Betaine Dye Research Articles

Synthesis and structures of crystalline solvates formed of pyridinium N-phenoxide (Reichardt's-type) betaine dyes and alcohols

Four new betaine dyes of the Reichardt's type featuring two tolyl substituents in different attachment (2–4) or being an analogous 1-naphthyl derivative (5) have been synthesized and described with reference to their negative solvatochromism. The dinaphthyl derivative 5 and also a corresponding intermediate nitrophenol 9d were shown with variable-temperature NMR spectroscopy to form conformational atropisomers in solution. Crystal structures of seven alcoholic solvent complexes including the unsubstituted parent compound (1) and different alcohols [1·EtOH (1 : 1), 1·i-PrOH (1 : 1), 2·MeOH (1 : 2), 3·i-PrOH (1 : 1), 3·n-BuOH (1 : 1), 4·EtOH (1 : 2) and 5·MeOH (1 : 3)] have been studied using X-ray diffraction methods. The betaine dyes exist as genuine zwitterion ground state structures in the solid state with twisted conformation between the phenoxide and pyridinium rings. With the exception of 3a [3·i-PrOH (1 : 1)], the alcohol guests in the complexes are hydrogen bonded to the oxygen atom of the phenoxide units, whereas in the i-PrOH complex of 3, the alcohol forms trimeric clusters without specific interaction with the betaine framework. From the packing modes in the crystals, the solvated betaines may be classified either as co-ordination type inclusion compounds with pocket-like host arrangements [1·EtOH (1 : 1), 1·i-PrOH (1 : 1), 2·MeOH (1 : 2), 3·n-BuOH (1 : 1), 4·EtOH (1 : 2) and 5·MeOH (1 : 3)], or a true clathrate with channel-type topology [3·i-PrOH (1 : 1)].

A Pyridinium–Barbiturate–Betaine Dye with Pronounced Negative Solvatochromism: A New Approach for Molecular Recognition

World record: The betaine dye 1 exhibits the highest negative solvatochromic range yet seen. Because of its pronounced push–pull system, 1 is suitable for the detection of polarity changes, acid–base reactions, and the formation of complexes with complementary hydrogen-bond sequences, which can even be followed by the naked eye.

Towards a unified view of the solvatochromism of phenolate betaine dyes

AbstractAn attempt has been made in order to unify the three types of solvatochromisms (negative, positive and inverted) of phenolate betaine dyes by a working model which describes them as particular cases of a general behavior. The model, based on the calculation (gas phase) of the chemical hardness of donor and acceptor fragments, was applied to 56 examples from the literature. As a result, the investigated compounds were grouped according to the sum of the hardnesses of their (non‐interacting) fragments, this sum being larger for a negative, intermediate for an inverted, and smaller for a positive solvatochromic behavior. Copyright © 2009 John Wiley & Sons, Ltd.

Solvent Motions and Solvation Processes in a Short-Time Regime: Effects on Excited-State Intramolecular Processes in Solution

We propose a method for treating equation of motions for atoms taking into account the inertial term with an interaction site model for capturing solvent dynamics attributed to solvent motions in a short-time regime, t < 100 fs. We show a prescription for solving the equation which governs the development of the fluctuation of solvent number density with the inertial term, and the results of the van Hove space-time correlation function of water are compared with those by a molecular dynamics simulation. Also, the procedure is applied to the study of solvation dynamics of the simplest betaine dye molecule pyridinium N-phenoxide in water in the excited state. It is shown that the coupling between solvation and a fast intramolecular reaction such as charge transfer is likely to play an important role in solvation dynamics of the simplest betaine, and the importance of tracking solvation process associated with electronic reorganization in the solute molecule in the short-time region is indicated.

Multiprobe Spectroscopic Investigation of Molecular-level Behavior within Aqueous 1-Butyl-3-methylimidazolium Tetrafluoroborate

