What Can You Learn from a Molecular Probe? New Insights on the Behavior of C343 in Homogeneous Solutions and AOT Reverse Micelles

Switching of the Polarity-Sensitive Aggregation Pattern of a Thiosemicarbazone-Based Anticancer Luminophore and Its Involvement in Cellular Apoptosis of the Human Lung Cancer Cell Line

Elucidation of the photophysical and biochemical properties of small molecules can facilitate their applications as prospective therapeutic imaging (theragnostic) agents. Herein, we demonstrate the luminescence behavior of a strategically designed potential therapeutic thiosemicarbazone derivative, (E)-1-(4-(diethylamino)-2-hydroxybenzylidene)-4,4-dimethylthiosemicarbazide (DAHTS), accompanied by the illustration of its solvation and solvation dynamics using spectroscopic techniques and exploring its promising antitumor activities by adopting the necessary biochemical assays. Solvent-dependent photophysical properties, namely UV-vis absorption, fluorescence emission, and excitation profiles, concentration-dependent studies, and time-resolved fluorescence decays, serve as footprints to explain the existence of DAHTS monomers, its excited-state intramolecular proton transfer (ESIPT) product, and dimeric and aggregated forms. The emission intensity progressively intensifies with increasing polarity and proticity of the solvents up to MeOH, but in water, a sudden dip is seen. Solvent polarity and H-bonding modulate the fluorescence behavior of the primary emission peak and significantly influence the formation of the dimer and DAHTS aggregates. The designed luminophore (DAHTS) exhibits significant antiproliferative activity against the human lung cancer (A549) cell lines with inhibitory concentrations (IC₅₀) of 16.88 and 11.92 μM for 24 and 48 h, respectively. DAHTS effectively reduces the cell viability and induces cytotoxicity with extensive morphological changes in A549 cells in the form of spikes when compared to the normal HEK cell lines. More importantly, it increases the p53 expression at the mRNA level that consolidates its potential therapeutic activity. The effect of DAHTS on apoptotic pathways against the A549 cell line has been investigated to determine its probable mechanism of cell death. Thus, the all-inclusive understanding of the photophysical properties and the necessary biochemical assays put forward important steps toward tailoring the thiosemicarbazone core structure for favorable cancer theragnostic applications in academic and pharmaceutical research.

Study of structure of nonaqueous reverse micelles with o-nitroaniline and methyl orange as molecular probes: comparison with an aqueous reverse micelles

Instead of water reversed micelles can also be formed with polar organic solvents possessed with high dielectric constant and very low solubility in oil phase. Nonaqueous reverse micelles or microemulsions represent an interesting microreactors for various reactions, especially for reactions, where reagents can react with water. Study of localization places of molecular probes in organic polar pockets of reverse micelles is topical. The solvatochromic behavior of optical probes ortho-nitroaniline (o-NA) and methyl orange (MO) was studied in nonaqueous reverse micelles on the basis of surfactants sodium bis (2-ethylhexyl) sulfosuccinate (AOT) and polyoxyethylene (4) lauryl ether (C12E4) and polar organic solvents (acetonitrile, dimethylformamide, glacial acetic acid, etc.) insoluble in oil phase hexane. The strength of binding of o-NA and MO to AOT and C12E4 reversed micelles was assesssed via binding constant (K b ) and association degree (α) respectively. Donor, acceptor, or dipole-dipole interactions ability of the solvent to the head groups of surfactant was taken into account in order to explain results obtained with UV–visible spectroscopic method. The binding constants of o-NA with reverse AOT micelles in the presence of various solvents in the pockets of reversed micelles increase in the following row water < glacial acetic acid < acetonitrile < dimethylformamide < dimethyl sulfoxide, but this sequence is reversed when o-NA binds to C12E4 reverse micelles. The high value of the proton donor or acidity parameter in the water molecule (x d  = 0.37) determines the weak binding of o-NA to the head AOT groups (K b  = 20.8) in case of aqueous reverse micelles. The high value of the dipole parameter in the dimethylformamide molecule (x n  = 0.40) promotes its strong interaction with nonionic polyoxyethylene groups of C12E4, which results in low value of binding constant (K b  = 26.5) in case of optical probe o-NA and low value of association degree (α = 0.60) using MO as absorption probe. The results of this article will contribute to the improvement of the concept of interfacial processes, viz.: (i) some issues of supramolecular chemistry, (ii) revealing the contribution of parameters of donor, acceptor or dipole-dipole interaction in a polar organic solvent at the surfactant/nonpolar organic solvent interface, and (iii) features of the dissolution of optical probes in non-aqueous reverse micelles.

