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Substituent effects may tune and alter the optical and electronic properties of ligands and the complexes which they comprise. We review the effect of electron-withdrawing and -donating groups on the dipyridophenazine (dppz) framework. The observation of selected modulation of the properties associated with the phenazine or phenanthroline MOs is observed and reflected in the electrochemical and optical properties. The effect of donor groups that can give rise to ligand-centred charge-transfer optical transitions is also discussed. The effect of substituents on complexes with triazole ligands is examined; in stark contrast to the findings for dppz systems, and virtually regardless of the type of triazole ligand, substituents have only a muted effect on optical and electrochemical properties.

Raman spectroscopy was used to investigate how the effect of pre-treatment protocols, with combinations of hydrochloric acid (HCl), sodium hypochlorite (NaOCl) and hydrogen peroxide (H2O2), for molar-incisor hypo-mineralisation (MIH) altered the penetration depth of polymer infiltrants (ICON, DMG, Hamburg, Germany). Furthermore, the effect on the structure of the MIH portions of the teeth with treatment is examined using multivariate analysis of spectra. It was found that pre-treatment protocols improved penetration depths. The structure of the MIH portion post-treatment appeared much closer to that of normal enamel suggesting a diminution of protein in the MIH region with treatment.

Avian eggshells are variable in appearance, including colouration. Here we demonstrate that Raman spectroscopy can provide accurate diagnostic information about major eggshell constituents, including the pigments biliverdin and protoprophyrin IX. Eggshells pigmented with biliverdin showed a series of pigment-diagnostic Raman peaks under 785 nm excitation. Eggshells pigmented with protoporphyrin IX showed strong emission under 1064 nm and 785 nm excitation, whereas resonance Raman spectra (351 nm excitation) showed a set of protoporphyrin IX informative peaks characterisitic of protoporphyrin IX. As representative examples, we identified biliverdin in the olive green eggshells of elegant crested tinamous (Eudromia elegans) and in the blue eggshells of extinct upland moa (Megalapteryx didinus). This study encourages the wider use of Raman spectroscopy in pigment and colouration research and highlights the value of this technique for non-destructive analyses of museum eggshell specimens.

Visual observations of the hydration process of single carbamazepine (CBZ) crystals in water and in various excipient solutions [(1% w/v) – hydroxypropyl cellulose (HPC), poly(vinyl pyrrolidone) (PVP), sodium carboxymethylcellulose (CMC) at pH 7.5 and 3.0, and polyethylene glycol (PEG)] using scanning electron microscopy (SEM) are reported in this paper. Raman microscopy was used to confirm the chemical structures of the unconverted CBZ and the CBZ dihydrate (DH) needles. It was found that defect structures were a more important driving force than the nature of crystal faces for the initiation of the hydration, but face differences became obvious after 6 h immersion. The biggest crystal face grown from methanol, (100), was the slowest one to be covered with DH needles. A comparison of the molecular arrangements along the three crystal faces [(100), (010) and (001)] was carried out using crystal structure visualization software, and fewer polar groups exposed on the (100) face than on the (001) and (010) faces were found, explaining the comparatively weak interaction of the (100) face with water during hydration. Furthermore, investigation of the influence of excipients on the hydration of CBZ showed that both HPC and PVP strongly inhibited conversion, and no conversion of CBZ to DH was found after 18 h immersion in water. PEG and CMC (pH 7.5) were less potent inhibitors than HPC and PVP, and DH needles were observed on all the faces except the (100) face after 18 h immersion. No conversion was detected for the crystal immersed in CMC solution at pH 3.0. This is likely to be caused by the decreased polarity of CMC in water at pH 3.0 (p K a ,cmc = 4.3), and thus a higher surface adsorption of CMC to the CBZ crystals in dispersion. The influence of excipients on the conversion of CBZ observed in this study agreed well with our previous quantitative studies using Raman spectroscopy. In this study, visual observation using electron microscopy has been demonstrated to be a unique and powerful tool to improve our understanding of polymorphic conversions of CBZ in aqueous suspension.

The propensity of molecules to form polymorphs increases with increasing functionality. Each polymorph is a separate patentable entity and may have different therapeutic properties. It is therefore important to develop methods for the identification and quantification of polymorphs alone and within active pharmaceutical ingredients. Various vibrational spectroscopic techniques have had promising results in the quantification of polymorphs in binary mixtures. Ranitidine hydrochloride exists as two polymorphs and has been used as a test compound in the assessment of various quantification techniques (e.g. X-ray powder diffraction, Raman spectroscopy, diffuse reflectance infra-red Fourier transform spectroscopy). This study investigates the accuracy of near-infrared spectroscopy when quantifying polymorphic binary mixtures of ranitidine hydrochloride. Ranitidine hydrochloride polymorphs may be identified and quantified from near-infrared spectra; however, not to the level of accuracy displayed by Raman spectroscopy.

The steady-state and transient emission properties of unsubstituted terthiophene and a series of 3'-[E-2-(4-R-phenyl)ethenyl]-2,2':5',2' '-terthiophenes (where R = H, MeO, NH(2), CN, NMe(2), NO(2)) have been examined. The R = NO(2) compound is nonemissive at room temperature in all solvents but cyclohexane. All of the other compounds show measurable steady-state emission in a variety of solvents. The behavior of these spectra may be split into two groups. The first group, those substituted compounds with R = CN, NH(2) and NMe(2), show solvatochromic behavior, where their Lippert-Mataga plots suggest changes in dipole upon photoexcitation ranging from 12.5 to 16.0 D. For the second group, where R = H and MeO (and unsubstituted terthiophene as well), the Lippert-Mataga plots indicate dipole moment changes ranging from 0 to 7.9 D. The difference in behavior between the two groups of emissive compounds can be attributed to a charge-transfer character of the emitting state in the first group. This conclusion is supported by density functional theory calculations, which show that the frontier MOs in the group one compounds are spatially separated whereas those of group two have frontier MOs that are delocalized over both the styryl and terthiophene moieties. Picosecond time-resolved fluorescence spectroscopy reveals that unsubstituted terthiophene has the shortest emission lifetime of 140 ps in acetonitrile. For the styryl substituted terthiophenes, the lifetimes are much longer and range from 320 to 670 ps for R = CN and NMe(2) respectively, a result that can be explained in terms of a smaller rate of intersystem crossing in these compounds.

