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.     

Phenylene alkylene dendrons with site-specific incorporated fluorescent pyrene probes

This report deals with the synthesis and the spectroscopic properties of two second generation (G2) dendrons with site-specific incorporated phenyl pyrene derivatives as solvatochromic fluorescent probes. The generations that do not carry the probe are equipped with volume dummies, pyrene moieties that do not show a solvatochromic effect. Two complementary G2 phenylene alkylene dendrons were synthesized using Suzuki-Miyaura cross coupling. Most of the reactions used in the 10-step sequence generating the target compounds proceeded in good yields. The incorporated probes can be selectively photoexcited and show solvatochromic shifts that are of the same magnitude as for the free probes in a homogeneous solvent environment. In addition to the charge-transfer fluorescence, a broad emission band is observed that is assigned to an intramolecular exciplex formation between the aryl pyrene chromophores.     

Linear solvation energy relationship of the solubility of very polar gases: Sulfur dioxide,hydrogen chloride,hydrogen bromide,and ammonia

A linear free energy relationship was found for the log (mole fraction) of solutes in a wide variety of organic solvents with the solvatochromic parameters and the Hildebrand solubility parameter. The solutes were the highly dipolar gases sulfur dioxide, hydrogen chloride, hydrogen bromide, and ammonia at 25°C and 1 atm. partial pressure of the solute. It was found that correlations were greatly improved if solvatochromic parameters for the solvent as a monomer were used rather than the values for the bulk solvent. In solutions with these very dipolar gases, the mole ratio of solute to solvents approaches unity in many of the solutions, so a molecule of solute is interacting primarily with a particular molecule of the solvent. Therefore, the use of the solvatochromic parameters for the solvent as monomer is physically reasonable.     

The classification of solvents based on solvatochromic characteristics: the choice of optimal parameters for artificial neural networks

The Taft-Kamlet-Abboud hydrogen-bond acidity, hydrogen-bond basicity and polarity-polarizability are widely used as empirical characteristics of solvent-solute interactions. These solvatochromic parameters are determined from the absorption band positions of solvatochromic probes in the standard medium and in the medium under study. The practice of solvatochromic probing is growing rapidly, and the values of solvatochromic parameters are refined from time to time. As these values are rather close for many media, the classification of media based on these values can be tedious. This increases the choice of algorithms that can be employed in order to decrease the ambiguity of classification. The classification algorithms stable to small variations of solvatochromic parameters are of special interest. The artificial neural networks (ANN) proved to be a powerful tool for the supervised classification. The paper focuses on the search of optimal parameters of probabilistic, dynamic, Elman, feed-forward, and cascade ANN for the classification of solvent on the basis of their solvatochromic characteristics. Also, the influence of data variation on the stability of classification is examined. The dynamic and probabilistic neural networks have been found to be error-free and stable; they have significantly become such a common tool for supervised classification as linear discriminant analysis.      

A New Method to Investigate the Clustering Phenomena in Supercritical Fluids

EstimationoflocaldensityofsolventaboutthesoluteSolvatochromicbehaviorsofspectroscopicprobesarewidelyusedtoestimatethesol-ventstrengthofsupercriticalfluids(SCF,).i-3lnthiswork,thesolvatochrondcshiftofthen-n*transitionbandforacetone(O.o37mo1.L-')insupercrihcal(SC)CO2wasde-terminedbyUVspectroscopytostUdythesolvationeffect.TheMcRae-BaylissexpressionbasedonthedielectriccontinUUInmodelgivestherelahonshipbetWeenso1vatochromicshiftandpo1arizabilityofnonPolarsolvents4-5asfollows:wherevisthewave…     

The interaction of solvatochromic pyridiniophenolates with cyclodextrins

The interactions of six solvatochromic pyridiniophenolate dyes with α- and β-cyclodextrins were investigated with the aid of UV-vis and ¹H NMR spectroscopies, and molecular dynamics simulations. The deduced mode of encapsulation of these dyes within the hydrophobic host cavity was employed as a measure of the relative contributions of the donor and acceptor moieties to their solvatochromic properties.     

