Photophysical Properties and Photochemical Behaviour of Ruthenium(II) complexes containing the 2,2′-bipyridine and 4,4′-diphenyl-2,2′-bipyridine ligands

The temperature dependence of the emission lifetime of the series of complexes Ru(bpy)_n(4,4′-dpb) (bpy = 2,2′bipyridine, 4,4′-dpb = 4,4′-diphenyl-2,2′-bipyridine) has been studied in propionitrile/butyronitrile (4:5 v/v) solutions in the range 90–293 K. The obtained photophysical parameters show that the energy separation between the metal-to-ligand charge tranfer (³MLCT) emitting level and the photoreactive metal-centered (³MC) level changes across the series (ΔE = 3960, 4100, 4300, and 4700 cm^?1 for Ru(bpy)), Ru(bpy)2(4,4′-dpb)²⁺, Ru(bpy)(4,4′-dpb), and Ru(4,4′-dpb), respectively, where ΔE is the energy separation between the minimum of the ³MLCT potential curve and ³MLCT – ³MC crossing point. Comparison between spectral and electrochemical data indicated that the changes in ΔE are due to stabilization of the MLCT levels in complexes containing 4,4′-dpb with respect to Ru(bpy)²⁺₃. The photochemical data for the same complexes (as I^? salts) have been obtained in CH₂Cl₂ in the presence of 0.01M Cl^? upon irradiation at 462 nm. The complexes containing 4,4′-dpb are more photostable than Ru(bpy). Comparison between the data for thermal population of the ³MC photoreactive state and those for photochemistry indicated that the overall photochemical process is governed by (i) a thermal redistribution between the emitting and photoreactive excited states, and (ii) mechanistic factors, likely related to the size of the detaching ligand.     

Photophysical, electrochemical and electrochromic properties of copper-bis(4,4′-dimethyl-6,6′-diphenyl-2,2′-bipyridine) complexes

The synthesis, solution and solid state structural characterization, photophysical and electrochemical properties of two redox forms of an electrochromic copper-bis(4,4′-dimethyl-6,6′-diphenyl-2,2′-bipyridine) complex, [Cu(3)₂]ⁿ (n=+1, +2), are presented. Both complexes were characterized in the solid state by X-ray diffraction methods on single-crystals showing that both forms exist in a pseudo-tetrahedral coordination, and a comparison with other structures was made. Like most copper(I) complexes, the red [Cu(3)₂]⁺ complex shows a rather weak emission (Φ_em=2.7×10⁻⁴, dichloromethane). The lifetime of the emitting MLCT state is 34±1 ns, as observed with time resolved emission, and transient absorption (in deoxygenated dichloromethane). Typical emission and transient absorption spectra are presented. The transient absorption spectra indicate that the MLCT state absorbs stronger than the ground state, which is relatively uncommon for metal bipyridine complexes, i.e. no ground state bleaching is observed. The green [(3)₂Cu]²⁺ complex does not show any observable emission or transient absorption, which is a common feature for Cu(II) complexes of this type. The electronic absorption spectra of the chemically and electrochemically produced copper(I/II) complexes are identical. The repeated electrochemical conversion of the Cu(I) center into Cu(II) and vice versa does not cause any decomposition. This is consistent with a fully reversible Cu(I)/Cu(II) redox couple in the corresponding cyclic voltammogram, (E_1/2 (Cu(I)/Cu(II))=+0.68 V vs. SCE=+0.23 V vs. Fc/Fc⁺). These observations indicate that no large structural reorganization occurs upon electrochemical timescales (sub second), and that the different ways of generating the complexes does not effect their final structure, apart from the small differences observed in the X-ray structures of both forms. These characteristics make these complexes rather well suited for their incorporation into an electrochromic display configuration.     

