Fluorescent properties of cationic-anionic polymethine dyes

The fluorescence spectra were studied and the quantum yields of the fluorescence of a number of cationic-anionic polymethine dyes were measured in polar, low-polarity, and nonpolar solvents. It was shown that the fluorescence spectra of cationic-anionic dyes in polar solvents, like the absorption spectra, represent the sum of the fluorescence spectra of the corresponding cationic and anionic dyes. For dyes in which the absorption bands of the anion and cation are close and a new short-wave band arises in the ion pairs, excitation into this band virtually does not lead to fluorescence, which is a consequence of the forbidden nature of the long-wave transition that arises as a result of the interaction of the chromophores. For a number of cationic-anionic dyes in ion pairs an energy transfer is observed: When an ion possessing short-wave absorption is excited, an ion with long-wave absorption fluoresces.N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2532–2539, November, 1992.     

Cis-trans-isomerization of cationic-anionic polymethine dyes

The effect of solvent polarity and ion pair formation oncis-trans-isomerization of cationic-anionic polymethine dyes and of related simple cationic and anionic dyes is studied by flash photolysis. The change in the rate constant for reversecis-trans- isomerization of photoisomers due to the interaction of a cation with an anion in an ion pair is observed in nonpolar solvents. A drop in the yield of the photoisomers to zero is observed for a number of cationic-anionic dyes in weakly polar and nonpolar solvents which is possibly due to steric hindrances in the photoisomerization process in ion pairs.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 719–724, April, 1993.     

Study of fluorescent aggregates of polymethine dyes

Absorption, fluorescence, and fluorescence excitation spectra have been studied for a number of anionic, cationic, and cationic-anionic polymethine dyes in low-polar and nonpolar solvents, as well as in binary mixtures of solvents differing in polarity. For most of the dyes studied, fluorescent aggregates have been found to form. Their broad fluorescence bands are located in the long-wave region with respect to those of the initial dyes. The quantum yield of the aggregate fluorescence is normally higher than that of the initial dyes. Fluorescence excitation spectra of some cationic-anionic dyes in nonpolar solvents disagree with their absorption spectra because of contact and solvent-separated ion pairs simultaneously present in the solution.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 69–75, January, 1993.     

Exciplex and radical ion intermediates in the photochemical reaction of 9-cyanophenanthrene with 2,3-dimethyl-2-butene

The photochemical reaction of 9-cyanophenanthrene and 2,3-dimethyl-2-butene, first reported by Mizuno, Pac and Sakurai, has been reinvestigated. The formation of a [2+2]-cycloadduct via a singlet exciplex is the exclusive reaction in the nonpolar solvents benzene and ethyl acetate. Photochemical behavior in polar solvents is far more complicated than previously reported. Mechanisms consistent with the effects of solvent polarity, methanol concentration, methanol deuteration, and light intensity upon product yields are proposed. Formation of a 9-cyanophenthrene anion radical and 2,3-dimethyl-2-butene cation radical is the primary photoinitiated process in polar solvent. The cation radical can undergo deprotonation to yield an allyl radical or nucleophilic attack by methanol to yield a methoxyalkyl radical. Covalent bonding of these radicals and the 9-cyanophenanthrene anion radical gives rise to the acyclic adducts obtained in polar solvents. The anion radical can also be protonated, leading ultimately to the formation of 9,10-dihydro-9-cyanophenanthrene.     

PHOTOPHYSICS STUDIES OF ORGANIC COMPOUNDS——NANOSECOND LASER PHOTOLYSIS AND TRANSIENT ABSORPTION SPECTRA STUDIES OF PYRENE-AROMATIC AMINES

Nanosecond time-resolved transient absorption spectra of pyrene-triphenylamine, pyrenediphenylamine, pyrene-N, N-dibenzylaniline systems in various solvents have been investigated. In nonpolar solvent, pyrene-triphenylamine exciplex and pyrene-N, N-dibenzylaniline exciplex were observed directly. In acetonitrile, the pyrene anion radical, triphenylamine and diphenylamine cation radicals were detected. On the basis of the present experimental facts, the mechanism of fluorescence quenching processes of pyrene in polar and nonpolar solvents has been established.     

