Enhanced fluorescence of triphenylmethane dyes in aqueous surfactant solutions at supramicellar concentrations—effect of added electrolyte (original) (raw)
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Absorption, fluorescence emission spectra and fluorescence lifetimes of N-alkyl-4-(p-N,N-dimethyl aminostyryl) pyridinium dyes of varying lengths of alkyl chain have been measured in different organic solvents (protic, dipolar aprotic and aprotic) and in different surfactant solutions. The spectra for the dyes are similar in a single solvent but vary with solvent type. The Stokes shift for the dye does not vary with the solvent parameter as predicted by Lippert–Mataga equation. The fluorescence decay of the dyes shows two lifetimes in organic solvents except in a few solvents where a single or three lifetimes were obtained. The lifetime results are interpreted in terms of emission from cis and quinoid (or intramolecular charge transfer, ICT) forms of the dye in the excited state. The spectra and fluorescence lifetime results for the cis isomer (synthesized as a stable compound) in organic solvents confirmed the coexistence of multiple species. In surfactant solutions, the spectra and fluorescence lifetimes of the dyes depend upon the length of the alkyl chain of the dye and the concentration of the surfactant, namely, premicellar or post micellar. Dye–surfactant complexes were identified in a few cases in SDS and CTAB premicellar solutions. TX-100 surfactant is found to stabilize the cis isomer for all the dyes, whereas both SDS and CTAB surfactants stabilize the trans isomer predominantly.
Journal of Molecular Liquids, 2021
Attractive smart and emissive nanomaterials are designed by embedding the methylene blue (MB) in the complex of pyrene labeled poly(acrylic acid) (PAA25Py3) and dodecyltrimethylammonium chloride (C 12 TAC) using the supramolecular host-guest strategy. The investigation methods were surface tension, UV-vis, steady-state fluorescence, electrokinetic potential, dynamic light scattering and microscopy. A comparative study about the adsorption at air/water interface of anionic polymer and oppositely charged surfactant complexes without (PS) and with MB (PS/MB) was made. The photophysical properties of PS and PS/MB assemblies were highlighted by both pyrene (Py) and MB. The self-aggregation and conformation of polymer with MB in the PS matrix were analyzed. At low surfactant concentration, small and well dispersed PS/MB complexes form hydrophobic environments as detected by Py label. The PS complexes quenched the MB emission. At high surfactant amounts, the Py label signaled an unusual micropolarity. Thus, the formation of iceberg-like environments due to the cation-л interactions in large aggregates of PS complexes was proved by polarity index. In these high polar and rigide nanoenvironments of PS aggregates, the dye fluorescence is enhanced. The obtained results have the potential applications in chemical sensing and imaging.
Journal of Photochemistry and Photobiology A: …, 2004
Steady-state and time-resolved fluorescence studies have been done using a ketocyanine dye in heterogeneous media containing binary mixtures of sodium dodecyl sulphate (SDS) and triton X-100 (TX-100), and SDS + polyvinyl pyrrolidone (PVP). The dye molecules are found to distribute between core and interfacial region of the micelles. The band corresponding to the dye molecule in the core region exhibits red edge excitation shift. Study of lifetime in picosecond domain reveals that the de-excitation of the excited state of the dye via radiative pathway (k r) is independent of environment. The non-radiative decay constant (k nr) on the other hand has been found to depend on the nature of environment, the core region being characterised by a faster decay rate. The slower decay rate in the interfacial region has been explained as due to hydrogen bonding interaction of the carbonyl group of the dye with protic solvents. Interesting variation of k nr in the core region with surfactant composition has been observed which is explained in terms of surfactant-surfactant interaction in the micelles. Microviscosities at the micelle-water interface has been determined. For binary mixture of surfactants, the value of microviscosity has been found to deviate from ideality. An index of deviation from ideality has been proposed.