PMR study of Cd(II) complexes with 2,2′-bipyridine

The NMR method has been used to study the structure of the complexes [Cd(bipy)]SO₄.4H₂O, [Cd(bipy)](NO₃)₂.2H₂O, [Cd(bipy)₂](NO₃)₂.$\text{1}\text{2}$H₂O and [Cd(bipy)₃](NO₃)₂.7H₂O. The influence of the central ion and of diamagnetic currents of the rings in these complexes on the PMR spectrum has been investigated. In the complexes [Cd(bipy)](NO₃)₂.2H₂O and [Cd(bipy)]SO₄.4H₂O two kinds of hydration isomers, with different PMR spectra, have been obtained.     

Diastereoselective Ion Pairing of TRISPHAT Anions and Tris(4,4′-dimethyl-2,2′-bipyridine)iron(II)

Two configurationally stable, chiral anions (TRISPHAT, 1 ) behave as efficient hosts that control the configuration of a configurationally labile iron(II ) complex as the guest with high diastereoselectivity (>96 % de) upon ion pairing. The diastereoselectivity increases with decreasing solvent polarity.     

Structural study of Mn(III)-tetraarylporphyrin complexes by fast atom bombardment mass spectrometry

A series of 27 Mn(III)-tetraarylporphyrins bearing heterogeneous substituents on the phenyl rings at the meso positions were subjected to positive ion fast atom bombardment mass spectrometry The source spectra yielded the molecular ion and a few peaks confirmative of the chemical structure. Major processes were hydrogenolytic loss of the aryl rings or of their substituents. Molecules carrying a side-chain underwent loss of the chain either as a solution process (amide linkage) or as a gas-phase process (phenolic ether linkage). Collisionally activated dissociation mass-analysed ion kinetic energy spectroscopy allowed discrimination between the two types of fragmentation processes and some other previously unreported gas-phase reaction channels to be recognized.     

Nuclear magnetic resonance of Zn(II) complexes with 2,2′-bipyridine

The complexes Zn(bipy)Cl₂ and Zn(bipy)₂Cl₂ as well as 2,2′-bipyridyl in aqueous solution (D₂O) have been examined by the NMR method. The presence of the monocationic bipy D⁺ form in aqueous bipyridyl solution has been found. The changes of chemical shifts of bipyridyl protons for complexes Zn(bipy)₃Cl₂ and Zn(bipy)Cl₂ have confirmed explicitly the essential influence of diamagnetic currents on the NMR spectrum of Zn(bipy)₃Cl₂. The comparison of the spectra of 2,2′-bipyridyl (in CH₃OH) and of Zn(bipy)Cl₂ may also suggest the presence of the nonbonding metal-proton 6 interaction.     

Design of effective systems for controlled radical polymerization of styrene: Application of 4,4′-dimethyl and 5,5′-dimethyl 2,2′-bipyridine copper(II) complexes

[Cu(II)(4,4′-dimethyl-2,2′-bipyridine)₃](PF₆)₂ ( 2 ) and [Cu(II) (5,5′-dimethyl-2,2′-bipyridine)₃](PF₆)₂ ( 4 ) were used together with aluminium isopropoxide and (1-bromoethyl)benzene in the controlled radical polymerization of styrene resulting in polystyrenes with predetermined molecular weight and narrow molecular weight distribution. The received polymers are colorless with a content of copper lower than 210 ppm. The substitution pattern at the bipyridine ligands has a distinct influence on the polymerization. The rate of polymerization of styrene using 2 /[(CH₃)₂CHO]₃Al/C₆H₅CH(CH₃)Br is two times larger than utilizing 4 /[(CH₃)₂CHO]₃Al/C₆H₅CH(CH₃)Br.     

