Preparation, spectroscopic characterization, and photochemical and electrochemical properties of some bis(2,2'-bipyridyl)ruthenium(II) and tetracarbonyltungsten(0) complexes of 6-p-tolyl-2,2'-bipyridyl and of 6-p-styryl-2,2'-bipyridyl and its copolymers

Platinum(IV) Complexes with Tridentate, NNC-Coordinating Ligands: Synthesis, Structures, and Luminescence

Platinum(II) complexes of NNC-cyclometalating ligands based on 6-phenyl-2,2'-bipyridine (HL¹) have been widely investigated for their luminescence properties. We describe how PtL¹Cl and five analogues with differently substituted aryl rings, PtL^2-6Cl, can be oxidized with chlorine and/or iodobenzene dichloride to generate Pt(IV) compounds of the form Pt(NNC-Lⁿ)Cl₃ (n = 1-6). The molecular structures of several of them have been determined by X-ray diffraction. These PtLⁿCl₃ compounds react with 2-arylpyridines to give a new class of Pt(IV) complex of the form [Pt(NNC)(NC)Cl]⁺. Elevated temperatures are required, and the reaction is accompanied by competitive reduction processes and generation of side-products; however, four examples of such complexes have been isolated and their molecular structures determined. Reaction of PtL¹Cl₃ with HL¹ similarly generates [Pt(NNC-L¹)₂]²⁺, which we believe to be the first example of a bis-tridentate Pt(IV) complex. The lowest-energy bands in the UV-vis absorption spectra of all the PtLⁿCl₃ compounds are displaced to higher energy relative to the Pt(II) precursors, but they red-shift with the electron richness of the aryl ring, consistent with predominantly ¹[π_Ar → π*_NN] character to the pertinent excited state. A similar trend is observed for the [Pt(NNC)(NC)Cl]⁺ complexes. They display phosphorescence in solution at room temperature, centered around 500 nm for [PtL¹(ppy)Cl]⁺ and [Pt(L¹)₂]²⁺, and 550 nm for methoxy-substituted derivatives. The lifetimes are in the microsecond range, rising to hundreds of microseconds at 77 K, consistent with triplet excited states of primarily ³[π_Ar → π*_NN] character with relatively little participation of the metal.

Polymer matrix: A good substrate material for oxygen probes used in pressure sensitive paints

Over the past few years, surface pressure measurement has fundamental importance in many areas, particularly, aerodynamic research. Conventional methods involve pressure taps, but due to the nature of these pressure taps, only pressure information of isolated points on model surface is available, which limit their applications in aerodynamics studies. Recently the newly developed approach, pressure sensitive paint (PSP) has revolutionized such pressure measurements and various PSP materials have been developed for aerodynamics research. Hence, the main focus of this review is to study the interactions of polymers with different oxygen probes and polymeric role as supporting material in the maturation of PSP. In this review, the selected PSP materials are categorically elucidated in terms of their advantages and limitations to give a fair insight about their applicability. Further, we have summarized and articulated such particular optical oxygen sensing materials either that have been used as PSP or have potential to be used as PSP materials.

Synthesis, Characterization, and Acid - Base Properties of Ruthenium(II) Complexes Containing N-ethyl-4-([1,10]-phenanthroline[5,6 - f]imidazol-2-yl)carbazole

Three new ruthenium(ii) polypyridyl complexes, [Ru(phen)2(Hecip)]2+ (1), [Ru(phen)(Hecip)2]2+ (2), and [Ru(Hecip)3]2+ (3) complexes (phen = 1,10-phenanthroline, Hecip = N-ethyl-4-([1,10]-phenanthroline[5,6–f]imidazol-2-yl)carbazole) were synthesized and characterized by ES-MS, 1H NMR spectroscopy, elemental analysis, and cyclic voltammetry. The emission spectra of complexes were measured both at room temperature and at 77 K in a 4/1 (v/v) EtOH/MeOH matrix. All three complexes display luminescence properties which are close to that featured by the parent [Ru(phen)3]2+ species. The pH effects on the UV-vis and emission spectra of RuII complexes were also studied, and complexes 1, 2, and 3 were found to act as ‘on–off’ luminescent pH switches with maximum on–off ratios of 17, 230, and 90, respectively.

