Optical and electrochemical properties of cyclometalated Pd(II) and Pt(II) complexes with a metal-metal chemical bond

Cyclometalated [M(C^N)(μ-(N-S))]₂ complexes ((M = Pd(II), Pt(II)), (C^N)^? are the deprotonated forms of 2-tolylpyridine and benzo[h]quinoline, and (N-S)^? are pyridine-2-thiolate and benzothiazole-2-thiolate ions) are studied by ¹H NMR, IR, electronic-absorption, and emission spectroscopy, as well as by voltammetry. It is shown that the formation of the metal-metal chemical bond and the σ _dz2 ^* orbital as a HOMO of complexes leads to the long-wavelength spin-allowed (410–512 nm) and spin-forbidden (595–673 nm) optical transitions σ _dz2 ^* ?π _(C^N) ^* in the absorption and phosphorescence spectra, as well as to the two-electron and successive one-electron oxidation with the formation of binuclear Pt(III) and Pd(III) complexes. The substitution of Pt(II) by Pd(II) is characterized by hypso- and bathochromic shifts of the spin-allowed and forbidden σ _dz2 ^* ?π _(C^N) ^* optical transitions in the absorption and phosphorescence spectra of complexes, by phosphorescence quenching of Pd(II) complexes in liquid solutions, and by an anodic shift of the oxidation potential of Pd(II) complexes compared with Pt(II) complexes.     

Spectroscopy and photophysics of binuclear ruthenium(II) complexes with nitrogen-containing heterocyclic bridging ligands

The absorption spectra at room temperature and the spectra, the quantum yields, and the decay times of the luminescence at 77 K of binuclear complexes [X(bpy)₂Ru(BL)Ru(bpy)₂Cl]²⁺ (bpy = 2,2′-bipyridyl; X = Cl, BL = pyrazine, 4,4′-bipyridyl, trans-1,2-bis(4-pyridyl)ethylene, and trans-1,2-bis(4-pyridyl)ethane and X = NO₂, BL = 4,4′-bipyridyl) in alcoholic (4: 1 EtOH-MeOH) solutions are studied. It is shown that the interaction between the metal centers (MCs) of the complexes affects the characteristics of the electronically excited states (EESs) of each of them and facilitates increasing the transition dipole moment Ru(d_π)→BL(π_*). The deactivation rate constants of the lowest electronically excited metal-to-ligand charge transfer (³MLCT) state of the complexes are determined. In an asymmetric binuclear complex, the energy transfer from MC(NO₂) to MC(Cl) is revealed, with the rate constant of this transfer being not smaller than 3.2 × 10¹⁰ s^?1.     

Effect of the nature of heterocyclic ligands on spectral and luminescent properties of Pt(II) and Pd(II) complexes

Optics and Spectroscopy - The spectral and luminescent properties of Pt(II) and Pd(II) complexes with heterocyclic imine ligands—1-phenylpyrazolate, 2-phenylpyridinate, and...     

Spectral and luminescent properties of new Pt(II) complexes with bis(salicylidene)ethylenediamine ligands

The results of synthesis of new Pt(II) complexes with N,N′-ethylene-bis(3-methoxysalicylideneiminate) and N,N′-2,3-dimethylbutane-2,3-diyl-bis(3-methoxysalicylideneiminate) ligands and their investigation by X-ray photoelectron spectroscopy and UV-visible absorption and emission spectroscopy are discussed. The degradation channels of excited electronic states of the complexes are determined.     

Spectroscopic and electrochemical properties of dichlorobenzoquinoline complexes of Au(III), Pt(II), and Pd(II)

The dichloride complexes of Au(III), Pt(II), and Pd(II) with 2,2′-biquinoline are obtained and characterized by ¹H NMR spectroscopy, electronic spectroscopy, and cyclic voltammetry. It is shown that the low efficiency of the metal-ligand (2,2′-biquinoline) interaction leads to almost the same positions of the intraligand bands in the absorption and fluorescence spectra of the complexes and to the closeness of their reduction potentials.     