Theoretical studies on the structural and optical properties of a series of Os(II) diimine complexes [Os(NN)(CO)2I2] (NN = 2,2′-bipyridine(bpy), 4,4′-di-tert-butyl-2,2′-bipyridine(dbubpy), 4,4′-dichlorine-2,2′-bipyridine(dclbpy))

The ground- and excited-state structures for a series of Os(II) diimine complexes [Os(NN)(CO)₂I₂] (NN = 2,2′-bipyridine (bpy) (1), 4,4′-di-tert-butyl-2,2′-bipyridine (dbubpy) (2), and 4,4′-dichlorine-2,2′-bipyridine (dclbpy) (3)) were optimized by the MP2 and CIS methods, respectively. The spectroscopic properties in dichloromethane solution were predicted at the time-dependent density functional theory (TD-DFT, B3LYP) level associated with the PCM solvent effect model. It was shown that the lowest-energy absorptions at 488, 469 and 539 nm for 1–3, respectively, were attributed to the admixture of the [d_xy (Os) → π^*(bpy)] (metal-to-ligand charge transfer, MLCT) and [p(I) → π^*(bpy)] (interligand charge transfer, LLCT) transitions; their lowest-energy phosphorescent emissions at 610, 537 and 687 nm also have the ³MLCT/³LLCT transition characters. These results agree well with the experimental reports. The present investigation revealed that the variation of the substituents from H → t-Bu → Cl on the bipyridine ligand changes the emission energies by altering the energy level of HOMO and LUMO but does not change the transition natures.     

Field desorption mass spectrometry,fast atom bombardment mass spectrometry and fast atom bombardment tandem mass spectrometry of echinacoside,the main caffeoyl-glycoside from Echinacea angustifolia roots (Asteraceae)

The mass spectral fragmentation of echinacoside, a pharmacologically active caffeoyl-glycoside isolated from Echinacea angustifolia roots, has been investigated using different soft-ionization techniques, field desorption and fast atom bombardment (positive and negative ions) mass Spectrometry. Both ionization modes are successful in molecular mass determination and furnish approximately equivalent structural information. A fast atom bombardment tandem mass spectrometry approach (negative ions) was developed for the study of the fragmentation pathways and for the detection of echinacoside in crude plant extracts. The results demonstrate the usefulness of this technique for the rapid search of this important caffeoyl-glucoside directly in natural complex matrices.     

Structures of 3,3′-dicarbometoxy-2,2′-bipyridine complexes with silver(I) and copper(II) cations

The structures of 3,3′-dicarbometoxy-2,2′-bipyridine (dcmbpy) complexes with copper(II) and silver(I) cations have been determined using single crystal X-ray-diffraction. The crystals of Cu(dcmbpy)Cl₂ are monoclinic, C2/c, a = 16.966(3), b = 18.373(3), c = 13.154(2) Å, β = 126.543(3)°. The crystals of Ag(dcmbpy)NO₃ · H₂O are also monoclinic, C2/c, a = 16.7547(13), b = 11.0922(9), c = 18.7789(18) Å, β = 100.228(7)°. The results have been compared with the literature data on the complexes of dcmbpy and its precursors: 2,2′-bipyridine (bpy) and 3,3′-dicarboxy-2,2′-bipyridine (dcbpy). Two types of complexes of 3,3′-carboxy derivatives of bpy are distinguished: (1) with metal atom bonded to two N atoms of the same molecule and (2) with metal atom bonded to two N atoms of two different molecules. The Cu(dcmbpy)Cl₂ complex belongs to the first type, whereas Ag(dcmbpy)NO₃ · H₂O belongs to the second type.     

Mechanism for dehalogenation reactions in fast atom bombardment mass spectrometry

The mechanism of a dehalogenation reaction that occurs during fast atom bombardment (FAB) mass spectrometry was examined using halogenated nucleosides as model compounds. For aglycone-halogenated nucleosides, an inverse linear relationship exists between the extent of FAB dehalogenation and the calculated electron affinity of an individual nucleoside. The degree of dehalogenation for a given nucleoside also varies inversely with the calculated electron affinity of most FAB matrices. The observed dehalogenation reaction can be completely inhibited when matrices with positive electron affinities, such as 3-nitrobenzyl alcohol and 2-hydroxyethyl disulfide, are used. High-performance liquid chromatographic analysis of the bulk glycerol matrix following exposure to the FAB beam indicates measurable amounts of dehalogenated product, suggesting that this reaction occurs in the condensed phase prior to gas-phase ion formation. A dehalogenation mechanism involving thermal electron capture and subsequent negative charge stabilization is consistent with these observations.     