FT-Raman spectroscopy has been used to investigate interactions between lecithin and cholesterol. Raman spectra of lecithin show multiple peaks which can be classified into three regions: hydrophobic chain, interfacial, and headgroup regions. Binary lipid mixtures (1:1, w/w, lecithin:cholesterol) were prepared by physical mixing, granulation, coprecipitation, hydration and heating (65 degrees C), and heating (120 degrees C). Regardless of the preparation method, no changes in the spectra were observed in the hydrophobic region. A shift in the wavenumber of the choline methyl asymmetric stretching mode was observed when the samples were prepared by coprecipitation, hydration and heating (65 degrees C), and heating (120 degrees C). This may indicate a modification of phospholipids in the headgroup region in these samples. The difference in degrees of frequency shift (physical mixing approximately granulationcoprecipitation approximately hydration and heating (65 degrees C)heating (120 degrees C)) suggests that different levels of hydrogen bonding may have occurred in mixtures prepared with these methods. Multivariate analysis utilizing partial least squares regression based on selected wavenumber ranges was applied for the quantitative analysis of the amount of lecithin in lipid mixtures. Calibration models from physical mixing and heating (120 degrees C) exhibited lower R2 and root mean square error of cross validation (RMSECV) values compared to the other models suggesting lower sample homogeneity for these preparation methods. Low values of the mean absolute residues and mean Mahalanobis distances imply that the calibration model generated from physical mixing samples may be appropriate for quantitative analysis of lecithin in lipid mixtures prepared by any of the other techniques.

In an aqueous environment, polymorphic forms I–III of carbamazepine all convert to the dihydrate. This study investigated the conversion of each polymorphic form individually and of a mixture of forms III and I to the dihydrate. Two batches of form I with different crystal morphology were used. Samples were dispersed independently in water at 23 ± 1 °C and recovered at various timepoints varying from 10 to 210 min. Scanning electron microscopy, X-ray powder diffraction and Raman spectroscopy were used to characterize the initial polymorphic forms and the recovered samples after 210 min. Raman spectroscopy combined with partial least squares analysis was used to generate quantitative models of binary and ternary mixtures of the different polymorphic forms with the dihydrate. On the basis of these models the conversion kinetics of the polymorphic forms I–III were characterized. First-order kinetics with an unconverted portion were used to model the data (R2 ≥ 0.95). The unconverted portions ranged from 16 to 51% after dispersion for 210 min. The conversion kinetics were similar between polymorphic forms with comparable crystal morphology, but differed significantly between batches of the same polymorph (form I) with different crystal morphology. Furthermore, the conversion of forms III and I in the aqueous suspension was not influenced by the presence of the other polymorph when dispersed together.

Mono- and binuclear complexes of (Re(CO)3Cl) with dipyrido[2,3-a:3',2'-c]-6,7-dimethylphenazine (ppbMe2) were synthesised and their photophysical properties probed using picosecond time-resolved infrared spectroscopy (TRIR). Excitation of these complexes in solution at 400 nm produces short-lived excited states. The IR spectrum of the excited state of the mononuclear [Re(CO)3Cl(ppbMe2)] have nu(CO) bands shifted to higher wavenumber relative to those of the ground state. This is consistent with formation of a (3)MLCT excited state. The IR spectrum of the excited state of the bimetallic [(Re(CO)3Cl)2(micro-ppbMe2)] shows the formation of two distinct groups of nu(CO) bands. This is interpreted as the formation of two distinct Re sites arising from a localised MLCT state with formally oxidised Re centre and a formally reduced bridging ligand. The nu(CO) bands of the adjacent Re centre are affected by the reduction of the bridging ligand. On the IR timescale the excited state structure is best formulated as [Cl(CO)3Re(II)(micro-ppbMe2 *-)Re(I)(CO)3Cl].

To counter the growth of herbal medicines adulterated with pharmaceuticals crossing borders, rapid, inexpensive and non-destructive analytical techniques, that can handle complex matrices, are required. Since mid-infrared (MIR), near infrared (NIR) and Raman spectroscopic techniques meet these criteria, their performance in identifying adulterants in seized weightloss herbal medicines is definitively determined. Initially a validated high pressure liquid chromatography methodology was used for reference identification and quantification of the adulterants sibutramine H2O·HCl, fenfluramine HCl and phenolphthalein. Of 38 products, only sibutramine and phenolphthalein were detected by HPLC. The spectroscopic measurements showed Raman was ill-suited due to sample burning and emission while NIR lacked adulterant selectivity. Conversely, MIR demonstrated apt identification performance, which manifested as spectrally meaningful separation based on the presence and type of adulterant during principal component analysis (test set validated). Partial least squares regression models were constructed from the MIR training sets for sibutramine and phenolphthalein - both models fitted the training set data well. Average test set prediction errors were 0.8% for sibutramine and 2.2% for phenolphthalein over the respective concentration ranges of 1.7-11.7% and 0.9-34.4%. MIR is apposite for the screening of anorectic and laxative adulterants and is the most viable technique for wider adulterant screening in herbal medicines.

In this study for the first time temperature dependent terahertz pulsed spectroscopy was performed on a pharmaceutical drug. The polymorphic conversion process of carbamazepine form III to I was studied at varying temperatures. Furthermore, the solid-state transformation at isothermal conditions below the melting point of carbamazepine was investigated. The ability to study solid-state reactions with terahertz pulsed spectroscopy could be demonstrated.

The structural changes that occur when [Cu(pqx)(PPh(3))(2)](+) (pqx is 2-(2'-pyridyl)quinoxaline) undergoes excitation through a metal-to-ligand charge-transfer (MLCT) transition are investigated using resonance Raman excitation profiles coupled with density functional theory (DFT). The DFT calculations predict bond lengths to within 3 pm and absolute deviations of 7 cm(-1) for the vibrational frequencies of [Cu(pqx)(PPh(3))(2)](+). TD-DFT calculations of oscillator strengths (f = 0.089) and band positions (419 nm) showed close agreement with experiment (f = 0.07, 431 nm). Resonance Raman spectra show the 527 cm(-1) (nu(29)) and 1476 cm(-1) (nu(75)) modes undergo the largest dimensionless displacement (Delta = 1.5 and 1.1, respectively) following photoexcitation into the MLCT Franck-Condon region. The solvent couples strongly to the MLCT transition and resonance Raman intensity analysis (RRIA) gives a solvent reorganization energy of 3400 cm(-1) for dichloromethane and 2800 cm(-1) for chloroform solutions. A large inner-sphere reorganization of 3430 cm(-1) in dichloromethane solution (3520 cm(-1) in chloroform solution) was found for [Cu(pqx)(PPh(3))(2)](+), indicating that the molecule as a whole undergoes significant distortion following MLCT excitation.