Solvatochromism as an alternative for contact angle measurements in the characterisation of modified polymer surfaces

Polyolefine surfaces have been pre-treated by UV/ozone and UV/water methods. The increase in polar groups on a polymer surface and the contribution of these polar groups to the adhesion of the polymer has been investigated by using contact angles and tensile strength tests. Because contact angle measurements do not give information about the specific polar groups on the surface we have used solvatochromic analyses to identify specific polar groups. The results showed that solvatochromic analyses is a promising method to discriminate between different kinds of polar groups and therefore solvatochromic surface characterisation may become an important surface analytical tool in adhesive technology.     

Determination of solvatochromic solvent polarity parameters for the characterisation of some nematic liquid crystal in anisotropic and isotropic phases

Characterisation of liquid crystals (LCs) as solvents is needed, to obtain the polarity and solvatochromic polarity parameters of these media. Polarity parameters demonstrate the effects of LC media on the photo-physical behaviour of solute molecules in an anisotropic medium. The practical limitations in determining solvent polarity scale parameters for LCs can overcome the overlapping absorption band of LCs and solvent-sensitive standard compounds or their insolubility in LCs. In this work, we report Kamlet–Abboud–Taft polarity functions of some nematic LCs in different temperatures and phases, isotropic and anisotropic, with the solvatochromic method, using the Reichardt's dye and 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)-phenolate standard probe. In addition, a new azo and coumarin dye were used as probes to obtain some solvatochromic polarity parameters. Finally, a new polarity parameter, the LC anisotropic matrix, is introduced.     

Structure of microemulsions with gemini surfactant studied by solvatochromic probe and diffusion NMR

The structure of microemulsions prepared by the anionic gemini surfactant didodecyl diphenyl ether disulfonate (C12-DADS) was investigated by a solvatochromic probe and nuclear magnetic resonance (NMR) diffusion measurements. The NMR measurements indicate the presence of bicontinuous and oil-in-water microemulsions depending on microemulsion composition. The absorbance spectra of the solvatochromic probe, Nile red, indicate the solubilization of the probe in different sites, in agreement with the NMR findings. It was also found that the microemulsions were capable of dissolving the hydrophobic probe, Nile red, up to four times better than expected if it were simply dissolved in the toluene phase.     

Use of fluorescence probes for studying Kamlet-Taft solvatochromic parameters of micellar system formed by binary mixture of sodium dodecyl sulfate and Triton-X 100

Fluorescence probes have been used to estimate Kamlet-Taft solvatochromic parameters alpha and pi* representing hydrogen-bond donation ability and dipolarity/polarizability, respectively, of sodium dodecyl sulfate (SDS)-Triton X 100 (TX100) mixed aggregates with varying compositions. The hydrogen-bond donation ability of the mixed aggregate has been found to increase with SDS composition, whereas the dipolarity/polarizability parameter decreases. The relative contribution of electrostatic and steric effect toward the total free energy of micellization have been calculated for the mixture. The solvatochromic parameters alpha and pi* depend linearly on the total free energy of micellization, indicating a correlation between aggregational and solvatochromic properties.     

UV solvatochromic shifts of 4-hydroxy-benzophenone and 2,4-dihydroxy-benzophenone in ethanol-acetonitrile mixtures

The anomalous UV spectroscopic behavior of 4-hydroxy-benzophenone and 2,4-dihydroxy-benzophenone in ethanol-acetonitrile mixtures has been investigated using theoretical and experimental methods. Band I of these compounds, associated to strong pi-->pi* transitions, suffers a blue shift when the polarity of the ethanol-acetonitrile solutions increases. The magnitude of the solvatochromic shifts suffered by the analyzed benzophenones (BPs) changes inversely with the planarity of their molecules. The experimental solvatochromic shifts of the compounds were correlated with the permittivity and the solvation parameters alpha and pi* that characterize the ethanol-acetonitrile mixtures used. In order to explain theoretically the observed solvatochromic shifts, it was proposed that in solution, the two compounds form an association complex of stoichiometry 1:1 with a molecule of ethanol. These complexes are formed by means of an intermolecular hydrogen bond between the hydrogen atom of 4-OH group of the solutes and the oxygen atom of ethanol. The calculations performed at the HRF/6-31G(d) level of theory using Onsager's and Tomasi's models showed that these solute-ethanol association complexes have an elevated thermodynamic stability. Good linear relations were obtained between the experimental absorption frequencies of BPs and the theoretical absorption frequencies of the association complexes. These frequencies were also very satisfactorily correlated with the properties of the above mentioned ethanol-acetonitrile mixtures. It was concluded that the magnitude of the analyzed solvatochromic shifts is determined by the degree of occurrence of solute-solvent interactions, which essentially depend on the polarity, polarizability and hydrogen bond donating ability of the ethanol-acetonitrile mixtures.     