Colloids and Surfaces A-physicochemical and Engineering Aspects, 2011
The interactions between an anionic dye and cationic surfactants were investigated using surface tension measurements, spectroscopy, conductometry, and pulsed field gradient NMR (PFG-NMR). Spectroscopic and surface property characterization of the solution as a function of surfactant concentration in the presence of the dye revealed formation of three species: a dye-surfactant ion pair, small mixed aggregates of the dye and surfactant (below the critical micelle concentration (CMC) of these surfactants), and micelles composed of the cationic surfactant. Above the CMC, the dye reverted to its monomeric state or bound to the surface of the micelle. Chemometric resolution analysis confirmed the formation of three species. The hydrodynamic radii of the micelles were determined by self-diffusion coefficient measurements. The average size of the micelles was larger in the presence than in the absence of the dye. Regular solution theory was used to describe the synergistically enhanced ability to form mixed aggregates of dyes and surfactants.
Journal of luminescence, 2001
Absorption, fluorescence emission spectra and fluorescence lifetimes of N-alkyl-4-(p-N,N-dimethyl aminostyryl) pyridinium dyes of varying lengths of alkyl chain have been measured in different organic solvents (protic, dipolar aprotic and aprotic) and in different surfactant solutions. The spectra for the dyes are similar in a single solvent but vary with solvent type. The Stokes shift for the dye does not vary with the solvent parameter as predicted by Lippert-Mataga equation. The fluorescence decay of the dyes shows two lifetimes in organic solvents except in a few solvents where a single or three lifetimes were obtained. The lifetime results are interpreted in terms of emission from cis and quinoid (or intramolecular charge transfer, ICT) forms of the dye in the excited state. The spectra and fluorescence lifetime results for the cis isomer (synthesized as a stable compound) in organic solvents confirmed the coexistence of multiple species. In surfactant solutions, the spectra and fluorescence lifetimes of the dyes depend upon the length of the alkyl chain of the dye and the concentration of the surfactant, namely, premicellar or post micellar. Dye-surfactant complexes were identified in a few cases in SDS and CTAB premicellar solutions. TX-100 surfactant is found to stabilize the cis isomer for all the dyes, whereas both SDS and CTAB surfactants stabilize the trans isomer predominantly.
Langmuir, 2005
In this paper, we demonstrate that the behavior of a set of eight large-sized negatively solvatochromic pyridinium N-phenolate betaine dyes reflects the principle transformations, occurring in aqueous micellar solutions of three cationic surfactants. As surfactants, cetyltrimethylammonium bromide (CTAB), n-octadecyltrimethylammonium chloride (OTAC), and N-cetylpyridinium bromide (CPB) were used. Normally, for such probes coupled with micelles, a red shift of the vis absorption band is expected as a result of a hydrophobization ("drying") of the micellar interface. However, under addition of electrolytes with anions such as tosylate, salicylate, and some n-alkanesulfonates or n-alkanecarboxylates to the micellar solutions, an unexpected effect was observed. Instead of a red shift, a blue shift of the vis absorption band of some of the dissolved betaine dyes was registered, as compared with the spectrum measured in pure aqueous micellar solutions of CTAB, OTAC, or CPB (∆λmax up to ca. 80 nm). This blue shift, indicating an increase in the polarity of the dye microenvironment, is explained by displacing the large dye dipoles from the thinned micelles toward the aqueous phase. The effect is well expressed at concentrations of C(betaine dye) ≈ 10 -5 M, C(cationic surfactant) ≈ 0.001 M, and C(organic anion) ≈ 0.01 M. Transmission electron microscopy of dried samples confirms the distinct changes occurring in the studied micellar systems upon the addition of organic anions. The excess of inorganic salts [C(NaBr, KBr, or KCl) ) 0.5-4.0 M] restored the position of the vis absorption band or even shifted it toward the red. Moreover, some of the betaine dyes studied (i.e., the more hydrophobic ones) stay in the micellar pseudophase or precipitate under the aforementioned concentration conditions. The peculiarities of the behavior of these betaine dyes are in agreement with their molecular structure.