Density functional calculations at the B3LYP/6-31G(d) level are used to predict the vibrational spectra for a series of substituted thiophenes and terthiophenes containing the emitter unit diethenylbenzene (DEB). The calculations show that cyano substitution induces non-planarity, particularly for the terthiophene compound. This was verified by the absorption and emission data, which suggest that the ground state is less planar than the excited state. The solution phase electronic spectroscopy reveals that some of the compounds are very emissive; however, CN substitution quenches this emission. Electroluminescent devices may be constructed using these emitter materials and it is found that the efficiency of the CNDEB compounds may be improved with the introduction of a different hole transporting layer.

The light emitting devices using ruthenium(II)(4,7-diphenyl-1,10-phenanthroline) 3 ([Ru(dphphen) 3 ] 2+ ) complex as dopant and emitter in poly( N -vinylcarbazole) (PVK)-based blend matrix have been studied in different structures. In comparison with the indium-tin-oxide glass (ITO)/PVK:2-(4-biphenyl)-5-(4-ter-butylphenyl)-1,3,4-oxadiazole (PBD):[Ru(dphphen) 3 ] 2+ /tris-(8-hydroxyquinoline) aluminum (Alq 3 )Al,ITO/PVK:PBD:[Ru(dphphen) 3 ] 2+ /2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/Alq 3 /LiF/Al, and ITO/PVK: N , N ′-diphenyl- N , N ′ -bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine (TPD):PBD:[Ru(dphphen) 3 ] 2+ /BCP/Alq 3 /LiF/Al devices, the ITO/PVK:PBD:[Ru(dphphen) 3 ] 2+ /Alq 3 /BCP/Alq 3 /LiF/Al device shows efficient improvement in device brightness and efficiency. Furthermore, the chromacity-tunable electroluminescence is obtained by the hybrid emission from [Ru(dphphen) 3 ] 2+ and Alq 3 species in such a device structure.

The ligands 11-bromodipyrido[3,2-a:2',3'-c]phenazine and ethyl dipyrido[3,2-a:2',3'-c]phenazine-11-carboxylate have been prepared and coordinated to ruthenium(II), rhenium(I), and copper(I) metal centers. The electronic effects of substitution of dipyrido[2,3-a:3',2'-c]phenazine (dppz) have been investigated by spectroscopy and electrochemistry, and some photophysical properties have been studied. The crystal structures of [Re(L)(CO)(3)Cl] (L = ethyl dipyrido[3,2-a:2',3'-c]phenazine-11-carboxylate or 11-bromodipyrido[3,2-a:2',3'-c]phenazine) are presented. Density functional theory calculations on the complexes show only small deviations in bond lengths and angles (most bonds within 0.02 Angstroms, most angles within 2 degrees) from the crystallographic data. Furthermore, the vibrational spectra of the strongest Raman and IR bands are predicted to within an average 6 cm(-1) for the complexes [Re(L)(CO)(3)Cl] and [Cu(L)(triphenylphosphine)(2)]BF(4) (in the 1000-1700 cm(-1) region). Spectroscopic and electrochemical evidence suggest that reduction of the complex causes structural changes across the entire dppz ligand. This is unusual as dppz-based ligands typically have electrochemical properties that suggest charge localization with reduction on the phenazine portion of the ligand. The excited-state lifetimes of the complexes have been measured, and they range from ca. 200 ns for the [Ru(L)(2,2'-bipyridine)(2)](PF(6))(2) complexes to over 2 mus for [Cu(11-bromodipyrido[3,2-a:2',3'-c]phenazine)(PPh(3))(2)](BF(4)) at room temperature. The emission spectra suggest that the unusually long-lived excited states of the copper complexes result from metal-to-ligand charge transfer (MLCT) transitions as they are completely quenched in methanol. Electroluminescent films may be fabricated from these compounds; they show MLCT state emission even at low doping levels [0.1% by weight in poly(vinylcarbazole) polymer matrix].

The electronic absorption spectra of a series of alkoxy-styryl substituted terthiophenes, their corresponding sexithiophenes, and the oxidation products of both have been measured. The terthiophenes studied sigma-dimerize to sexithiophenes during the oxidation process and there is clear evidence of sexithiophene radical cations, dications, and pi-dimers in the electronic absorption spectra. The oxidation of concentrated solutions produces predominantly pi-dimer bands, as expected. The absorption spectrum of the styryl-functionalized sexithiophene dication without alkoxy substitution closely resembles that of unsubstituted sexithiophene, while alkoxy substitution induces changes in the wavelength of the dication band maximum and the overall band shape. Time-dependent density functional theory (TDDFT) calculations have shown that styryl-based molecular orbitals are important in the transitions of the neutral molecules as well as the charged species, the dication in particular. Kinetics analyses confirm the stabilization effect induced by the alkoxy substituents. The presence of a reversible pi-dimer equilibrium was verified by cyclic voltammetry. It is clear from the experimental observations and the theoretical calculations that both the styryl and alkoxy groups are influencing the electronic properties of this class of molecules.

A group of diethenylbenzene-linked oligothiophenes were investigated using vibrational spectroscopy in conjunction with quantum calculations. Geometry calculations revealed dihedral angles that are sensitive to both the presence of cyano substituents on the ethylene linkages and the identity of the attached oligothiophene. In particular, cyano substitution in the presence of terthiophene groups leads to a significant loss of planarity. The resultant loss of conjugation has been observed in the experimental Raman spectra on the basis of a band at ∼1520 cm−1, the wavenumber and intensity of which are dependent on conjugation length. In the case of the diethenylbenzene-linked terthiophene, the wavenumber of this band suggests a conjugation that extends across both terthiophene and the diethenylbenzene species. The calculated vibrational spectra successfully predict the wavenumber shifts upon cyano substitution in both the infrared and Raman spectra. The presence of the cyano groups has the greatest influence on the Mulliken charge distribution, whereas the identity of the oligothiophene has little effect. This study shows that quantum calculations, particularly when combined with experimental parameters such as vibrational spectroscopy, can be informative in understanding the electronic structure of molecules of this type. Copyright © 2005 John Wiley & Sons, Ltd.