New solvatochromic inorganic complexes

The solvatochromic behaviours of bis-cyclopentadienyl titanium(IV) dithiocyanate and of the hexacyanobis-2,2′-bipyridyltungstate(IV) and tricyano-2,2′-bipyridyloxotungstate(IV) anions are described. The solvent sensitivities of these complexes are compared with those of biscyanobis-2,2′-bipyridyliron(II) and other established inorganic solvatochromic species.     

The polarity of solutions of electrolytes

The polarity of solutions of LiClO₄ in acetic acid has been investigated. However, polarity scales based on light absorption, e.g. the π*₁-scale, are interfered by aggregation phenomena of the used solvatochromic dyes, whereas solvatochromic fluorescent dyes give proper results.     

Structure,solvatochromism, and solvation of trans-[CoIII(cyclam)(NCS)2](NCS) and the structure of [CoII(Me4cyclam) (NCS)]2[Co(NCS)4]MeOH

The structures of trans-[CoIII(cyclam)(NCS)2](NCS) and of [CoII(Me4cyclam)(NCS)]2[Co(NCS)4]·MeOH have been established by X-ray diffraction methods. The solvatochromic behavior of the trans-[Co(cyclam)(NCS)2]+ cation in several binary aqueous solvent mixtures is reported. Transfer chemical potentials for this complex from H2O into MeOH-H2O mixtures have been established from solubility measurements on its thiocyanate salt. The solvatochromic behavior of this cation is discussed in the context of other solvatochromic inorganic complexes; its transfer chemical potentials are discussed in relation to those of other cobalt(III) complexes.     

Linear and nonlinear optical properties of a macrocyclic trichromophore bundle with parallel-aligned dipole moments

A macrocyclic trichromophore bundle 1 with parallel-aligned dipole moments has been synthesized to study the influence of aggregation and orientation of a nonlinear optical (NLO) chromophore on its optical properties. The linear and nonlinear optical properties of 1 and a single chromophore standard 2 have been studied by UV-vis absorption, fluorescence, solvatochromic spectrometry, and hyper-Rayleigh scattering (HRS). Reduced first-order hyperpolarizability beta, hypsochromic shift, enhanced solvatochromic shifts, and fluorescence quenching for individual chromophores were observed when 1 was compared with 2. Analysis of the data showed that the transition dipole moment changes only slightly when the chromophores are parallel aligned in the bundle architecture. However, the apparent hyperpolarizability of the individual chromophores decreased significantly by about 20%. The reduction in beta for the individual chromophores in 1 is largely due to the hypsochromic shift, i.e., excitation energy increase of the interband (charge-transfer) energy gap and the reduced difference between the ground-state and excited-state dipole moments. The hypsochromic shift and fluorescence quenching are consistent with exciton theory. Possible reasons for the enhanced solvatochromic shift are discussed.     

Carbazole-based donor-acceptor compounds: highly fluorescent organic nanoparticles

Carbazole-based donor-acceptor compounds 1,2-dicyano-trans-1,2-bis-4-(carbazolyl)phenylethylene (1) and 1,2-dicyano-trans-1,2-bis-4-(3,6-di-tert-butylcarbazolyl)phenylethylene (2) were synthesized. 1 and 2 show negative solvatochromic absorption behavior, but show both positive and negative solvatochromic behavior in the fluorescence spectra. In a water/THF mixture, 1 as well as 2 aggregate into 50-150 nm nanoparticles. The emission of nanoparticles of the new types of fluorescent organic nanoparticles (FONs) 1 and 2 is much higher than that of either 1 or 2 in solution.     

