Refractive Index Of Solvent Research Articles

Metal complex assembly controlled by surface ligand distribution on mesoporous silica: Quantification using refractive index matching and impact on catalysis

The catalytic activity of discrete metal complexes can be dictated by the local ligand environment. By covalently immobilizing ligands on a surface, the ability of a single metal to engage multiple ligands is controlled by the overall surface loading and distribution. Using an azide functionalized mesoporous silica prepared via co-condensation, the surface loading of 1,10-phenanthroline (phen), a bidentate chelating ligand, can be varied systematically to form preferentially mono-, bis-, or tris-phen ligated metal complexes. Solvent refractive index matching enables in situ transmissive spectroscopic quantification of intense metal-to-ligand charge transfer bands of the immobilized copper(I) bis-phen and iron(II) tris-phen complexes. Metal complex formation agrees well with a random distribution model of the phen ligands on the surface, providing a means to quantitatively correlate immobilized species interactions and overall catalytic performance. Rapid epoxidation catalysis is obtained with surface distributions that maximize mono- or bis-phen ligated manganese centers.

Near‐Infrared Plasmonic 2D Semimetals for Applications in Communication and Biology

Localized surface plasmon resonance (LSPR) has many applications which require meeting specific wavelength windows. The most prominent examples are photothermal therapy in biology, matched to the biological window (650–1350 nm), and communication relying on photodetection in optoelectronics, matched to the communication window (1260–1675 nm). However, for the classic noble metals (Au, Ag), tuning LSPRs from visible region to these two windows is still a demanding task due to their intrinsic limitations on charge density and dielectric function. Here, the discovery of near‐infrared biological and communication window‐matched plasmonic properties of semimetal TiS2 nanosheets (NSs) is reported for the first time. Developed synthesis procedures allow fine‐tuning width and thickness of single‐crystal TiS2 NSs. During characterization a new and intensive absorption peak in the 1000–1400 nm range is observed from both TiS2 NS colloid solutions and films. This peak is attributed to LSPR due to its dependence on particle shape and on the refractive index of solvents. The superiority of such LSPRs is demonstrated in both, biological and optical applications: excitation at 808 and 980 nm generates a ≈50 °C photothermal temperature rise, while excitation at 1310 nm results in two‐times enhanced photocurrents of PbS photodetectors compared to untreated devices.

Effect of Solvent on the O2(a(1)Δg) → O2(b(1)Σg(+)) Absorption Coefficient.

Radiative transitions between the three lowest-lying electronic states of molecular oxygen have long provided a model to study how collision-dependent perturbations influence forbidden processes. In an isolated oxygen molecule, transitions between the O2(X(3)Σg(-)), O2(a(1)Δg), and O2(b(1)Σg(+)) states are forbidden as electric-dipole processes. For oxygen dissolved in organic solvents, the probabilities of radiative transitions between these states increase appreciably. Attempts to interpret solvent-dependent changes in the radiative rate constants have principally relied on O2(b(1)Σg(+)) and O2(a(1)Δg) emission experiments. However, the dominant nonradiative deactivation channels of O2(b(1)Σg(+)) make it difficult to quantify solvent effects on the O2(b(1)Σg(+)) → O2(a(1)Δg) radiative process. Thus, an appreciable amount of important information has heretofore not been available. In the present study, we examined the effect of 17 common organic solvents on the O2(a(1)Δg) → O2(b(1)Σg(+)) absorption transition at ∼5200 cm(-1) (i.e., ∼1925 nm). The solvent-dependent absorption coefficients at the band maximum, εmax, range from 5 to 50 M(-1) cm(-1) and correlate reasonably well with the solvent refractive index; εmax is largest in solvents with the largest refractive index. This observation is consistent with a model in which oxygen is perturbed to a greater extent by solvents with a large electronic polarizability. Through the Strickler-Berg equation, we also used these absorption data to obtain the radiative rate constant for the O2(b(1)Σg(+)) → O2(a(1)Δg) transition, and the results are consistent with a model in which the O2(a(1)Δg) → O2(X(3)Σg(-)) transition is said to steal intensity from the O2(b(1)Σg(+)) → O2(a(1)Δg) transition.

