Determination of ground and excited state dipole moments of some naphthols using solvatochromic shift method

Solvatochromic behavior of 1-naphthol (N1) and 2-naphthol (N2) has been studied in different solvents at room temperature (298 K). The ground and first excited singlet state dipole moments are estimated using solvatochromic shift method. Bakhshiev and Kawski and Bilot correlations based on bulk solvent polarity parameters are applied. The results are further verified by using the microscopic solvent polarity parameter E_T^N. For both molecules investigated, the excited state dipole moments are larger than the corresponding values in the ground state. Moreover, for N1, the values obtained in aprotic solvents are much less than those obtained when protic solvents are included, which underlines the presence of specific interaction in case of protic solvents.     

Spectroscopic Studies of Some Organic Compounds: Aprotic Solvent Effects on Electronic Absorption Spectra of Nicotinamide

Abstract

The electronic absorption spectra of nicotinamide were measured in seventeen aprotic solvents. The solvatochromic method is used to unravel solvent polarity and hydrogen bonding effects on π ? π? transition. Solvent effects are rationalized in terms of the solvatochromic parameters: π?, δ, α, and β.     

Editorial

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.     

具有延长共轭的绿色发光蛋白生色团的反向溶剂化斯托克斯(Stokes)位移

Chromophore structures inspired by natural green fluorescent protein (GFP) play an important role in the field of bio-imaging. In this work, photochemical properties of a new class of GFP-like chromophores are investigated using computational approaches. Thermodynamically stable isomers are identified in vacuum and in solvent. Spectral Stokes shifts are computed and compared to experiments. An inverted solvatochromic shift between absorption and emission emerging in this new class of GFP-like chromophores is observed, and attributed to the stabilized charge transfer and inhibited rotational structural reorganization in solvent.     

Stilbene-Like Molecules as Fluorescent Probes Applied for Monitoring of Polymerization Process

2-(p-N,N-dimethylaminostyryl)benzoxazole (OS), 2-(p-N,N-dimethylaminostyryl)-benzothiazole (SS) and 2-(p-N,N-dimethylaminostyryl)naphtiazole (PS) were prepared and their absorption and fluorescence spectra were measured in various solvents at room temperature. On the basis of the solvatochromic behavior the ground state (μ_g) and excited state (μ_e) dipole moments of these pN,N-dimethylaminostyryl derivatives were evaluated. The dipole moments (μ_g and μ_e) were estimated from solvatochromic shifts of absorption and fluorescence spectra as function of the dielectric constant (ɛ) and refractive index (n) of applied solvents. The absorption spectra only slightly are affected by the solvent polarity in contrast to the fluorescence spectra that are highly solvatochromic and display a large Stokes shift. The analysis of the solvatochromic behavior of the fluorescence spectra as function of Δf (ɛ, n) revealed that the emission occurs from a high polarity excited state. The large dipole moment change along with the strongly red-shifted fluorescence, as the solvent polarity is increased, demonstrate the formation of an intramolecular charge transfer state (ICT). Compounds under the study were used as fluorescence probes for monitoring the kinetics of polymerization. The study on the changes in fluorescence intensity and spectroscopic shifts of studied compounds were carried out during thermally initiated polymerization of methyl methacrylate (MMA) and during photoinitiated polymerization of 2-ethyl-2-(hydroxymethyl)propane-1,3-diol triacrylate (TMPTA).     

Solvent and pH Effects on the Fluorescence of 7-(Dimethylamino)-2-Fluorenesulfonate