Fluorescent aggregates of cation-anionic polymethine dyes with simple structures

The absorption, fluorescence, and excitation spectra of two cation-anionic dyes with simple structures, which have the identical anions and variable cations, were studied in weakly polar and nonpolar solvents as well as in binary mixtures of solvents with different polarity. Under these conditions heterogeneous fluorescent aggregates were found at 20 °C. The structure of the cation has a significant influence on the formation and properties of the aggregates of cation-anionic polymethine dyes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 476–480, March, 1995.     

Electronic Structure and Structure of Ion Pairs of Anionic σ Adducts of Polynitroarenes with Acetonate Ion

The anionic Yanovskii adducts of 1,3,5-trinitro- and 1,3-dinitrobenzenes, 1,3-dinitronaphthalene, and 3,5-dinitrobenzoic acid with sodium, potassium, and tetrabutylammonium acetonates in low-polarity solvents exist mostly as contact ion pairs, while in polar solvents, as solvent-separated ion pairs and free ions. Lowering the temperature increases the fraction of solvent-separated ion pairs in low-polarity solvents and of free ions in polar solvents, by shifting the equilibria to stronger solvated ionic species. By quantum-chemical calculations of the geometry and electronic structure of the anions and of the electronic absorption spectra of the free ions and ion pairs, as well as by a spectrophotometric study of adducts with solvents of various polarity it was established that the cation on ion-pair formation coordinates with the 4-nitro group with respect to the pyramidal node.     

Solution viscosity behavior of polystyrene-based cationic ionomers. Effects of ion content and solvent

Dilute-solution viscosities of polystyrene-based cationic ionomers containing ammonio or phosphonio groups were measured in several solvents. In polar solvents with dielectric constant (ε_r) beyond 10, the ionomers showed a typical polyelectrolyte behavior, indicating that a large part of ionic groups were dissociated into ions. In nonpolar solvents with low ε_r, the reduced viscosity of the ionomers linearly decreased with a decreasing ionomer concentration. At low polymer concentrations, every ionomer gave a reduced viscosity lower than that of the corresponding chloromethylated polystyrene. With an increasing ion content, the intrinsic viscosity progressively decreased if the nonpolar solvents had a low acceptor number (A_N), such as toluene or tetrahydrofran (THF). In the halogenated solvents with high A_N value, such as chloroform, however, the intrinsic viscosity was hardly dependent on the ion content. This indicates that the intramolecular aggregation among the ionic groups is inhibited in the halogenated solvents due to a strong anion solvation. An addition of a protic solvent to a nonpolar solvent eliminates the aggregation between ionic groups and leads to polyelectrolyte behavior. © 1994 John Wiley & Sons, Inc.     

Photoinduced electron transfer in ion pairs of cation-anion polymethine dyes

Photoinduced electron transfer in ion pairs of cation-anion polymethine dyes was studied by flash photolysis. The formation of radicals, which are the products of photoinduced transfer of an electron from an anion to a cation in the ion pairs, was observed during photoexcitation of a number of cation-anion dyes in nonpolar and some weakly polar solvents (in particular, in toluene and chloroform). Photoinduced electron transfer is also observed during triplet sensitization of ion pairs of the cation-anion dyes. The redox potentials of the cations and anions constituting the dyes were measured; the radical yields were compared with the free energies of photoinduced electron transfer. Photoinduced electron transfer in the systems under study was compared with similar process in cyanineborate ion pairs.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 878–884, May, 1995.The authors thank I. Ya. Levitin for help in measuring redox potentials.This work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-4217).     

Photostability of the sunscreening agent 4-tert-butyl-4′-methoxydibenzoylmethane (avobenzone) in solvents of different polarity and proticity