Solvatochromism of a novel betaine dye derived from purine

A novel solvatochromic betaine dye has been synthesized from xanthosine and characterized spectroscopically by UV-vis in a broad range of solvents. The dye 9-(2',3',5'-tri-O-acetyl-beta-d-ribofuranosyl)-2-(pyridinium-1-yl)-9H-purin-6-olate, 1a, exhibits solvent-induced spectral band shifts that are (2)/(3) as large as that of the betaine known as Reichardt's dye, which forms the basis of the E(T)(30) solvent polarity scale. Moreover, the dye 1a is a ribonucleoside and hence has the potential application as a polarity probe for application in RNA oligonucleotides. The isomeric dye 6-(pyridinium-1)-yl-9H-purin-2-olate, 2a, has also been synthesized and exhibits slightly smaller solvatochromic band shifts. The new betaine dyes have also been studied by comparing the experimental and calculated solvatochromic shifts based on the calculation of the UV/vis absorption spectra, using a combination of methods with density functional theory (DFT). The COSMO continuum dielectric method, an applied electric field term in the Hamiltonian, and time-dependent density functional theory (TD-DFT) methods were used to obtain absorption energies, ground-state dipole moments, and the difference dipole moment between the ground and excited states. The calculations predict a lower energy absorption band of charge-transfer character that is highly solvatochromic, and a higher energy absorption band that has pi-pi character which is not solvatochromic, in agreement with the experimental data. For Reichardt's dye the difference dipole moment between the ground and excited state (Deltamu = mu(e) - mu(g)) was also calculated and compared to experiment: Deltamu(calcd) = -6 D and Deltamu(exptl) = -9 +/- 1 D.(1) The ground-state dipole moment was found to be mu(g)(calcd) = 18 D and mu(g)(exptl) = 14.8 +/- 1.2 D.(1).     

Studies on the electronic absorption spectra of some monoazo derivatives

The electronic absorption spectra of a series of azo dye compounds containing -Cl, -SO3H and -OH groups were recorded in twenty one solvents with different polarities. The solvents were selected to cover a wide range of parameters (refractive index, dielectric constant and hydrogen bonding ability). Solvent-induced effect on the maximum absorption band frequencies of azo dye compounds are described in terms of solute-solvent interactions. Multiple linear regression equation for νmax was performed using polarizability-polarity parameters and Kamlet-Taft solvatochromic parameters. The results help to assign the solvent-solute interactions and the solvatochromic potential of the investigated compounds. It is concluded that the electronic of the substituent and hydrogen bonding acceptor ability of the solvents are the major factors to the interaction in solutions.     

Monomeric and polymeric anionic gemini surfactants and mixed surfactant systems in micellar electrokinetic chromatography. Part II: characterization of chemical selectivity using two linear solvation energy relationship models

Sodium di(undecenyl) tartarate monomer (SDUT), a vesicle-forming amphiphilic compound possessing two hydrophilic carboxylate headgroups and two hydrophobic undecenyl chains, was prepared and polymerized to form a polymeric vesicle (i.e., poly-SDUT). The anionic surfactants of SDUT and poly-SDUT (carboxylate head group) and sodium dodecyl sulfate, SDS (sulfate head groups) as well as mixed surfactant systems (SDS/SDUT, SDS/poly-SDUT, and SDUT/poly-SDUT) were applied as pseudostationary phases in micellar electrokinetic chromatography (MEKC). Two linear solvation energy relationship (LSER) models, i.e., solvatochromic and solvation parameter models, were successfully applied to investigate the effect of the type and composition of pseudostationary phases on the retention mechanism and selectivity in MEKC. The solvatochromic and solvation parameter models were used to help understand the fundamental nature of the solute-pseudostationary phase interactions and to characterize the properties of the pseudostationary phases (e.g., solute size and hydrogen bond-accepting ability for all pseudostationary phases). The solute types were found to have a significant effect on the LSER system coefficients and on the predicted retention factors. Although both LSER models provide the same information, the solvation parameter model is found to provide much better results both statistically and chemically than the solvatochromic model.     

Dual Solvatochromism of Neutral Red

Abstract— The effect of solvent polarity on the electronic absorption and fluorescence properties of neutral red (NR), a phenazine-based dye of biological importance has been investigated in several neat and mixed solvents. An unusual dual solvatochromic behavior has been observed that reveals the existence of two closely spaced electronic excited states in NR. In low-polarity solvents the fluorescence of the NR is mainly emitted from the localized excited state, whereas in high-polarity solvents the emission from the charge transfer state dominates. The dipole moments of the localized and charge transfer states of NR have been estimated from the solvatochromic shifts. The dipole moment of the localized excited state (4.8 D) is only slightly higher than that of the ground state (2.0 D), while that of the charge transfer state is drastically higher (17.5 D). Fluorescence quantum yields and the life-times of NR have been determined in different solvents and correlated with the solvatochromic shifts.