QSPR study on refractive indices of solvents commonly used in polymer chemistry using flexible molecular descriptors

A predictive Quantitative Structure–Property Relationship (QSPR) for the refractive indices of 370 solvents commonly used in the processing and analysis of polymers is presented, using as chemical information descriptors the simplified molecular input line entry system (SMILES). The model employs a flexible molecular descriptor and a conformation-independent approach. Various well-known techniques, such as the use of an external test set of compounds, the cross-validation method, and Y-randomization were used to test and validate the established equations. The predicted values were finally compared with published results from the literature. The simple model proposed correlates the refractive index values with good accuracy, and it is not dependent on 3D-molecular geometries.

Structural, Optical, and Catalytic Support Properties of γ-Al2O3 Inverse Opals

Colloidal crystal templating is a versatile and inexpensive method for the fabrication of 3-dimensional photonic crystals. Here we describe the successful use of the method to fabricate γ-alumina (γ-Al2O3) inverse opal thin films and powders, possessing pseudo photonic bandgaps (PBGs) along the [111] direction at visible wavelengths. The optical properties of γ-Al2O3 inverse opal films were investigated in detail for the first time and closely obeyed a modified Bragg’s law expression. The PBGs red-shifted on immersion in organic solvents, with the magnitude of the shift being directly proportional to the solvent refractive index. Calcination of the γ-Al2O3 inverse opals (BET area 250–275 m2 g–1) at temperatures from 550 to 1200 °C resulted in the stepwise transformation γ-Al2O3 → δ-Al2O3 → θ-Al2O3 → α-Al2O3. The onset temperatures for the latter polymorphic transitions were ca. 50–100 °C higher for Al2O3 inverse opals compared to a sol–gel alumina nanopowder, suggesting that the inverse opal architecture ...

Determination of Excited Singlet-State Dipole Moments of Methoxy and Dimethylamino Substituted Benzylidenebenzosuberones Using Solvatochromic Method

The solvent effects on the electronic absorption and emission fluorescence spectra for a series of chalcone cyclic analogues were studied. The singlet-state excited dipole moments and the ground state dipole moments of the cyclic chalcone analogues E-2- benzylidene-1-benzosuberone E-2-(4′-methoxybenzylidene)-1-benzosuberone E-2-(4′-dimethylaminobenzylidene)-1-benzosuberone were calculated by using solvatochromic shift method by means of equations using the variations of Stokes’ shift with the solvent's dielectric constant and refractive index values. It was found that the excited state dipole moments calculated by the solvatochromic shift method were greater than the ground state dipole moments indicating a substantial redistribution of the pi-electron densities in a more polar excited state for each derivative.

Estimation of ground and excited states dipole moments of α-hydroxy phenyl hydrazone derivatives: Experimental and quantum chemical methods

The ground state (μg) and excited state (μe) dipole moments of the studied α-hydroxy phenylhydrazones are determined by using solvatochromism theory which is based on the variation of Stokes shift with solvent's relative permittivity and refractive index. Excited state dipole moments are found as larger than the ground state dipole moment due to substantial redistribution of the π-electron density in more polar excited state. External electric field (EF) effect on HOMO–LUMO gap (HLG) and dipole moment is studied by GGA level of theory. Density of states (DOS) and HOMO, LUMO plots are also investigated by GGA method. Solvent accessible surface (SAS) and molecular electrostatic potential (MEP) are visualized as a result of DFT calculations.

Dependence of the Absorption and Optical Surface Plasmon Scattering of MoS2 Nanoparticles on Aspect Ratio, Size, and Media

The optical and electronic properties of suspensions of inorganic fullerene-like nanoparticles of MoS2 are studied through light absorption and zeta-potential measurements and compared to those of the corresponding microscopic platelets. The total extinction measurements show that, in addition to excitonic peaks and the indirect band gap transition, a new peak is observed at 700-800 nm. This spectral peak has not been reported previously for MoS2. Comparison of the total extinction and decoupled absorption spectrum indicates that this peak largely originates from scattering. Furthermore, the dependence of this peak on nanoparticle size, shape, and surface charge, as well as solvent refractive index, suggests that this transition arises from a plasmon resonance.