Spectral and luminescent properties of mono- and binuclear cyclometalated complexes of Pd(II) and Pt(II) based on 4,6-diphenylpyrimidine with ethylenediamine and orthophenanthroline

The [M(N_^∧N)(Hdphpm)]ClO₄ and [(M(N_^∧N))₂(μ-dphpm)](ClO₄)₂ complexes (M = Pd(II), Pt(II); (N_^∧N) is ethylenediamine (En) and orthophenanthroline (Phen); Hdphpm^? and dphpm^2? are the mono- and bisdeprotonated forms of 4,6-diphenylpyrimidine) are obtained and characterized by ¹H NMR spectroscopy and electronic absorption and emission spectroscopy. The magnetic nonequivalence of protons of (N_^∧N) ligands is explained by a difference in the trans-effect of the carbanion and pyrimidine parts of the cyclometalated ligand. The long-wavelength absorption bands and the vibrationally structured luminescence bands of ethylenediamine complexes are attributed to optical transitions in the {M(Hdphpm)} and {M₂(μ-dphpm)} metal-complex fragments. The complexes with orthophenanthroline exhibit two low-energy optical transitions involving π* orbitals localized on the cyclometalated and chelating ligands; the difference in their energies depends on the metal and is much larger for Pt(II) than for Pd(II). It is found that the replacement of Pd(II) by Pt(II) in the [(M(phen))₂(μ-dphpm)]²⁺ complexes changes the direction of the photoexcitation energy degradation due to the energy transfer between the {M₂(μ-dphpm)} bridging fragment and peripheral phenanthroline ligands.     

Synthesis and spectral-luminescent properties of Pt(II) and Pd(II) complexes with 2,3,5,6-tetrakis(2-pyridyl)pyrazine

A method for synthesis of seven Pt(II) and Pd(II) complexes with 2,3,5,6-tetrakis(2-yridyl)pyrazine is developed. The spectral-luminescent properties of the complexes in the solid phase and solution are studied at 77 and 298 K. The types of excited electronic states responsible for the luminescence and nonradiative excitation energy relaxation in the complexes are determined.     

Mixed-ligand complexes of Pt(II) and Pd(II) with 2-phenylbenzothiazole

The mixed-ligand cyclometalated [M(Bt)(μ-Cl)]₂ and [(M(N∧N))(Bt)]⁺ complexes (M = Pd(II), Pt(II); Bt^? is the deprotonated form of 2-phenylbenzothiazole; and ( N∧N) is ethylenediamine (En) and orthophenanthroline (Phen)) are studied and described by ¹H NMR spectroscopy, electronic absorption and emission spectroscopy, and voltammetry. The one-electron reduction of complexes is attributed to the electron transfer to the π * orbitals of both diimine and cyclometalated ligands. The long-wavelength absorption bands and vibrationally structured luminescence bands are assigned to optical transitions that are localized mainly on the M(Bt) metal-complex fragment.     

Azobenzene Pd(II) complexes with N^N- and N^O-type ligands

Methods of synthesis of cyclometalated azobenzene palladium(II) complexes of [Pd(N^N)Azb]ClO₄ and [Pd(N^O)Azb]ClO₄ types (where Azb^– is the deprotonated form of azobenzene; N^N is 2NH₃, ethylenediamine, or 2,2′-bipyridine; and (N^O)^– is the deprotonated form of amino acid (glycine, α-alanine, β-alanine, tyrosine, or tryptophan)) are developed. The electronic absorption and the electrochemical properties of these complexes are studied.     