The Journey of 1-Keto-1,2,3,4-Tetrahydrocarbazole Based Fluorophores: From Inception to Implementation

Carbazole is a unique template associated with several biological activities. It is due to the diverse and versatile biological properties of carbazole derivatives that they are of immense interest to the research community. 1-keto-1,2,3,4-tetrahydrocarbazoles are important synthetic intermediates to obtain carbazole derivatives. Several members of this family emit fluorescence on photoexcitation. In the context of biochemical and biophysical research, designing and characterising small molecule environment sensitive fluorophores is extremely significant. This article aims to be a state of the art review with synthetic and photophysical details of a variety of fluorophores based on 1-keto-1,2,3,4-tetrahydrocarbazole skeleton.

Coumarin 343 in aqueous solution: theoretical analysis of absorption

Vibronic coupling and hydration were taken into account when describing the absorption of coumarin C343 (both neutral and anionic forms) in an aqueous media. It was shown that the B3LYP functional with the 6-31 +  + G(d,p) basis set and the IEFPCM solvent continuum model give theoretical vibronic absorption spectra, which are coincide with the experimental ones. Of the structural differences between C343⁰ and C343^-, there is a different twisting of the carboxyl group additionally changing due to excitation. Upon excitation, a significant shift in the electron density occurs from the C10 atom to the C4 atom only. Thus, a charge transfer on the scale of the entire molecule does not occur. Different hydration complexes with strongly bound water molecules have been analyzed.

Altered relaxation dynamics of excited state reactions by confinement in reverse micelles probed by ultrafast fluorescence up-conversion

Chemical reactions in confined environments are important in areas as diverse as heterogenous catalysis, environmental chemistry and biochemistry, yet they are much less well understood than the equivalent reactions in either the gas phase or in free solution. The understanding of chemical reactions in solution was greatly enhanced by real time studies of model reactions, through ultrafast spectroscopy (especially when supported by molecular dynamics simulation). Here we review some of the efforts that have been made to adapt this approach to the investigation of reactions in confined media. Specifically, we review the application of ultrafast fluorescence spectroscopy to measure reaction dynamics in the nanoconfined water phase of reverse micelles, as a function of the droplet radius and the charge on the interface. Methods of measurement and modelling of the reactions are outlined. In all of the cases studied (which are focused on ultrafast intramolecular reactions) the effect of confinement was to suppress the reaction. Even in the largest micelles the result in the bulk aqueous phase was not usually recovered, suggesting an important role for specific interactions between reactant and environment, for example at the interface. There was no simple one-to-one correspondence with direct measures of the dynamics of the confined phase. Thus, understanding the effect of confinement on reaction rate appears to require not only knowledge of the dynamics of the reaction in solutions and the effect of confinement on the medium, but also of the interaction between reactant and confining medium.

Structure and Energetics of Dye-Sensitized NiO Interfaces in Water from Ab Initio MD and Large-Scale GW Calculations

The energy-level alignment across solvated molecule/semiconductor interfaces is a crucial property for the correct functioning of dye-sensitized photoelectrodes, where, following the absorption of solar light, a cascade of interfacial hole/electron transfer processes has to efficiently take place. In light of the difficulty of performing X-ray photoelectron spectroscopy measurements at the molecule/solvent/metal-oxide interface, being able to accurately predict the level alignment by first-principles calculations on realistic structural models would represent an important step toward the optimization of the device. In this respect, dye/NiO surfaces, employed in p-type dye-sensitized solar cells, are undoubtedly challenging for ab initio methods and, also for this reason, much less investigated than the n-type dye/TiO₂ counterpart. Here, we consider the C343-sensitized NiO surface in water and combine ab initio molecular dynamics (AIMD) simulations with GW (G₀W₀) calculations, performed along the MD trajectory to reliably describe the structure and energetics of the interface when explicit solvation and finite temperature effects are accounted for. We show that the differential perturbative correction on the NiO and molecule states obtained at the GW level is mandatory to recover the correct (physical) interfacial energetics, allowing hole transfer from the semiconductor valence band to the highest occupied molecular orbital (HOMO) of the dye. Moreover, the calculated average driving force quantitatively agrees with the experimental estimate.