Effect of solvent polarity and temperature on the spectral and thermodynamic properties of exciplexes of 1-cyanonaphthalene with hexamethylbenzene in organic solvents

Study of the effect of solvent polarity and temperature is done on the exciplex emission spectra of 1-cyanonaphthalene with hexamethylbenzene. Exciplex system is studied in the range of partially polar solvents and in solvent mixture of propyl acetate and butyronitrile. The unique feature of this solvent mixture is that only the solvent polarity changes (6.0≤εs≤24.7) with the change in the mole fraction of solvents whereas the solvent viscosity and refractive index remains unaffected. Thermodynamic properties are calculated according to the models developed by Weller and Kuzmin. Fluorescence lifetimes for both the fluorophore as well as the exciplex are evaluated in all used solvents. Exciplex energetics as a function of solvent polarity and temperature are also discussed. Kuzmin model of self-consistent polarization is used for the explanation of the exciplex emission spectra. The effects of solvent polarity and temperature on energy of zero–zero transitions (hv0/), Huang–Rhys factor (S), Gauss broadening of vibronic level (σ) and the dominant high-frequency vibration (hνν) are investigated. The strong dependence of exciplex stability and energetics upon the solvent polarity and temperature are observed. Full charge transfer exciplexes were observed in solvents of all polarities and stronger exciplex with large emission intensities were found in solvents of low polarities but with the increase in solvent polarity the exciplex becomes weak and they dissociate fastly into radical ion pairs. The kinetic model of Kuzmin was observed to reduce into the Weller kinetic model for this exciplex system with ∆GET = −0.22eV and the spectral shift, h∆ν>0.2eV.

Electronic excitations in a dielectric continuum solvent with quantum Monte Carlo: acrolein in water.

We investigate here the vertical n → π(*) and π → π(*) transitions of s-trans-acrolein in aqueous solution by means of a polarizable continuum model (PCM) we have developed for the treatment of the solute at the quantum Monte Carlo (QMC) level of the theory. We employ the QMC approach which allows us to work with highly correlated electronic wave functions for both the solute ground and excited states and, to study the vertical transitions in the solvent, adopt the commonly used scheme of considering fast and slow dielectric polarization. To perform calculations in a non-equilibrium solvation regime for the solute excited state, we add a correction to the global dielectric polarization charge density, obtained self consistently with the solute ground-state wave function by assuming a linear-response scheme. For the solvent polarization in the field of the solute in the ground state, we use the static dielectric constant while, for the electronic dielectric polarization, we employ the solvent refractive index evaluated at the same frequency of the photon absorbed by the solute for the transition. This choice is shown to be better than adopting the most commonly used value of refractive index measured in the region of visible radiation. Our QMC calculations show that, for standard cavities, the solvatochromic shifts obtained with the PCM are underestimated, even though of the correct sign, for both transitions of acrolein in water. Only by reducing the size of the cavity to values where more than one electron is escaped to the solvent region, we regain the experimental shift for the n → π(*) case and also improve considerably the shift for the π → π(*) transition.

Solvent effect on the dipole moments and photo physical behaviour of 2,5-di-(5-tert-butyl-2-benzoxazolyl) thiophene dye

The absorption and emission spectra of fluorescent thiophene dye, namely, 2,5-di-(5-tert-butyl-2-benzoxazolyl) thiophene, have been recorded at room temperature in solvents of different polarities. The excited state dipole moments (μe) were estimated from Lippert’s, Bakhshiev’s, and Kawski–Chamma–Viallet’s equations using the variation of Stoke’s shift with the solvent dielectric constant and refractive index. The optimized geometry of the molecule and μgwere calculated theoretically by Gaussian 03 software using B3LYP/6-31g* level of theory. The μgand μewere calculated by means of solvatochromic shift method and μewas determined in combination with μg. It was observed that μewere higher than those of the μg, indicating a substantial redistribution of the π-electron densities in a more polar excited state for the selected thiophene dye. Further, the change in the dipole moment (Δμ) was calculated both from solvatochromic shift method and on the basis of microscopic empirical solvent polarity parameter [Formula: see text] and values are compared.