A novel water-soluble solvatochromic molecule, 7-(dimethylamino)-2-fluorenesulfonate (2,7-DAFS), was prepared by a three-step reaction from 2-nitrofluorene in good overall yield. The pH and solvent effects on the UV-VIS absorption and fluorescence spectra of 2,7-DAFS have been studied. Protonation of the dimethylamino group switches the absorption from intramolecular charge-transfer (ICT) to π → π* transition. The ground state pKa value of 2,7-DAFS was determined as 4.51. The fluorescence spectrum of the excited basic form, *(DAFS), shows a structureless single band with a large Stokes shift, whereas that of the acidic form, *(⁺HDAFS), exhibits a structured band with a small Stokes shift. The emission intensities of the basic and acidic forms versus pH/Ho plots show stretched sigmoidal curves and indicate that (1) the rate of deprotonation of *(⁺HDAFS) is comparable to the fluorescence decay of the species, and (2) the efficient proton-induced quenching of *(DAFS) fluorescence occurs. The pKa* was estimated as −1.7 from the fluorescence titration curve. The fluorescence maximum of *(DAFS) is blue-shifted as the polarity of solvent decreases. However, no clear dependency of the emission intensity and spectral half width, and thus fluorescence quantum yield, on the solvent polarity was revealed. It appears that the fluorescence sensitivity of 2,7-DAFS is 15 ∼ 25 times greater than the sensitivity of a widely utilized fluorescent probe, 5-(dimethylamino)-1-naphthalenesulfonate. This higher sensitivity, together with the ease of derivatization, would provide the fluorene-based fluorescent molecules significant advantages for a variety of applications.     

Fluorescent probe 4-dimethylaminochalcone: Solvatochromism according to the data of semiempirical and quantum-chemical calculations

The solvatochromic regularities observed in solutions of 4-dimethylaminochalcone (DMCh) are investigated in terms of two independent theoretical approaches, i.e., semiempirical and quantum-chemical, and the results of these investigations are directly compared with each other for the first time. It has been shown that the values of the absolute solvation shift of the long-wavelength DMCh electronic absorption band determined by different methods are in a good quantitative agreement both with each other and with experimental data. This fact can be considered as a substantial additional justification of the conclusion on the predominantly nonspecific origin of intermolecular forces determining the mechanisms by which the DMCh fluorescent probe functions in biological systems.     

Tuning the photophysics of a bio-active molecular probe ‘3-pyrazolyl-2-pyrazoline’ derivative in different solvents: Dual effect of polarity and hydrogen bonding

The solvatochromic behavior of 3-pyrazolyl 2-pyrazoline derivative (PYZ), a newly synthesized molecular probe having pharmaceutical importance, has been studied in various solvents of different polarity. The Kamlet and Taft solvatochromic comparison method was utilized to rationalize the solute-solvent interactions from absorption and emission measurements. Spectroscopic studies reveal that the solvatochromic behavior of the dye depends not only on the polarity of the medium but also on the hydrogen-bonding properties of the solvents. The non-radiative relaxation process is facilitated by an increase in the polarity of the media. The photophysical response of PYZ in different solvents has been explained considering solute-solvent interactions.     

Correlation between IR-characteristics vibrations and solvent parameters. Koppel-Palm's multiparameter equation

Using the medium's parameters introduced by Koppel and Palm, correlation equations are derived, which describe the solvatochromic shift of the CO and NH stretching vibrations for acetophenone and pyrrole. The statistical properties of the equations are examined using data on a set of 37 solvents and it is proved that the influence of the nonspecific solvation cannot be described as a sum of the terms dependent on the medium's polarity and polarizability.     

UV-spectral changes for some azo compounds in the presence of different solvents

The electronic absorption spectra of four azo dyes with different substituents (such as Cl, I, OH) are determined at room temperature in twenty-one solvents with different polarities. The electronic transitions of azo dyes are interpreted. Linear solvation energy relationships have been investigated for solvatochromic behaviors and solute-solvent interactions of azo dyes. Linear solvation energy relationships were performed by multiple linear regression analysis using dielectric function, refractive index function and Kamlet-Taft parameters. We have observed that the hydrogen bonding acceptor ability and the induction-dispersive forces of solvent molecules have caused the bathochromic shift in absorption maxima of azo dyes.     

Pressure broadening and shifting parameters for the spectral lines in the fundamental vibration-rotation bands of HBr and HI in mixtures with rare gases

We report measurements of the line broadening and shifting coefficients in the (1 ← 0) fundamental absorption bands of the HBr and HI molecules in mixtures with rare gases He, Ne, Ar, Kr, and Xe. Comparison is given with the published data on other HHal-Rg systems. The measured line shifts are separated into terms symmetric and asymmetric in the line number m. The magnitudes of the symmetric shifts change in a regular manner in the series of rare gases and reach perturber-specific asymptotic values at higher ∣m∣. It is found that the asymptotic values of the symmetric line shifts linearly correlate with the respective C₆ potential energy constants and that the slopes of these correlations are proportional to the vibrational ground state dipole moments squared of the hydrogen halide molecules.     

