Synthesis and spectral properties of malononitrile-based merocyanine dyes

Di-, tetra-, and hexamethine merocyanines derived from malononitrile and heterocycles with moderate (dyes 1–6), strong (7–9), and weak (10 and 11) electron-releasing ability were synthesized. The electronic structures of merocyanines 10 and 11 are similar to the neutral polyene state, whereas those of 7–9 are similar to the ideal polymethine state. These tendencies become more pronounced with increasing length of the polymethine chain. The merocyanines derived from heterocyclic residues with weak or moderate electron-releasing ability exhibit a positive solvatochromism, whereas those with strong electron-releasing ability show a negative solvatochromism. An increase in the polarity of the solvent makes the former compounds more similar to polymethines, whereas the latter become more similar to polyenes bearing opposite charges on the end groups. The nature of the factors (nonspecific solvation, specific nucleophilic and electrophilic solvation, and vibronic interactions) responsible for the observed characteristic features was analyzed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2726–2735, December, 2005.     

Synthesis and spectral properties of merocyanine dyes based on polynitrofluorenes

The di-, tetra- and hexamethinemerocyanines derived from di-, tri- and tetranitrofluorene, containing heterocyclic indolylidene residue were synthesized and their absorption spectra in the solvents of different polarity were investigated. A quantum-chemical analysis of the electronic structure of the synthesized merocyanines was performed and the types of electronic transitions in their molecules were calculated using DFT and TDDFT methods with the B3LYP/6-31G(d,p) basis. It was shown that with increasing electronacceptor properies of the fluorene core the electronic structure of the merocyanines can change from a neutral polyene to an ideal polymethine, which significantly affects the position, intensity and shape of the absorption bands, as well as vinylene shifts and deviations.     

Sulfur- and selenium-containing merocyanine dyes

The corresponding merocyanine dyes were obtained by reaction of aminomethylene derivatives of 5-pyrazolone and 5-thio- and 5-selenopyrazolones with tetramethylindoleninium and phenanthridinium salts. Their UV spectra and the possibility of the formation of spiropyrans from them were studied.     

Photodynamics of polyene-polymethine transformations and spectral fluorescent properties of merocyanine dyes

Absorption and fluorescence spectrum band moments (center of gravity, width, asymmetry, excess, and fine structure) have been determined in a wide range of solvents with different polarities for inverse solvatochromic di-, tetra-, and hexamethinemerocyanines derived from 1,3-diphenyl-2,3-dihydro-1H-benzimidazole. Juxtaposition of the quantum-chemically calculated (by the semiempirical AM1 method) charges, bond orders, and dipole moments of the merocyanine molecules in the ground and excited singlet states with the experimentally observed spectral fluorescent characteristics suggests that the molecular electronic structure in the two states can vary from a nonpolar polyene via a polymethine to a charge-separated polyene, depending on the length of the polymethine chain and the medium polarity. As shown, solvatofluorochromism gives rise to smaller spectral band shifts than those of solvatochromism. This effect is attributable to weaker intermolecular solute-solvent interactions in the fluorescent excited state due to the more equalized charges as compared to those of the ground state. A lack of mirror symmetry of the absorption and fluorescence spectra has been revealed for di- and tetramethinemerocyanines (broadened fluorescence bands) as well as for hexamethinemerocyanines (narrowed fluorescence bands); the two cases are accounted for by the different behavior of vibronic and intermolecular interactions in the course of absorption and emission. As found for merocyanines, the electronic structure of their fluorescent state approaches the cyanine limit and the ground state becomes increasingly polyene-like with lengthening of the polymethine chain. A close vicinity of the excited state to the cyanine limit causes a dramatic increase in fluorescence quantum yields and a decrease in Stokes shifts observed for higher merocyanine vinylogues.     