New members of the [Ru(diimine)(CN)4]2−family: structural, electrochemical and photophysical properties

A series of complexes of the type K(2)[Ru(NN)(CN)(4)] has been prepared, in which NN is a diimine ligand, and were investigated for both their structural and photophysical properties. The ligands used (and the abbreviations for the resulting complexes) are 3-(2-pyridyl)pyrazole (Ru-pypz), 2,2'-bipyrimidine (Ru-bpym), 5,5'-dimethyl-2,2'-bipyridine (Ru-dmb), 1-ethyl-2-(2-pyridyl)benzimidazole (Ru-pbe), bidentate 2,2':6',2'''-terpyridine (Ru-tpy). The known complexes with = 2,2'-bipyridine (Ru-bpy) and 1,10-phenathroline (Ru-phen) were also included in this work. A series of crystallographic studies showed that the [Ru(NN)(CN)(4)](2-) complex anions form a range of elaborate coordination networks when crystallised with either K(+) or Ln(3+) cations. The K(+) salts are characterised by a combination of near-linear Ru-CN-K bridges, with the cyanides coordinating to K(+) in the usual 'end-on' mode, and unusual side-on pi-type coordination of cyanide ligands to K(+) ions. With Ln(3+) cations in contrast only Ru-CN-Ln near-linear bridges occurred, affording 1-dimensional helical or diamondoid chains, and 2-dimensional sheets constituted from linked metallamacrocyclic rings. All of the K(2)[Ru(CN)(4)] complexes show a reversible Ru(II)/Ru(III) couple (ca.+0.9 V vs. Ag/AgCl in water), the exception being Ru-tpy whose oxidation is completely irreversible. Luminescence studies in water showed the presence of (3)MLCT-based emission in all cases apart from Ru-bpym with lifetimes of tens/hundreds of nanoseconds. Time-resolved infrared studies showed that in the (3)MLCT excited state the principal C-N stretching vibration shifts to positive energy by ca. 50 cm(-1) as a consequence of the transient oxidation of the metal centre to Ru(III) and the reduction in back-bonding to the cyanide ligands; measurement of transient decay rates allowed measurements of (3)MLCT lifetimes for those complexes which could not be characterised by luminescence spectroscopy. A few complexes were also examined in different solvents (MeCN, dmf) and showed much weaker emission and shorter excited-state lifetimes in these solvents compared to water.

Bidentate ligands that contain pyrrole in place of pyridine

A series of ligands are prepared that are analogues of benzo-fused derivatives of 2,2'-bipyridine (bpy), in which pyrrole has been substituted for a pyridine ring. These ligands include 2-(2'-pyridyl)-indole, 2-(2'-pyrrolyl)-quinoline, and pyrrolo[3,2-h]quinoline. A novel reductive cyclization approach to the latter species is presented. All these ligands react with [Ru(bpy-d8)2Cl2], undergoing cyclometalation with concurrent deprotonation, to form complexes of the type [Ru(L)(bpy-d8)2]+ where L binds as a monoanionic ligand. The complexes are readily characterized by their 1H NMR spectra. Changes in the redox potentials and the electronic absorption spectra of both the ligands and the complexes are interpreted in terms of charge delocalization on the ligand.

Ruthenium(II) Complexes of 2-Aryl-1,10-phenanthrolines: Synthesis, Structure, and Photophysical Properties

The synthesis, characterization, and photochemical investigation of a series of Ru(II) complexes having 2-phenyl- and 2,9-diphenyl substituted phenanthroline ligands are reported. Structural characterization of some of the complexes revealed that the phenyl substituents of the phenanthroline ligand are oriented nearly perpendicular to the phenanthroline ring and pi-stack with adjacent coordinated 2,2'-bipyridyl ligands. Most of the complexes are nonluminescent at room temperature, and temperature-dependent luminescence studies suggest nonradiative relaxation in solution is dominated by rapid thermally activated internal conversion from the initially populated (3)MLCT state to a ligand field (LF) state which decays rapidly to the ground state. The photochemical lability of the complexes was investigated, and it was found that, while the complexes efficiently populate the substitutionally labile LF state, yields for ligand loss are less than expected on the basis of comparison to closely related complexes lacking the phenyl groups which are capable of pi-stacking interactions.