Confocal Raman microscopy was applied to detect the partitioning of a volatile compound, trans-2-hexenal, into bovine milk fat globules (MFGs). The interactions between trans-2-hexenal and individual MFGs were reflected by a change of spectral intensity of the volatile compound in the Raman shift region. At a relatively high concentration of trans-2-hexenal (5%, v/v), stronger intensities of the characteristic Raman spectra were found in the interior of the MFGs compared with the milk fat globule membrane (MFGM) region after reaching equilibrium, revealing that the MFG as a whole, rather than the MFGM, plays the major role in volatile compound absorption processes. The current study reports on an innovative instrumental method to investigate interactions among specific volatile compound and individual emulsion droplets.

The polymorphic behaviour of drugs is a major concern of the pharmaceutical industry as it may have considerable formulation, therapeutic, legal and commercial implications. It is therefore crucial to be able adequately to identify and quantify different polymorphic forms of drugs as early as possible in the drug discovery and development process. The aim of the present study was to investigate the application of Raman spectroscopy and principal components analysis (PCA) to the quantitative analysis of polymorphic mixtures of carbamazepine forms III and I, based on both individual peak areas and heights in the Raman spectra and whole wavenumber ranges. Various linear regressions indicated that in general using every fourth wavenumber value of a larger region of the Raman spectrum gives better quantitative results than choosing defined peak areas and peak heights, as the spectral differences between the polymorphs were only subtle. Baseline correction of the spectral data did not appear to improve the quantitative analysis, with detection and quantification limits being the lowest (0.33 and 1.09%, respectively) and R2 being the highest (0.96) when using every fourth wavenumber value from 2950 to 3100 cm−1 as input data for the PCA analysis without baseline correction. This study demonstrated that PCA of Raman spectroscopic data provides a sensitive method for the quantitative analysis of polymorphic forms, with a quantitation limit of

An improved method for the synthesis of the polypyridyl ligand [2,3-a:3′,2′-c]dipyridophenazine (ppb) is reported. In addition, the syntheses of the new ppb-based ligands L (L=[2,3-a:3′,2′-c]dipyridophenazine, [2,3-a:3′,2′-c]dipyrido-6,7-dimethylphenazine, [2,3-a:3′,2′-c]dipyrido-6,7-dichlorophenazine, [2,3-a:3′,2′-c]dipyrido[1,2-e]benzophenazine, [2,3-a:3′,2′-c:3″,2″-e]tripyridoquinoxaline and [2,3-a:3′,2′-c]dipyrido-5-methylphenazine) are detailed. The complexes [Os(ppb)(bpy)2]2+ and [Os(L)(bpy)2]2+ have been synthesised and their electrochemical, electronic absorption and UV–Vis spectrochemical properties measured. Syntheses of the rhenium(I) complexes fac-[Re(L″)(CO)3Cl] (L″ = [2,3-a:3′,2′-c]dipyridophenazine, [2,3-a:3′,2′-c]dipyrido-6,7-dimethylphenazine, [2,3-a:3′,2′-c]dipyrido-6,7-dichlorophenazine, [2,3-a:3′,2′-c]dipyrido[1,2-e]benzophenazine) are also reported. The osmium(II) complexes [Os(L′)(bpy)2]2+ (L′ = 2,3-di-(2-pyridyl)quinoxaline, 6,7-dimethyl-2,3-di-(2-pyridyl)quinoxaline, 6,7-chloro-2,3-di-(2-pyridyl)quinoxaline, 2,3-di-(2-pyridyl)benzo[g]quinoxaline, 4-methyl-di-(2-pyridyl)quinoxaline) have also been prepared and studied. The electronic spectra of the Os and Re complexes are dominated by strong MLCT transitions. The lowest energy MLCT transitions correlate linearly with the first reduction potential for the [Os(L)(bpy)2]2+ series. Electrochemical oxidation of the [Os(L)(bpy)2]2+ and [Os(L′)(bpy)2]2+ complexes results in the appearance of LMCT transitions in the visible region while reduction of the [Os(L)(bpy)2]2+ complexes produces complex electronic spectra. Comparison with the reduced fac-[Re(L″)(CO)3Cl] complexes allows assignment of L″ − π→π* transitions in the NIR (1200–1000 nm) and red (850–700 nm) regions. The nonsymmetrical ligands [2,3-a:3′,2′-c:3″,2″-e]tripyridoquinoxaline and [2,3-a:3′,2′-c]dipyrido-5-methylphenazine both coordinate to the [Os(bpy)2]2+ unit in a stereospecific manner to give a single geometric isomer. The crystal structure of [Re(CO)3(ppb)Cl] is reported, in which the polypyridyl ligand deviates significantly from planarity.

The application of terahertz pulsed spectroscopy to polymorphic, liquid crystalline and amorphous forms of pharmaceutical compounds has been investigated. The different polymorphic forms of carbamazepine and enalapril maleate exhibit distinct terahertz absorbance spectra. In contrast to crystalline indomethacin and fenoprofen calcium, amorphous indomethacin and liquid crystalline fenoprofen calcium show no absorption modes, which is likely to be due to a lack of order. These findings suggest that the modes observed are due to crystalline phonon and possibly hydrogen-bonding vibrations. The large spectral differences between different forms of the compounds studied is evidence that terahertz pulsed spectroscopy is well-suited to distinguishing crystallinity differences in pharmaceutical compounds.

The drug carbamazepine has been modeled, using ab initio density functional theory calculations [B3LYP/6–31G(d)], both as a single molecule and as a dimer. The predicted geometry of the single molecule calculation is compared with the crystallographic data on each of the polymorphs (carbamazepine forms I and III). From the predicted geometry it is possible to calculate the IR and Raman spectra; these predictions compare favorably with the observed spectra of both polymorphs of carbamazepine for most of the bands. The spectral differences between the polymorphs are more striking in the IR than the Raman spectra, with strong IR bands at 1688 and 1396 cm−1 in form I shifting to 1678 and 1388 cm−1 in form III. Analysis of the potential energy distributions for the calculated normal modes reveals that the vibrations are localized across different ring systems of the carbamazepine structure. Most notably, the polymorph-sensitive modes in the IR spectra are localized to the pendant CONH2 group; it is these modes that show the greatest disparity from the calculated spectra, and it is this group that is perturbed in the polymorph crystal structures. The calculated dimer structure is similar to that of the single molecule, but the polymorph-sensitive IR modes are significantly better predicted by the dimer calculation. Copyright © 2004 John Wiley & Sons, Ltd.

