Polyimine Complexes Research Articles

Photophysical study of [Ru(2,2′-bipyridine)3]2+ and [Ru(1,10-phenanthroline)3]2+ encapsulated in the Uio-66-NH2 metal organic framework

Metal organic frameworks are stable porous materials that provide an excellent environment for the encapsulation of photoactive guests. The ruthenium(II) polyimine complexes, in particular, ruthenium(II) tris-(1,10-phenanthroline) (RuPhen) and ruthenium(II) tris-(2,2′-bipyridine) (RuBpy) are ideal candidates for encapsulation due to their unique photophysics. Here the excited state properties of RuPhen and RuBpy encapsulated within the zirconium oxide based MOF Uio-66 and the amine derivatized MOF Uio-66-NH2 are reported. The encapsulated complexes exhibit stabilization of the excited triplet metal to ligand charge transfer state (3MLCT) resulting in a bathochromatic shift of the emission band and extension of the emission lifetime. The introduction of an amine functional group into the Uio-66 framework gives rise to a reduction in lifetimes relative to the parent Uio-66 framework materials that may arise from perturbation to low lying singlet in character MLCT states.

Lighting the Flavin Decorated Ruthenium(II) Polyimine Complexes: A Theoretical Investigation.

The emission properties of a series of flavin (FL) decorated Ru (II) polyimine complexes were investigated by extensive time-dependent (TD) density functional theory (DFT) and DFT based calculations. We attributed the moderate emission properties of FL decorated Ru(II) polyimine complex (Ru-1), such as triplet lifetime and luminescence quantum yield, to the dominant fast nonradiative decay due to the small adiabatic energy gap between the ground state and the lowest lying triplet state (Δ Ead) and the slow radiative decay owing to the ligand localized triplet (3IL) nature of the emissive state. Electron withdrawing groups such as F and Cl were attached to the FL moiety of Ru-1 to alter Δ Ead. Both the radiative and nonradiative decay rates were found to be sensitive to Δ Ead and may result in a drastic change of the photophysical properties of the Ru(II) complexes. Specifically, substitution with F leads to an increase in the Δ Ead from 1.85 to 1.93 eV, resulting in a nearly doubled phosphorescent quantum yield and triplet lifetime with respect to Ru-1. These findings are vital for the rational design of phosphorescent transition metal complexes.

Synthesis and photophysical properties of ruthenium(ii) polyimine complexes decorated with flavin

A bipyridine ruthenium(ii) complex (Ru-1) with a flavin moiety connected to one of the bipyridine ligands via an acetylene bond was designed and synthesized, and its photophysical properties were investigated. Compared with the tris(bipyridine) Ru(ii) complex (Ru-0), which has an extinction coefficient ε = 1.36 × 104 M-1 cm-1 at 453 nm, the introduction of the flavin moiety endows Ru-1 with strong absorption in the visible range (ε = 2.34 × 104 M-1 cm-1 at 456 nm). Furthermore, Ru-1 exhibits phosphorescence (λem = 643 nm, ΦP = 1%, τP = 1.32 μs at 293 K and 4.53 μs at 77 K). We propose that the emission of Ru-1 originates from the low lying triplet excited state of 3IL according to the time-resolved transient difference absorption spectra, the calculated T1 spin density and the T1 thermo-vibration modes localized on the flavin-decorated bipyridine ligand. This is the first time that the phosphorescence of flavin was observed within Ru(ii) complexes. Consequently, Ru-1 was used for triplet-triplet annihilation upconversion, showing a reasonable quantum yield of 0.7% with respect to the phosphorescence quantum yield of 1%. These findings pave the way for the rational design of phosphorescence transition metal complexes. Also, further approaches that may improve the performance of flavin-decorated Ru(ii) bipyridine complexes are proposed.

Pulp delignification with oxygen and copper(II)-polyimine complexes

Abstract Ten Cu(II)-polyimine complexes were tested as potential catalysts in oxygen delignification of softwood kraft pulps. The ligands were chosen from the terpyridine and the phenanthroline families, including several neocuproines. One diamine-phenanthrene (daphen) was also investigated. The main purpose was to examine whether the presence of methyl or phenyl substituents would direct the oxidation toward lignin. As a catalyst for comparison, unsubstituted 1,10-phenanthroline was selected, which is known to activate both delignification and carbohydrate degradation during oxygen bleaching of kraft pulp. The variation of ligands was aiming at the complex solubility and redox potential of the parameters. The experiments were performed on a mixture of mechanical pulp and fully bleached kraft pulps, a fully bleached pulp alone, and an industrial unbleached pulp. Concerning the oxygen activation in delignification of kraft pulp, 4,7-diphenyl-1,10-phenanthroline was as good as 1,10-phenanthroline, but appeared to be more selective, which resulted in a higher DPv of cellulose after treatment. This was interpreted by the structural similarities between the ligand and the kraft lignin and by a better stability of the intermediate complex with lignin. Two Cu(II)-phenanthroline derivatives complexes (4,7- and 5,6-dimethyl-1,10-phenanthroline) were also identified as effective oxygen activators for the removal of native lignin.