Optical and electrochemical characteristics of ethylenediamine complexes of Pt(II) and Ir(III) with metalated 2-phenyl- and 2-naphthylbenzothiazole

The cyclometalated complexes [Pt(С^N)En]PF₆ and [Ir(C^N)₂En]PF₆ ((C^N)^– are deprotonated forms of 2-phenylbenzothiazole or 2-naphthylbenzothiazole and En is ethylenediamine) are studied by ¹Н NMR, IR, electronic absorption, and emission spectroscopy, as well as by voltammetry. Metalation of heterocyclic ligands leads to the formation of five-membered {M(C^N)} cycles in the composition of squareplanar Pt(II) complexes and octahedral Ir(III) complexes of the cis-С,С structure. A bathochromic shift of the metal-to-cyclometalated ligand charge transfer bands and a decrease in the potential difference between the single-electron waves of metal-centered oxidation and ligand-centered reduction of complexes upon substitution of 2-phenylbenzothiazole by 2-naphthylbenzothiazole and of Pt(II) by Ir(II) are shown. The phosphorescence of complexes in the visible region is assigned to the radiative transition from the metal-modified intraligand electronic excited state.     

Synthesis, structure and luminescence properties of zinc (II) complexes with terpyridine derivatives as ligands

Five zinc (II) complexes (1-5) with 4′-phenyl-2,2′:6′,2″-terpyridine (ptpy) derivatives as ligands have been synthesized and fully characterized. The para-position of phenyl in ptpy is substituted by the group (R), i.e. tert-butyl (t-Bu), hexyloxy (OHex), carbazole-9-yl (Cz), naphthalen-1-yl-phenyl-amine-N-yl (NPA) and diphenyl amine-N-yl (DPA), with different electron-donating ability. With increasing donor ability of the R, the emission color of the complexes in film was modulated from violet (392 nm) to reddish orange (604 nm). The photoexcited luminescence exhibits significant solvatochromism because the emission of the complexes involves the intra-ligand charge transfer (ILCT) excited state. The electrochemical investigations show that the complexes with stronger electro-donating substituent have lower oxidation potential and then higher HOMO level. The electroluminescence (EL) properties of these zinc (II) complexes were studied with the device structure of ITO/PEDOT/Zn (II) complex: PBD:PMMA/BCP/AlQ/LiF/Al. Complexes 3, 4 and 5 exhibit EL wavelength at 552, 600 and 609 nm with maximum current efficiency of 5.28, 2.83 and 2.00 cd/A, respectively.     

Synthesis and spectroscopic and electrochemical properties of binuclear complexes of Au(III) bridged by 6,7-dimethyl-2,3-di(2-pyridyl) quinoxaline

A method of synthesis of new diimine complexes of Au(III) with a four-dentate bridging ligand 6,7-dimethyl-2,3-di(2-pyridyl) quinoxaline (Ddpq), [Au₂(μ-Ddpq)Cl₄]Cl₂ and [(AuN^N)₂(μ-Ddpq)](NO₃)₆, where N^N is ethylenediamine, 2,2′-bipyridyl, or 1,10-phenanthroline, is described and the composition, structure, and properties of these complexes are studied. The coordination-induced chemical shifts in the ¹H NMR spectra are determined, as well as the spectral-luminescent and electrochemical parameters of the complexes. The nature of the energetically lowest spin-allowed ¹(π-d*)-and spin-forbidden ³(π-π*) states is established.     

Synthesis, thermal and optical properties of metal(II) complexes with a novel ligand derived from pyrazolone-5

Three novel metal(II) complexes, CoL₂, NiL₂ and CuL₂ (L = (Z)-4-(2-(1,3-dimethyl-5-oxo-1H-pyrazol-4(5H)-ylidene)hydrazinyl)-1,5-dimethyl-2-phenyl-1,2-dihydropyrazol-3-one were synthesized. Their structures were postulated based on elemental analyses, ¹H NMR, ESI-MS, FT-IR spectra and UV-vis spectra. The effect of different central metal(II) ions on absorption bands of the metal(II) complexes in CHCl₃ solutions was researched. The result indicates that the bathochromic shift is CuL₂ > NiL₂ > CoL₂. The absorption properties of thin films and thermal stability of these complexes are also discussed. In addition, the optical constants (complex refractive index N=n+ik) and thickness of the complex thin films on polished single-crystal silicon substrates were measured by spectroscopic ellipsometry. Results indicate that the metal(II) complexes would be a promising recording medium candidate for blu-ray recordable optical storage system due to good absorption at 405 nm, high thermal stability and sharp thermal decomposition, and a high n values of 1.35–1.45 and a low k values of 0.33–0.39.     