In this work, an array of molecular-level solvent features--including solute--solvent/solvent--solvent interactions, dipolarity, heterogeneity, dynamics, probe accessibility, and diffusion--were investigated across the entire composition of ambient mixtures containing the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF4], and pH 7.0 phosphate buffer, based on results assembled for nine different molecular probes utilized in a range of spectroscopic modes. These studies uncovered interesting and unusual solvatochromic probe behavior within this benchmark mixture. Solvatochromic absorbance probes--a water-soluble betaine dye (betaine dye 33), N,N-diethyl-4-nitroaniline, and 4-nitroaniline--were employed to determine ET (a blend of dipolarity/polarizability and hydrogen bond donor contributions) and the Kamlet-Taft indices pi* (dipolarity/polarizability), alpha (hydrogen bond donor acidity), and beta (hydrogen bond acceptor basicity) characterizing the [bmim][BF4] + phosphate buffer system. These parameters each showed a marked deviation from ideality, suggesting selective solvation of the individual probe solutes by [bmim][BF4]. Similar conclusions were derived from the responses of the fluorescent polarity-sensitive probes pyrene and pyrene-1-carboxaldehyde. Importantly, the fluorescent microfluidity probe 1,3-bis(1-pyrenyl)propane senses a microviscosity within the mixture that significantly exceeds expectations derived from simple interpolation of the behavior in the neat solvents. On the basis of results from this probe, a correlation between microviscosity and bulk viscosity was established; pronounced solvent-solvent hydrogen-bonding interactions were implicit in this behavior. The greatest deviation from ideal additive behavior for the probes studied herein was consistently observed to occur in the buffer-rich regime. Nitromethane-based fluorescence quenching of pyrene within the [bmim][BF4] + phosphate buffer system showed unusual compliance with a "sphere-of-action" quenching model, a further manifestation of the microheterogeneity of the system. Fluorescence correlation spectroscopic results for both small (BODIPY FL) and macromolecular (Texas Red-10 kDa dextran conjugate) diffusional probes provide additional evidence in support of microphase segregation inherent to aqueous [bmim] [BF4].

Polarity of the acid chain of esters and transesterification activity of acid catalysts

The effect of polarity of the esters on the transesterification reaction rate has been investigated. The effect was studied in homogeneous and heterogeneous catalysts. The polarity of different ethyl alkanoate esters was varied by (i) increasing the number of carbon atoms in the acid alkyl chain of the esters and (ii) introducing Br and hydroxy substituents at the end of the acid chain of ethyl hexanoate. Polarity was determined through the λ max of the UV–Vis spectrum of the betaine dye dissolved in the investigated esters (E T(30) scale). The transesterification reaction was carried out with methanol and by using sulfuric acid and a Dowex DR2030 sulfonic resin as homogeneous and heterogeneous catalysts, respectively. It was observed that, in addition to steric hindrance, the polarity of the ester chain has an effect on the reaction rate of the heterogeneous acid catalysts. It is proposed that the positive or negative effect of the polarity is due to repulsive or attractive interactions of the ester chain with the polar groups of the resin and/or with the methanol molecules present in the pores. A very positive effect is found in heterogeneous acid catalysis if H-bonds can stabilize the active intermediate participating in the rate determining step. The attractive or repulsive interactions are absent in the homogeneous case.

New Urea-Based Surfactants Derived from α,ω-Amino Acids

New anionic urea-based surfactants derived from alpha,omega-amino acids and in particular from beta-alanine were synthesized and their solution properties characterized by electrical conductivity, equilibrium surface tension, and steady-state fluorescence spectroscopy techniques. Double-chain surfactants and the single-chain surfactant containing a sulfate head group exhibited the lowest critical micelle concentration (cmc) values and superior efficiency in lowering surface tension. All surfactants promoted adsorption relative to micellization, and micellar parameters were sensitive to the hydrophobicity of the amino acid residue. The polarity of the interfacial region, measured with the solvatochromic probe E(T)(30) (Reichardt's betaine dye), was similar to sodium dodecyl sulfate (SDS) micelles.

Formation of specific dipolar microenvironments complementary to dipolar betaine dye by nonionic peptide lipids in nonpolar medium

