Photophysics of mixed ligand complexes of ruthenium(II) with 2,2′-bipyridyl and phosphines

Luminescence of mixed ligand complexes of ruthenium(II) of the types cis-Ru(bpy)₂X₂(I), cis-[Ru(bpy)₂(PPh₃)X](BF₄)(II), and cis-Ru(bpy)(PP)X₂(III) (X = CN, NO₂, PPh₃ is triphenyl phosphine; PP is 1,2-bis(diphenylphospino)ethane (dppe) and cis-,2-bis(diphenylphosphino)ethylene (dppene)) is studied in alcohol matrices (EtOH/MeOH, 4:1) frozen at 77 K. A sequence of complexes I–III exhibits an additive (in the number of phosphorous atoms) blue shift of the absorption and luminescence bands and an increase in the quantum yield of luminescence and in the excited-state lifetime. The rate constant of nonradiative deactivation of the excited state decreases more than by an order of magnitude in the sequence I–III of cyano complexes and only by three times in a sequence of nitro complexes. This is assumed to be caused by a specific (in the hydrogen bond type) interaction of nitro groups of complexes with a proton solvent.     

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.     

Study on spin configuration in photoresponsive iron mixed-valence complexes by Mössbauer spectroscopy

We have investigated magnetic properties in a series of photoresponsive dithiooxalato (dto)-bridged iron mixed-valence complexes, (SP-R)[Fe^IIFe^III(dto)₃] (SP-R = R-substituted pyridospiropyran cation; R = Me, Et, and Pr; abbreviated as 1 ^Me, 1 ^Et, and 1 ^Pr, respectively). As for our previous reports, 1 ^Me and 1 ^Et show two-step succeeding ferromagnetic transitions at T _C?=?25 & 8 K and 22 & 5 K, respectively. However, 1 ^Et has no hysteresis in the magnetic susceptibility, while 1 ^Me undergoes the charge transfer phase transition with thermal hysteresis around 75 K. To elucidate the two-step transitions of them, we measured ⁵⁷Fe Mössbauer spectra of 1 ^Et. The spectra of Fe^II (S?=?2) and Fe^III (S?=?1/2) in the HTP were observed in the magnetically ordered state as well as the paramagnetic state, and revealed that only HTP exists in a temperature range up to 5 K. The result is consistent with that of 1 ^Pr, where one ferromagnetic phase transition occurs at T _C?=?10 K. ⁵⁷Fe Mössbauer spectroscopy is useful to clarify the origin of the succeeding magnetic transition for these systems.     

Synthesis, X-ray structure and magnetic properties of the quinone cobalt complexes [Co(3,5-DTBSQ)(bpy)2]x2 (x=BF4, ClO4)

Double oxidation of [Co^III(3,5-DTBCat)(3,5-DTBSQ)(bpy)] (1,ls-Co(III)) by AgBF₄ and of [Co^II(3,5-DTBSQ)₂(bpy)] (1,hs-Co(II)) by a mixture of HClO₄/H₂O₂ yielded [Co^III(3,5-DTBSQ) (bpy)₂]X₂, where X⁻=BF₄⁻ (4) and ClO₄⁻ (5), respectively. The mechanism for the double-oxidation process that leads to a loss of one of the quinone ligands and in some cases to a redistribution of the electronic charge is discussed here.     

Synthesis,Crystal Structures and Photo- and Electro-Luminescence of Copper(I) Complexes Containing Electron-Transporting Diaryl-1,3,4-Oxadiazole

Two mononuclear Cu(I) complexes based on 2-(2-pyridyl)benzimidazolyl derivative ligand containing electron-transporting 1,3,4-oxadiazole group (L), [Cu(L)(PPh₃)₂](BF₄) and [Cu(L)(DPEphos)](BF₄), where L?=?1-(4-(5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl)benzyl)-2-(pyridin-2-yl)benzimidazole and DPEphos?=?bis[2-(diphenylphosphino)phenyl]ether, have been successfully synthesized and characterized. The X-ray crystal structure analyses of the ligand L and the complex [Cu(L)(PPh₃)₂](BF₄) were described. The photophysical properties of the complexes were examined by using UV–vis, photoluminescence spectroscopic analysis. The doped light-emitting devices using the Cu(I) complexes as dopants were fabricated. With no electron transporting layers employed in the devices, yellow electroluminescence from Cu(I) complexes were observed. The devices based on the complex [Cu(L)(DPEphos)](BF₄) possess better performance as compared with the devices fabricated by the complex [Cu(L)(PPh₃)₂](BF₄). The devices with the structure of ITO/MoO₃ (2 nm)/NPB (40 nm)/CBP:[Cu(L)(DPEphos)](BF₄) (8 wt%, 30 nm)/BCP (30 nm)/LiF (1 nm)/Al (150 nm) exhibit a maximum efficiency of 3.04 cd/A and a maximum brightness of 4,758 cd/m².     