Molecular Mechanics (MM3) Parameters for Ruthenium(II)-Polypyridyl Complexes

We have developed molecular mechanics parameters for Ru(II)-polypyridyl coordination compounds with the MM3 force field in MacroModel. X-ray structures, together with a B3LYP frequency calculation on a model system, have been utilized in the parametrization. The performance of the force field and the quality of each parameter is analyzed. A clear qualitative correlation have been found between coordination geometry and emission properties for the ruthenium polypyridyl complexes examined in this paper.

Preparation and Photophysical Properties of Amide-Linked, Polypyridylruthenium-Derivatized Polystyrene

The polymer poly(4{2-[N,N-bis(trimethylsilyl)amino]ethyl}styrene), prepared by anionic polymerization and of low polydispersity (M(w)/M(n) = 1.10-1.18), has been derivatized by amide linkage to [Ru(II)(bpy)(2)(4-(CO-)-4'-CH(3)-bpy)-](2+) (bpy is 2,2'-bipyridine; 4-(CO-)-4'-CH(3)-bpy is 4-carbonyl-4'-methyl-2,2'-bipyridine). Unreacted amine sites were converted into acetamides by treatment with acetic anhydride to give derivatized polymers of general formula [PS-CH(2)CH(2)NHCO(Ru(II)(n)()Me(m)())](PF(6))(2)(n)(), where m + n = 11, 18, or 25, PS represents the polystyrene backbone, and Ru(II) and Me represent the attached complex and acetamide, respectively. Spectral and electrochemical properties of the derivatized polymers are similar to those of the model [Ru(bpy)(2)(4-CONHCH(2)CH(2)C(6)H(5)-4'-CH(3)-bpy)](2+) (4-CONHCH(2)CH(2)C(6)H(5)-4'-CH(3)-bpy is 4'-methyl-2,2'-bipyridinyl-4-(2-phenylethylamide)), but emission quantum yields (phi(em)) and time-resolved emission decays are slightly dependent on the level of Ru(II) loading, with nonexponential, irradiation-dependent decays appearing at high loadings. The decays could be fitted satisfactorily to the first derivative of the Williams-Watts distribution function. These results are discussed with reference to possible structural and multichromophoric effects on excited-state decay.

Synthesis, Structure, and Photophysical Properties of Novel Ruthenium(II) Carboxypyridine Type Complexes

A series of Ru(II) compounds and salts have been synthesized: [Ru(6-carboxylato-bpy)(2)] (5), [Ru(6-carboxylato-bpy)(tpy)]PF(6) (9), [Ru(tpy)(2)](PF(6))(2) (8), and [Ru(bpy)(2)(Pic)]PF(6) (11), where 6-carboxy-bpy (1) = 6-carboxy-2,2'-bipyridine, tpy (2) = 2,2':6',2"-terpyridine, and Pic = 2-carboxylatopyridine. The compounds have been characterized by NMR, electrospray mass spectrometry (ESI-MS), cyclic voltammetry, absorption and emission spectroscopy (at 100, 140, and 298 K), and single-crystal X-ray diffraction (complex 5). Complex 5 crystallizes in the monoclinic system, space group P2(1)/n, formula RuC(22)H(14)N(4)O(4).C(2)H(5)OH, with a = 11.088(3) Å, b = 11.226(3) Å, c = 35.283(9) Å, beta = 91.41(2) degrees, and Z = 8. A linear dependence on the number of coordinated carboxylato groups and the electrochemical redox potentials was found, ca. 0.4 V lower reduction potential for the oxidation step (Ru(II/III)) per carboxylate group. Also, to the best of our knowledge, these are the first examples (9, 11) of mononuclear Ru(II) complexes containing a carboxypyridine-ruthenium moiety displaying any luminescence emission.