Fluorescence Characteristics of Bisphenol A in Room Temperature Ionic Liquids

Room temperature ionic liquids (RTILs) are emerging as a new class of 'green' solvents for use in a wide range of chemical processes. RTILs can sensitize or quench fluorescence of organic chemicals and their interactions still remain unclear, especially for weakly fluorescent chemicals. Herein, we report the effects of six RTILs on the fluorescence behavior of bisphenol A (BPA). The fluorescence intensities (FIs) of BPA in a RTIL-acetonitrile system were significantly quenched compared to acetonitrile. The quenching effect was stronger for [CnMIM]BF4 than [CnMIM]PF6. A decreasing trend of fluorescence lifetime (FL) of BPA was observed for [C6MIM]PF6 (4.26 to 3.86ns) and [C14MIM]PF6 (4.15 to 3.78ns) with increasing RTIL concentrations in the range of 1-10mM. The quenching mode was consistent with a static quenching mechanism based on the consistency of FL and FI results. The emission bands of BPA and RTILs did not interfere with each other when RTILs were used as the solvent. The investigated RTILs enhanced the FIs of strongly fluorescing chemicals (12.0 ~ 19.0-fold for norfloxacin and 6.1 ~ 8.5-fold for dansyl chloride), but quenched those of weakly fluorescing chemicals (BPA). These results demonstrate that RTILs have different fluorescent effects on organic chemicals with different fluorophores. The interactions between RTILs and BPA result from many factors in addition to viscosity, such as solvent electrostatic dielectric constant, refractive index, density, polarization and molecular interaction. These results provide a theoretical foundation for application of RTILs in the analysis of weakly fluorescing chemical.

Molecular modelling and spectral investigation of some triphenyltetrazolium chloride derivatives

AbstractThe molecular parameters of 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) and some compounds based on triphenylformazans (TPFs) — resulting from the enzymatic transformation of TTC, were subjected to comparative investigation on the basis of semi-empirical quantum-chemical simulations, revealing some changes in dipole moment and polarisability in the TPFs in comparison with TTC. Chemical shift due to substituents was discussed using electronic absorption bands in the UV-VIS range recorded for diluted solutions in various solvents as well as the absorption spectra recorded in the infrared range for KBr dispersions. The correlation of the spectral shift of the electronic absorption bands with a specific function on the solvent refractive index, as recommended by theoretical studies focused on solute-solvent interactions, revealed the major role played by dispersive and induction forces. For several solvents, a different behaviour could be assigned to specific interactions overlapping with universal solute-solvent interactions.

Photonic crystal slot-microcavity circuit implemented in silicon-on-insulator: High Q operation in solvent without undercutting

We report the fabrication and characterization of a silicon-based photonic integrated circuit consisting of a photonic crystal slot-cavity, waveguides, and grating couplers, designed as a robust, easy-to-use device for enhancing light-matter interactions at a precise location inside a fluidic medium, while minimizing fabrication complexity. Measured Q values in excess of 7500 for circuits immersed in hexane and operating near 1.5 μm are obtained, in good agreement with simulations. The detection limit for changes in solvent refractive index unit (RIU) for these structures, which have not been optimized, is 2.3×10−5 RIU.

Estimation of ground and excited-state dipole moments of 1, 2-diazines by solvatochromic method and quantum-chemical calculation

Using the theory of solvatochromism, the difference in the excited-state (μe) and ground-state (μg) dipole moments was determined from Lippert–Mataga, Bakhshiev, Kawski–Chamma–Viallet, and McRae equations for three 1,2-diazines (pyrrolo-pyridazine derivatives). All of these equations are based on the variation of Stokes shift with solvent's relative permittivity and refractive index. Further, the change in dipole moment value (Δμ) was also calculated using the variation of Stokes shift with the molecular-microscopic empirical solvent polarity parameter. Theoretical μg values were evaluated by quantum chemical calculations using the DFT method by adopting B3LYP/6-31G* level of theory (Gaussian 03) and using the AM1 method (Chem3D Ultra 8.0). It was observed that, dipole moments of diazines in the excited-state (μe) were greater than the corresponding ground-state values (μg), indicating a substantial redistribution of the π-electron densities in a more polar excited-state. Also, with the increase in the polarity of the solvent, the fluorescence emission peak undergoes a red-shift, confirming a π→π* transition.

