Auxiliary Chromophores Research Articles

Tuning photophysical and electroluminescent properties of phenanthroimidazole decorated carbazoles with donor and acceptor units: Beneficial role of cyano substitution

Four new multi-functionalized carbazole derivatives featuring phenanthroimidazole, N-phenylcarbazole and cyano-substituents are designed and synthesized. The dyes are characterized by photophysical, electrochemical and thermal properties and the dependency of auxiliary chromophores on the functional properties critically analyzed. The dyes showed tunable emission from violet to blue region depending on the chromophore attached to the carbazole core. The cyano-substituted dyes exhibited enhanced intramolecular charge transfer in optical properties as compared to N-phenylcarbazole substituted dyes. Consequently, cyano-substituted dyes displayed solvatochromism in emission and possess large Stokes shift. All the dyes showed remarkable thermal stability attributable to robust phenanthroimidazole and carbazole chromophores. The fluorescent sensory properties of all the dyes toward acid are also explored and found that the emission of cyano derivatives displayed blue shift due to protonation of phenanthroimidazole unit. Finally, the dyes are employed as dopant emitter in multilayer solution-processed organic light-emitting diode which displayed blue electroluminescence.

Effects of different electron donating groups on dye regeneration and aggregation in phenothiazine-based dye-sensitized solar cells

A series of phenothiazine-based dyes containing different auxiliary chromophores (TP, TTP, EP, and EEP) bring about unusual power conversion efficiency (PCE) for the corresponding dye-sensitized solar cells (DSSCs): EEP with the best electron-donating capability provides the lowest PCE of 2.24%, while TP with the weakest electron-donating capability leads to the highest PCE of 8.07%. The underlying influencing factors have been investigated by considering the electronic structures and aggregation properties based on density functional theory and Marcus theory. We found that the energy-mismatch between electron-donating units and the PTZ moiety results in poor EEP dye regeneration. Additionally, molecular dynamics simulations illustrate that the increased intermolecular interaction energy induced by preferable electron-donating groups aggravates the intermolecular aggregation. Especially, the calculated average values of the time-dependent intermolecular lateral charge transfer rate k for (EEP)2 are nearly one order of magnitude higher than those of (TP)2, revealing a more robust π-π stacking interaction induced by the donor unit of EEP. Importantly, the dye-TiO2 interactions have been taken into account, which are absent in many previous theoretical work but crucial for accurate describing the aggregations. These deeper insights into the regeneration process and the aggregation mechanism induced by different donor units encourage researchers to balance various properties in designing novel components for photovoltaic devices.

A systematic study of phenoxazine-based organic sensitizers for solar cells

We perform a systematic theoretical and computational investigation of phenoxazine (POZ)-based organic dyes to rationalize the marked difference in the energy conversion efficiency. The geometries, electronic structures and absorption spectra of the dyes and their adsorbed dye-TiO2 systems are carried out by means of density functional theory (DFT) and time-dependent DFT methods. The relevant physical parameters that dominate the performance of the cell, such as the light harvesting efficiency (ΦLHE), exciton binding energy (Eb), the driving force for electron injection (ΔGinj), the conduction band shift (ΔECB), and transferred charges (nc) are assessed in detail to determine their contributions to either the short-circuit photocurrent density (Jsc) or the open-circuit photovoltage (Voc), and establish the structure-property relationships. The calculated results elucidate that the extension of π-spacer, the introduction of di-anchoring group and auxiliary chromophores make significant influence on the PCE of the cells. The designed dyes with the introduction of elongated π-spacer, N-phenlycarbazole substitution at the 7-position of POZ and thiophene-linked di-anchoring group could be potential POZ-based candidates used in DSSCs. We hope that our calculations give a more in-depth physical insight on structure-property relationship for POZ-based dyes and provide a hint to design and screen novel high performance POZ-like dyes.