Negative-ion fast atom bombardment mass spectrometry of N-phosphoamino acids

The fragmentation patterns of N-phosphoamino acids in negative-ion fast atom bombardment mass spectrometry (FABMS) showed different characteristics to those in positive-ion FABMS. Six typical N-diisopropyloxyphorphorylamino acids all had intense [M ? 1]^? peaks, and they underwent similar fragmentation pathways. In general, the elimination of one alkene molecule followed by the loss of one molecule of alcohol occurred. They also favoured an N → O rearrangement reaction, followed by fragmentation to (RO)₂ PO₂^? and (RO) (HO)PO₂^?.     

The analysis of salen complexes by fast atom bombardment mass spectrometry and atmospheric pressure chemical ionization mass spectrometry

Fast atom bombardment (FAB) mass spectrometry provides useful structural information about salen complexes and salen-based oxo transfer catalysts that are not appreciably soluble in organic solvents. It was discovered that initial dissolution of these complexes in trifluoroacetic acid was crucial for producing good FAB mass spectra. Trifluoroacetic acid helps dissolve the salen-based catalysts, concentrates the analyte molecules at the matrix surface, and most importantly, suppresses the reduction process, which is a well-known phenomenon when protic matrices are used. The best FAB matrices for these catalysts were found to be thioglycerol and “magic bullet.” However, dechlorination occurred under the acid conditions for complexes containing iron chloride and manganese chloride. Demetalation also occurred for nickel-containing oxo transfer salen-based complexes. When the salen-based complexes are soluble in LC solvents, they can be analyzed easily by atmospheric pressure chemical ionization (APCI) mass spectrometry without the employment of relatively nonvolatile matrices. In addition, APCI/MS provides much more sensitive detection for manganese-salen complexes when compared with FAB results. No dechlorination or demetalation were observed when a negative ion mode APCI was employed. To our knowledge, this is the first time that an intact molecule of this type of complex has been observed by mass spectrometry.     

Syntheses of mixed ligands complexes of Ru(II) with 4,4′-dicarboxy-2,2′-bipyridine and substituted pteridinedione and the use of these complexes in electrochemical photovoltaic cells

The synthesis, spectral and photoelectrochemical studies of mixed ligand complexes of [Ru(dcbpy)₂(LL)]Cl₂, where LL=2,4-(1,3-N,N′-dimethyl)pteridinedione (DMP), 6,7-dimethyl-2,4-(1,3-N,N′-dimethyl)pteridinedione (MDMP), 6,7-diphenyl-2,4-(1,3-N,N′-dimethyl)pteridinedione (PhDMP), dibenzo[h,j]-(1,3-N,N′-dimethyl)isoalloxazine (BIAlo), 6,7-bis(pyrid-2-yl)-2,4-(1,3-N,N′-dimethyl) pteridinedione (PyDMP) were carried out. These complexes were attached to sol–gel processed TiO₂ electrodes and the photocells fabricated were illuminated with polychromatic radiation in the presence of I₂/I₃⁻ as redox electrolyte. The incident photon to current conversion efficiency determined was found to be 20–48%.     

ResonanceRaman spectra of Iron(II) complexes with 4,4′-didodecyloxy-2,2′-bipyridine and 4,4′-dioctadecyloxy-2,2′-bipyridine

The resonanceRaman spectra of Fe(LC ₁₂)₃Cl₂ and Fe(LC ₁₈)₃Cl₂ (whereLC ₁₂ andLC ₁₈ denote 4,4′-didodecyloxy-2,2′-bipyridine and 4,4′-dioctadecyloxy-2,2′-bipyridine, respectively) have been measured along with their excitation profiles. The exciting lines of an Ar⁺ laser have been used. The bands appearing in theRR spectra within 1 200–1 600cm^?1 (expected to arise from thebipy moiety C-N and C-C vibrations) suffer the greatest resonance enhancements. Both depolarization ratios of theRaman bands and excitation profiles reveal the interaction of the resonant electronic states.     