Structure and fluorescence properties of merocyanine dyes derived from dimethylbarbituric acid

The fluorescence properties of positively and negatively solvatochromic di-, tetra-, and hexamethinemerocyanines derived from 1,3-dimethylbarbituric acid in solvents of various polarities were studied. The range of solvatofluorochromic effect for these compounds is narrower than the range of solvatochromic effect. Extension of the polymethine chain of these compounds causes in the fluorescence spectra, in contrast to the absorption spectra, an increase in vinylene shifts, a decrease in deviations, and band narrowing. The electronic structure of the merocyanines was analyzed by the AM1 method. Transitions between the ideal states (neutral polyene, polymethine, and charged polyene) were examined. The electronic structure of the merocyanines in the excited state was found to approach the cyanine limit. Its attainment accounts for a sharp increase in the quantum yields of the fluorescence and a decrease in the Stokes shifts in going to higher vinylogs, and also with an increase in the solvent polarity for positively solvatochromic merocyanines and with its decrease for the negatively solvatochromic derivatives.     

Synthesis and investigation of merocyanine dyes

New merocyanine dyes — derivatives of 1-unsubstituted, 1-methyl-, and l-phenyl-3,4-pyrroline-2,5-diones — were synthesized by the reaction of quaternary salts of 2-methyl — substituted heterocyclic nitrogen bases with the appropriate 3,4-dihalopyrrolinedione and sodium benzenesulfinate or with 3-phenylamlno-4-phenylsulfonylpyrroline-2,5-diones.The effect of substituants attached to the nitrogen atom of 3,4-dihalo-3,4-pyrroline-2,5-diones on the nature of the products formed by reaction with aniline and sodium benzene-sulfinate was investigated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1387–1390, October, 1971.     

Structure and fluorescence properties of indole cyanine and merocyanine dyes with partially locked polymethine chain

The fluorescent properties of a series of symmetric cationic cyanine dyes and merocyanines with trimethylene bridge connecting N-atom of the indole residue with α-position of the polymethine chain have been explored in detail. It is shown that the constraining group influences their fluorescent properties both by steric and electronic effects. It revealed an essential decrease of the fluorescence quantum yields of the constrained symmetric cyanine dyes in comparison with those of their analogues without bridge group in their chromophore. This effect diminishes essentially at polymethine chain lengthening. In the case of merocyanines the bridge group can cause a decrease as well a substantial increase of their fluorescence quantum yields depending on their type of solvatochromism and solvent polarity. The conclusions made on the basis of the experimental data are in good agreement with the results of semiempirical quantum-chemical calculations.     

Synthesis and spectral properties of merocyanine dyes based on fluorene and its derivatives

The di-, tetra- and hexamethine merocyaninyes, the derivatives of fluorene, diphenyl 9H-fluorene-2,7-disulfonate, and bis(2,2,3,3,4,4,5,5-octafluoropentyl) 9H-fluorene-2,7-disulfonate, as well as the derivatives of the heterocycles of moderate (indolylidene and benzotiazolylidene), weak (benzo[c,d]indolylidene and 2,6-diphenylpyrane) and strong (2,6-diphenylpyridine) electron-donor properties were synthesized and their absorption spectra in solvents of different polarity were studied. The quantum-chemical analysis of electronic structure of the synthesized merocyanines was performed and the types of electronic transitions in them were found by the DFT and TDDFT methods with the B3LYP/6-31G(d,p) basis.     

Syntheses and absorption-structure relationships of some new photosensitizer cyanine dyes

New biheterocyclic compound was synthesized as starting material to prepare new photosensitizers mono-, tri-, substituted tri-, azadimethine and mixed cyanine dyes. Absorption-structure relationship of the synthesized cyanine dyes were determined by studying their electronic spectral behaviour in ethanol. The structure of the compounds were identified by elemental analysis, IR and¹HNMR spectral data.     