Effect of Auxiliary Chromophores on the Optical, Electrochemical, and Photovoltaic Properties of Carbazole‐Based Dyes

AbstractOrganic dyes containing 2‐diphenylaminocarbazole donors and decorated with auxiliary chromophores at the diphenylamine moiety have been synthesized and characterized. The nature of the chromophores on diphenylamine unit alters the light‐harvesting properties and HOMO/LUMO energies of the dyes. Butoxy substitution raises the HOMO and lowers the LUMO energies. But the incorporation of fluorenyl units fine‐tunes the LUMO upwardly, which improves the thermodynamic driving force for electron injection into the conduction band of TiO2 and hikes the incident photon‐to‐current conversion efficiency. Consequently, a dye with fluorene in the donor unit and thiophene in the π‐conjugation pathway is the most efficient (5.76 %) and has the highest photocurrent density (14.60 mA cm−2) in the series. Electrochemical impedance analysis of the devices showed the importance of fluorene units in suppressing electron recombination.

The utility of dimolybdenum tetrakis(μ-isovalerate) and tetrakis(μ-pivalate) in the stereochemical studies of various transparent compounds

The aim of the present work was to verify the usefulness of dimolybdenum tetrakis(μ-pivalate) and tetrakis(μ-isovalerate) as auxiliary chromophores for determining the absolute configuration of optically active vic-diamines, vic-amino alcohols, α-amino and α-hydroxy acids by means of electronic circular dichroism (ECD). To this end, a series of measurements designed to check the dependence of ECD and UV-Vis spectra on time and concentration was carried out. The experimental results were supported by a separate set of detailed DFT calculations. The results obtained allowed us to determine the most probable structure of dominating chiral complexes formed in situ in solution for all ligands studied.

Dimolybdenum Tetracarboxylates as Auxiliary Chromophores in Chiroptical Studies ofvic-Diols

The aim of the present work was to check the suitability of dimolybdenum carboxylates, other than commonly used [Mo2(OAc)4], as auxiliary chromophores for determining the absolute configuration of optically active vic-diols by means of electronic circular dichroism (ECD). To this end, a set of dimolybdenum tetracarboxylates was synthesized, and subsequently, the two most promising compounds were selected, namely dimolybdenum tetrakis(μ-pivalate) and tetrakis(μ-isovalerate). The selection was based on their solubility in commonly used solvents, their stability in solution, their tolerance to air exposure, as well as their utility for dichroic studies. The stability of the obtained in situ chiral complexes was verified by measuring the dependence of ECD, UV-vis, and NMR spectra on time, temperature, and concentration. We have shown that the ECD spectra of diverse vic-diols with these complexes are suitable for configurational assignment based on the correlation between signs of Cotton effects (CEs) arising in the spectra and the stereostructure of the ligand. Furthermore, to aid in the interpretation of experimental results, a separate set of DFT calculations has been incorporated to provide additional insight into the structure of the chiral complexes involved. In contrast to the earlier assumptions, experiments showed that the chelating mode of ligation is preferred for the studied complexes.

2,7-Diaminofluorene-Based Organic Dyes for Dye-Sensitized Solar Cells: Effect of Auxiliary Donor on Optical and Electrochemical Properties

New organic dyes containing a diarylaminofluorene unit as an electron donor and cyanoacrylic acid as acceptor and anchoring group in a donor-π-donor-π-acceptor architecture have been synthesized and characterized as sensitizers for nanocrystalline TiO(2)-based dye-sensitized solar cells. They have shown three major electronic absorptions originating from the π-π* and charge-transfer transitions covering the broad visible range (250-550 nm) in solution. The charge-transfer transition of the dyes exhibited negative solvatochromism, suggesting a polarized ground state. They have also displayed acidochromism in solution owing to the presence of a protonation-deprotonation equilibrium. On comparison with the triphenylamine and carbazole-based parent dyes (E)-2-cyano-3-(4-(diphenylamino)phenyl)acrylic acid and (E)-2-cyano-3-(9-ethyl-9H-carbazol-3-yl)acrylic acid they exhibited longer wavelength absorptions and facile oxidation, indicating the stronger electron-donating ability of the auxiliary chromophores. In addition, they exhibited nearly two times larger light-to-electron conversion efficiency under simulated AM 1.5 G irradiation (100 mW cm(-2)) with an aperture mask when compared to the parent dyes. Among the new dyes, the one containing the naphthylphenylamine segment showed better device characteristics attributable to the higher HOMO energy level which probably facilitates the regeneration of the dye and effective suppression of the back reaction of the injected electrons with the I(3)(-) in the electrolyte. The optical properties of the dyes were modeled using TDDFT simulations employing different theoretical models (B3LYP, CAM-B3LYP, and MPW1K), and the best correlations with the observed parameters have been found for CAM-B3LYP and MPW1K calculations. The electron lifetimes extracted from the electrochemical impedance measurements of the dye-sensitized solar cells were used to interpret the solar cell efficiency alternations.

