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This review provides a comprehensive examination of the applications of the seminal coupling principle introduced by Siegfried Dähne and Dieter Leupold in 1966. Their heuristic and groundbreaking work proposed that combining multiple polymethine subunits within a single chromophore enables orbital coupling, consequently narrowing the HOMO–LUMO gap, and yielding redshifted optical properties. These outcomes are particularly valuable for developing organic dyes tailored for visible‐to‐near‐infrared applications. Despite their potential, coupled polymethines remain relatively underexplored, with most reported instances being serendipitous discoveries over the last six decades. In light of this, our review compiles and discusses the reported coupled polymethine structures, covering synthetic, spectroscopic, theoretical and applicative aspects, offering insights into the structure‐property relationships of this unique class of dyes and perspectives for their future applications. [ABSTRACT FROM AUTHOR]

Polymethine dyes of tetraanionic nature comprising 1,3,2‐dioxaborine rings in the polymethine chain and end‐groups of different electron‐accepting abilities have been synthesized. They can be considered as oligomeric polymethines, where a linear conjugated π‐system passes through three 1,3,2‐dioxaborine units and a number of tri‐ and dimethine π‐bridges between two end‐groups. The obtained dyes exhibit near‐infrared absorption and fluorescence, with molar absorption coefficients reaching as high as 564000 M−1 cm−1 in DMF, rendering them among the strongest absorbers known. The novel compounds are bright NIR fluorophores, with fluorescence quantum yields up to 0.13 in DMF. A comparative analysis of the electronic structure of the obtained dyes with respective dianionic and trianionic oligomers was conducted through quantum chemical calculations. [ABSTRACT FROM AUTHOR]

Polymethines containing an allyl group have been synthesized. Their films are produced by physical vapor deposition (PVD) on glass, silicon (Si), gold (Au), polytetrafluoroethylene (PTFE), and nanostructured plastic substrates. Optical spectra recorded during the deposition showed no decomposition of molecules. The influence of dye structure and substrate on the morphology of the deposits is studied using atomic force microscopy (AFM). Depending on the dye structure and the substrate material, various nanostructures are grown. Dichroic nanowires (NWs) are formed by self‐assembly on Au and Si substrates. On the Si surface, NWs grow between the edges of neighboring Au stripes. Several methods are used for the selective opening of the allyl group. Smooth films are produced with optical spectra similar to those deposited by PVD. The morphology of the films is dependent on the activation conditions. The thermal stability of the films exceeds the stability of those deposited via PVD. [ABSTRACT FROM AUTHOR]

Merocyanines, thanks to their easily adjustable electronic structure, appear to be the most versatile and promising functional dyes. Their D–π–A framework offers ample opportunities for custom design through variations in both donor/acceptor end‐groups and the π‐conjugated polymethine chain, and leads to a broad range of practical properties, including noticeable solvatochromism, high polarizability/hyperpolarizabilities, and the ability to sensitize various physicochemical processes. Accordingly, merocyanines are applied and extensively studied in various fields, such as light‐converting materials for optoelectronics, nonlinear optics, optical storage, solar cells, fluorescent probes, and antitumor agents in photodynamic therapy. This review encompasses both classical and novel more important publications on the structure–property relationships in merocyanines, with particular emphasis on the results by A. I. Kiprianov and his followers in Institute of Organic Chemistry in Kyiv, Ukraine. [ABSTRACT FROM AUTHOR]

Trianionic polymethines of the A′‐π‐A‐π‐A‐π‐A′ type comprising dioxaborine rings (A) and different electron‐accepting end groups (A′) have been synthesized. The obtained dyes absorb and emit light in the near‐infrared region with remarkably high molar attenuation coefficients (ϵ up to 495 000 M−1 cm−1 in DMF) and fluorescence quantum yields (Φf up to 0.73 in DMF). Thus, the novel trianionic dyes stand among the brightest individual fluorophores known to date – with a magnitude of fluorescence brightness (ϵ⋅Φf) of 313 000 M−1 cm−1 in DMF. The synthesized dyes demonstrate a minor negative solvatochromism and small Stokes shifts. X‐ray data reveal the nearly planar geometry of the trianionic chromophore. All the obtained compounds are stable in the solid state and in a solution, although the relative stability is much higher in polar aprotic than in protic solvents. [ABSTRACT FROM AUTHOR]

Cyanines are one of the few kinds of molecules whose absorbance and emission can be shifted in a broad spectral range from the ultraviolet to the near infrared. They can easily transform into J‐aggregates with narrow absorption and emission peaks, along with a redshift in their spectra. This mini‐review presents cyanine dyes and their J‐aggregates and discusses their structure and spectral properties that illustrate their specificities. We summarize the theoretical and experimental state of the art on cyanine J‐aggregates and their applications, also laying the groundwork for cyanine J‐aggregates synthesis and characterization methods. [ABSTRACT FROM AUTHOR]