Organic light-emitting diodes may be fabricated using transition metal complexes as the emitting molecules. These have some advantages because of their photo-robustness and because they may be engineered to be very effective charge-carriers thus readily being excited by EL excitation.

The vibrational spectra (Raman and IR) of 1,10-phenanthroline (phen), its perdeuterated analogue (d8-1,10-phenanthroline, d8-phen), and the copper(I) complexes [Cu(phen)(PPh3)2]+ and [Cu(d8-phen)(PPh3)2]+ have been measured. These spectra may be modeled using DFT calculations (B3LYP/6-31G(d)). The calculated structure compares favorably with crystallographic data. The time-resolved resonance Raman spectra of the copper(I) complexes were used to provide spectral signatures of phen• - and d8-phen• -. Geometries and vibrational spectra of the radical anions may be calculated in two ways: first as phen• -, which has been previously shown to be a 2B1 state. Calculations with B3LYP require the 6-311+G(d,p) basis set in order to predict this state correctly for the radical anion, rather than the close-lying 2A2 state, therefore giving a reasonable prediction of the geometry and spectra. Second, using [Cu(phen• -)(PH3)2] it is possible to model the radical anion at the B3LYP/6-31G(d) level because the metal cent...

Light-emitting devices, using ruthenium(II)(4,7-diphenyl-1,10-phenanthroline)3 ([Ru(dphphen)3]2+) as dopant and emitting center have been investigated, in a structure of indium-tin-oxide glass (ITO)/poly(N-vinylcarbazole) (PVK):2-(4-biphenyl)-5-(4-ter-butylphenyl)-1,3,4-oxadiazole (PBD):[Ru(dphphen)3]2+/tris-(8-hydroxyquinoline) aluminum (Alq3)/Al. Instead of the long response time observed at high doping concentration, instantaneous light emission from [Ru(dphphen)3]2+ is obtained at a doping concentration at which the electronic coupling between the [Ru(dphphen)3]2+ molecules is eliminated by the host matrix. This is attributed to the direct exciton formation at [Ru(dphphen)3]2+ molecule by charge trapping from PVK and PBD. The emission is isolated to [Ru(dphphen)3]2+ by inserting a layer of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) between PVK:PBD:[Ru(dphphen)3]2+ and Alq3 layers.

Light-emitting diodes based on dipyrido[3,2-a:2 ′ ,3 ′ -c]phenazine (dppz) and Re(CO) 3 Cl-dipyrido[3,2-a:2 ′ ,3 ′ -c]phenazine (Re(CO) 3 Cl(dppz)) dyes incorporated into a poly( N -vinylcarbazole) (PVK) host have been fabricated. The dppz dyes doped into PVK show PL spectra that have large Stokes shifts (more than 9000 cm −1 ), but the dppz emission does not appear in the EL spectra. The Re-based dyes show virtually no emission in the PL spectra when doped into PVK, however, the emission from the Re-based dyes dominates the EL spectra. This is because the Re-based dyes are able to transport efficiently hole and electron carriers leading to electronic excitation of the dye excited state through charge-carrier mechanisms.

Molecular structures of a series of 3'-[1E-2-(4-R-phenyl)ethenyl]-2,2':5',2"-terthiophenes have been modeled using ab initio calculations. The potential energy surfaces of three important dihedral angles were calculated using the HF/3-21G(d) method. Each dihedral angle is represented by a distinct potential energy surface, while the identity of the R group has only a modest influence. DFT methods (B3LYP/6-31G(d)) were used to calculate the geometry and vibrational spectra of each molecule. Analysis of the theoretical vibrational data reveals numerous conserved modes that are localized on the terthiophene or phenyl groups. There is good agreement between the observed and calculated vibrational spectra of the molecules. Conformational changes have only a minor effect on the spectra. The calculated molecular orbitals, which are supported by electronic absorption measurements, suggest that the first excited state should have charge-transfer features for the molecules with strongly electron withdrawing or donating substituents.

Light-emitting devices based on ruthenium(II)(4,7-diphenyl-1,10-phenanthroline)3 ([Ru(dphphen)3]2+) as emitter have been fabricated. The effect of an electron transport layer of tris-(8-hydroxyquinoline) aluminum (Alq3) on device performance has been investigated. The emission, peaking at 630 nm, for the indium–tin–oxide (ITO)glass/[Ru(dphphen)3]2+/Ag device reaches maximum luminance after about 15 min at a turn on voltage of 2.5 V. The use of an ITO/[Ru(dphphen)3]2+/Alq3/Ag device reduces this response time to about 120 s at a turn on voltage of 7 V. A maximum brightness of 1300 cd/m2 can be obtained at 15 V within 2 s, with a luminous efficiency of 0.27 cd/A. Based on the charge transporting characteristics of [Ru(dphphen)3]2+ and Alq3 films determined by surface photovoltage spectroscopy, the improved device response time and efficiency are attributed to the enhanced electron injection at [Ru(dphphen)3]2+/Alq3 interface.

Exciplex electroluminescence of indium-tin-oxide glass (ITO)/poly( N -vinylcarbazole)(PVK): N , N ′ -diphenyl- N , N ′ -bis(3-methylphenyl)-[1,1 ′ -biphenyl]-4,4 ′ -diamine(TPD):2,5-bis (5-tert-butyl-2-benzoxazolyl) thiophene (BBOT)/Al devices have been investigated in comparison with ITO/PVK:BBOT/Al device. While the ITO/PVK:BBOT/Al device shows emission dominated by exciplex interaction of PVK with BBOT, the ITO/PVK:TPD:BBOT/Al devices show emission color adjustable by the hybrid exciplex interaction of TPD with BBOT, and this exciplex becomes the primary recombination center at a critical TPD doping concentration. The device efficiency can be improved markedly by incorporating hole transporting poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) and electron transporting 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/tris-(8-hydroxyquinoline) aluminum (Alq 3 ) layers in a structure of ITO/PEDOT:PSS/PVK:TPD:BBOT/BCP/Alq 3 /Al.