Soft Matter, 2013
A quantitative empirical model is presented, which relates the total surfactant concentration with the fluorescence intensity and the mean translational diffusion coefficient of dyes in micellar solutions, as determined by Fluorescence Correlation Spectroscopy (FCS). Based on this model a systematic data analysis method is defined for the precise determination of the dye binding equilibrium constant, the critical micelle concentration, the translational diffusion coefficients, and the hydrodynamic radii of dyes 10 and micelles and related properties. The method can be used for the routine and automatic determination of the cmc of surfactant solutions. The model is applied to dyes with very different hydrophobicity in aqueous solutions of the non-ionic surfactant Triton X-100. As a reference the cmc of Triton X-100 is also determined directly from changes in the absorbance of its phenyl-ring applying a ratiometric method. 65 characterization of a surfactant solution, for example for the determination of the cmc, it is imperative to take the dye exchange equilibrium into account.
The interaction of a series of cationic dialkyloxacarbocyanine perchlorate (DiOCn) dyes of different degrees of hydrophobicity with micelles of an anionic surfactant, sodium dodecylsulfate (SDS), has been studied spectrophotometrically in aqueous solutions. The Benesi–Hildebrand equation was used to calculate binding constants (Kb) of the dyes to surfactant micelles, the fraction of dye bound to the micelles (fmic), and the standard free-energy change (ΔG0) for the transfer of dye from the aqueous to micellar phase. It has been shown that the interaction of oppositely charged dye molecules and surfactant micelles is controlled by both electrostatic and hydrophobic interactions. A small increase in dye hydrophobicity due to lengthening of the hydrocarbon radical has been shown to cause an abrupt nonlinear increase of the fmic value. This points to a key role of hydrophobic interactions in the binding of dye molecules with the micelles.
The Journal of Physical Chemistry, 1987
The cationic xanthene dyes thiopyronine and selenopyronine are solubilized in the Stern regions of anionic micelles. Upon photoexcitation, the excited triplet states of the dyes are observed to decay via unimolecular processes (k , z 2 X lo3 s-l) for the case of one dye per micelle and via bimolecular processes (k2 5 X lo6 S-I) for the case of more than one dye per micelle. If the number of dye triplet states that undergo slow decay is measured, the number of micelles can be obtained and thus the micellar aggregation numbers can be evaluated. The aggregation numbers of several surfactant alkanesulfonates, 2,5-dialkylbenzenesulfonates with a total of 14 carbon atoms in the alkyl chains, and other detergents, which are determined in this manner, are in agreement with corresponding values determined by using other photophysical methods and with literature values. The aggregation numbers of the dialkylbenzenesulfonate surfactants increase from 38 to 56 with increasing effective chain length. The fluorescence lifetime and fluorescence depolarization of thiopyronine solubilized in the dialkylbenzenesulfonate micelles are consistent with a low local polarity and high local viscosity for the interior of these micelles, compared to micelles of aliphatic detergents. Investigations using sodium 1 l-(3-hexyl-1-indolyl)undecyl sulfate (6-In-1 1) as a fluorescence probe suggest that the polarity of the interior of the dialkylbenzenesulfonate micelles is similar to that of liquid hydrocarbons. These results suggest a compact structure for the dialkylbenzenesulfonate micelles with low water penetration into the micelles.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1997
The hydrophobic interaction of amphiphilic hemicyanine dyes, i.e. (dimethylamino)stilbazolium butyl sulphonate (I) and (dihexylamino)stilbazolium butyl sulphonate (H) with cetyltrimethyl ammonium bromide (CTAB), a cationic surfactant and lithium dodecyl sulphate (LDS), an anionic surfactant, was studied through absorption spectra as a function of the concentration of surfactants above and below their critical mice!le concentrations. The different lengths of dialkyl chains present on these dyes exhibited hydrophobic interaction with rnicelles of CTAB and LDS; as a result visible spectra of both the dyes exhibited red shifts of different magnitudes when the dye molecules were solubilized into micelles. The approximate number of dye molecules per micelle was also estimated at a particular concentration of each surfactant. The solubilization depends on the dilakyl chain length of the dye together with the nature of surfactant head groups.