Is it Necessary for the Use of Fluorinated Compounds to Formulate Reverse Micelles in a Supercritical Fluid? Searching the Best Cosurfactant to Create "Green" AOT Reverse Micelle Media

Herein, we report the effect of employing two different alcohols, such as n-pentanol and 2,2,3,3,4,4,5,5-octafluoro pentanol (from now on F-pentanol), into 1,4-bis-2-ethylhexylsulfosuccinate (AOT) reverse micelles (RMs), to determine the interfacial activity and establish the best candidate to act as a cosurfactant in supercritical RMs. Dynamic light scattering (DLS), Fourier transform infrared (FT-IR), and fluorescence emission spectroscopy allowed us to determine and understand the behavior of alkanols in RMs. As a result, we found interesting displacements of alkanol molecules within the RMs, suggesting that the electrostatic interaction between SO₃^- and Na⁺ weakens because of new interactions of n-pentanol with SO₃^- through H-bonds, changing the curvature of the micellar interface. According to FT-IR and DLS studies, F-pentanol forms a RM polar core interacting through intermolecular H-bonds, suggesting no perturbations of the AOT RM interface. Hence, n-pentanol was selected as a cosurfactant to form supercritical RMs, which is confirmed by red edge excitation shift studies, using C343 as a molecular probe. Herein, we were able to create RMs under supercritical conditions without the presence of modified surfactants, fluorinated or multitailed compounds, which, to the best of our knowledge, was not shown before.

Activation of Electrophile/Nucleophile Pair by a Nucleophilic and Electrophilic Solvation in a SNAr Reaction

Nucleophilic aromatic substitution reactions of 4-chloroquinazoline toward aniline and hydrazine were used as a model system to experimentally show that a substrate bearing heteroatoms on the aromatic ring as substituent is able to establish intramolecular hydrogen bond which may be activated by the reaction media and/or the nature of the nucleophile.

Anomalous Spectral Modulation of 4-Aminophthalimide inside Acetonitrile/AOT/ n-Heptane Microemulsion: New Insights on Reverse Micelle to Bicontinuous Microemulsion Transition

The behavior of acetonitrile/sodium 1,4-bis(2-ethylhexyl)sulfosuccinate (AOT)/ n-heptane microemulsion, whether it remains as reverse micelle (RM) or bicontinuous microemulsion (BMC), has been controversial and even termed as a "problem system". Herein, we investigate the microemulsion using spectral and dynamical responses of a hydrophilic solvatochromic fluorophore 4-aminophthalimide (4-AP) at different w_s values (=[acetonitrile]/[AOT]). Interestingly, we found that emission parameters of 4-AP within the microemulsion vary differently at low and high w_s regimes. The quantum yield (ϕ_f) and lifetime (τ_f) of 4-AP first increase up to w_s = ∼1 and, thereafter, decrease upon a further increase in the w_s values. The emission maximum of 4-AP significantly shifts to a higher wavelength from 445 nm at w_s = 0 to 475 nm at w_s = 8. Interestingly, unlike aqueous RMs, the emission maximum at w_s = 1 matches with the emission maximum in neat acetonitrile and the emission maximum shifts to even longer wavelength at a higher w_s. Steady-state anisotropy also shows a break around w_s = 1; anisotropy decreases very sharply from w_s = 0 to 1 and, thereafter, remains nearly constant. Solvation dynamics becomes progressively faster with an increase in the acetonitrile content only in the low w_s regimes but remains almost independent of w_s after w_s > 2. All of the results collectively indicate that the morphology of the microemulsion may change at an intermediate w_s (∼1); below this, the system behaves like reverse micelles, and above this, the system may remain as BMC. The conjecture was further supported by dynamic light scattering measurements, where we observed a gradual increment of the average size at the low acetonitrile content (up to w_s = 1) but, thereafter, the size distribution becomes multimodal and sizes cannot be estimated correctly.