An analysis of the X-ray structure, vibrational and electronic spectra of BrRe(CO)4daad, 2, and a spectroscopic study of the radical anion 2 − are presented (daad=2,6-diazaanthracene-9,10-dione). Strong π-stacking is seen in the crystal structure of 2. Electronic absorption, resonance Raman vibrational analysis and electrochemistry of 2 support an assignment of the HOMO and LUMO to a predominately metal dπ and ligand π* orbital (localised on the quinoidal ring), respectively. There is poor orbital overlap between donor Re (dπ) and acceptor ligand π* MOs. 2 undergoes a ligand-based reduction process at −0.24 V vs. decamethylferrocene to give 2 − which was investigated by spectroelectrochemistry and isolated as the [Cp2Co]+ salt. Insoluble [XRe(CO)3daad]n and unstable XRe(CO)3(daad)2 complexes, where X=Br or Cl, were also identified.

The light emitting devices using ruthenium(II)bis(2,2′-bipyridine)(4,7-dimethyl-1,10-phenanthroline) [Ru(bpy)2DIM]2+ complex as emitter have been fabricated in two structures: indium–tin-oxide glass (ITO)/poly(N-vinylcarbazole) (PVK):[Ru(bpy)2DIM]2+/Al and ITO/PVK:[Ru(bpy)2DIM]2+/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/tris-(8-hydroxyquinoline) aluminum (Alq3)/Al. In ITO/PVK:[Ru(bpy)2DIM]2+/Al, the emitter concentration influences both the turn on voltage and the emission wavelength. At 6 wt% [Ru(bpy)2DIM]2+ concentration, the device has a turn on voltage of 16 V and the emission peak at 600 nm. At 36 wt% [Ru(bpy)2DIM]2+ concentration, the device turn on voltage can be reduced to 3 V, with the emission peak at 620 nm. ITO/PVK:[Ru(bpy)2DIM]2+ (36 wt%)/BCP/Alq3)/Al obtains a quantum efficiency one order of magnitude higher than ITO/PVK:[Ru(bpy)2DIM]2+ (36 wt%)/Al.

The resonance Raman and infrared spectra of the bridging ligand 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz) have been studied. Ab initio calculations on bptz and the radical anion bptz·− are able to predict the frequencies and intensities of the vibrational spectra. This analysis is used to interpret the vibrational spectroscopy of the bridged binuclear complexes [(bpy)2Ru(μ-bptz)Ru(bpy)2]4+ (1) and [(PPh3)2Cu(μ-bptz)Cu(PPh3)2]2+ (2) and their redox products. The resonance Raman spectroscopy of 1 reveals the bichromophoric nature of the complex, with bpy and bptz ligand modes being enhanced selectively as a function of excitation wavelength. The UV/Vis spectrum of 1+ reveals a strong IVCT band suggesting the mixed-valent species is Class III in nature. This is consistent with findings for other metal moieties with the bptz ligand. The resonance Raman spectrum of 1+ is also consistent with a Class III formulation. The resonance Raman spectrum of 2− is used to model bptz·− and the ab initio calculations show some correlation with the observed spectrum. The excited-state resonance Raman spectra of 1, generated with 532 and 633 nm excitation, show spectral features that are not strongly characteristic of bptz·−. This appears to be a consequence of the delocalised nature of the molecular orbitals involved in the excited-state of 1.

Several binuclear Re(I) and Re(I)Os(II) complexes with polypyridyl bridging ligands, 6,7-dimethyl-2,3-di(2-pyridyl)quinoxaline (dpqMe2) and [2,3-a:3′,2′-c]dipyrido-6,7-dimethylphenazine (ppbMe2), were synthesized and studied. The visible region of the electronic absorption spectrum is dominated by a single metal-to-ligand charge-transfer band (ca 600 nm) and a dpqMe2- or ppbMe2-based ligand-centred band (ca 400 nm). The resonance Raman spectra of these complexes were recorded at several excitation wavelengths. Analysis of the resonance Raman spectra identified a number of strongly enhanced chromophore-specific signatures with excitation wavelengths coincident with the main absorption bands, and weakly enhanced chromophore-specific signatures at intermediate excitation wavelengths. Resonance Raman excitation profiles (RREPs) are presented for selected marker bands. Analysis of the chromophore-specific signatures and the RREPs allowed a more complete assignment of the features in the electronic absorption spectra to be made. Copyright © 2002 John Wiley & Sons, Ltd.

A series of donor-acceptor compounds based on triphenylamine and hexaazatrinaphthalene are investigated. Using a variety of linker units, it is possible to tune the intensity of low energy transition from 8,000 M-1 cm-1 to 24,000 M-1 cm-1 and vary the wavelength between 430 to 490 nm. The effect of the linker may be observed in the resonance Raman spectra with linker unit modes showing strong enhancement when they are coupled to the charge transfer transition. This is evident in the case of the C≡C and triazolyl linker units. Charge transfer is consistent with DFT calculations, which implicate some linkers as having pseudo-donor like behaviour. The emission spectra of the dyes are solvatochromic with Stokes shift versus solvent parameter gradients of 20,000 cm-1. This shows that the dipole change is still large even when the bridge becomes involved in the transition.

This review article includes an introduction to the principals of Raman spectroscopy, an outline of the experimental systems used for Raman imaging and the associated important considerations and limitations of this method. Common spectral analysis methods are briefly described and examples of interesting published studies which utilised Raman imaging of pharmaceutical and biomedical devices are discussed, along with summary tables of the literature at this point in time.

Exciton coupling is investigated in a copper azadipyrrin complex, Cu(L-aza)2. Exciton coupling in Cu(L-aza)2 assuming a single π-π* state on the L-aza ligand fails to account for the electronic structure of Cu(L-aza)2, which displays two almost equal intensity transitions at 15 600 cm(-1) and 17 690 cm(-1). TD-UB3LYP/6-31G(d) calculations suggest multiple π-π* transitions for the L-aza ligands and simple vector addition of the transition dipoles predicts two nearly orthogonal co-planar excitonic transitions that correctly reproduce the absorption band profile. Empirical modelling of absolute resonance Raman intensities using wavepacket dynamics confirms Cu(L-aza)2 has two equal intensity orthogonal exciton transitions. The phenyl substituents at the α- and γ-positions of the pyrrole rings play a central role in determining the orientation of the transition dipoles. Consequently the π-π* transitions for the L-aza ligands are oriented towards the substituent groups and are not in the plane of the pyrrole rings. Mode displacements in the Franck-Condon (FC) region obtained from the wavepacket model suggest that pyrrole ring and phenyl modes control the exciton FC dynamics. Our results suggest that Cu(L-aza)2 is an ideal model for theoretical, computational and experimental investigations of molecular excitons in molecular systems.