1,2,5‐Triphenylpentadienyl cation fused with a dibenzobarrelene skeleton was synthesized. The pentadienyl cation was persistent in the solution and characterized by 1H and 13C NMR spectroscopies. The cation abstracts a hydride from Et2O at the 5‐position to give the 5‐H derivative together with acetaldehyde and ethene. The reaction with H2O provided the 5‐OH derivative and not the 1‐OH precursor. The hydride reduction of the pentadienyl cation with silanes or NaBH4 occurred at the 3‐ and 5‐positions, and the ratio was dependent on the bulkiness of reducing reagents. The cation in dichloromethane exhibited long‐wavelength absorptions at 678, 523, and 443 nm and an emission maximum at 729 nm with the emission quantum yield of 0.175, which are longer and larger than those of the referenced 1,5‐diphenylpentadienyl cation. TD‐DFT calculations show that the absorptions are due to the π‐π* excitations on 1,2,5‐triphenylpentadienyl and dibenzobarrelene benzene rings. [ABSTRACT FROM AUTHOR]

The Historical Dyestuff Collection at the Technical University Dresden houses a large collection of colorants, such as more than 20 000 synthetic organic dyes, more than 500 natural organic dyes and a comprehensive collection of inorganic natural and synthetic pigments, as well as more than 3 000 shade cards and a variety of other objects related to dyestuff chemistry. Moreover, all theses performed at the Institute of Color and Textile Chemistry, the home of the Dyestuff Collection, together with all substance probes prepared during the qualification works of the students, were deposited here and can be used on demand. From the theses and much additional literature collected here, the history of industrial dyestuff chemistry and the photographic industry as well as the contributions of the scientists working at the Institute since 1892, including W. König and H. T. Bucherer as some of the more famous examples, can be reflected upon and studied in detail. [ABSTRACT FROM AUTHOR]

Azulene-substituted donor-acceptor polymethines, bi-, ter-, and quinqueazulenes composed of the 1,6'-biazulene unit have been successfully prepared from corresponding Zincke salts. The synthesis of polymethines through the reaction of Zincke salts with several amines, followed by a Knoevenagel reaction with malononitrile, was accomplished in moderate to high yields (40-92 %). Meanwhile, the reaction of Zincke salts with secondary amines and the subsequent sequential condensation-cyclization with cyclopentadienide ions, so-called Ziegler-Hafner method, produced the corresponding 1,6'-biazulenes, 1,6';3,6''-terazulenes, and quinqueazulene, respectively. The structural, optical, and electrochemical properties of the azulene-substituted donor-acceptor polymethines, bi-, ter-, and quinqueazulenes were revealed by single-crystal X-ray structure analysis, UV/vis spectroscopy, voltammetry analysis, spectroelectrochemistry, and theoretical calculations. These results suggested that the substituents on the azulene ring and their substitution positions directly affect their reactivities, optical and electrochemical properties. [ABSTRACT FROM AUTHOR]

Small‐molecule organic fluorophores, spectrally active in the 900–1700 nm region, with tunable wavelength and sensing properties are sought‐after for in vivo optical imaging and biosensing. A panel of fluorescent dyes (CX) has been developed to meet this challenge. CX dyes exhibit the wavelength tunability of cyanine dyes and have a rigidified polymethine chain to guarantee their stability. They are chemo‐ and photo‐stable in an aqueous environment and have tunable optical properties with maximal absorbing/emitting wavelength at 1089/1140 nm. They show great potential in high‐contrast in vivo bioimaging and multicolor detection with negligible optical cross talk. Förster resonance energy transfer (FRET) between CX dyes was demonstrated in deep tissue, providing an approach for monitoring drug‐induced hepatotoxicity by detection of OONO−. This report presents a series of NIR‐II dyes with promising spectroscopic properties for high‐contrast bioimaging and multiplexed biosensing. [ABSTRACT FROM AUTHOR]

Abstract: The first sensitive fluorescence .OH probe (1) that is capable of monitoring the generation of trace .OH in iron autoxidation is presented. The probe 1 was designed by utilizing both the unique aromatic hydroxylation and the electrophilicity of .OH, and prepared by incorporating a strong electron‐donating methoxy group into a cyanine fluorochrome to enhance the trapping ability for .OH. Reaction of 1 with .OH leads to a larger π‐conjugation formation and near‐infrared fluorescence off–on response. The capability of probe 1 has been demonstrated by imaging .OH generated in living cells under iron autoxidation as well as various stimuli, which reveals that the basal level of .OH in RAW 264.7 cells is lower than that in HeLa cells. The superior analytical performance of probe 1 makes it useful for detecting trace .OH in some critical physiological and pathological processes associated with iron autoxidation. [ABSTRACT FROM AUTHOR]