This paper describes the host-guest interaction between nonionic peptide lipids and solvatochromic dipolar betaine dyes in nonpolar aprotic organic solvent. We have serendipitously found that the colour of Reichardt's Dye (referred to as ET(30) hereafter, although the term ET(30) has been used as a polarity parameter) in chlorobenzene unusually blue-shifted in the presence of L-glutamic acid-derived peptide lipid 1 with a benzyloxycarbonylated Gly headgroup. Since it is widely accepted that ET(30) shows negative solvatochromism, i.e., the visible absorption band of this dye blue-shifts as the solvent polarity increases, the blue-shift indicates that ET(30) was in contact with the more polar microenvironment produced by the peptide lipid 1 rather than chlorobenzene under aggregate-free conditions. The binding site was assumed to be N-H(delta+) and CO(delta-) attached to both sides of the Gly residue, respectively, i.e., the O- and N+ of ET(30) complementarily bound to N-H(delta+) and CO(delta-) through hydrogen bonding and ion-dipole interaction, respectively. Since ET(30) is practically non-fluorescent, it was not feasible to use fluorescence spectrometry, which is a powerful method for the study of host-guest interactions, in order to specify the binding mode of ET(30). Therefore, a synthetic approach, although very laborious but reliable, has been used in conjunction with solvatochromic probing using visible absorption spectroscopy to specify the binding site on peptide lipid 1. The binding site has been found to be located on two dipoles, i.e., N-H(delta+) and CO(delta-) attached to both sides of the Gly residue, respectively, because introducing steric hindrance into the Gly moiety using several L-alpha-amino acids with bulky -substituents interfered with the binding of ET(30). Similar specific binding behaviour of ET(30) was observed by replacing the Gly residue of the lipid 1 with sarcosine (Sar). It was found that self-assembly of the peptide lipid was necessary for effective capture of ET(30). The molecular structural requirements of the peptide lipids that form such specific polar microenvironments complementary to dipolar betaine dyes have also been investigated.

Solvatochromic absorbance probe behavior within 1-butyl-3-methylimidazolium hexafluorophosphate+propylene carbonate: Preferential solvation or solvent–solvent interaction?

Abstract Physicochemical properties of ionic liquids (ILs) can be favorably modified by addition of appropriate cosolvents. Solvatochromic absorbance probes are used to assess physicochemical properties of the mixture of a common IL 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) and propylene carbonate. Parameter E T N obtained from electronic absorbance of Reichardt's betaine dye within the mixture is observed to be higher than that predicted from ideal additive behavior. Absorbance from N,N-diethyl-4-nitroaniline and 4-nitroaniline in concert with absorbance from Reichardt's dye is used to obtain dipolarity/polarizability (π*), hydrogen-bond donating (HBD) acidity (α), and hydrogen-bond accepting (HBA) basicity (β) of the mixture. While π* and α of the mixture are observed to be higher than those expected from ideal additive behavior, β is observed to be lower. Solvatochromic absorbance probe behavior suggests solute-specific preferential solvation; FTIR absorbance of the mixture implies negligible specific solvent–solvent interaction(s) within the mixture. Combined nearly ideal binary solvent/Redlich–Kister (CNIBS/R–K) equation is demonstrated to predict the solvatochromic parameters satisfactorily.

Environmental Effects on Photochemical Properties of Betaine Dyes in Rigid Media

We report luminescence of 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)phenolate (B30)- or other betaine dye-dispersed rigid media at 77 K and at room temperature (r.t.). Their luminescence in acetone at 77 K were remarkably influenced by water addition. UV-excited blue ∼ bluish green luminescence of B30-dispersed polymers at r.t. we reported in our previous reports appeared to resemble that of B30-dispersed acetone at 77 K in the presence of water. It suggests the participation of protonation and/or deprotonation processes in the UV-excited states of B30. A weak emission shoulder in visible emission wavelength range was also observed for B30-dispersed polymeric solids at r.t., similar to those emission bands for betaine dye-dispersed polymeric solids or organic solvents at 77 K.

Consequences of Strong Coupling between Solvation and Electronic Structure in the Excited State of a Betaine Dye

The electronic ground and excited-state structures of the betaine dye molecule pyridinium- N-phenoxide [4-(1-pyridinio)phenolate] are investigated both in the gas phase and in aqueous solution, using the reference interaction site model self-consistent-field (RISM-SCF) procedure within a CASSCF framework. We obtain the total free energy profiles in both the ground and excited states with respect to variation in the torsion angle between the phenoxide and pyridinium rings. We analyze the effect of solvent on the variation of the solute dipole moment and on the charge transfer character in the excited state. In the gas phase, it is shown that the potential energy profile in the excited-state decreases monotonically toward a perpendicular ring orientation and the dipole moment decreases along with decreasing charge localization. In water, the free energy surface for twisting is better characterized as nearly flat along the same coordinate for sterically accessible angles. These results are analyzed in terms of contributions of the solvation free energy, the solute electronic energy, and their coupling. Correspondingly, the dependence of the charge transfer character on solute geometry and solvation are analyzed, and the important roles in the excitation and subsequent relaxation processes for the betaine dye are discussed. It is found that there is considerable solute electronic reorganization associated with the evolution of solvation in the excited state, and it is suggested that this reorganization may contribute significantly to the early time evolution of transient spectra following photoexcitation.