Summary The New Zealand mānuka shrub, Leptospermum scoparium, and the Australian L. morrisonii produce herbicidal β-triketones in their leaves. The localization of these potential self-toxicants has not been proven. We investigated the localization of these compounds in leaves using Raman microscopy. The results are presented as heat maps derived from principal component analysis (PCA) of the Raman spectra from sampling grids of leaf sections. This approach used undirected, data-driven analysis to qualitatively distinguish localized plant chemistry. The presence of β-triketones and lipophilic flavonoids was confirmed by GC-MS and 1H NMR spectroscopy. Grandiflorone was compartmentalized within the leaf oil glands of L. morrisonii. Leptospermum scoparium also contained high concentrations of grandiflorone, previously reported as only a trace component in essential oils, localized in the oil glands in the leaves of varieties from diverse geographical locations. Raman microscopy was used to probe the chemistry of oil glands in several ornamental mānuka varieties, revealing high concentrations of bioactive flavonoids localized in these glands. The compartmentalization of β-triketones within oil glands inside leaves of Leptospermum shrubs may defend the plants against herbicidal activity.

International audience; Electroreduction of 4-nitrobenzenediazonium ions at highly ordered pyrolytic graphite (HOPG) gives a nitrophenyl film that is shown by noncontact atomic force microscopy (AFM) to be continuous and of multilayer thickness. Investigation of the same surface by ultrahigh vacuum scanning tunneling microscopy (UHV-STM) reveals molecular species immobilized on the step edges, but only mobile species on the basal planes. After several scans across an area of basal plane, atomic-level resolution images of clean, defect-free graphite surfaces are obtained. The same behavior is observed with a film deposited by reduction of 4-((triisopropylsilyl)ethynyl)benzenediazonium ion. Throughout extensive STM measurements we find no evidence for covalent attachment of aryl groups to the basal plane and conclude that our results can be best explained by the formation of films of physisorbed oligomeric species. After heating above 300 °C, nitrophenyl films are more stable to STM imaging but no longer contain nitro groups. Increased cross-linking within the film from coupling of radicals formed by thermal decomposition of nitrophenyl groups may be responsible for the more robust film structure.

A series of dipyrido[3,2-a:2',3'-c]phenazine (dppz)-based ligands with electron-withdrawing substituents and their [Re(CO)3(L)Cl] and [Re(CO)3(L)(py)]PF6 complexes have been studied using Raman, resonance Raman, and transient resonance Raman (TR(2)) and time-resolved infrared (TRIR) spectroscopic techinques in conjunction with computational chemistry as well as electrochemical studies, emission, and absorption of ground and excited states. DFT (B3LYP) frequency calculations show good agreement with nonresonant Raman spectra, which allowed these to be used to identify phenanthroline, phenazine, and delocalized modes. These band assignments were used to establish the nature of chromophores active in resonance Raman spectra, probed with wavelengths between 350.7 and 457.9 nm. X-ray crystallography of [Re(CO)3(dppzBr2)Cl] and [Re(CO)3(dppzBr)(py)]PF6 showed these crystallize in space groups triclinic P1 and monoclinic P2(1/n), respectively. Electrochemical studies showed that substituents have a strong effect on the phenazine MO, changing the reduction potential by 200 mV. Transient absorption studies showed that generally the [Re(CO)3(L)(py)]PF6 complexes had longer lifetimes than the corresponding [Re(CO)3(L)Cl] complexes; the probed state is likely to be (3)π → π* (phz) in nature. TR(2) spectra of the ligands provided a marker for the triplet π → π* state, and the TR(2) spectra of the complexes suggest an intraligand (IL) π,π* state for [Re(CO)3(L)(py)](+) complexes, and a potentially mixed IL/MLCT state for [Re(CO)3(L)Cl] complexes. TRIR spectroscopy is more definitive with THEXI state assignments, and analysis of the metal-carbonyl region (1800-2100 cm(-1)) on the picosecond and nanosecond time scales indicates the formation of MLCT(phen/phz) states for all [Re(CO)3(L)Cl] complexes, and IL π → π* (phen) states for all [Re(CO)3(L)(py)](+) complexes, with all but [Re(CO)3(dppzBr(CF3))(py)](+) showing some contribution from an MLCT(phen) state also.

This report reviews work on vibrational spectroscopy of N-donor ligand metal complexes from 2008–2013. The particular focus is on the examination of excited states using resonance Raman spectroscopy, transient resonance Raman spectroscopy and time-resolved infrared spectroscopy. The report describes some of the basic concepts around each technique and then highlights work from the review period that exemplifies the utility of each method. In addition tables are included that summarise the work using these methods over the review period.

A facile synthesis of metal complexes incorporating functionalised pyridines using a ruthenium(II) tetrakis(4-formylpyridine)dichloride building block is described. These complexes have been studied using electrochemistry, electronic absorbance and resonance Raman techniques. The molecules are able to be tuned electronically by varying the functionality attached to the pyridine in the complexes derived from ruthenium(II) tetrakis(4-formylpyridine)dichloride.

Conventional descriptions of excitons in semiconducting polymers do not account for several important observations in polymer:fullerene photovoltaic blends, including the ultrafast time scale of charge photogeneration in phase separated blends and the intermediate role of delocalized charge transfer states. We investigate the nature of excitons in thin films of polymers and polymer:fullerene blends by using broadband ultrafast photoluminescence spectroscopy. Our technique enables us to resolve energetic relaxation, as well as the volume of excitons and population dynamics on ultrafast time scales. We resolve substantial high-energy emission from hot excitons prior to energetic relaxation, which occurs predominantly on a subpicosecond time scale. Consistent with quantum chemical calculations, ultrafast annihilation measurements show that excitons initially extend along a substantial chain length prior to localization induced by structural relaxation. Moreover, we see that hot excitons are initially highly mobile and the subsequent rapid decay in mobility is correlated with energetic relaxation. The relevance of these measurements to charge photogeneration is confirmed by our measurements in blends. We find that charge photogeneration occurs predominately via these delocalized hot exciton states in competition with relaxation and independently of temperature. As well as accounting for the ultrafast time scale of charge generation across large polymer phases, delocalized hot excitons may also account for the crucial requirement that primary charge pairs are well separated in efficient organic photovoltaic blends.