Abstract: The first sensitive fluorescence .OH probe (1) that is capable of monitoring the generation of trace .OH in iron autoxidation is presented. The probe 1 was designed by utilizing both the unique aromatic hydroxylation and the electrophilicity of .OH, and prepared by incorporating a strong electron‐donating methoxy group into a cyanine fluorochrome to enhance the trapping ability for .OH. Reaction of 1 with .OH leads to a larger π‐conjugation formation and near‐infrared fluorescence off–on response. The capability of probe 1 has been demonstrated by imaging .OH generated in living cells under iron autoxidation as well as various stimuli, which reveals that the basal level of .OH in RAW 264.7 cells is lower than that in HeLa cells. The superior analytical performance of probe 1 makes it useful for detecting trace .OH in some critical physiological and pathological processes associated with iron autoxidation. [ABSTRACT FROM AUTHOR]

Abstract: NIR‐sensitized photoinduced atom‐transfer radical polymerization (ATRP) is possible by using ppm of CuII/tris(2‐pyridylmethyl)amine (TPMA) as the catalyst, a polymethine as the photosensitizer, and α‐bromophenylacetate as the alkyl halide initiator. Among the polymethines investigated with cationic, zwitterionic, or anionic structures, only the zwitterionic 2 exhibited sensitization activity under NIR light at room temperature resulting in the formation of polymers with controlled molecular weight characteristics and functionalities. The barbital group placed at the meso‐position of 2 caused the activity in this photo‐ATRP framework. The chain‐end fidelity of the polymers was confirmed by chain extension and block copolymerization experiments. The polymerization system exhibits high photostability under NIR light exposure and irradiation dependency as demonstrated by light on/off experiments. [ABSTRACT FROM AUTHOR]

Bright fluorophores in the near-infrared and shortwave infrared (SWIR) regions of the electromagnetic spectrum are essential for optical imaging in vivo. In this work, we utilized a 7-dimethylamino flavylium heterocycle to construct a panel of novel red-shifted polymethine dyes, with emission wavelengths from 680 to 1045 nm. Photophysical characterization revealed that the 1- and 3-methine dyes display enhanced photostability and the 5- and 7-methine dyes exhibit exceptional brightness for their respective spectral regions. A micelle formulation of the 7-methine facilitated SWIR imaging in mice. This report presents the first polymethine dye designed and synthesized for SWIR in vivo imaging. [ABSTRACT FROM AUTHOR]

Background and Purpose: The paradigm that GPCRs are able to prolong or initiate cellular signalling through intracellular receptors recently emerged. Melatonin binds to G protein-coupled MT1 and MT2 receptors. In contrast to most other hormones targeting GPCRs, melatonin and its synthetic analogues are amphiphilic molecules easily penetrating into cells, but the existence of intracellular receptors is still unclear mainly due to a lack of appropriate tools.Experimental Approach: We therefore designed and synthesized a series of hydrophilic melatonin receptor ligands coupled to the Cy3 cyanin fluorophore to reliably monitor its inability to penetrate cells. Two compounds, one lipophilic and one hydrophilic, were then functionally characterized in terms of their affinity for human and murine melatonin receptors expressed in HEK293 cells and their signalling efficacy.Key Results: Among the different ligands, ICOA-13 showed the desired properties as it was cell-impermeant and bound to human and mouse MT1 and MT2 receptors. ICOA-13 showed differential activities on melatonin receptors ranging from partial to full agonistic properties for the Gi /cAMP and ERK pathway and β-arrestin 2 recruitment. Notably, ICOA-13 enabled us to discriminate between Gi /cAMP signalling of the MT1 receptor initiated at the cell surface and neuronal mitochondria.Conclusions and Implications: We report here the first cell-impermeant melatonin receptor agonist, ICOA-13, which allows us to discriminate between signalling events initiated at the cell surface and intracellular compartments. Detection of mitochondrial MT1 receptors may have an important impact on the development of novel melatonin receptor ligands relevant for neurodegenerative diseases, such as Huntington disease. [ABSTRACT FROM AUTHOR]

