PF6) 2(PF6) (dpbH = 1,3-dipyridin-2-ylbenzene, tpy = 2,2';6,2"-terpyridine) with inverted functional group pattern are described. A combination of resonance Raman spectroscopic and computational techniques shows that all intense visible range absorption bands arise from mixed Ru → tpy/Ru → dpb metal-to-ligand charge transfer (MLCT) excitations. 2(PF6) is weakly phosphorescent at room temperature in fluid solution and strongly emissive at 77 K in solid butyronitrile matrix, which is typical for ruthenium(II) polypyridine complexes. Density functional theory calculations revealed that the weak emission of 2(PF6) arises from a (3)MLCT state that is efficiently thermally depopulated via metal-centered ((3)MC) excited states. The activation barrier for the deactivation process was estimated experimentally from variable-temperature emission spectroscopic measurements as 11 kJ mol(-1). In contrast, 1(PF6) is nonemissive at room temperature in fluid solution and at 77 K in solid butyronitrile matrix. Examination of the electronic excited states of 1(PF6) revealed a ligand-to-ligand charge-transfer ((3)LL'CT) as lowest-energy triplet state due to the very strong push-pull effect across the metal center. Because of the orthogonality of the participating ligands, emission from the (3)LL'CT is symmetry-forbidden. Hence, in this type of complex a stronger push-pull effect does not increase the phosphorescence quantum yields but completely quenches the emission.

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Section: Inorganic Chemistrymentioning

confidence: 95%

Understanding the Excited State Behavior of Cyclometalated Bis(tridentate)ruthenium(II) Complexes: A Combined Experimental and Theoretical Study

et al. 2015

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“…19,31,36 Another possibility to acylate the amino group is by employing acid chlorides at elevated temperatures. 57 The synthesis of the dinuclear dipeptide 3 4+ was effected in a four-step synthesis starting from the ethyl ester of the ruthenium amino acid 5 2+ . The first step was acidic cleavage of the ester to the amino acid 1 2+ .…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…57 Characterization of Mono-and Dinuclear Amides. The successful formation of the pentafluorophenylesters of 6 2+ and 1 2+ is easily evidenced in the 1 H NMR spectra of 7 2+ and 8 2+ because the resonances of the protons H 2 are shifted downfield by ∼0.15 ppm.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Dual Emission and Excited-State Mixed-Valence in a Quasi-Symmetric Dinuclear Ru–Ru Complex

et al. 2014

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The synthesis and characterization of the new dinuclear dipeptide [(EtOOC-tpy)Ru(tpy-NHCO-tpy)Ru(tpy-NHCOCH3)](4+) 3(4+) of the bis(terpyridine)ruthenium amino acid [(HOOC-tpy)Ru(tpy-NH2)](2+) 1(2+) are described, and the properties of the dipeptide are compared to those of the mononuclear complex [(EtOOC-tpy)Ru(tpy-NHCOCH3)](2+) 4(2+) carrying the same functional groups. 3(4+) is designed to serve a high electronic similarity of the two ruthenium sites despite the intrinsic asymmetry arising from the amide bridge. This is confirmed via UV-vis absorption and NMR spectroscopy as well as cyclic voltammetry. 4(2+) and 3(4+) are emissive at room temperature, as expected. Moreover, 3(4+) exhibits dual emission from two different triplet states with different energies and lifetimes at room temperature. This is ascribed to the presence of a unique thermal equilibrium between coexisting [Ru(II)(tpy-NHCO-tpy(·-))Ru(III)] and [Ru(III)(tpy-NHCO-tpy(·-))Ru(II)] states leading to an unprecedented excited-state Ru(II)Ru(III) mixed-valent system via the radical anion bridge tpy-NHCO-tpy(·-). The mixed-valent cation 3(5+), on the other hand, shows no measurable interaction of the Ru(II)Ru(III) centers via the neutral bridge tpy-NHCO-tpy (Robin-Day class I). Reduction of 3(4+) to the radical cation 3(3+) by decamethylcobaltocene is bridge-centered as evidenced by rapid-freeze electron paramagnetic resonance spectroscopy. Interestingly, all attempts to observe 3(3+) via NMR and UV-vis absorption spectroscopy only led to the detection of the diamagnetic complex 3-H(3+) in which the bridging amide is deprotonated. Hence 3-H(3+) (and 4-H(+)) appear to reduce protons to dihydrogen. The ease of single and double deprotonation of 4(2+) and 3(4+) to 4-H(+), 3-H(3+), and 3-2H(2+) was demonstrated using a strong base and was studied using NMR and UV-vis absorption spectroscopies. The equilibrating excited triplet states of 3(4+) are reductively quenched by N,N-dimethylaniline assisted by hydrogen bonding to the bridging amide.

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“…Reduction is located at the estersubstituted tpy ligands, while oxidation is essentially confined to the ruthenium center. [35,[46][47][48] Spin densities calculated by DFT are exemplarily depicted for complex [3] 2+ in its reduced and oxidized forms ( [3] + and [3] 3+ ; Figures 4a and 4b). The plot illustrates the location of reduction and oxidation processes in [3] 2+ .…”

Section: Resultsmentioning

confidence: 99%

“…[1](PF 6 ) 2 -[3](PF 6 ) 2 are photostable and chemically stable as a result of their tridentate coordination mode; they feature a sophisticated push-pull substitution with high directionality due to electron-withdrawing ester and electron-donating amino groups. [35][36][37][46][47][48] The push-pull substitution lowers the HOMO-LUMO gap (and hence increases the energy difference between the 3 MLCT and 3 MC states) and leads to emission in the red spectral region (λ em = 729-744 nm, Table 1). [35,36,46,47] Red light and NIR emission are particularly favorable for noninvasive bioimaging, telecommunication, night-vision-readable displays, downconversion and triplet-triplet annihilation upconversion.…”

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Push‐Pull Design of Bis(tridentate) Ruthenium(II) Polypyridine Chromophores as Deep Red Light Emitters in Light‐Emitting Electrochemical Cells

et al. 2013

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Keywords: Ruthenium / Molecular electronics / Tridentate ligands / Luminescence / N ligands Light-emitting electrochemical cells (LECs) with a simple device structure were prepared by using heteroleptic bis(tridentate) ruthenium(II) complexes [1](PF 6 ) 2 -[3](PF 6 ) 2 as emitters. The push-pull substitution shifts the emission energy to low energy, into the NIR region. The devices emit deep red light up to a maximum emission wavelength of 755 nm [CIE (International Commission on Illumination) coordinates: x = 0.731, y = 0.269 for [3](PF 6 ) 2 ], which, to the best of our knowledge, is the lowest emission energy for LECs containing

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Dinuclear bis(terpyridine)ruthenium(II) complexes by amide coupling of ruthenium amino acids: Synthesis and properties

Cited by 21 publications

References 54 publications

Understanding the Excited State Behavior of Cyclometalated Bis(tridentate)ruthenium(II) Complexes: A Combined Experimental and Theoretical Study

Understanding the Excited State Behavior of Cyclometalated Bis(tridentate)ruthenium(II) Complexes: A Combined Experimental and Theoretical Study

Dual Emission and Excited-State Mixed-Valence in a Quasi-Symmetric Dinuclear Ru–Ru Complex

Push‐Pull Design of Bis(tridentate) Ruthenium(II) Polypyridine Chromophores as Deep Red Light Emitters in Light‐Emitting Electrochemical Cells

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