Ultrafast Photosensitization of Phthalocyanines through Their Axial Ligands

We have studied the energy transfer properties of a novel silicon phthalocyanine that coordinates two anthracene-9-carboxylate groups in the form of trans axial ligands. Our objectives were to generate a system with auxiliary chromophores that enhance the light absorption properties of the macrocycle in a specific region in the UV and to evaluate the efficiency and time scales for energy transfer. The ligand coordination through a carboxylate group directly attached to the anthracenic system allows for close proximity of the donor and acceptor chromophores. The energy transfer process was observed to be nearly 100% efficient and to occur on a time scale of 370 fs. From the energy relations of the donor and acceptor states and the observed dynamics, the initial energy transfer step is likely to involve upper electronic states of the phthalocyanine rather than the states of the lowest-energy vibroelectronic Q bands.

Dinuclear Transition Metal Complexes as Auxiliary Chromophores in Chiroptical Studies on Bioactive Compounds

AbstractFor Abstract see ChemInform Abstract in Full Text.

Dinuclear Transition Metal Complexes as Auxiliary Chromophores in Chiroptical Studies on Bioactive Compounds

Chiroptical methods, the circular dichroism spectroscopy (CD) in particular, appear to be sensitive, fast and convenient methods for determination of absolute configuration of chiral compounds in solution. For the CD to be applicable, however, the investigated compounds have to be not only optically active but also should absorb circularly polarized light in an accessible spectral range. To carry out the circular dichroic studies on compounds transparent in the UV-vis region, a suitable chromophoric system needs to be introduced into the molecule in the immediate vicinity of stereogenic center. In such manner the inherently transparent compounds are transformed into so-called cottonogenic derivatives. The method proposed in this work consists of the generation of chiral complexes in situ by mixing the chiral but non-absorbing substance with a solution of an achiral transition metal complex acting as auxiliary chromophore. Such complexes of general formula [M2(COOR)4]k+ X-k where M = Mo, Rh, and Ru can exchange in situ one or more of its carboxylate units with other ligands to form chiral complexes of a bridging or a chelating structure. In all cases, i.e., irrespective of the complexation mode, the CD arising within the d-d absorption bands of the metal cluster depends solely upon the chirality of the compound acting as ligand(s). A variety of biologically important compounds like e.g., amino and hydroxy acids, alcohols, amines, diols, aminols etc., are investigated as potential ligands for these studies. The examination of the CD spectra of the in situ formed chiral complexes allows assignment of the absolute configuration and conformational features of the ligands as well. Keywords: dinuclear transition metal complexes, auxiliary chromophores, chiroptical studies, bioactive compounds, circular dichroism spectroscopy, hydroxy acids

ChemInform Abstract: Transition‐Metal Complexes as Auxiliary Chromophores in Chiroptical Studies on Carbohydrates

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Transition Metal Complexes as Auxiliary Chromophores in Chiroptical Studies on Carbohydrates