Observation of the room temperature phosphorescence of Bodipy in visible light-harvesting Ru(ii) polyimine complexes and application as triplet photosensitizers for triplet–triplet-annihilation upconversion and photocatalytic oxidation

Two Ru(II) polyimine complexes containing a boron-dipyrromethene (Bodipy) chromophore were prepared. The two complexes are different in the linker which connects the Bodipy part and the Ru(II) coordination centre. The Bodipy core and the Ru(II) centre are in π-conjugation in Ru-1, whereas in Ru-2 the Bodipy part is linked in a non-conjugated way to the Ru(II) centre. Ru(bpy)3[PF6]2 (Ru-3) was used as a reference complex. Both Ru-1 and Ru-2 show strong absorption in the visible region (e = 65 200 M−1 cm−1 at 528 nm for Ru-1 and e = 76 700 M−1 cm−1 at 499 nm for Ru-2). The fluorescence of the Bodipy ligands was almost completely quenched in Ru-1 and Ru-2. Ru-1 shows room temperature phosphorescence of the Bodipy chromophore, as well as the residual fluorescence of the Bodipy ligand. Ru-2 shows only the residual fluorescence of the Bodipy ligand. A long-lived Bodipy-localized triplet excited state was observed for both Ru-1 and Ru-2 upon visible light excitation (τT is up to 279.7 μs, the longest T1 state lifetime observed for the Bodipy moiety in the transition metal complex). Application of the complexes in triplet–triplet-annihilation upconversion and singlet oxygen (1O2)-mediated photo-oxidation proved that Ru-1 is more efficient (e.g. singlet oxygen quantum yield ΦΔ = 0.93) as a triplet photosensitizer than Ru-2 (ΦΔ = 0.64). Therefore, direct connection of the π-core of the Bodipy chromophore to the coordination centre, i.e. by establishing π-conjugation between the visible light-harvesting chromophore and the metal coordination centre is essential to enhance the effective visible light-harvesting of the Ru(II) complexes.

Ruthenium(II)–Polyimine–Coumarin Light‐Harvesting Molecular Arrays: Design Rationale and Application for Triplet–Triplet‐Annihilation‐Based Upconversion

Ru(II)-bis-pyridine complexes typically absorb below 450 nm in the UV spectrum and their molar extinction coefficients are only moderate (ε<16,000 M(-1) cm(-1)). Thus, Ru(II)-polyimine complexes that show intense visible-light absorptions are of great interest. However, no effective light-harvesting ruthenium(II)/organic chromophore arrays have been reported. Herein, we report the first visible-light-harvesting Ru(II)-coumarin arrays, which absorb at 475 nm (ε up to 63,300 M(-1) cm(-1), 4-fold higher than typical Ru(II)-polyimine complexes). The donor excited state in these arrays is efficiently converted into an acceptor excited state (i.e., efficient energy-transfer) without losses in the phosphorescence quantum yield of the acceptor. Based on steady-state and time-resolved spectroscopy and DFT calculations, we proposed a general rule for the design of Ru(II)-polypyridine-chromophore light-harvesting arrays, which states that the (1)IL energy level of the ligand must be close to the respective energy level of the metal-to-ligand charge-transfer (MLCT) states. Lower energy levels of (1)IL/(3)IL than the corresponding (1)MLCT/(3)MLCT states frustrate the cascade energy-transfer process and, as a result, the harvested light energy cannot be efficiently transferred to the acceptor. We have also demonstrated that the light-harvesting effect can be used to improve the upconversion quantum yield to 15.2 % (with 9,10-diphenylanthracene as a triplet-acceptor/annihilator), compared to the parent complex without the coumarin subunit, which showed an upconversion quantum yield of only 0.95 %.

Ruthenium(II) Polyimine Complexes with a Long‐Lived 3IL Excited State or a 3MLCT/3IL Equilibrium: Efficient Triplet Sensitizers for Low‐Power Upconversion

Ruthenium(II) Polyimine Complexes with a Long‐Lived ³IL Excited State or a ³MLCT/³IL Equilibrium: Efficient Triplet Sensitizers for Low‐Power Upconversion

Ruthenium(II) Polyimine Complexes with a Long‐Lived 3IL Excited State or a 3MLCT/3IL Equilibrium: Efficient Triplet Sensitizers for Low‐Power Upconversion

Hoch hinaus! Die langlebigen angeregten 3IL-Zustände von Ruthenium(II)-Polyimin-Komplexen erwiesen sich als effizientere Sensibilisatoren für die Upconversion unter Triplett-Triplett-Auslöschung (TTA) und Energietransfer (TTET) als 3MLCT-Zustände mit kürzeren Lebensdauern (siehe Bild). Die Upconversion geht mit Anti-Stokes-Verschiebungen bis 0.77 eV einher.

ChemInform Abstract: A Family of Luminescent Coordination Compounds. Iridium(III) Polyimine Complexes

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A family of luminescent coordination compounds: iridium(iii) polyimine complexes

30 years of IrIII coordination chemistry with polyimine-type ligands are summarized. Over the years, milder reaction conditions have been used for their synthesis, allowing the incorporation of various functional substituents. Complexes are described with bidentate and terdentate ligands, with both N- and C-donor sites. All complexes are luminescent, with predominantly charge-transfer or ligand-centred emissive states depending on the charge density donated from the ligands to the metal. IrIII excited state lifetimes range from nanoseconds to microseconds. A wide range of properties are obtained: [IrN6]3+ complexes are strong photooxidants while tris-cyclometallated [IrN3C3] complexes are strong photoreductants.

Redox chemistry of the polyimine complexes of manganese(II), -(III), and -(IV) in acetonitrile

Redox chemistry of the polyimine complexes of manganese(II), -(III), and -(IV) in acetonitrile