噻菁染料的合成及吸收光谱的研究

合成了阳离子型、两性离子型和阴离子型的噻菁染料，对它们的结构进行了表征，并研究了染料的结构(阴离子和取代基的改变) 对吸收光谱的影响。     

Solvent polarity indicators: Extraction of some coumarin indicator dyes

Study of the extraction of ten different coumarins (unsubstituted, 6-methyl-, 7-methyl-, 4-hydroxy-, 7-hydroxy-, 7-hydroxy-4-methyl-, 7-methoxy-, 7-amino-4-methyl-, 7-diethyl-amino-4-methyl-, and 3-carboxy-) with nine organic solvents shows that the percentage extraction is generally high. Cyclohexanone and heptane were found to be, respectively, the most and least effective extracting solvents for the compounds under study. The results are discussed in terms of the effect of different solvent polarity parameters on the extraction process.     

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).     

Fast and slow processes of thermal deactivation of excited stilbazolium merocyanine dyes

The long living triplet states play important role in sensitizing action in all photochemical reactions. The yield of generation of triplet states of dyes can be evaluated on the basis of measurements of their slow (microsecond) thermal deactivation (TD). All experiments were carried out in the oxygen presence, it means under quenching dye triplets. The pulse dye laser generates in the investigated solution pressure signal. The high of the amplitudes of first maximum of this pressure wave-form signal in the solution of the investigated dye and in the reference sample were measured. Reference sample exhibits only fast processes of TD. The comparison of the first maximum of wave-form photothermal signal of sample and of reference enable to calculate part of energy exchanged into heat in time longer than time resolution of arrangement. The fluorescence yields of investigated dyes were also established. On the basis of such data, using procedure described in literature, the yield of singlet–triplet intersystem crossing (ISC) was evaluated. It was shown that this yield depends on the length of stilbazolium merocyanine chain. The product of triplet state yield and energy was lower for merocyanines with longer chains. At lower temperatures the yield of fluorescence increases and amount of excitation exchanged in short time into heat decreases. The slow TD process increases in low temperature because of the decrease in the quenching of the dyes triplet states by oxygen. The amount of energy exchanged into heat in a time longer than time resolution of apparatus is due predominantly through TD of the dye triplet states.     

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.     

Bis(merocyanine) Homo-Folda-Dimers: Evaluation of Electronic and Spectral Changes in Well-Defined Dye Aggregate Geometries

A series of three bis(merocyanine) dyes comprising chromophores of different conjugation lengths has been synthesized and the intramolecular aggregation process was investigated by UV/Vis absorption spectroscopy. The spectral changes observed upon variation of the solvent polarity reveal a folding process resulting in a cofacial π-stack of two chromophores with a decrease of the aggregation tendency with increasing chromophore length and solvent polarity. Solvent-dependent UV/Vis studies of the monomeric reference dyes show a significant increase of the polyene-like character for dyes with longer polymethine chains in nonpolar solvents, which is reversed upon aggregation due to the polarizability effect of the adjacent chromophore within the dye stack. The pronounced hypsochromic shift of the absorption band observed upon aggregation indicates strong coupling of the dyes’ transition dipole moments, which was confirmed by quantum-chemical analysis.     

Solvent effect on the absorption spectra ofN-2,6-trichlorobenzoquinonimine

The absorption spectra of solutions ofN-2,6-trichlorobenzoquinonimine in organic solvents of varying polarities are investigated. The ability of the compound to form molecular complexes in ethanol is discussed. The stability constants of the molecular complexes are determined from the spectra in mixed solvents. The equilibrium constant of the reaction involving the acquisition of a proton by the solute is calculated in water and in water—acetone mixtures.

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Lösungsmitteleffekte auf das Absorptionsspektrum vonN-2,6-trichlorbenzochinonimin

Zusammenfassung Die Absorptionsspektren wurden in Lösungsmitteln verschiedener Polarität untersucht und die Fähigkeit zur Bildung von Molekülkomplexen des Substrats in Ethanol diskutiert, wobei die Stabilitäskonstanten aus Messungen in Lösungsmittelgemischen errechnet wurden. Die Gleichgewichtskonstanten der Protonierung in Wasser und Wasser—Aceton wurden ebenfalls bestimmt.

     

Study of the absorption spectra and ionic equilibria of cationic-anionic polymethine dyes

The absorption spectra of a number of cationic-anionic polymethine dyes in polar, low-polarity, and nonpolar solvents were studied. It was established that in polar solvents the absorption spectra represent the sum of the absorption spectra of the cation and anion, whereas in nonpolar and low-polarity solvents, in many cases the appearance of a short-wave absorption band is observed, due to interaction of the chromophores of the cation and anion in ion pairs. In solvents of intermediate polarity (for example, in chloroform and ethyl acetate), a concentration dependence of the absorption spectra is observed, determined by the equilibria of ionic dissociation. The ionic dissociation constants of a number of cationic-anionic dyes in chloroform and ethyl acetate were determined by a conductometric method. The thermodynamic data obtained are compared with the spectral data.N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2524–2532, November, 1992.     