Synthesis, electronic, and electro-optical properties of emissive solvatochromic phenothiazinyl merocyanine dyes

Phenothiazinyl merocyanine dyes with variable substitution patterns on the peripheral benzene ring were synthesized in good yields by Knoevenagel condensation of the corresponding phenothiazinyl aldehydes and N-methylrhodanine or indan-1,3-dione. The electronic properties were investigated by cyclic voltammetry, absorption, electro-optical absorption, and emission spectroscopy. All these merocyanines reveal reversible redox behavior that stems from the phenothiazinyl-centered oxidation to give stable radical cations. The redox potentials strongly correlate with Hammett σ(p) parameters. All merocyanines reveal large Stokes shifts. They also display a pronounced emissive solvatochromism, which is caused by large dipole moment changes upon excitation from the ground to the excited state. These findings are supported by solvatochromism studies and time-dependent DFT computations.     

Syntheses and spectroscopic properties of substituted diazaborepins with large stokes shift

The substituted diazaborepins (DABs) with halogen (Cl, Br), methoxyl and ethyl ester group on the fifth position of indole unit have large stokes shift, high fluorescence quantum yields and would be used in biomedicine. Their absorption and emission properties were studied in different solvents. Electron-withdrawing group tended to a bathochromic shift of the absorption and fluorescence probably due to its D-π-A structure. Solvatochromic effects were also studied based on Lippert-Mataga equation. DAB-5 with ethyl ester group exhibits more pronounced fluorescence solvatochromic effects than DAB-3 with Br group. The energy gap and simulated stick spectra of DABs based on Density Functional Theory (DFT) and Time-dependent Density Functional Theory (TD-DFT) calculation was obtained.     

Heteroatom-substituted rhodamine dyes: Structure and spectroscopic properties

This review summarized the structures and photophysical properties of heteroatom-substituted rhodamines.     

Heteroatom-substituted rhodamine dyes: Structure and spectroscopic properties

Rhodamine is one class of most popular dyes used in fluorescence imaging due to the outstanding photoproperties including high brightness and photostability. In recent years, replacement the xanthene oxygen with other elements, especially silicon, has attracted great attentions in the development of new rhodamine derivatives. This review summarized the structures and photophysical properties of heteroatom-substituted rhodamines. We hope this review can help to understand the structure-property relationships of rhodamine dyes and then elucidate the way to create derivatives with improved photoproperties.     

Interaction of protonated merocyanine dyes with amines in organic solvents

2,6-Diphenyl-4-(2,4,6-triphenylpyridinium-1-yl)phenolate (1a) and 4-[(1-methyl-4(1H)-pyridinylidene)-ethylidene]-2,5-cyclohexadien-1-one (2a) were protonated in organic solvents (dichloromethane, acetonitrile, and DMSO) to form 1b and 2b, respectively. The appearance of the solvatochromic bands of 1a and 2a was studied UV-vis spectrophotometrically by deprotonation of 1b and 2b in solution in the presence of the following amines: aniline (AN), N-methylaniline (NMAN), N,N-dimethylaniline (NDAN), n-butylamine (BA), diethylamine (DEA), and triethylamine (TEA). Titrations of 1b and 2b with the amines were carried out and the binding constants were determined from the titration curves in each solvent, using a mathematical model adapted from the literature which considers the simultaneous participation of two dye: amine stoichiometries, 1:1 and 1:2. The data obtained showed the following base order for the two compounds in DMSO: BA>DEA>TEA, while aromatic amines did not cause any effect. In dichloromethane, the following base order for 1b was verified: TEA>DEA>BA?NDAN, while for 2b the order was: TEA>DEA>BA, suggesting that 1b is more acidic than 2b. The data in acetonitrile indicated for 1b and 2b the following order for the amines: DEA>TEA>BA. The diversity of the experimental data were explained based on a model that considers the level of interaction of the protonated dyes with the amines to be dependent on three aspects: (a) the basicity of the amine, which varies according to their molecular structure and the solvent in which it is dissolved, (b) the molecular structure of the dye, and (c) the solvent used to study the system.     