Circular dichroism is obtained only within absorption bands. Carbohydrates, but also alcohols, amines, ethers etc. are transparent in the UV-VIS region of commercially CD spectropolarimeters. In order to see Cotton effects of such compounds, new chromophors have to be introduced in their molecules to form so-called cottonogenic derivatives. One procedure for this is the in situ formation of chiral complexes by mixing the optically active but non­ absorbing substance with a solution of an achiral transition metal complex. By examination of the CD bands of these chiral complexes, configurational and conformational features of the ligands can be determined. Some of our investigations exemplify the application of this approach to carbohydrates: a) Pyranose sugars, bearing free 1,2,3-hydroxyl groups, react with acidic molybdate solutions and form stable Mo-sugar complexes in the pH-range 5-6. They exibit, depending on the sugar structure, two kinds of typical CD curves, whose parameters are correlated, according to a chirality rule, with the sugar configurations. b) Cuprammonium complexes were used first by Reeves to determine configurations and conformations of sugars. Cotton effects of 1,2-diol and 1,2,3-triol pyranoside sugar-cuprammonium complexes are closely examined; for these compounds a helicity rule is verified and proposed. c) Dinuclear transition metal acylates have bee·n widely used recently as chromophores for cottonogenic derivatives. CD spectra of 1,2- and 1,3-diols (including sugar dials) with dimolybdenum tetraacetate as well as the corresponding chirality and sector rules are presented in detail and discussed. d) It is shown that dimolybdenum tetraacetate does not form chiral complexes with monohydroxyalcohols. Dirhodium acetate has more affinity to such ligation. Some complexes of dirhodium tetracis(trifluoroacetate) with monohydroxyalcohols of sugar series have been prepared in situ. Finally the possibility is discussed applying a bulkiness rule to correlate the alcohol geometry with the sign of one of the CD bands of the corresponding rhodium-alcohol-complex.

緑膿菌の赤色々素の産生に関する研究(第III報)

Three red pigments have been produced from Ps. aeruginosa, strain No.145, in the synthetic medium containing glutamic acid.A pigment P-I has been isolated in pure state and its structure has been supposed to be a new derivative having a aminophenazine skeleton with the formula C17H19N3O9.P-I can not be extracted from the culture with usual organic solvents and has been isolated using, column chromatography on the cross linked dextran gel, Sephadex G-25M and aluminium oxide treated with acid.P-I concentrated to the top zone in a Sephadex column, and is not adsorbed on the acid washed alumina.The red pigment, P-I isolated as crude crystals from the culture filtrate has been finally recrystallized several times from distilled water. The original culture contains about 1 mg of the purified P-I per liter.The purified material has been obtained as deep purple red, needles(m. p. >250°C, dec.) and it is characterized by a beautiful green color reaction with concd. sulfuric acid. This reaction has been known as a common color reaction for aminophenazine derivatives.Anal: Calcd. for C17H19O9N3. C 49.88, H 4.68, N 10.27. M. W.409.35. Found: C 49.80, H 4.54, N 10.35.P-I is soluble in water, insoluble in non-polar solvents, dialysable, unstable in alkaline solution, reduced to yellow substance which is reoxidized with hydrogen peroxide or with air to. original pigment and considerably stable in aq. solution at pH 3-10. The acidic solution shows a reddish violet and a yellow color in alkaline solution. pKa = 3.14, Distance of Electromigration: + 0.5 (McIlvaine's buffer pH 6.0,0.73mA/cm,5 hrs.)The ultraviolet and visible absorption spectrum in distilled water exhibits four maxima E1%1cm 1480 at 234mμ, E1%1cm 2040 at 283 mμ, E1%1cm 500 at 396 mμ and E 1%1cm 584 at 515 mμ, these are shifted to 236mμ,287mμ,390mμ,546mμ in 0.1N-HCl solution and 233 mμ,271mμ,374mμ,460mμ in 0.1 N-NaOH solution respectively.The nuclear magnetic resonance spectrum of P-I suggests a existence of following groups; τ=7.08(-H-CH3)and τ=8.18(CH3_??_).In the infrared absorption spectrum, aromatic signals (1635,1520 cm-1) and a broad peak of amino group (3400 cm-1) are observed.From results mentioned above, P-I was supposed to be one of amino-phenazine, However, by the comparison with several phenazines of the absorption spectrum over the range 220-600mμ the spectrum of P-I has been found to be very similar to that of 2,6-diaminophenazine. It is presumed that the red pigment has a phenazine structure substituted at C2 and C6 with some auxiliary chromophores.