The most widely used UVA absorber in broad-spectrum sunscreens is 4-tert-butyl-4′-methoxydibenzoylmethane (avobenzone). However, the photostability of avobenzone is solvent-dependent. The aim of this work was to investigate the photostability of avobenzone in solvents of different polarity and proticity. Four solvents were employed, namely, cyclohexane, ethyl acetate, dimethylsulfoxide and methanol. The cause of the instability of avobenzone in these solvents was determined by means of UV spectroscopy, high performance liquid chromatography, gas chromatography–mass spectrometry and nuclear magnetic resonance spectroscopy. The effect of oxygen on the photo-instability was also determined. Avobenzone was found to lose absorption efficacy as a result of photoisomerisation from the enol to the keto form and/or photodegradation to form photoproducts that absorb principally in the UVC region, depending on the solvent. It was found to be essentially photostable in the polar protic solvent methanol but photoisomerised in the polar aprotic solvent dimethylsulfoxide. In the nonpolar solvent cyclohexane, it photodegraded appreciably. Both photoisomerisation and photodegradation occurred to a similar extent in the moderately polar aprotic solvent ethyl acetate. Photoisomerisation occurred only in the presence of oxygen whereas photodegradation occurred irrespective of oxygen. This knowledge is important in order to achieve the correct formulation for sunscreens incorporating avobenzone.     

Electronic spectroscopy and photochromic mechanism of bis-Schiff bases, N, N''''-bis(2-hydroxy-1-naphthylidene)-1,4-phenyldiamine

The steady state and transient state absorption spectra and fluorescence spectra of N,N'-bis(2-hy-droxy-1-napbthylidcne)-1,4-phenyldiamme ( BNP ) in cyclohexane and acetonitrile were determined.The pho-tochromic mechanism was discussed In nonpolar solvents,BNP exists mainly in the enol form and has the absorption maximum in the UV region In polar solvents,however,both the enol and proton transfer tautomer are formed,but the farmer is the main one Fluorescence emissions result from the excited state of proton transfer product.     

Relationship between ionic conductivity of perfluorinated ionomeric membranes and nonaqueous solvent properties

Ionic conductivity and swelling data are measured for Nafion^® perfluorinated ionomeric membranes in nonaqueous solvents and solvent mixtures and correlated with solvent physical properties. The dependence of ionic conductivity on solvent uptake and cation type is examined for Nafion^® 117 membranes with a nominal equivalent weight of 1100 g/eq. The most important factors determining ionic conductivity in membranes swollen with polar nonaqueous solvents are the solvent viscosity, molar volume, donor properties, and the solvent uptake by the membrane. Ionic conductivity is generally limited by dissociation of the cation from the fixed anion site indicating that the ionomer fixed anion site basicity is the critical membrane property. Means for increasing membrane ionic conductivity are discussed.     

吡啶酮偶氮分散染料光谱性能

吡啶酮分散染料应用性能优异 ,其色谱主要为黄色及橙色 ,尤以黄色为主 [1～ 3]。Cheng和 Peng等 [2 ,3] 对以氨基噻二唑类和苯系芳胺为重氮组分的吡啶酮类染料的可见光谱及互变异构进行了研究 ,Ertan等 [4 ] 研究了以氨基噻唑和氨基苯并噻唑为重氮组分的吡啶酮偶氮染料的可见光谱 ,结果表明上述染料色谱主要仍为黄色。为得到具有更深色谱的吡啶酮类染料 ,我们用不同的重氮组分合成了一系列吡啶酮分散染料 ,研究了其在不同溶剂及不同 p H值下的光谱 ,发现该类染料亦可达到红、甚至蓝色谱 ,其中染料 1 a、1 b及 2 b3个染料结构未见报道。O2 …     

Thermochemistry of mixing imidazole-based ionic liquids with water and organic solvents

The results of the calorimetric studies of the enthalpies of mixing of some ionic liquids, 1-butyl-3-methylimidazolium chloride and acetate, with water, pentanol, dimethyl sulfoxide and dimethylformamide are presented. Protic solvents interact with the ionic liquid anion, wheras aprotic, with the cation. The mixing enthalpy depends on the dissociation degree of the ionic liquid.     

The Peculiar Nature of Molecular Interactions between an Imidazolium Ionic Liquid and Acetone

We present novel insights into the molecular interactions between polar solvents and imidazolium ionic liquids using the example of 1‐ethyl‐3‐methylimidazolium ethyl sulfate and acetone. Recently published volumetric property data of this particular system have revealed peculiarities which could not be fully explained by steric effects. In order to shed light on the behavior at a molecular level, we apply IR spectroscopy and analyze solvent‐induced line shifts as well as the excess IR spectra. From the spectroscopic results a conclusive picture of the site‐specific molecular interactions is developed and our explanation is in concert with the volumetric effects. The data suggest the initial formation of trimers in which acetone interacts with existing ion pairs through interactions of the acetone oxygen atom with the imidazolium ring rather than forming directed hydrogen bonds at the CH moieties. With further addition of acetone, tetramers are formed which significantly weaken the interionic interactions and eventually initiate ion pair dissociation. Once the ions are released, the anion is rapidly saturated with acetone while the cation solvation proceeds more slowly with acetone addition.     