Syntheses and some properties of N-unsubstituted sulfilimines

A variety of S-aminosulfonium mesitylenesulfonates, R¹R²S⁺NH₂·X⁻, were prepared in high yields by the reaction of sulfides with O-mesitylenesulfonylhydroxylamine (MSH). The thermal stability of the derived sulfilimines was examined. Reaction of allyl sulfides with MSH afforded directly the salts of allylamines in good yields, presumably via [2,3]-sigmatropic rearrangement of unisolable allylsulfilimines followed by S---N bond cleavage. The reactions of disulfides and thioketone with MSH are also described.     

Solvent effects in the interaction of methyl-beta-cyclodextrin with solvatochromic merocyanine dyes

The UV-vis spectroscopic behavior of dyes: 2,6-diphenyl-4-(2,4,6-triphenylpyridinium-1-yl)phenolate (1) and 4-[(1-methyl-4(1H)-pyridinylidene)-ethylidene]-2,5-cyclohexadien-1-one (2) was investigated in solutions of methyl- beta-cyclodextrin (methyl-beta-CyD), using water, methanol, ethanol, propan-2-ol, butan-1-ol, acetone, acetonitrile, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMA), chloroform and dichloromethane as solvents. In aqueous solutions of dye (2) the addition of M-beta-CD leads to a bathochromic shift (of the maximum absorption), showing that the probe was transferred to a microenvironment of lower polarity and suggesting the formation of a 1 : 1 dye (2) : CyD inclusion complex, with a binding constant of 128.5 +/- 3.5 dm(3) mol(-1). Data for dye 2 in alcohols showed hypsochromic shifts, which increased in the following order: methanol < ethanol < propan-2-ol < butan-1-ol. These observations appear to reflect dye-solvent interactions through hydrogen bonding. If dye-solvent interactions are strong, the CyD-dye interactions are consequently weak, but the latter increase in importance when the dye-solvent interaction becomes weaker. With hydrogen-bond accepting solvents, data for both dyes showed clearly increasing hypsochromic shifts following the order: DMSO < DMA < DMF < acetone < acetonitrile. This order is exactly the inverse of the increasing order of basicity of the medium. This indicates that the dominant factor for the observed effects in these solvents is the solvent-CyD interaction through hydrogen bonding involving the hydroxyl groups of the CyD and the basic groups of the solvents. These interactions diminish in intensity if the basic character of the medium is reduced, increasing the capability of the dye to interact with the CyD using its phenoxide donor moiety. The largest hypsochromic shifts were obtained in chloroform (66.0 nm) and dichloromethane (67.5 nm) with dye after addition of methyl-beta-CyD. In these specific situations, solvents display weak basic and acid properties, that enhanced CyD-dye interactions to such an extent that association complexes formed through hydrogen bonding could be detected (K11) values of 24.8 +/- 4.9 dm3 mol(-1) in dichloromethane and 66.1 +/- 8.0 dm3 mol(-1) in chloroform).     

Syntheses and thermal properties of some complexes with 2-mercaptonicotinic acid

The biological activity of a kind of hetero-bimetallic Schiff-base complex was studied using Escherichia coli (E. coli) cell as the target. By microcalorimetry, the difference of anti-bacterial activity between the binuclear Schiff-base and the ligand was determined and analyzed. To analyze the inhibition of the bacterial growth internally, the E. coli cells grown in the presence of hetero-bimetallic Schiff-base complex were observed by scanning electron microscopy. The images in high resolution revealed the damage of outer cell membrane caused the inhibitory effect on E. coli. Inductively coupled plasma-mass spectrometry results proved the absorption of the complex by cells, which confirmed the interaction between the Schiff-base and biological macromolecule.     

Electrical and optical properties of some azo dyes

The dipole moments of six monoazo dyes were obtained from measurements of their static dielectric constants and refractive indices of dilute solutions in benzene and carbon tetrachloride at temperatures between 20°C and 40°C. Also their lightfastness and absorption spectra (λ_max) were measured.From the results obtained, it was found that there is a linear relationship between the dipole moment, lightfastness and maximum absorption (λ_max) of the monoazo dyes under investigation.