A series of free-base, zinc and mixed free-base-zinc porphyrin dimers were investigated using electrochemistry, electronic absorption, resonance Raman and emission studies. The spectroelectrochemistry of these compounds was also examined. The electronic absorption and resonance Raman data suggest that the two porphyrins in the dimer are behaving as independent chromophores with limited communication. However, emission studies show that energy transfer occurs between the two units. The linking unit is seen to have limited influence on the properties of chromophores.

The electronic absorption and resonance Raman spectra of a series of rhenium(I) and copper(I) complexes with substituted dipyrido[3,2-a : 2′,3′-c]phenazine (dppz) ligands were investigated. The ligands were ben[i]dipyrido[3,2-a : 2′,3′-c]phenazine, 11,12-dimethyldipyrido[3,2-a : 2′,3′-c]phenazine, 10-methyldipy- rido[3,2-a : 2′,3′-c]phenazine and 11-methyoxydipyrido[3,2-a : 2′,3′-c]phenazine. The spectroelectrochemistry of the reduced complexes and the emission and resonance Raman spectra of the excited states are reported. Vibrational wavenumber calculations of the unsubstituted ligand suggest the presence of normal modes that are localized to various sections of the ligand structure; the resonance Raman spectra of the complexes are interpreted with reference to these calculations. The analysis of the spectra revealed that the Franck–Condon state initially formed by visible photoexcitation (450 nm) is metal-to-ligand charge-transfer in nature. Spectroelectrochemical resonance Raman and electronic absorption measurements revealed the spectral signatures for the radical anions of each of the ligands used in this study. These spectral features were used to assign the excited states formed by the complexes. Most of the complexes studied show spectral features in their excited-states that suggest that the predominant state formed within 5 ns of excitation is ligand-centred. Copyright © 2000 John Wiley & Sons, Ltd.

The resonance Raman spectra of the ground- and lowest excited-states for a series of binuclear copper(I) complexes with bridging ligands based on 2,3-di-(2-pyridyl)quinoxaline have been measured. Analyses of the ground-state resonance Raman spectra show strong enhancement of an inter-ring stretching mode and quinoxaline-based modes; consistent with the Frank–Condon state having bonding changes about the copper(I) centre and on the quinoxaline ring system. The electronic absorption data also suggest the initially formed MLCT-state is localised towards the quinoxaline ring system. The excited-state resonance Raman spectroscopy shows similar spectral features for complexes which have substituent changes at the pyridyl rings of the bridging ligand. They show spectra associated with the radical anion of the bridging ligand. This is consistent with the formation of an excited-state which is metal-to-ligand charge-transfer in nature and where the radical anion is localised on the quinoxaline ring system of the bridging ligand.

Binuclear complexes of the type [(bpy)2Ru(BL)Cu(PPh3)2]3+, where bpy = 2,2′-bipyridine, BL = 2,3-di-2-pyridylpyrazine (dpp), 2,3-di-2-pyridylquinoxaline (dpq), or 6,7-dimethyl-2,3-di-2-pyridylquinoxaline (dpqMe2), were readily formed by the reaction of [Cu(PPh3)4]+ with mononuclear complexes [Ru(bpy)2(BL)]2+. The binuclear complexes are stable in CH2Cl2 solution at concentrations above 10–3 mol dm–3 having equilibrium constants for formation in the range 1000–2500 dm3 mol–1. Single crystal structures for [(bpy)2Ru(dpp)Cu(PPh3)2]3+ and [(bpy)2Ru(dpqMe2)Cu(PPh3)2]3+ show distortions of the bridging ligand in the form of twisting and splaying of the ring systems. Electrochemical and UV/Visible data suggest the {Cu(PPh3)2}+ moiety has little affect in stabilising the BL π* orbital. Resonance Raman spectra show the bichromophoric nature of the visible absorptions of the heteroleptic complexes; both bpy and BL ligand vibrations are enhanced depending on the excitation wavelength. Observation of a Ru–N vibration suggests that the dominant transition in the visible region is Ru(dπ)→BL(π*) CT.

Several new ferrocene-functionalised porphyrins and a ruthenocene-functionalised porphyrin have been synthesized and studied using electrochemistry, electronic absorbance and resonance Raman spectroelectrochemical techniques. The porphyrin and ferrocene are observed to have limited effect on each other with the properties of the porphyrin dominating the spectroscopy of these molecules.

A series of four binuclear rhenium (I) complexes of the general form [Re(CO)3Cl]2BL, where BL is a polypyridyl bridging ligand, have been studied using ultrafast time-resolved UV/visible (TRVIS) and infrared (TRIR) spectroscopies. Visible excitation produces a metal-to-ligand charge-transfer (MLCT) excited state. Kinetic measurements show that the lifetime of this MLCT state varies between 100 and 1900 ps, depending on the structure of the bridging ligand. TRIR difference spectra show that each complex forms a similar MLCT state which has mixed valence character.

In TiO2-based dye-sensitized nanocrystalline solar cells, efficiencies of up to 11% have been obtained using Ru dyes, but the limited availability of these dyes together with their undesirable environmental impact have led to the search for cheaper and safer organic-based dyes. In this Letter, we report the synthesis, electronic, and photovoltaic properties of novel green porphyrin sensitizers. All six porphyrin dyes give solar cell efficiencies of ≥5%, but the best performing dye under standard global AM 1.5 solar conditions gives a short circuit photocurrent density (jsc) of 14.0 ± 0.20 mA/cm2, an open circuit voltage of 680 ± 30 mV, and a fill factor of 0.74, corresponding to an overall conversion efficiency of 7.1%, which, for porphyrin-based sensitizers, is unprecedented. This same dye gives an efficiency of 3.6% in a solid-state cell with spiro-MeOTAD as the hole transporting component, comparable to solid-state cells incorporating the best performing ruthenium dyes.