A near-infrared (NIR) polymethine dye ( 1), consisting of a cyclohepta[1,2- b;4,3- b′]dithiophene and two phenol moieties, was synthesized. This dye exhibited pH-responsive changes in its photophysical properties due to a two-step acid-base equilibrium that produced a protonated cation ( 1H+) and an anion ( 1−). While 1H+ showed an intense fluorescence in the red region of the visible spectrum, 1− exhibited a strong absorption in the NIR region. The tropylium ion character in 1H+ induces high p Ka1 and p Ka2 values for 1. Moreover, a stable radical ( 1.) was prepared, which showed a NIR absorption band with a maximum at circa 1600 nm. The cyclic voltammogram of 1. revealed a two-step reversible redox process that produced 1− and the cation 1+, which is different from 1H+. These redox processes accompany drastic electrochromic changes in the vis-NIR region. Overall, 1 is susceptible to multiple interconversions between five forms, due to the multifaceted character of the cycloheptadithiophene skeleton. [ABSTRACT FROM AUTHOR]

DFT method can severely overestimate the response properties for π-conjugation systems. The range-separated exchange and recently developed optimal IP-tuning process are evaluated on the prediction of static second hyperpolarizabilities of streptocyanines of increasing molecular length. The finite field results have shown that the exact exchange at midium and long distance can relieve only a part of the overshooting but still beyond satisfaction. The exact exchange at short distance has the oppsite effects showing the failure of converntional hGGA. The optimal tuned range-separated exchange functionals show little improvements performing worse than the default ones. Importantly, the electronic structure-property relationship, bond order alternation- γ, is not well established with DFT method. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

We have investigated the properties of polymethine dyes (PMD) and the purpose of using them as sensors of hazardous gases presence. Research indicates that in case of utilizing PMD as a sensor of hazardous gases we need to use the monochromatic light which wavelength corresponds to the inflection point of the long-wave absorption edge of PMD. Such sensor of hazardous gases can detect changes in the optical density of the sensor layer or the light intensity transmitted through the layer. [ABSTRACT FROM AUTHOR]

We present direct evidence of enhanced non-radiative energy transfer between two J-aggregated cyanine dyes strongly coupled to the vacuum field of a cavity. Excitation spectroscopy and femtosecond pump-probe measurements show that the energy transfer is highly efficient when both the donor and acceptor form light-matter hybrid states with the vacuum field. The rate of energy transfer is increased by a factor of seven under those conditions as compared to the normal situation outside the cavity, with a corresponding effect on the energy transfer efficiency. The delocalized hybrid states connect the donor and acceptor molecules and clearly play the role of a bridge to enhance the rate of energy transfer. This finding has fundamental implications for coherent energy transport and light-energy harvesting. [ABSTRACT FROM AUTHOR]

Polymethine dyes as photosensitizers for dye-sensitized solar cells (DSCs) are reviewed. The review provides a summary of design strategies, the main synthetic routes, and the optical and photovoltaic properties of polymethine dyes applied in hybrid photovoltaics. In particular, we focus on cyanine and squaraine dyes and their structure-properties relationships, highlighting the role of the active molecule design on device performance. [ABSTRACT FROM AUTHOR]

New photosensitive polymeric film composites based on oligomer containing ferrocenyl and carbazolyl fragments doped with symmetric polymethine dye are synthesized. Their photoelectric properties are investigated. Photovoltaic properties of these composites are detected. The mechanisms and peculiarities of the photovoltaic and photodielectric effects are discussed. [ABSTRACT FROM AUTHOR]

Directed by the solvent polarity, the prevalent conformation of a polymethine dye bearing a branched π-conjugated junction can be switched from a heptamethine donor-acceptor (DA) merocyanine-type π-conjugated system to a nonamethine DAD cyanine-type π-conjugated scaffold. Concomitantly the absorption maximum shifts from 585 nm in dichloromethane to 748 nm in methanol solution. [ABSTRACT FROM AUTHOR]

Despite significant progress in the clinical application of antibody drug conjugates (ADCs), novel cleavage strategies that provide improved selectivity are still needed. Herein is reported the first approach that uses near-IR light to cleave a small molecule from a biomacromolecule, and its application to the problem of ADC linkage. The preparation of cyanine antibody conjugates, drug cleavage mediated by 690 nm light, and initial in vitro and in vivo evaluation is described. These studies provide the critical chemical underpinning from which to develop this near-IR light cleavable linker strategy. [ABSTRACT FROM AUTHOR]

The interactions of a dicarbocyanine dye 3,3′-diethylthiadicarbocyanine, DiSC2(5), with DNA G-quadruplexes were studied by means of a combination of various spectroscopic techniques. Aggregation of excess dye as a result of its positive charge is promoted by the presence of the polyanionic quadruplex structure. Specific high-affinity binding to the parallel quadruplex of the MYC promoter sequence involves stacking of DiSC2(5) on the external G-tetrads; the 5′-terminal tetrad is the favored binding site. Significant energy transfer between DNA and the dye in the UV spectral region is observed upon DiSC2(5) binding. The transfer efficiency strongly depends on the DNA secondary structure as well as on the G-quadruplex topology. These photophysical features enable the selective detection of DNA quadruplexes through sensitized DiSC2(5) fluorescence in the visible region. [ABSTRACT FROM AUTHOR]