Spectroscopy and photophysics of chloro-bis-bipyridyl complexes of ruthenium(II) with pyridine ligands

The absorption, luminescence, and luminescence excitation spectra of ruthenium(II) complexes cis-[Ru(bpy)₂(L)Cl]⁺[bpy=2,2′-bipyridyl; L=NH₃, pyrazine, pyridine, 4-aminopyridine, 4-picoline, isonicotinamide, 4-cyanopyridine, 4,4′-bipyridyl, or trans-1,2-bis(4-pyridyl)ethylene] in alcoholic (4: 1 EtOH-MeOH) solutions are studied. At 77 K, the quantum yields and decay times of the luminescence of the complexes are measured and the deactivation rate constants of the lowest electronically excited metal-to-ligand charge transfer state (³MLCT) are determined. The linear correlation between the energy of the lowest state ³MLCT d _π(Ru)>π*(bpy) of the cis-[Ru(bpy)₂(L)Cl]⁺ complexes and the parameter pK_a of the free 4-substituted pyridines and pyrazine used as ligands is established.     

Spectral and luminescent investigations of ammonia cyclometalated Pt(II) complexes

A method of synthesis of ammonia cyclometalated Pt(II) complexes [Pt(NH₃)₂C∧N]ClO₄, where C∧N is 2-phenylpyridinate or 2-phenylbenzothiazole ion, is developed. The electronic absorption and emission properties of the complexes are studied. It is found that the state responsible for intense long-lived luminescence is the excited charge-transfer state of the ³(d-π*) type, the π* orbital being localized at the corresponding cyclometalating ligand. Formation of platinum blue is observed in air-saturated aqueous solutions of ammonia cyclometalated complexes.     

XAFS investigations of copper(II) complexes with tetradentate Schiff base ligands

X‐ray absorption fine structure spectra have been investigated at the K‐edge of copper in copper(II) salen/salophen complexes: [Cu(salen)] (1), [Cu(salen)CuCl₂].H₂O (2), [Cu(salophen)] (3) and [Cu(salophen) CuCl₂].H₂O (4), where salen^2? = N,N′‐ethylenebis (salicylidenaminato); salophen^2? = o‐phenylenediaminebis(salicylidenaminato). Complexes 1 and 3 are supposed to have one type of copper centers (called (Cu1)) and complexes 2 and 4 two types of copper centers (called (Cu1) and (Cu2)) having different coordination environments and geometries. A theoretical model has been generated using the available crystallographic data of complex 1 and it has been used for analysis of the extended X‐ray absorption fine structure (EXAFS) data of the four complexes to obtain the structural parameters for (Cu1) center. For this center, the obtained Cu–Cu distance (3.2 Å) verifies the binuclear nature of all the complexes. For determining the coordination geometry around (Cu2) center in 2 and 4, a theoretical model has been generated using the crystal structure of a Cu(II) complex, [Cu(C₁₆H₁₂N₂O₂Cl₂)]. This theoretical model has been fitted to the EXAFS data of 2 and 4 to obtain the structural parameters for (Cu2) center. The present analysis shows that (Cu1) center has square pyramidal geometry involving 2N and 3O donor atoms, whereas (Cu2) center has distorted tetrahedral geometry with 2O and 2Cl donor atoms. The values of the chemical shifts and presence of typical Cu(II) X‐ray absorption near‐edge spectroscopy features suggest that copper is in the +2 oxidation state in all these complexes. The intensity of ls → 3d pre‐edge feature has been used to investigate the geometry and binuclear nature of the complexes. Copyright © 2012 John Wiley & Sons, Ltd.     