Solvent Effect on the Fluorescence Properties of Two Biologically Active Thiophene Carboxamido Molecules

The absorption and fluorescence spectra of two thiophene carboxamido molecules namely 2–( - trimethoxy phenyl) imino–3–N–ethylcarboxamido–4, 5, tetramethylene thiophene (X) and 2-( -N, N-dimethylaminophenyl) imino-3-(N- methylphenyl carboxamido)-4, 5, tetramethylene thiophene (Y) have been recorded at room temperature. The ground (mg) and excited (me) state dipole moments are estimated from Lippert, Bakhshiev, Kawski-Chamma-Viallet equations by using the variation of Stokes shift with microscopic solvent dielectric constant (e) and refractive index (n). The excited dipole moments were also estimated by using the variation of Stokes shift with microscopic empirical solvent polarity parameter and the values are compared. It was estimated that dipole moments of the excited state were higher than those of the ground state of both the molecules. Further, the change in dipole moment (Dm) were calculated both from solvatochromic shift method and on the basis of microscopic empirical solvent polarity parameter .

溶剂折射率对Rh6G液体随机激光输出特性的影响

溶剂折射率对Rh6G液体随机激光输出特性的影响

Environment Reaction Fields for Lipophilic Fluorophores using Solvatochromic Shifts

Biological activities such as permeability, and the energetics of protein insertion are governed, in part, by differences in polarity across the phospholipid membrane. Environment polarity can also induce changes in absorption or emission maxima, for a given fluorophore. This is termed solvatochromism. In this study we investigated the relationship between solvatochromic shifts and the membrane polarity for curcumin and aluminum phthalocyanine disulfonic acid (AlPcS2). From the Lippert equation, fluorophore solvatochromism was analyzed using the reaction field of Onsager and later iterations. Each reaction field model predicted the solvatochromic shift based on the solvent dielectric constant, solvent refractive index, and allowed for polarizability of the solute. In addition, the models were extended to consider the effect of dispersion forces. For curcumin, the reaction field of Block and Walker gave the strongest agreement between experimental and predicted values (r = 0.977, p<0.0001). For AlPcS2, the reaction field of Wertheim, based on statistical mechanics, gave the best agreement (r = 0.951, p = 0.001), only when dispersion forces and solute polarizability were considered. These results allowed identification of fluorophore environment polarity upon binding to lipid bilayers. In addition, we correlated the model predictions to the Dimroth-Reichardt ET (30) solvent polarity scale used by Frimer and colleagues. This technique can qualitatively estimate the location of a fluorophore in the lipid membrane. Using the models, curcumin was estimated to be in the acyl chain region of the lipid bilayer, compared to AlPcS2, at the fatty acid carbonyl. This investigation provides a general method to link easily obtained absorption and emission spectra of a given lipophilic fluorophore to its location in a lipid bilayer via classically derived reaction field models.

Novel Synthesis of Chalcopyrite CuxInyS2 Quantum Dots with Tunable Localized Surface Plasmon Resonances

The burgeoning field of thin film quantum dot photovoltaics has made considerable strides toward efficient and inexpensive forms of third generation solar cells. However, these technologies have largely been based upon toxic metal-containing materials, limiting their foreseeable applications. Here we present a synthesis of nontoxic and stable CuxInyS2 quantum dots with tunable size and band gap. Interestingly, this synthesis leads to the presence of a broad-band and size-dependent absorption peak in the infrared (IR), attributed to localized surface plasmon resonances (LSPRs). Due to the sensitivity of their LSPR peak to quantum dot size and solvent refractive index, these quantum dots provide an attractive candidate for tunable plasmon resonance applications. And, if these LSPRs are found to be coupled with excitonic transitions, they may result in sizable increases in photovoltaic efficiency.

Polymer-Modulated Optical Properties of Gold Sols

The optical properties of a series of gold nanoparticles (D ≈ 2.3–8 nm) grafted with a stabilizing polymer with a wide range of chain lengths (Mw ≈ 6.5K–29.5K) have been studied quantitatively in different dielectric solvents. Mie–Drude dipolar theory was applied to model the localized surface plasmon resonance (SPR) peak position, as well as the peak width of the absorption spectra, using the dielectric function of gold. The modeled spectra yielded information on the dielectric function of the polymer shell, ϵs, from which the average polymer concentration in the shell was deduced. Combining information from optical modeling and structural properties obtained from small-angle neutron scattering (SANS) on the polymer shell thickness and from transmission electron microscopy (TEM) on the gold core size, the SPR peak shifts and their attenuated sensitivity to solvent refractive index were characterized. The SPR behaviors for all of the gold colloids with different core sizes and graft chain lengths were thu...