NLOphoric Carbazole-Containing Push-Pull Extended Styryl Chromophores: Study of Photophysical Properties by Solvatochromic and DFT Method

Carbazole based extended Donor-π-Acceptor styryl dyes with intramolecular charge transfer characteristics were examined for their linear and nonlinear optical properties using solvatochromism, shifts in emission and density functional theory computations. All the extended styryls demonstrated positive solvatochromism. The extended styryl dyes showed largely improved photophysical properties and large Stokes shifts. The donor-acceptor interactions of the extended styryls were investigated by using generalized Mulliken-Hush method. Oscillator strengths and transition state dipole moments have been studied to understand charge transfer within the molecules. The nonlinear optical properties of the extended styryl were investigated by solvatochromic and density functional theory method.     

Red Emitting Coumarin—Azo Dyes : Synthesis,Characterization, Linear and Non-linear Optical Properties-Experimental and Computational Approach

The coumarin molecules with 7-(N,N-diethylamino) substitution and aryl azo (Ar–N=N-) at 3-position were synthesized, by reacting diazonium salt of substituted amines and 7-(N, N-diethylamino)-4-hydroxy coumarin under basic conditions. They were found to be fluorescent despite the presence of azo group. The azo group rotation was blocked by complexing with -BF₂, so as to get a red shift in absorption. The azo molecules show charge transfer, whereas BF₂-complexes do not. The dipole moment ratios between the ground and excited states calculated suggest highly polar excited state and an intra-molecular charge transfer at the excited state in the case of azo dyes. The NLO properties were calculated by solvatochromic method and computationally. Second order hyperpolarizability was found to be 46 to 1083 times more than urea. DFT and TDTDF calculations were performed to understand the electronic properties of the molecules at the ground as well as excited states.     

Solvatochromism of Ternary Iron (II) Diimine Cyanide Complexes in 2-Ethyl-2-(hydroxymethyl) 1,3-Propanediol (Trimethylol Propane)

The solvatochromic behaviour of bis-(2,2′-bipyridyl)-biscyanoiron (II) and 2,2′- bipyridyltetracyanoiron (II) in 2-ethyl-2-(hydroxymethyl)-1,3-propanediol has been established. The significance and sensitivities of the solvatochromic shifts of these charge-transfer bands are outlined for the two iron complexes above.     

NLOphoric Red Emitting Bis Coumarins with O-BF<Subscript>2</Subscript>-O core - Synthesis,Photophysical Properties and DFT Studies

The red emitting dyes were synthesized by employing coumarin core as a donor and boron-bonded coumarin as an acceptor. 7-(N,N-Diethylamino)-coumarin 3-aldehyde was reacted with 3-acetyl-4-hydroxy-coumarin, 7-(N,N-diethylamino)-3-acetyl-4-hydroxy-coumarin and 3-acetyl-4-hydroxy-1-methyl-quinolone to form the corresponding chalcones. The synthesized chalcones were though red shifted as compared to the parent coumarin, and were not emitting in red region. The BF₂-complexation was used as a tool to introduce a red shift in the molecules. The BF₂-complexes synthesized were found to be red emitting and show higher one photon absorption cross section. The solvatochromism shown by these dyes was studied in the light of solvent polarity parameters. DFT calculations were used to understand the photophysical properties of the synthesized dyes. NLO properties of the dyes were estimated by solvatochromic and computational methods. All the molecules synthesized were characterised with the HRMS and NMR spectral Analysis.     

Solvatochromic and Fluorescence Behavior of Sulfisoxazole

The Fluorescence spectroscopic and solvatochromic behavior of Sulfisoxazole, a sulfa drug with antimicrobial activities, in various pure solvents of different polarity and hydrogen bonding capability is reported. The fluorescence emission spectrum of sulfisoxazole was found to be solvent polarity dependent, where a notable red shift in emission maximum was observed with increasing solvent polarity as well as hydrogen bonding capability. The effects of the latter two solvent parameters were quantitatively investigated using the methods of Lippert–Mataga and solvatochromic comparison method (SCM) that is based on the Kamlet-Taft equation. Particularly, the Lippert–Mataga method was applied to estimate the dipole moment of the excited state (μ_e) upon plotting Stokes shift versus solvent polarizability (Δf), where a value of 11.54 Debye was obtained. On the other hand, applying the multiple regression analysis to the SCM method revealed that solvent polarizability (π*) and hydrogen-bond donor capability (α) approximately equally stabilize sulfisoxazole in the excited state with minor destabilization contribution by the hydrogen-bond acceptor capability (β). These findings revealed that the excited state of sulfisoxazole is stabilized by polar solvents, indicating that this drug molecules exhibit larger dipole moment in the excited state than in the ground state, which in turn implies that a potential intramolecular charge transfer (ICT) occurs after excitation.     