Enhancing the photoluminescence of surface anchored metal-organic frameworks: mixed linkers and efficient acceptors

We present two approaches to enhance the photoluminescence quantum yield (PLQY) of surface-anchored metal-organic frameworks (SURMOFs). In the first approach we fabricate SURMOFs from a mix of an emissive linker with an optically-inert linker of equivalent length, diluting the emissive linker while maintaining the SURMOF structure. This approach enhances the internal PLQY. However, the increase in internal PLQY is achieved at the expense of a drastic reduction in optical absorption, thus the external PLQY remains low. To overcome this limitation, a second approach is explored wherein energy-accepting guest chromophores are infiltrated into the framework of the active linker. At the correct acceptor concentration, an internal PLQY of 52% - three times higher than the previous approach - is achieved. Additionally, the absorption remains strong leading to an external PLQY of 8%, an order of magnitude better than the previous approach. Using this strategy, we demonstrate that SURMOFs can achieve PLQYs similar to their precursor chromophores in solution. This is of relevance to SURMOFs as emitter layers in general, and we examine the optimized emitter layer as part of a photon upconversion (UC) SURMOF heterostructure. Surprisingly, the same PLQY is not observed after triplet-triplet annihilation in the UC heterostructure as after its normal photoexcitation (although the UC layers exhibit low thresholds consistent with those reported in our previous work). We discuss the potential bottlenecks in energy transport that could lead to this unexpected reduction in PLQY after excitation via triplet-triplet annihilation, and how future design of SURMOF UC multilayers could overcome these limitations.

How Does Nanoconfinement within a Reverse Micelle Influence the Interaction of Phenazinium-Based Photosensitizers with DNA?

The major focus of the present work lies in exploring the influence of nanoconfinement within aerosol-OT (AOT) reverse micelles on the binding interaction of two phenazinium-based photosensitizers, namely, phenosafranin (PSF) and safranin-O (SO), with the DNA duplex. Circular dichroism and dynamic light-scattering studies reveal the condensation of DNA within the reverse micellar interior (transformation of the B-form of native DNA to ψ-form). Our results unveil a remarkable effect of the degree of hydration of the reverse micellar core on the stability of the stacking interaction (intercalation) of the drugs (PSF and SO) into DNA; increasing size of the water nanopool (that is, w ₀) accompanies decreasing curvature of the DNA duplex structure with the consequent effect of increasing stabilization of the drug:DNA intercalation. The marked differences in the dynamical aspects of the interaction scenario following encapsulation within the reverse micellar core and the subsequent dependence on the size of the water nanopool are also meticulously explored. The differential degrees of steric interactions offered by the drug molecules (presence of methyl substitutions on the planar phenazinium ring in SO) are also found to affect the extent of intercalation of the drugs to DNA. In this context, it is imperative to state that the water pool of the reverse micellar core is often argued to approach bulk-like properties of water with increasing micellar size (typically w ₀ ≥ 10), so that deviation from the bulk water properties is likely to be minimized in large reverse micelles (w ₀ ≥ 10). On the contrary, our results (particularly quantitative elucidation of micropolarity and dynamical aspects of the interaction) explicitly demonstrate that the bulk-like behavior of the nanoconfined water is not truly achieved even in large reverse micelles.

Theoretical rationalisation of the photophysics of a TICT excited state of cinnamoyl–coumarin derivatives in homogeneous and biological membrane models

Analysis of the potential energy barriers and structural dynamics of a new TICT-probe for monitoring biological environments.

Solvent effect on a model SNAr reaction in ionic liquid/water mixtures at different compositions

A biphasic behavior observed on the reaction rate of a model S_NAr reaction in ionic liquid/water mixtures was explained by preferential solvation effects in water rich mixtures, and an anion effect in mixtures with high ionic liquid content.

Altering intra- to inter-molecular hydrogen bonding by dimethylsulfoxide: A TDDFT study of charge transfer for coumarin 343

DFT and TDDFT methods were carried out to investigate the influences of intramolecular and intermolecular hydrogen bonding on excited state charge transfer for coumarin 343 (C343). Intramolecular hydrogen bonding is formed between carboxylic acid group and carbonyl group in C343 monomer. However, in dimethylsulfoxide (DMSO) solution, DMSO 'opens up' the intramolecular hydrogen bonding and forms solute-solvent intermolecular hydrogen bonded C343-DMSO complex. Analysis of frontier molecular orbitals reveals that intramolecular charge transfer (ICT) occurs in the first excited state both for C343 monomer and complex. The results of optimized geometric structures indicate that the intramolecular hydrogen bonding interaction is strengthened while the intermolecular hydrogen bonding is weakened in excited state, which is confirmed again by monitoring the shifts of characteristic peaks of infrared spectra. We demonstrated that DMSO solvent can not only break the intramolecular hydrogen bonding to form intermolecular hydrogen bonding with C343 but also alter the mechanism of excited state hydrogen bonding strengthening.