Unusual Solvatochromism within 1-Butyl-3-methylimidazolium Hexafluorophosphate + Poly(ethylene glycol) Mixtures

Hybrid "green" solvent systems composed of room-temperature ionic liquids (ILs) and poly(ethylene glycols) (PEGs) may have enormous future potential. Solvatochromic absorbance probe behavior is used to assess the physicochemical properties of the mixture composed of IL 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]) and PEG (average molecular weights of 200, 400, 600, and 1500) at ambient conditions. Lowest energy intramolecular charge-transfer absorbance maxima of a betaine dye, i.e., E(T)(N), indicates the dipolarity/polarizability and/or hydrogen-bond donating (HBD) acidity of the [bmim][PF 6] + PEG mixtures to be even higher than that of neat [bmim][PF(6)], the solution component with higher dipolarity/polarizability and/or HBD acidity. Dipolarity/polarizability (pi*) obtained separately from the electronic absorbance response of probe N, N-diethyl-4-nitroaniline shows a trend similar to E(T)(N ) thus confirming the unusually high dipolarity/polarizability of the [bmim][PF(6)] + PEG mixtures. Similar to E(T)(N ) and pi*, the HBD acidity (alpha) of [bmim][PF(6)] + PEG mixtures is also observed to be anomalously high. Contrary to what is observed for E(T)(N ), pi*, and alpha, the hydrogen-bond accepting (HBA) basicity (beta) of the [bmim][PF(6)] + PEG mixtures is observed to be lower than that predicted from ideal additive behavior indicating diminished HBA basicity of the mixture as compared to its neat components. A four-parameter simplified combined nearly ideal binary solvent/Redlich-Kister (CNIBS/R-K) equation is shown to satisfactorily predict the solvatochromic parameters within [bmim][PF(6)] + PEG mixtures. It is demonstrated that [bmim][PF(6)] + PEG mixtures possess physicochemical properties that are superior to those of either the neat IL or the neat PEG.

Synthesis of Pyridinium – indan-1,3-dion-2-ide Betaine Dyes and Use as Indicators of Carboxylic Acids’ Polarity

2-[4-(2,4,6-Triarylpyridinium-1-yl)phenyl]indan-1,3-dion-2-ides 5a–d, (N+C-) betaine dyes, were synthesised by reaction of 2,4,6-triarylpyrylium perchlorates 6a–d with 2-(4-aminophenyl)indan-1,3-dione 7. The solvatochromic effect of compounds 5 was investigated. The betaines obtained are suitable for polarity determination of carboxylic acids and their anhydrides.

Polarization and solvatochromic shift of ortho-betaine in water

Betaine dyes are known to show very large transition energy shifts in different solvents. The ortho-betaine molecule – a simple two-ring prototype of the E T(30) Reichardt dye – has been investigated theoretically from a combined statistical and quantum mechanics approach. Using sequential Monte Carlo (MC) simulations and MP2/cc-pVDZ calculations the in-water dipole moment of ortho-betaine is obtained as 12.30 ± 0.05 D. This result shows a considerable increase of 75% compared to the in-vacuum dipole moment. For comparison, the use of a polarizable continuum model using the same MP2/cc-pVDZ leads to an in-water dipole moment of 11.6 D, in good agreement. This large polarization is incorporated in the classical potential for another MC simulation to generate solute–solvent configurations and to obtain the contribution of the polarization effect in the solvatochromic shift. Using statistically uncorrelated configurations and supermolecular INDO/CIS calculations, including the solute and, explicitly, 230 solvent water molecules, the statistically converged calculated shift is obtained here as 6360 cm −1, in good agreement with the experimental result of 7550 cm −1.

Pyridinium-N-phenolate betaine dyes as empirical indicators of solvent polarity: Some new findings

Abstract Solutions of the zwitterionic betaine dye 2,6-diphenyl-4-(2,4,6-triphenylpyridinium-1-yl)phenolate (hereinafter called standard betaine dye) and its derivatives are solvatochromic, thermochromic, piezochromic, and halochromic. That is, the position of its longest-wavelength intramolecular charge-transfer (CT) absorption band depends on solvent polarity, solution temperature, external pressure, and the type and concentration of salts (ionophores) added to the betaine dye solution. The outstanding large negative solvatochromism of this standard betaine dye has been used to establish UV/vis spectroscopically a comprehensive set of empirical parameters of solvent polarity, called E T(30) resp. E T N values, now known for many molecular and ionic solvents as well as for a great variety of solvent mixtures. This report describes relevant physicochemical properties of this standard betaine dye as well as the definition and some more recent practical applications of these solvent polarity parameters, derived from the standard betaine dye and its derivatives. In particular, the perichromism of the standard betaine dye can be used to study the polarity of microheterogeneous solutions (e.g., micelles and other organized media), surfaces (e.g., silica, alumina, cellulose), glasses (e.g., sol-gel systems), and solids (e.g., polymers), and for the construction of chemical sensors. As extension to solvatochromism, the more general term perichromism describes UV/vis band shifts of chromophore-containing solutes which are caused not only by changes in the surrounding solvent sphere, but also by their embedding in other surroundings such as micelles, vesicles, glasses, polymers, solids, interfaces, and surfaces. Some representative examples for such extended applications of the perichromic standard betaine dye are given.