Rotational Diffusion and Solvatochromic Correlation of Coumarin 6 Laser Dye

Rotational diffusion of coumarin 6 (C6) laser dye has been examined in n-decane and methanol as a function of temperature. The rotational reorientation of this probe has been measured in these solvents. It is observed that the decrease in viscosity of the solution is responsible for the decrease in the rotational relaxation time of the probe molecule. The molecule C6 has long reorientation times in n-decane solvent as compared to methanol over all temperatures. It is found that the coumarin 6 rotates slower in n-decane than in methanol especially at higher values of viscosity over temperature. Two methods are chosen to determine the ground state and excited state dipole moments. The change in dipole moments is estimated from Bakhshiev-Chamma-Viallet equations and, the ground and excited state dipole moments from Kawski et al. equations, by using the variations of the Stokes shifts with the dielectric constant and refractive index of the solvent. Our results are quite reliable which are solvatochromic correlation obtained using solvent polarity functions. The reported results show that excited state dipole moment is greater than ground state dipole moment, which indicates that the excited state is more polar than the ground state.     

Quantum-chemical study of relation of spectral and luminescent properties of positively solvatochromic malononitrile-based merocyanine dyes with their structure

The electronic structure, the spectra, and the efficiency of photophysical processes of energy deactivation are calculated by a semiempirical method for three positively solvatochromic merocyanine dyes with different polymethine chain lengths. The electronic structure and spectra calculated by different modifications of the INDO method at different molecular geometries are compared, and the optimum geometry of the isolated molecule is chosen. The absorption spectra of dyes are interpreted, including the short-wave-length bands related to transitions to highest excited states. The possibility of a specific electrophilic solvation of these compounds in the ground and fluorescent states, as well as the contribution of specific intermolecular interactions to the total interaction with the medium, is estimated. The role played by the trans-cis isomerization of isolated merocyanine molecules in the deactivation of their excited states is considered.     

Solvatochromic behavior of dyes with dimethylamino electron‐donor and nitro electron‐acceptor groups in their molecular structure

Six dyes with N,N‐dimethylaminophenyl and 4‐nitrophenyl or 2,4‐dinitrophenyl groups in their molecular structures were prepared and characterized. These compounds have different conjugated bridges (C?C, C?N, and N?N) connecting the electron‐donor and the electron‐acceptor groups. All compounds are solvatochromic, with reverse solvatochromism occurring. The solvatochromic band observed in each spectrum for the dyes is due to a π ? π* transition, of an intramolecular charge transfer nature, which occurs from the electron‐donor N,N‐dimethylaminophenyl group to the electron‐acceptor group in the molecules, which is reinforced by the structures of the compounds optimized by applying density functional theory, which exhibit high planarity. The reverse solvatochromism was explained considering two resonance structures. The benzenoid form is better stabilized in less polar solvents and characterizes the region displaying positive solvatochromism, while the dipolar form is better stabilized in more polar solvents, in the region of negative solvatochromism. The Catalán multiparametric approach was used to study the contribution of solvent acidity, basicity, dipolarity, and polarizability to the solvatochromism exhibited by the compounds. These compounds are good candidates for the investigation of the polarizability and, to a lesser extent, the dipolarity of the medium, with very little interference from specific interactions of the solvent through hydrogen bonding. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of relaxation of the geometric structure on the solvatochromic shift in electronic spectra of molecules

The influence of relaxation effects on the solvatochromic shifts observed in the electronic spectra of organic compounds in solvents is investigated using quantum-chemical methods. The calculations are performed in the framework of the time-dependent density functional theory. It is revealed that, in 40% of the cases under consideration, the relaxation contribution accounts for more than 20% of the total solvatochromic shift. The most pronounced effects are associated with the observed changes in the dihedral angles between molecular fragments.