Synthesis and EPR spectroscopy of nitroxyl derivatives of the C60 fullerene

The 2,2,5,5-tetramethyl-3-imidazoline-3-oxy-1-oxyl-4-(azidophenyl) derivatives of the C₆₀ fullerene with one (compound I), two (compound II), and three (compound III) nitroxyl groups are synthesized and studied by EPR spectroscopy. It is demonstrated that successive addition of nitroxyl radicals to C₆₀ leads to a decrease in the rotational mobility of molecules. Chromatographically inseparable isomers are found for compounds II and III.     

Orange Fluorescent Ru(III) Complexes Based on 4′-Aryl Substituted 2,2′:6′,2″-Terpyridine for OLEDs Application

A series of ruthenium (III) complexes of the formulae [Ru(4-Mephtpy)₂]Cl₃(1) [Ru(L ₁ )], [Ru(3,4,5-tmphtpy)₂]Cl₃(2) [Ru(L ₂ )], and [Ru(4-thptpy)₂]Cl₃(3) [Ru(L ₃ )], (where L?=?terpy?=?2.2′:6′2″ terpyridine ligands) are synthesized. The complexes were characterized by elemental analyses, spectroscopic and electrochemical data. The density functional theory (DFT) outlines the geometric optimisation and electronic charge transition of these complexes. Photophysical studies describe that the luminescence of Ru(III) complexes is due to electronic transition between the energy levels of singly unoccupied molecular orbitals (SUMO) and singly occupied molecular orbitals (SOMO). It also exhibits the potential charge transfer to π–π* and n–π* states due to MLCT and ILCT processes of the complexes. The observed bands centered at 591 and 620 nm demonstrate that these emissions originated from the transition of SUMO to SOMO energy levels, that is, from the radiative decay from the doublet exciton. Due to the heavy metal effect of Ru(III) ions the photophysical behaviour depends on the MLCT process. In conclusion, that the all three Ru(L ₁ -L ₃ ) complexes are fallen orange emission.     

Theoretical studies of ground and excited states in a series of Zn(II) complexes,derived from thiourea and thiosemicarbazide

Theoretical studies for a series of mono- and binuclear zinc (II) complexes Zn(CH₃COO)₂(H₂L)₂ [H₂L = N-2-propenyl-N ^′-2-pyridinylthiourea] (A), Zn₂(CH₃COO)₂(H₃L-a)₂ [H₃L-a = 2-[(2-hydroxy phenyl)methylene]hydrazine-N-phenylcarbothioamide] (B), and Zn(H₃L-b)₂ [H₃L-b = 2-[(2-hydroxy phenyl)methylene]hydrazine-N-(2-propenyl)carbothioamide] (C) have been performed on their structures and excited-state absorption spectra. The singlet ground-state geometries are fully optimised at three DFT levels, i.e., B3LYP, B3PW91, and M06. Different geometries, i.e., strongly distorted tetrahedral coordination environment in complex A, distorted square-pyramidal environment in complex B, and irregular octahedral mode in complex C are identified. Consequently, the spectroscopic properties are calculated by means of time-dependent density functional theory (TDDFT) with the Polarisable Continuum Model (PCM) based on the optimised gas-phase geometries. Three absorption peaks are identified for every complex, which are in good agreement with the experimental ones. For complex A, all three absorption peaks centered at 280.33 nm, 268.09 nm, and 250.87 nm, respectively, are ascribed to the (p,π) → π* transition with a mixed intraligand charge-transfer (ILCT)/ligand-ligand charge-transfer (LLCT) character. The composition of frontier orbitals involved in major absorption bands for the three complexes shows similarities, which results in the almost homologous transition attributions and characteristics. A remarkable bathochromic shift in the lowest-lying absorption band is observed for complexes B and C as compared with complex A, which is attributed to the decreased H (HOMO)-L (LUMO) energy gap (ΔE |HOMO-LUMO|) by the formation of conjugate metallocycles in complexes B and C.     