Dynamics of different steps of the photopyrolytic cycle of an eminent anticancer drug topotecan inside biocompatible lyotropic liquid crystalline systems

Dynamics of different steps of photopyrolytic processes of an eminent anticancer drug topotecan have been investigated inside different lyotropic liquid crystalline systems.

Improvement of the amphiphilic properties of a dialkyl phosphate by creation of a protic ionic liquid-like surfactant

Imim-DEHP, an interesting protic IL-like surfactant to create RMs in aliphatic and aromatic non-polar solvents and unilamellar vesicles in water.

Differences in Interactions of Benzoic Acid and Benzoate with Interfaces

The interaction of benzoic acid and benzoate with model membrane systems was characterized to understand the molecular interactions of the two forms of a simple aromatic acid with the components of the membrane. The microemulsion system based on bis(2-ethylhexyl)sulfosuccinate (AOT) allowed determination of the molecular positioning using 1D NMR and 2D NMR spectroscopic methods. Benzoic acid and benzoate were both found to penetrate the membrane/water interfaces; however, the benzoic acid was able to penetrate much deeper and thus is more readily able to traverse a membrane. The Langmuir monolayer model system, using dipalmitoylphosphatidylcholine, was used as a generic membrane lipid for a cell. Compression isotherms of monolayers demonstrated a pH dependent interaction with a lipid monolayer and confirming the pH dependent observations shown in the reverse micellar model system. These studies provide an explanation for the antimicrobial activity of benzoic acid while benzoate is inactive. Furthermore, these studies form the framework upon which we are investigating the mode of bacterial uptake of pyrazinoic acid, the active form of pyrazinamide, a front line drug used to combat tuberculosis.

Surface-enhanced Raman scattering of coumarin 343 on silver colloidal nanoparticles

Surface-enhanced Raman scattering (SERS) of coumarin 343 (C343) adsorbed on silver colloidal nanoparticles reduced by sodium citrate was investigated and the surface adsorption geometry of C343 on Ag was sought by optimizing C343-Ag complexes for neutral and deprotonated C343 molecules in the DFT simulations. The SERS of C343 showed a number of spectral changes upon solution pH change. We found that deprotonated C343 adsorbs on the Ag nanoparticles through the carboxylate group keeping a perpendicular geometry to the surface. When protonated, the adsorption geometry of C343 is changed into more or less flat to the surface as the cyclic ester group becomes a preferred surface adsorption site.

How the cation 1-butyl-3-methylimidazolium impacts the interaction between the entrapped water and the reverse micelle interface created with an ionic liquid-like surfactant

The behavior of the interfacial water entrapped in reverse micelles (RMs) formed by the ionic liquid-like surfactant 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT) dissolved in benzene (or chlorobenzene) was investigated using noninvasive techniques such as dynamic light scattering (DLS), static light scattering (SLS), FT-IR and (1)H NMR. The DLS and SLS results reveal the formation of discrete spherical and non-interacting water droplets stabilized by the bmim-AOT surfactant. Moreover, since the droplet size increases as the W0 (W0 = [water]/[surfactant]) value increases, water interacts with the RM interface. From FT-IR and (1)H NMR data, a weaker water-surfactant interaction in bmim-AOT RMs in comparison with the RMs created by sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) is detected. Consequently, there are less water molecules interacting with the interface in bmim-AOT RMs, and their hydrogen bond network is not completely disrupted as they are in Na-AOT RMs. The results show how the nature of the new cation impacts the interaction between the entrapped water and the RM interface, modifying the interfacial water structure in comparison with the results known for Na-AOT.