Direct evidence for preformed ions of porphyrins in the solvent matrix for fast atom bombardment mass spectrometry

The observation that protonated molecules are present in solvents utilized for fast atom bombardment (FAB) mass spectrometric studies has been demonstrated using visible absorption spectrometry. Addition of porphyrins to thioglycerol, a solvent used for FAB analyses, results in partial protonation of the molecule. This reaction can be monitored by observing the shift in visible absorption maxima associated with the molecular transition from free base to protonated structure. A good correlation is observed between the degree of protonation indicated by the appropriate absorption bands and the abundance of the [M + H]⁺ ion in the FAB spectrum of the corresponding solution. Addition of certain non-polar porphyrin molecules to thioglycerol does not result in the protonation of the molecule in solution; in these cases, analyses of the corresponding solutions by FAB do not yield [M + H]⁺ ions. Subsequent addition of trifluoroacetic acid to the solvent has proved sufficient to protonate the analyte molecule, as indicated by the visible absorption spectrum; FAB analyses of these non-polar porphyins in acidified solvent result in the observation of [M + H]⁺ ions. These experiments demonstrate that analyses of these analyte molecules requires that they be present as ions in solution prior to analysis by FAB. This study provides experimental evidence for the presence of ions in solutions employed for FAB analysis, suggesting that these ions are essential for the generation of the protonated molecules observed during FAB mass spectrometric analyses.     

Matrix effects in fast atom bombardment mass spectrometry of cationic iridium(III) and rhodium(III) coordination complexes

Fast atom bombardment mass spectra of cationic iridium(III) and rhodium(III) coordination complexes (M⁺Cl₂L₂, X^?; where the ligand L is a dinitrogenous aromatic system) have been obtained with thioglycerol, glycerol or tetraglyme as a matrix. Two kinds of reactions, initiated by particle bombardment, have been discovered between these complexes and the matrix. First, with thioglycerol one or two chlorine atoms are substituted by a thioglycerol radical, more rapidly for rhodium compounds; secondly, when the ligand L possesses a diazo function, this function is hydrogenated depending on the ability of the matrix to generate hydrogen radicals by bombardment.     

In situ N-phosphorylation of oligopeptides for fast atom bombardment mass spectrometry

Positive ion fast atom bombardment mass spectrometry (FABMS) of in situ N-phosphorylated oligopeptides showed intense quasi-molecular ions together with the successive alkene loss fragment ions, which afford multiple checks of the unequivocal reality of the relative molecular mass of the tested samples. More interesting, in a novel cleavage pattern only the N-phosphoryl fragment ions gave intense peaks, the C-terminal series ions being suppressed. For each of the N-terminal ions, losses of alkenes also occur to provide multiple checks for the existence of these ions. The FABMS of the in situ N- phosphorylated oligopeptides might provide an easily accessible routine method for peptide sequencing.     

Oxygen quenching of tris(2,2′-bipyridine) ruthenium(II) complexes in thin organic films

A study is presented of the quenching, by oxygen, of the luminescence of tris(2,2′-bipyridine) ruthenium(II) complexes immobilized in thin, transparent, polymer-based films. The film media consist of a water-insoluble linear polymer plasticized with a trialkylphosphate ester, in which the complex ruthenium cations are solubilized by ion pairing with organophilic anions such as tetraphenylborate.

Luminescence lifetimes were studied in relation oxygen concentration in a gas stream contiguous with the film medium, film thickness and concentration of the metal complex within the film medium. It is shown that the microheterogeneous environment of the luminescent complex, which has recently been implicated in the non-linear quenching responses of polymer-immobilized, transition metal complex oxygen sensors, may arise simply as a consequence of the limited solubility of the complex in the film medium. When solubility is limited, the partial precipitation of the complex results in a colloidal of luminescent particles which exhibit non- uniform susceptibilities to quenching by oxygen. Good solubility, and therefore linear quenching characteristics, are promoted by methyl substitution of the bipyridyl ligand and by use of a plasticizer (tributylphosphate) with marked cation solvating powers.