This report presents a simple strategy to introduce various functionalities in a cyanine dye (bis-indole- N-butylsulfonate-polymethine bearing a fused cyclic chloro-cyclohexene ring structure), and assess the impact of these substitutions in tumor uptake, retention and imaging. The results obtained from the structural activity relationship ( SAR) study demonstrate that certain structural features introduced in the cyanine dye moiety make a remarkable difference in tumor avidity. Among the compounds investigated, the symmetrical CDs containing an amino-phenyl thioether group attached to a cyclohexene ring system and the two N-butyl linkers with terminal sulfonate groups in benzoindole moieties exhibited excellent tumor imaging ability in BALB/c mice bearing Colon26 tumors. Compared to indocyanine green ( ICG), approved by FDA as a blood pooling agent, which has also been investigated for the use in tumor imaging, the modified CD selected on the basis of SAR study produced enhanced uptake and longer retention in tumor(s). A facile approach reported herein for introducing a variety of functionalities in tumor-avid CD provides an opportunity to create multi-imaging modality agent(s). Using a combination of mass spectrometry and absorbance techniques, the photobleaching of one of the CDs was analyzed and significant regioselective photooxidation was observed. [ABSTRACT FROM AUTHOR]

Organic thin film transistors (OTFTs) of a series of twenty dipolar donor-acceptor-substituted polymethine dyes (D-A dyes, dipole moments from 3-15 D) are investigated. The employed merocyanine dyes contain a dimethine bridge that is substituted with 1-alkyl-3,3-dimethylindolin-2-ylidene ('Fischer base'), 3-alkyl-2,3-dihydrobenzothiazol-2-ylidene or 1,3-benzodithiole-2-ylidene, respectively, as electron-donating unit and various acceptor heterocycles. These studies show that thin films formed by these D-A dyes upon deposition in high vacuum are all composed of antiparallel π-stacked dimers. However, they are either amorphous, discontinuous or highly crystalline due to the interplay between molecule-substrate and dimer-dimer interactions. With the help of single crystal X-ray analysis, out-of-plane X-ray studies (XRD), selected area electron diffraction (SAED), and atomic force microscopy (AFM), a correlation between the molecular structure, film ordering, and hole charge transport ability can be established. The mobility values are compared to Bässler's disorder charge transport theory and a film growth mechanism is proposed based on DFT calculations and single crystal structures. The results show that with carefully adjusted bulky substituents and high dipolarity an intimate centrosymmetric packing with a slipped, but tight π-stacking arrangement could be realized. This provides two-dimensional percolation pathways for holes and ultimately results in charge carrier mobilities up to 0.18 cm2 V−1 s−1. [ABSTRACT FROM AUTHOR]

Highly stable and highly soluble push-pull heptamethine hemicyanines based on the tricyanofuran electron-accepting group can be prepared on a 15 g scale. The compounds display giant second-order nonlinear figure of merit, μβ of up to 31 000×10−48 esu, and lead to a poled material with a second-order nonlinear response, r33 of 90 pm V−1 at 1.06 μm [ABSTRACT FROM AUTHOR]

Im Polymer eingeschlossen: Ein hydrophobes organisches Molekül, das im Nahinfrarot II (NIR ‐ II) fluoresziert, wurde durch den Einschluss in polymere Nanopartikel wasserlöslich und biokompatibel. Die Nanopartikel wurden mit hydrophilem Polyethylenglycol modifiziert; sie zeigten Fluoreszenz in der NIR ‐ II ‐ Region und gute Photostabilität in wässriger Umgebung und wurden zur In ‐ vivo ‐ Bildgebung in Mäusen verwendet. [ABSTRACT FROM AUTHOR]

In this high-technology application, age functional dyes especially polymethine dyes have captured much attention of the researchers due to their immense potential for high-tech uses. Polymethine dyes show promising absorption spectra in the visible range, which can be easily exploited for the use of written text copying, photographic imaging, or photothermographic recording materials. Keeping this in mind, our research is composed of an investigation of two triphenylamino-based polymethine dyes, a known polymethine dye 3 and a new one polymethine dye 5, which have been synthesized by the reaction of 4-(diphenylamino) benzaldehyde 2 and 4,4'-(phenylazanediyl) dibenzaldehyde 4 with 4,4'-vinylidene-bis(N, N-dimethylaniline) 1. Based on bis-dimethylaminophenylethylene moiety, the new polymethine dye showed more high absorption spectra in the range of 600-700 nm than that of the known polymethine dye based on bis-dimethylaminophenylethylene moiety. Their maximum spectra were exhibited at 637 nm and 653 nm, respectively. Their leuco-converted reversible colored forms were also investigated. [ABSTRACT FROM AUTHOR]