Nanoemulsions as an effective medium for encapsulation and stabilization of cholesterol/β-cyclodextrin inclusion complex

BACKGROUND

Inclusion complex formation between β-cyclodextrin (β-CD) and suitable guest molecules such as cholesterol (Ch) has regularly been exploited to design self-assembled structures. In the present study an effective nanoemulsion medium (lecithin/Tween 80/ethyl oleate/water) was selected for solubilizing and stabilizing Ch and Ch/β-CD inclusion complex. Phase solubility, spectroscopic, thermodynamic, Z-average diameter and morphological analyses were conducted.

RESULTS

Phase solubility data analysis demonstrated an increase in Ch solubility at low β-CD concentrations (0.01-0.35 mmol L(-1) ). Transmission electron microscopy and Z-average diameter data indicated the spherical nature of the droplets and confirmed the formation of nanoemulsions with an average size of less than 50 nm. The negative value of ΔG obtained during analysis further indicated that the binding was spontaneous in nature.

CONCLUSION

Primarily, this research demonstrates the use of nanoemulsions as a medium in food matrices, instead of water, for hosting Ch in β-CD.

Solvation Dynamics in Different Phases of the Lyotropic Liquid Crystalline System

Reverse hexagonal (HII) liquid crystalline material based on glycerol monooleate (GMO) is considered as a potential carrier for drugs and other important biomolecules due to its thermotropic phase change and excellent morphology. In this work, the dynamics of encapsulated water, which plays important role in stabilization and formation of reverse hexagonal mesophase, has been investigated by time dependent Stokes shift method using Coumarin-343 as a solvation probe. The formation of the reverse hexagonal mesophase (HII) and transformation to the L2 phase have been monitored using small-angle X-ray scattering and polarized light microscopy experiments. REES studies suggest the existence of different polar regions in both HII and L2 systems. The solvation dynamics study inside the reverse hexagonal (HII) phase reveals the existence of two different types of water molecules exhibiting dynamics on a 120-900 ps time scale. The estimated diffusion coefficients of both types of water molecules obtained from the observed dynamics are in good agreement with the measured diffusion coefficient collected from the NMR study. The calculated activation energy is found to be 2.05 kcal/mol, which is associated with coupled rotational-translational water relaxation dynamics upon the transition from "bound" to "quasi-free" state. The observed ∼2 ns faster dynamics of the L2 phase compared to the HII phase may be associated with both the phase transformation as well as thermotropic effect on the relaxation process. Microviscosities calculated from time-resolved anisotropy studies infer that the interface is almost ∼22 times higher viscous than the central part of the cylinder. Overall, our results reveal the unique dynamical features of water inside the cylinder of reverse hexagonal and inverse micellar phases.

Disentangling vibronic and solvent broadening effects in the absorption spectra of coumarin derivatives for dye sensitized solar cells

Individuation of vibronic and solvent contributions to the spectra of a family of coumarin dyes helps to understand the main differences in their lineshapes.

Photoisomerization and reorientational dynamics of DTDCI in AOT/alkane reverse micelles containing non-aqueous polar liquids

Molecular mobility of the symmetric carbocyanine fluorophore DTDCI was studied in AOT/alkane reverse micelles containing non-aqueous polar liquids DMF, formamide, ethylene glycol and glycerol by monitoring both the torsional photoisomerization and rotational reorientation, both of which were sensitive to microviscosity of the local environment. The DTDCI fluorophore resides completely within the AOT-polar liquid reverse micelle nano-droplets, where its dynamics were found to be significantly retarded irrespective of the polar liquid taken, due to a combination of electrostatic and hydrophobic forces that induce the guest DTDC(+) cation to attach to the AOT molecules of the host droplet. The addition of strong hydrogen-bond donating polar liquids like formamide, ethylene glycol and glycerol causes a systematic enlargement of the droplets. Rotational dynamics of the fluorophore inside the nano-droplets was characterized by a diffusion coefficient comparable to that in highly viscous solvents like ethylene glycol.