Electronic spectroscopy and photochromic mechanism of bis-Schiff bases, N, N′-bis(2-hydroxy-l-naphthylidene)-l, 4-phenyldiamine

The steady state and transient state absorption spectra and fluorescence spectra of N, Ń-bis(2-hydroxy-1-naphthylidene)-1, 4-phenyldiamine (BNP) in cyclohexane and acetonitrile were determined. The photochromic mechanism was discussed. In nonpolar solvents, BNP exists mainly in the enol form and has the absorption maximum in the UV region. In polar solvents, however, both the enol and proton transfer tautomer are formed, but the former is the main one. Fluorescence emissions result from the excited state of proton transfer product. Project supported by the National Natural Science Foundation of China and the Foundation of Chinese Academy of Sciences.     

Raman spectroscopic study on solvation of diphenylcyclopropenone and phenol blue in room temperature ionic liquids

We investigated the solvation of several room temperature ionic liquids by Raman spectroscopy using diphenylcyclopropenone (DPCP) and phenol blue (PB) as probe molecules. We estimated acceptor numbers (AN) of room temperature ionic liquids by an empirical equation associated with the Raman band of DPCP assigned as a C=C stretching mode involving a significant C=O stretching character. According to the dependence of AN on cation and anion species, the Lewis acidity of ionic liquids is considered to come mainly from the cation charge. The frequencies and bandwidths of the C=O and C=N stretching modes of phenol blue are found to be close to those in conventional polar solvents such as methanol and dimethyl sulfoxide. The frequencies of these vibrational modes show similar dependence upon the electronic absorption band center as is observed in conventional liquid solvents. However, peculiar behavior was found in the Raman bandwidths and the excitation wavelength dependence of the C=N stretching mode in room temperature ionic liquids. Both the bandwidth of the C=N stretching mode and the extent of the excitation wavelength dependence of the Raman shift of the C=N stretching mode tend to decrease as the absorption band center decreases, in contrast to the case of conventional solvents. This anomaly is discussed in terms of the properties of room temperature ionic liquids.     

Solvation Structure of Uracil in Ionic Liquids

The local solvation environment of uracil dissolved in the ionic liquid 1‐ethyl‐3‐methylimidazolium acetate has been studied using neutron diffraction techniques. At solvent:solute (ionic liquid:uracil) ratios of 3:1 and 2:1, little perturbation of the ion–ion correlations compared to those of the neat ionic liquid are observed. We find that solvation of the uracil is driven predominantly by the acetate anion of the solvent. While short distance correlations exist between uracil and the imidazolium cation, the geometry of these contacts suggest that they cannot be considered as hydrogen bonds, in contrast to other studies by Araújo et al. (J. M. Araújo, A. B. Pereiro, J. N. Canongia‐Lopes, L. P. Rebelo, I. M. Marrucho, J. Phys. Chem. B 2013, 117, 4109–4120 ). Nevertheless, this combination of interactions of the solute with both the cation and anion components of the solvents helps explain the high solubility of the nucleobase in this media. In addition, favourable uracil–uracil contacts are observed, of similar magnitude to those between cation and uracil, and are also likely to aid dissolution.     

Isomerization of ion pairs of symmetrical indopolycarbocyanine dyes

It was shown that from a polar solvent to a nonpolar solvent the rate constant of cis-trans isomerization of the dyes studied decreases sharply (by a factor of 10) on account of the formation of ion pairs (between the dye cation and anion in a nonpolar solvent). This is explained by an increase in the order of the bond of the polymethine chain of the dye, around which isomerization occurs. The formation of ion pairs was found to have virtually no effect on the lifetime of the triplet state of dyes; the sharp increase in the decay rate of the triplet state for dye 6 is due to the heavy-atom effect (the I^– anion).N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 107–113, January, 1992.