The quantum-chemical investigations by ab initio method (restricted Hartree-Fock/6-31G**) have been performed for a series of unsubstituted, monosubstituted, and disubstituted neutral polyenes and their double charged cations. The waves of charge alternation (characterized by the difference in the electron densities at the nearest carbon atoms or Δ q function) and bond length alternation (characterized by the lengths difference of the nearest carbon-carbon bonds or Δ l function) are reported. Comparisons are made with the corresponding monocationic polymethine molecules. We found that ionization by two electrons results in formation of two solitonic waves of charge alternation, rather than superposition of two overlapping solitonic waves into one. These waves behave similar to two independent elastic particles, which do not penetrate into each other despite the special confinement by the length of chromophore π-system. In monosubstituted polyene dication, Δ q and Δ l functions contain two waves each; however, only one wave is mobile and sensitive to a change of the chemical nature of the terminal group, whereas the second wave remains practically unchanged. The introduction of one oxymethyl or phenyl terminal groups leads to a relatively small shift of the mobile wave from the center to a direction of the terminal group. The effect of the amino or tropilium terminal groups is much more pronounced and leads to a shift of the mobile wave to the end of the molecule. In disubstituted polyene dication, both solitonic waves become mobile and shift symmetrically to both ends. The general principles of the charge localization described in this study may be used in molecular design and fine-tuning of the charge transport properties in plastic photovoltaics and other organic semiconducting materials. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Colorless 1,3-bis(dicyanomethylidene)indan is an organic acid (p Ka≈3.0) that turns blue in polar media owing to self-deprotonation. Moreover, its colored conjugate base shows potential as a minimal anionic polymethine dye for probing biomolecules in cells and in vivo through noncovalent complexation and near-infrared fluorescence signaling. [ABSTRACT FROM AUTHOR]

To see the effect of conjugation on molecular weight and conductivity, three symmetrical polymethine dyes are added in polymers either before or after polymerization. Dyes have conjugated bonds between nitrogen atoms. Among three dyes, it was observed that as conjugation increases, the conductivity also increases. Previous study with polyethylvinylketone and polymethylvinylketone support the idea that increased conjugation will increase the molecular weight and conductivity. For these polymers also, the dopant, phosphorylchloride increased the conductivities due to the double bond being transferred to the main chain and increased conjugation. The same method developed in this work can be applied to methyl methacrylate and styrene polymers to see the relationship between molecular weight, conductivity, and fluorescence intensity. When dyes were added to methylmethacrylate and styrene monomers before polymerization, much higher conductivities were obtained. Conductivity values are directly proportional to the irradiation times and molecular weights. Four-hour irradiation time results in a maximum molecular weight of 6.4 × 105 and a maximum conductivity of 2.25 μS for MMA polymers. Spectrofluorometric analysis of methyl methacrylate polymers indicates that as molecular weight of the dyes increases, the emission intensities at 375 and 425 nm also increases. In the same way, increased molecular weight of polymer also results higher emission intensities. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 [ABSTRACT FROM AUTHOR]