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.     

Decay of helicity in homogeneous turbulence

The self-similar relaxation of helicity in homogeneous turbulence has been considered taking into account integral invariants ∫ ₀ ^∞ r ^m 〈u(x)ω(x + r)〉 dr = I _m ^h (where ω = curlu and r = |r|). It has been shown that integral invariants with m = 3 for both helicity and energy are possible in addition to helical analogs of Loitsyanskii (m = 4) and Birkhoff-Saffman (m = 2) invariants associated with the conservation laws of momentum and angular momentum, respectively. Helicity always relaxes more rapidly than the energy. Its decay exponent is in the interval from ?3/2 to ?5/2 versus the interval from ?6/5 to ?10/7 for the energy.     

High-spin metal-cyanide clusters: species incorporating [Mn(salen)] complexes as a source of anisotropy

The use of N,N′-ethylenebis(salycylideneiminato) (salen) complexes of Mn^III in assembling high-spin metal-cyanide coordination clusters with significant magnetic anisotropy is demonstrated. The reaction of [Mn(salen)(H₂O)₂]⁺with [Cr(CN)₆]³⁻ in aqueous solution generates {Cr[CNMn(salen)(H₂O)]₆}[Cr(CN)₆]·6H₂O (1), a previously reported compound featuring a heptanuclear cluster with a distorted octahedral geometry. A fit to the variable-temperature magnetic susceptibility data for 1 revealed the presence of weak antiferromagnetic coupling of within the cluster, giving rise to an S=21/2 ground state. In addition, variable-field magnetization data collected at low temperatures revealed the presence of magnetic anisotropy in the ground state, with the best fit yielding zero-field splitting parameters of D=+0.19 cm⁻¹ and A reaction intended to produce a direct analogue of 1 by employing [Fe(CN)₆]³⁻ in place of [Cr(CN)₆]³⁻ instead gave an unusually complex compound of formula {Fe(CN)₄[CNMn(salen)(MeOH)]₂}{[Mn(salen)(H₂O)]₂}[Mn(salen)(H₂O)(MeOH)]₂[Fe(CN)₆]·4H₂O (2). The crystal structure and magnetic properties of this compound are reported.     

A Pulsed EPR and DFT Investigation of the Stabilization of Coordinated Phenoxyl Radicals in a Series of Cobalt Schiff-Base Complexes

We recently demonstrated how the aerobic addition of acetic acid to N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diamino Co^II, [Co(1)], leads to the formation of an unusual coordinated Co^III-phenoxyl radical. In this work, some of the structural aspects associated with the Schiff-base-derived ligand (1) that are crucial for the acid-mediated formation of the phenoxyl radical are investigated. For comparison with [Co(1)], we therefore studied the influence of acetic acid on two complexes: (1) the N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-ethane-diamino Co^II complex, [Co(2)], that lacks the cyclohexyl group of [Co(1)], and (2) the N′-disalicylidene-ethylenediamine Co^II salen complex, [Co(3)], that lacks both the tertiary butyl groups and the cyclohexyl groups. It is shown that the cyclohexyl group of [Co(1)] is not involved in the formation or stabilization of the phenoxyl radical, whereas the tertiary butyl groups of [Co(1)] play a crucial role. In addition, the characteristics of the phenoxyl radical, formed after aerobic addition of acetic acid to [Co(2)], are analyzed in detail by pulsed electron paramagnetic resonance, in combination with isotopic labeling. The experimental data are compared to density functional theory computations and to previous data on the acid-mediated phenoxyl radical of [Co(1)].     

Optical oxygen sensing materials based on trinuclear starburst ruthenium(II) complexes assembled in mesoporous silica

The preparation and oxygen sensing properties of optical materials based on two trinuclear starburst ruthenium(II) complexes: [Ru₃(bpy)₆(TMMB)]⁶⁺ (1) and [Ru₃(phen)₆(TMMB)]⁶⁺ (2) (bpy=2,2′-bpyridine, phen=1,10-phenathroline, TMMB=1,3,5-tris[2-(2′-pyridyl)benzimidazoyl]methylbenzene) assembled in two mesoporous silicate (MS) are described in this paper. The luminescence of Ru complexes/silicate assemble materials can be quenched by molecular oxygen with good sensitivity (I₀/I₁>5 for 2/MS and I₀/I₁>3 for 1/MS), indicating that trinuclear starburst Ru(II) complexes/MS systems are sensitive to oxygen molecules.     