Bis(merocyanine) Hetero-Folda-Dimers: Evaluation of Exciton Coupling between Different Types of π-Stacked Chromphores

Exciton coupling between different types of chromophores has been rarely investigated. Herein, a systematic study on the exciton coupling between merocyanine chromophores of different conjugation length with varying excited state energies is presented. In this work well-defined hetero-dimer stacks were obtained upon folding of bis(merocyanine) dyes in nonpolar solvents. They show distinctly different absorption properties in comparison with the spectra of the single chromophores, revealing a significant coupling between the different chromophores. The simulated absorption spectra obtained from time-dependent density functional theory (TD-DFT) calculations are in good agreement with the experimental spectra. Our theoretical analysis based on an extension of Kasha's exciton theory discloses strong coupling between the dyes’ transition dipole moments despite of an excited-state energy difference of 0.60 eV between the chromophores.     

Solvent- and guest-responsive self-assembly of Hamilton receptor tethered bis(merocyanine) dyes

A novel supramolecular building block (8) that consists of a Hamilton receptor and two merocyanine dyes has been synthesized, and the self-assembly based on orthogonal hydrogen bonding and dipolar interactions has been studied in detail. Different self-assembled species, including oligomers, polymers, and inverted micelles could be observed upon variation of the solvent polarity and the concentration. Moreover, this system is highly responsive toward molecular stimuli such as merocyanine molecules with the barbituric acid motif that are bound by the Hamilton receptors. Detailed UV/Vis absorption studies provided insight into isodesmic or cooperative steps during the self-assembly of 8 into different species. The size of the aggregates in solution and the morphology on substrates have been explored by a combination of dynamic light scattering (DLS), atomic force microscopy (AFM), and TEM investigations.     

The effects of solvation in the theoretical spectra of cationic dyes

We present a quantum-mechanical study on the solvent effects in the structure and electronic spectra of some cationic dyes: acridine orange, proflavine, safranine, neutral red, thionine and methylene blue. The geometry optimizations were carried out with the AM1 and DFT (with B3LYP functional) methods and the theoretical spectra of the dyes under study were obtained with Zindo time-dependent methods (TD–DFT and TD–HF). The solvation methodology adopted was the integral equation formulation (IEF) version of the polarizable continuum model (PCM).     

Solvent effects on photophysical properties of merocyanine 540

Absorption and corrected fluorescence emission spectra of merocyanine 540 (MC 540) were recorded in solvents with different physico-chemical parameters – dielectric constant ε_r, refractive index n, dipolarity/polarizability π^*, hydrogen-bonding ability α. Hypsochromic shifts of their maxima positions did not obey Lippert–Mataga equation. However, a correlation with π^* and α was observed. Relative quantum yields φ_f and rate constants of nonradiative deactivation processes k_nr of the dye in different solvents based on steady-state measurements were estimated. Dependence on hydrogen-bonding ability was indicated – with increasing α, φ_f decreased and k_nr increased. The interaction between MC 540 and solvent molecules is discussed in terms of the different interactions contributing to the solvent stabilization of merocyanine dyes. Our results indicate that hydrogen bonding may contribute to solvent stabilization of MC 540.     

Solvent and TMEDA effects on the configurational stability of chiral lithiated aryloxiranes

The employment of hexane/N,N,N',N'-tetramethylethylenediamine (TMEDA) dramatically hinders the racemization of those lithiated styrene oxides (trifluoromethyl-, chloro-, and phenylthio-substituted) that have been proven to be configurationally unstable in THF on the timescale of their reactions. The barriers to inversion and the activation parameters, calculated (Eyring equation) for reactions performed in THF, THF/TMEDA, and hexane/TMEDA, suggest the intervention of particular enantiomerization mechanisms for each case. The role of TMEDA in both coordinating and noncoordinating solvents has also been questioned and discussed in light of the kinetic data gathered and a model for deprotonation in hexane/TMEDA has also been proposed. The synthetic benefits of our results became apparent on establishing an asymmetric synthesis of an industrially important antifungal agent.     

Solvent effects in the absorption spectra of the Ninhydrin chromophore

Visible spectra of the Ninhydrin chromophore, Ruhemann's purple, were studied in dimethyl sulfoxide (DMSO), formamide, N, N-dimethylformamide (DMF), and pyridine, as well as in mixed aqueous-nonaqueous solvent media. Large differences in both the position of absorption maxima and extinction coefficients for the two bands in the visible spectra in the various solvent media were observed. Both the absorption maxima and the extinction coefficients of the Ninhydrin chromophore were a linear function of the composition of dimethyl sulfoxide-H₂O solvent media. The experimental evidence allows predictions of values for the two absorption maxima of Ruhemann's purple as a function of the nature of the solvent medium. In nonaqueous aprotic solvents (i.e., DMSO and DMF), the maxima should be near 605 and 420 mμ; in nonaqueous aprotic solvents capable of undergoing charge-transfer interactions (i.e., pyridine), near 550 and 420 mμ; and in nonaqueous protic solvents (i.e., formamide), near 575 and 410 mμ. The maxima in aprotic media will be displaced to about 575 mμ (higher wavelength band) and 410 mμ (lower wavelength band) on dilution with protic solvents.     

Solvent and substituent effects on the photochemistry of norbornadiene-diarylacetylene Pauson-Khand adducts

The photochemistry of Pauson-Khand cycloadducts of norbornadiene with a series of bis-aryl alkynes has been studied. Two types of photochemical transformation take place: photorearrangement to tricyclic ketones or photochemical 6π electrocyclization. High selectivity levels have been attained for each pathway, controlled by the polarity of the solvent, irradiation wavelength, and presence (or absence) of oxygen.