A series of merocyanines derived from 1,3‐indanedione and heterocycles of various electron‐donating properties was studied in detail. Their solvatochromic properties were explored in a wide range of solvent polarities to reveal the dependences of their chromacity and electronic structure on the key structural parameters – the properties of a donor heterocycle and the polymethine chain length. Also the dyes were studied by NMR spectroscopy and by quantum chemical calculations, both with the semiempirical AM1 and the non‐empirical density functional theory/B3LYP method. The solvatochromic properties of the explored dyes are rather close to those of merocyanines derived from malononitrile as acceptor group. Appreciable distinctions were observed only in protic ethanol; obviously, they are connected with the formation of solvent–solute H‐bonds in the case of 1,3‐indanedione derivatives. The electron‐acceptor properties of 1,3‐indanedione were found to be somewhat stronger in comparison with those of malononitrile even in aprotic solvents, contrary to the known literature data. Analysis of the merocyanines' molecular orbitals and simulation of their electronic spectra were carried out both in vacuum and in the solvent matrix, and the absorption electronic transitions were analyzed. Static nonlinear optical properties were calculated for both the new merocyanines and the corresponding cationic and anionic cyanine dyes. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Dyes derived from the biradicalic oxyallyl and cyclopentadienylium were calculated by time-dependent density functional theory (TDDFT) and the characteristics of the prominent low-energy transitions revealed by graphical means. According to theoretical and experimental studies, 4-aminophenyl-substituted dyes absorb intensely at long wavelengths up to the near infrared. If the amino groups are removed the absorption wavelengths are changed little. As found in the previous studies on the squaraine and croconaine oxyallyl dyes, the substituents play only a minor role in the spectral excitation. Charge-transfer-type excitations do not occur between the donor aryl substituents and the central oxyallyl or cyclopentadienylium acceptor group. This behaviour is exceptional since donor-acceptor compounds tend to produce charge-transfer- or polymethine-type electronic transitions. The hitherto rarely used electron density difference (EDD) maps clearly unveiled the spectral excitation features. The spectral excitation of the title compounds is predominantly localized at the oxyallyl and cyclopentadienylium groups, respectively. Characteristics of simple chromophoric compounds and of conventional CT- and polymethine dyes are given for comparison. The biradicaloid character of these dyes is supported by the calculated low singlet-triplet splitting energies. Spin properties were characterized in terms of expectation values of the S-operator and antiaromatic properties in terms of nucleus-independent chemical shifts (NICS). According to the Δ E and < S> criteria compounds with the acyclic oxyallyl fragment are more biradicaloid. The parent compounds oxyallyl, thioxyallyl and cyclopentadienylium, display extremely large < S> values. These compounds are triplets in the ground state. The absorption wavelengths of selected biradicaloid species were also calculated by the multi-reference SORCI method. Copyright © 2010 John Wiley & Sons, Ltd. Electron density difference maps are used to reveal the nature of electronic transitions of deeply coloured oxyallyl dyes. The excitation turned out to be mainly localized at the central part of the molecule. The same holds for dyes derived from cyclopentadienylium. The absorption characteristics of the oxyallyl chromophore differ strongly from those of charge transfer and polymethine type chromophores. In spite of the biradicaloid character of the dyes, the essentially monoconfigurational TDDFT calculations provided satisfactory results. [ABSTRACT FROM AUTHOR]

We present long-awaited answer to the puzzling question of why the TD-DFT fails to predict the excitation energies in polymethine dyes accurately. The density functional theory methods were suspected to be inaccurate due to self interaction error inherent in exchange-correlation potentials. Here we decisively show that it is the linear response approximation that is responsible for these inaccuracies. Next, we use frozen density to evaluate the excitation energy beyond the linear response and increase the accuracy of the predictions. This recipe uniformly improves the accuracy of the first absorption maxima prediction in cyanine homologous series to within 25 nm. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

Absorption and fluorescence spectroscopy, electrochemical techniques, and semiempirical calculations were employed to characterize the multiple complexation equilibria between two polymethine cyanine dyes (IR-786 and Indocyanine green-ICG, S) and β-cyclodextrin (β-CD, L), as well as the chemical reactivity of the complexed and uncomplexed species against the oxidizing agents hypochlorite (HC) and hydrogen peroxide (HP). IR-786 dimerization is favored with the increase in β-CD concentration in the form of (SL)2 complexes. In the case of ICG, free dimers (D) and SL complexes are favored. Both IR-786 and ICG react and discolor in the presence of HC and HP. For IR-786, the reaction with HP and HC proceeds with observed rate constants of 10-3 and 0.28 s-1 and second-order rate constants (k2) of ∼10-3 and 104 M-1s-1, respectively. The intermediate species observed in the bleaching reactions of IR-786 and ICG were shown, by cyclic voltammetry and VIS absorption, to result from one electron oxidation. IR-786 complexed with β-CD is protected against bleaching in the presence of HP and HC by factors of 20 and 4, respectively. This protection was not observed in ICG complexes. Superdelocalizability profile of both dyes and frontier orbital analysis indicates that β-CD does not protect ICG from oxidation by HP or HC, whereas the 2:2 IR-786/β-Cd complex is able to avoid the oxidation of IR-786. We concluded that the decrease in the chemical reactivity of the dyes against oxidant agents in the presence of β-CD is due to the formation of (SL)2 complexes. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