A Phenylbenzothiazole Derived Fluorescent Sensor for Zn(II) Recognition in Aqueous Solution Through “Turn-On” Excited-State Intramolecular Proton Transfer Emission

A highly selective and sensitive fluorescent Zn²⁺ sensor N-(2-(benzo[d]thiazol-2-yl)phenyl)-2-((pyridin-2-ylmethyl)amino)acetamide (1) that derived from 2-(2′-aminophenyl)benzothiazole has been developed. In aqueous solution (HEPES/CH₃CN=4/6, v/v, HEPES 20 mM, pH?=?7.4), sensor 1 displays highly selective recognition to Zn²⁺ over other metal ions with a distinct longer-wavelength emission enhancement. Sensor 1 binds Zn²⁺ through its amide form with a 1:1 binding stoichiometry, which switched on the excited-state intramolecular proton transfer (ESIPT). Graphical Abstract

A simple 2-(2′-aminophenyl)benzothiazole-based fluorescent “off-on” sensor for Zn²⁺ recognition in HEPES/CH₃CN(4/6, v/v, HEPES 20 mM, pH?=?7.4) solution through switching on ESIPT has been developed.     

Trovacenyl-based organometallic triradicals: Spin frustration, competing interactions and redox splitting

Two new triradicals based on trovacene [η⁷-tropylium)vanadium(η⁵-cyclopentadienyl)], 1,3,5-tri([5]trovacenyl) benzene4 and 1,3,5-tri([5]trovacenyl)-6-methoxybenzene5 were prepared and their magnetic properties were studied by continuous-wave X-band electron paramagnetic resonance (EPR) spectroscopy and by temperature-dependent magnetic susceptometry. The EPR spectra of4 and5 in liquid toluene solution demonstrate that the three unpaired electrons localized on the vanadium atoms interact with each other in both complexes. The data from magnetic susceptometry revealed that the electron spins in both triradicals are antiferromagnetically coupled despite themeta-phenylene bridge. The exchange coupling constants are equal in the C₃-symmetrical triradical4 (J=J′=?0.68 cm^?1), which leads to a twofold degenerate spin ground state (spin frustration). The symmetry lowering by methoxy substitution of the benzene spacer in5 results in the effect of c ompeting interactions (J=?1.83 cm^?1 andJ′=?2.38 cm^?1). In addition to magnetocommunication, the effect of ring substitution on electrocommunication is also discernable. It manifests itself indisparate redox splittings δE _1/2 (0/?, ?/2?) and δE _1/2 (?/2?, 2?/3?) for5, while these parameters are equal for the C₃-symmetrical trinuclear complex4.     

Targeted Singlet Oxygen Generation Using Different DNA-Interacting Perylene Diimide Type Photosensitizers

Singlet oxygen quantum yields (Φ _Δ) of different perylene diimides (PDIs) containing phenyl (PDI-Ph), pyrene (PDI-Pyr), and indole (PDI-In) units in bay positions of the ring were determined using 1,3-diphenylisobenzofuran (DPBF) method in toluene/methanol (99:1) system. Pyrene-substituted PDI were the most efficient singlet oxygen generator among the investigated photosensitizers with a quantum yield of Φ _Δ?=?0.93 in toluene/methanol. Additionally, their binding affinities to G-quadruplex DNA structure were investigated by steady-state measurements. There were marked red shifts of absorbance bands for PDI-Pyr/DNA strand complexes with respect to the absorption maxima of DNA-free solution of PDI-Pyr in phosphate buffer at pH 6.     