Photophysics of a coumarin in different solvents: use of different solvatochromic models

This study reported the photophysics of 7-(diethylamino)coumarin-3-carboxylic acid N-succinimidyl ester (7-DCCAE) in different neat solvents of varying polarity using steady-state absorption, fluorescence emission and picosecond time-resolved spectroscopy. In nonpolar solvents, the dye molecule predominantly exists in nonpolar structure and exhibits very low value of nonradiative decay rate constant (k(nr)), demonstrating the emission takes place from S(1) -LE to S(0) ground state. The fluorescence quantum yields, lifetime values of 7-DCCAE in different solvents are rationalized on the basis of intramolecular charge transfer (ICT) followed by twisted intramolecular charge transfer state formation (TICT) as well as specific solute-solvent interactions. Several solvatochromic models (such as Lippert, Dimroth, Kamlet-Taft, Catalán 3P and Catalán 4P models) were used to analyze the solvatochromic shift of 7-DCCAE in different solvents. The different empirical models show that the observed results are better correlate for nonchlorinated solvents and provide statistically significant best-fit result. A comparison was done between comparatively new solvatochromic model (Catalán 3P and Catalán 4P model) with Kamlet-Taft model. The ground state structure of the said molecule was optimized by using Density Functional Theory (DFT).

Probing the microenvironment of unimicelles constituted of amphiphilic hyperbranched polyethyleneimine using 1-methyl-8-oxyquinolinium betaine

Microenvironment of HPEI based core shell amphiphilic macromolecules has been assessed by using QB probe.

How TOPO affects the interface of the novel mixed water/AOT:TOPO/n-heptane reverse micelles: dynamic light scattering and Fourier transform infrared spectroscopy studies

The proportion of TOPO in water/AOT:TOPO/n-heptane reverse micelles produces dramatic changes in the water structure, droplet size and composition of the interface.

PRODAN dual emission feature to monitor BHDC interfacial properties changes with the external organic solvent composition

We have investigated the water/benzyl-n-hexadecyldimethylammonium chloride (BHDC)/n-heptane:benzene reverse micelles (RMs) interfaces properties using 6-propionyl-2-(N,N-dimethyl)aminonaphthalene, PRODAN, as molecular probe. We have used absorption and emission (steady-state and time-resolved) spectroscopy of PRODAN to monitor the changes in the RMs interface functionalities upon changing the external organic solvent blend. We demonstrate that PRODAN is a useful probe to investigate how the external solvent composition affects the micelle interface properties. Our results show that changes in the organic solvent composition in water/BHDC/n-heptane:benzene RMs have a dramatic effect on the photophysics of PRODAN. Thus, increasing the aliphatic solvent content over the aromatic one produces PRODAN partition and PRODAN intramolecular electron transfer (ICT) processes. Additionally, the water presence in these RMs makes the PRODAN ICT process favored with the consequent decreases in the LE emission intensity and a better definition of the charge transfer (CT) band. All this evidence suggests that the benzene molecules are expelled out of the interface, and the water-BHDC interactions are stronger with more presence of water molecules in the polar part of the interface. Thus, we demonstrate that a simple change in the composition of the external phase promotes remarkable changes in the RMs interface. Finally, the results obtained with PRODAN together with those reported in a previous work in our lab reveal that the external phase is important when trying to control the properties of RMs interface. It should be noted that the external phase itself, besides the surfactant and the polar solvent sequestrated, is a very important control variable that can play a key role if we consider smart application of these RMs systems.

Photophysical properties of 7-(diethylamino)coumarin-3-carboxylic acid in the nanocage of cyclodextrins and in different solvents and solvent mixtures

The photophysical properties of 7-(diethylamino) coumarin-3-carboxylic acid (7-DCCA) were studied in cyclodextrins (α, β, γ,-CDs), different neat solvents and solvent mixtures by using steady state absorption, emission and time-resolved fluorescence spectroscopy. We have observed that with gradual increase in concentration of β-CD the fluorescence quantum yield and lifetime decreased in a regular pattern whereas with gradual increase in concentration of γ-CD the fluorescence quantum yield and lifetime gradually increased. With addition of urea, the fluorescence quantum yield and lifetime of 7-DCCA in CDs increased. Binding constant calculation shows that 7-DDCA forms 1:1 complex with β-CD and with γ-CD it forms 1:1 and 1:2 (guest:host) inclusion complex. We proposed that the dye molecule formed capping complex with β-CD by means of hydrogen bonding and after addition of urea the hydrogen bonding network broke down and part of dye molecule entered inside the cavity of β-CD. The photophysics of 7-DCCA was studied in dioxane-water mixture and ethylene glycol-acetonitrile mixture to know the effect of polarity and viscosity of the media. The photophysics of 7-DCCA was also studied in different neat solvents. It was found that the photophysics of 7-DCCA depended on the structural feature of the solvents and solvent mixtures.