Specific features of spectra of cyclometalated Pt(II) and Pd(II) complexes in polyvinyl alcohol

The absorption spectra and luminescent properties of ethylenediamine complexes of Pt(II) and Pd(II) with cyclometalating ligands (2-phenylpyridinate and 2-2’-thienyl)pyridinate) in polyvinyl alcohol are studied. It is ascertained that, upon an increase in temperature, the nonradiative degradation of energy in palladium complexes occurs according to the mechanism of strong vibronic coupling, whereas platinum complexes show weak vibronic coupling.     

Spectral properties of 2-phenylpyridinate complexes of Au(III) with diimine ligands

The synthesis, identification, and optical spectra of 2-phenylpyridinate complexes of Au(III) with diimine ligands (2,2′-bipyridyl and 6,7-dimethyl-2,3-di(2-pyridyl) quinoxaline) are described. A difference in the nature of the energetically lowest electronically excited states responsible for the luminescence is established.     

全氟羧酸钕2,2’-联吡啶配合物的合成及其光学特性

合成了一系列全氟羧酸钕2,2’-联吡啶配合物:Nd(CF3COO)3.Dipy,Nd(C2F5COO)3.Dipy和Nd(C3F7COO)3.Dipy,并通过红外光谱、元素分析、热分析、紫外可见近红外吸收光谱和荧光光谱对其进行了表征。配合物的分解温度都高于260℃,最大失重温度超过340℃,说明它们具有良好的热稳定性。全氟羧酸的碳链长度和钕离子配位结构的差异,引起配合物的吸收跃迁强度的变化。根据紫外可见近红外吸收图谱,计算获得了Judd-Ofelt参数和受激辐射跃迁特性。配合物的受激发射面积分别为:3.63×10-20,2.36×10-20和1.49×10-20 cm2,可以和文献报道的无机材料媲美,它们将是非常有潜力的液体激光介质。     

Photophysical properties of polyacrylic acid with Ru (II) polypyridyl complexes

The nature of the conformational transition of the polymers with Ru (II) polypyridyl complexes covalently attached to poly(acrylic acid) (PAA) and poly(metacrylic acid) (PMAA) has been in studied in aqueous solutions at different pH values. The [PAA-Ru₄]⁸⁺ and [PMAA-Ru₄]⁸⁺ polymers has been investigated by means of the luminescence properties of the Ru(bpy)₃²⁺ moiety by steady-state and time-resolved luminescence spectroscopy. The pH markedly affects the luminescence spectra and quantum yields of both ruthenium-polyacid complexes in aqueous solution. Another feature investigated in this work was a comparative study of their luminescence quenching by acridinic dyes in solution. The analysis of the k_q values obtained indicates that the bimolecular quenching by acridinium and 9-aminoacridinium is more effective in the [PAA-Ru₄]⁸⁺ complex (6.4×10⁹ and 1.4×10⁹ M⁻¹ s⁻¹, respectively) compared to the [PMAA-Ru₄]⁸⁺ (2.6×10⁹ and 1.0×10⁹ M⁻¹ s⁻¹). Also, a similar behavior was evidenced for the Ru solely adsorbed onto pure PAA (9.0×10⁹ and 3.4×10⁹ M⁻¹ s⁻¹) and PMAA (1.8×10⁹ and 1.7×10⁹ M⁻¹ s⁻¹) in aqueous solution. The effect of enhancement of quenching rate constant in [PAA-Ru₄]⁸⁺ system could be ascribed to the higher density of Ru per polymer chain. The average number per chain is similar in both systems, but the molecular weight is lower for [PAA-Ru₄]⁸⁺. Furthermore, the larger hydrophilic environment provided by the PAA exposes the Ru probe to the outer surface of the polymer in solution.