Neutral and anionic duality of 1,2,4-triazole α-amino acid scaffold in 1D coordination polymers

A tiny supramolecular synthon, 4H-1,2,4-triazol-4-yl acetic acid (HGlytrz) which is bifunctional by design having an electronic asymmetry and conformational flexibility has been introduced to synthesize iron(II) complexes. Having 1,2,4-triazole or carboxylic extremities on the same framework HGlytrz could display dual functionality by acting as a neutral as well as anionic ligand based on the possibility of deprotonation of carboxylic group. Four new iron(II) HGlytrz complexes with ClO $_{4}^{-}$ (1), NO $_{3}^{-}$ (2), BF $_{4}^{-}$ (3) and CF₃SO $_{3}^{-}$ (4) anions were prepared. Formulation of their composition which is complicated due to ligand deprotonation is discussed. Unlike its ester protected counterpart ethyl-4H-1,2,4-triazol-4-yl-acetate (αGlytrz) which show hysteretic room temperature spin crossover, 1–4 remain in the high-spin state as revealed by ⁵⁷M?ssbauer spectroscopy. Prospects of such 1D coordination polymers with dangling unbounded carboxylic entities in the realm of self-assembled monolayer (SAM) are discussed.     

Sensitized Near-Infrared Luminescence From NdIII, YbIII and ErIII Complexes by Energy-Transfer From Ruthenium 1,3-Bis([1,10]Phenanthroline-[5,6-d]-Imidazol-2 -yl)Benzene

The luminescent ruthenium 1,3 -bis([1,10]phenanthroline-[5,6 -d]- imidazol-2 -yl)benzene (bpibH₂) complex, a potentially useful bridging ligand with a vacant diimine site, has been used as ‘metallo ligand’ to make heterodinuclear d–f complexes by attachment of a {Ln(dik)₃} fragment (dik?=?1,3-diketonate) at the vacant site. When Ln?=?Nd, Yb, or Er the lanthanide centre has low-energy f–f excited states capable of accepting energy from the ³MLCT excited state of the Ru(II) centre, there is quenching in the ³MLCT luminescence of the Ru(II) centre, that affords sensitized lanthanide(III) based luminescence in the near-IR region. Nd(III) was found to be the most effective at quenching the ³MLCT luminescence of the ruthenium component because of the high density of f–f excited states of the appropriate energy which make it as effective energy-acceptor compared to Er and Yb complexes.     

NMR Studies of the Reaction Path of the o-H2/p-H2 Spin Conversion Catalyzed by Vaska’s Complex in the Solid State

We have studied the o/p spin conversion of dihydrogen in contact with frozen solutions of Vaska’s complex Ir(CO)Cl(PPh₃)₂ (1) in C₆D₆ and with polycrystalline 1 at 77 K. The main purpose of this study was to elucidate the mechanism of this type of reactions found accidentally previously (Eisenschmid et al JACS 109:8089–8091, 1987 and Eisenberg ACS 24:110–116, 1991). The formation of p-H₂ was followed after thawing of the samples by ¹H nuclear magnetic resonance (NMR) spectroscopy at 298 K, where the oxidative addition of dihydrogen to 1 occurs leading to Vaska’s dihydride Ir(CO)ClH₂(PPh₃)₂ (2) which is known to exhibit para-hydrogen-induced polarization (PHIP). The PHIP signal was shown to be proportional to the concentration of p-H₂ as elucidated from the decrease of the signal of dissolved o-H₂. The reaction was found to be faster for the frozen solution as compared to the polycrystalline powder. Optical microscopy showed that small particles of 1 are separated from the solution during the freezing process, exhibiting a larger surface area as compared to the polycrystalline powder. When a mixture of H₂ and D₂ was exposed to the frozen solutions or to the polycrystalline powder, the formation of HD was observed by ¹H NMR. This finding indicates the presence of a chemical spin conversion involving two dihydrogen molecules. Additional ¹H NMR experiments of dihydrogen in frozen C₆D₆ at 110 K indicated the formation of larger pores containing gaseous H₂ as well as dihydrogen sites in interstitial sites between benzene molecules. Moreover, in the presence of 1, a signal at ?4.5 ppm was observed which was attributed to a dihydrogen in close contact with Ir.     

Perpendicularev mass fromW decay

We point out properties of the “perpendicularev mass”, defined in terms of transverse momentap _t byM _T ² (ev)=2|p _eT | |p _vT |?2p _eT ·p _vT , that make it particularly well suited toW mass and width determinations. We give an analytic expression for its distribution inW production and subsequentW→ev decay a \(\bar pp\) colliders, accurate to order 〈p _WT ² /M _W ² 〉≈1%. A maximum likelihood fit of this formula to the five UA1 events givesM _W=80.3 _?3 ⁺⁶ GeV.