On the basis of the 7,8-dihydrobenzo[c,d]furo[2,3-f]indole nucleus, a number of unsymmetrical carbocyanines as well as styryl dyes have been synthesized and their absorption spectra have been measured. Starting from the deviations of long-wavelength maxima, the value of electron-donor ability D has been estimated for the heterocycle under study and a number of dye end groups have been ranked by their electron-donor properties. Experimental inferences are supported by the quantum chemically calculated bond length alternations and energy levels for the dyes concerned. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Charge localization and dynamics in conjugated organic molecules, as well as their spectral signatures are of great importance for photonic and photovoltaic applications. Intramolecular charge delocalization in polymethine dyes occurs through π-conjugated bridges and contributes to the appearance of low-energy excited states that strongly influence their linear and nonlinear optical (NLO) properties. When the chain length in symmetrical cations exceeds the characteristic size of the soliton, the positive charge may localize at one of the terminal groups of the molecule and induce symmetry breaking of both the electron density distribution and molecular geometry. This charge localization is coupled with molecular vibrations and solvent effects. We investigated the mechanism of symmetry breaking in a series of cationic streptocyanines with different conjugated chain length and qualitatively predicted their electronic absorption spectra. This class of organic molecules is chosen as a model system to develop methodology which can subsequently be used to evaluate more complicated compounds for NLO applications. Our calculations show that the minimum number of vinylene groups in the conjugated chain necessary to break the symmetry of streptocyanines is eight in the gas phase and six in cyclohexane. We constructed the ground state potential energy surface (PES) in two dimensions using symmetry breaking and symmetry adapted coordinates. These were defined as the difference and the sum of the two central carbon–carbon bonds, respectively. This PES was found to have two equivalent minima for systems with symmetry breaking. The energy barrier between these two minima was estimated in the gas phase and in solution, which was taken into account by the polarizable continuum model. Charge localization in each minimum was found to be asymmetric. It is additionally stabilized by the solvent reaction field, which increases the energy barrier. The electronic absorption spectrum in solution is red shifted as compared to the gas phase. As the symmetry breaks, additional excited states with large oscillator strengths appear in the electronic spectrum. Geometry optimization and spectral predictions were also performed in a uniform external electric field in order to simulate nonequilibrium solvation effects due to the finite relaxation time of solvent molecules. Two asymmetric minima with different depths appear on the resulting PES. The lower minimum has charge localized at one of the two molecular terminal groups which is additionally stabilized by the solvent field, while the higher one has charge localized on another terminal group. This finding demonstrates the possibility that two forms with different charge distributions coexist in polar solvents. Our results suggest that nonequilibrium solvation may be a cause of absorption band broadening and splitting. This work is a first step in a larger study aimed at the analysis of the linear and nonlinear properties of long π-conjugated systems of interest for NLO applications and plastic photovoltaics. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]

New polymethine cyanine dyes, including tetramethine and bis-tetramethine cyanine dyes derived from benzo[2,3-b;2′,3′-b′]bis-pyrazolo[4,5-b]-1,4-(oxa-, thia- and pyra-)-zine-6,12-dione, were synthesised. Absorption spectra for all the synthesised cyanine dyes were examined in 95% ethanol. The solvatochromism and halochromism for some selected dyes were investigated in pure solvents and in aqueous universal buffer solutions, respectively. Structural confirmations were carried out through elemental and spectroscopic analysis. [ABSTRACT FROM AUTHOR]

A number of new styryl, aza-styryl, acyclic mero, cyclic mero and mixed cyanine dyes with a benzo[2,3- e; 2′,3′- e′]bis-1,3,4-oxadiazine nucleus were synthesised. The absorption spectra in the visible region of all the synthesised cyanine dyes in 95% ethanol solution were examined and studied in detail. Anti-bacterial activity for a number of selected dyes was evaluated against various bacterial strains. The structural determination was carried out using elemental and spectroscopic analysis. [ABSTRACT FROM AUTHOR]

Combined quantum-chemical and spectral studies of the features of electron transitions and absorption spectra of symmetrical and unsymmetrical polymethine dyes, derivatives of aminocoumarin, have been performed. It was established that the lowest two electron transitions are splitting transitions, involving solitonic level and two low positioned acceptor levels, in contrast to the cationic cyanine dyes, where two lowest transitions are connected with two splitting donor levels and solitonic level. The considerable interaction between two acceptor levels in symmetrical dyes provides an additional decrease of the first transition energy and hence leads to the relatively deep and intensive color, whereas the second transition with its negligible oscillator strength is practically unobserved. The higher electron transitions involve orbitals located mainly at the coumarin residue; the corresponding spectral bands appear in the short-wavelength region. Introduction of dialkylamino group in coumarin heterocycle shifts bathochromically the long-wavelength absorption band and considerably increases the intensity of S0 → S1 and S0 → S3 electron transitions. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A new class of open-shell polymethine monoradicals, possessing nonbonding molecular orbitals (NBMO) and very low excitation energies, was investigated theoretically. The radicals are derivatives of the stable 2-azaphenalenyl radical. Since in the ground state the NBMO is strictly localized within a molecular fragment, the electron transitions are connected with a substantial charge-transfer. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [ABSTRACT FROM AUTHOR]

Review: summary of design strategies, the main synthetic routes, and the optical and photovoltaic properties of cyanine and squaraine sensitizers applied in photovoltaics; 146 refs. [ABSTRACT FROM AUTHOR]

Review: 143 refs. [ABSTRACT FROM AUTHOR]