Effects of Molecular Structure on Luminescent Properties of Betaine Dyes

We compared spectral properties of Betaine-30 (B30) with other similar betaines or triphenylpyridine. They showed similar UV-absorption and shorter emission spectra in polymeric solids. The emission wavelength appeared to be red shifted with increasing polarity of the solvent or CT characteristics of dye molecule. Other dyes would be able to be used as B30 for a kind of polarity indicators, furthermore, B30 appeared to be most stable among them. We also compared their semiempirical M.O. calculation results. INDO/S calculations showed CT characteristics of their absorption bands in visible region.

Theoretical study of geometrical and nonlinear optical properties of pyridinum N-phenolate betaine dyes

This paper presents an ab initio quantum chemical investigation of the geometrical structures and the non-linear optical properties (NLO) of three structural isomers of pyridinium N-phenolate betaine dye. The ground state geometrical parameters and the first-order hyperpolarizabilities were calculated using the Hartree-Fock (HF) as well as the second-order perturbation Møller-Pleset (MP2) method with the 6-31G, 6-31G(d), 6-31G(d,p), 6-31+G(d), 6-31++G(d,p), 6-311+G(d), aug-cc-PVDZ and the recently developed Z3PolX basis sets. Moreover, the first-order hyperpolarizability was calculated at the coupled cluster singles and doubles (CCSD/6-31+G(d)) level of theory. The analysis of the results of calculations for the investigated isomers indicates that there are important differences in their NLO activities. Additionally, it was shown that Z3PolX basis set works reasonable well for betaine dyes.

Solute–solvent interactions within aqueous poly(ethylene glycol): solvatochromic probes for empirical determination and preferential solvation

Due to their vast industrial importance, poly(ethylene glycols) [PEGs] have become substances of major investigations. The hypothesis that aqueous PEG rather than pure PEG may provide substantially improved physicochemical properties for many industrial applications is addressed. Solvatochromic electronic absorbance probes are utilized to gather important information about these systems. Response from a water-soluble betaine dye suggests a decrease in dipolarity/polarizability and/or hydrogen-bond donating (HBD) acidity as the PEG is added to water. This is further confirmed by the response of N,N-diethyl-4-nitroaniline, which shows a decrease in dipolarity/polarizability and, in concert with the response from the betaine dye, a decrease in HBD acidity as the amount of PEG is increased. Response from 4-nitroaniline combined with dipolarity/polarizability is used to show that hydrogen-bond accepting (HBA) basicity increases with the addition of PEG to water. The extent of change in these important physicochemical properties depends on the PEG molecular mass. A simple mole-fraction weighted solvation model suggests significant preferential solvation of the betaine dye by PEG molecules in aqueous PEG solutions.

Dilute aqueous 1-butyl-3-methylimidazolium hexafluorophosphate: properties and solvatochromic probe behavior

Limitations of the properties of water, the most common ‘green’ solvent, may be overcome by adding small amounts of ionic liquids (ILs). Important physical properties, such as density, viscosity and refractive index, of dilute aqueous IL 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) are shown to be significantly different than those of pure water at different temperatures. Up to 2.00 wt% bmimPF6 behaves like a strong electrolyte in water. Solvatochromic absorbance probe investigation indicates sensitive spectral behavior of a water-soluble betaine dye upon bmimPF6 addition to water. With considerably modified physicochemical properties, dilute aqueous IL solutions may find use in a variety of chemical applications.

Thermosolvatochromism of Betaine Dyes Revisited: Theoretical Calculations of the Concentrations of Alcohol−Water Hydrogen-bonded Species and Application to Solvation in Aqueous Alcohols

Thermosolvatochromism of Betaine Dyes Revisited: Theoretical Calculations of the Concentrations of Alcohol−Water Hydrogen-bonded Species and Application to Solvation in Aqueous Alcohols