Non-specific Solute-solvent Interactions Research Articles

Green Solvent γ-Valerolactone (GVL) Facilitates Photocatalytic C-H Bond Activation.

Solvents can significantly influence chemical reactions in condensed phases. Their critical properties are increasingly recognized in various research domains such as organic synthesis and biomass valorization. However, in semiconductor photocatalysis, solvents are primarily viewed as mediums for dissolving and diffusing substances, with their potential beneficial effects on photocatalytic conversions often overlooked. Additionally, common photocatalysis solvents like acetonitrile (ACN) pose serious safety and environmental concerns. In this study, we demonstrate that novel and safe green solvents, such as γ-valerolactone (GVL), can significantly enhance the performance of semiconductor photocatalysis for C-H bond activation. Non-specific solvent-solute interactions are the primary contributors to increased photocatalytic activity in the self-coupling of benzylic compounds. Specifically, GVL's large dielectric constant and high refractive index lower the energy barrier for the rate-determining C-H bond activation step, facilitating a faster coupling reaction. The versatility of GVL is further demonstrated in reactions with multiple reagents and in various oxidation and reduction photocatalytic systems beyond classic C-H bond activation. This work not only pioneers the use of green solvents but also provides comprehensive insights for proper solvent selection in semiconductor photocatalysis.

Spectroscopic study of solvent effects on the electronic absorption spectra of morpholine and its complexes

The electronic absorption spectra of morpholine and its five morpholine complexes have been studied in different solvents of various polarities. The regression and correlation coefficients have been calculated with the SPSS program. Solvation energy relationships were deduced from spectral shifts and correlated with solvent parameters α (solvent hydrogen bond donor acidity), β (solvent hydrogen bond acceptor basicity), and π* (dipolarity/polarizability). The percentage contributions of the calculated solvatochromic parameters show that classic solvation effects play a major role in explaining the spectral shifts in all investigated complexes. The blue shift of [Fe(MOR)3Cl3]·4H2O, [Ni(MOR)4Cl2]·4H2O, and [Cu(MOR)4Cl2]·6H2O complexes is due to the formation of hydrogen bonds, which suggests the stabilization of the ground electronic state compared with the excited state. [CuNi(MOR)2Cl4]·4H2O and [CuZn(MOR)3Cl4]·2H2O are mixed metal complexes that suffer a red shift due to the solute-solvent interactions, which causes stabilization of the excited solute state with increasing solvent polarity. The bands are affected by specific solute-solvent interactions including hydrogen bond donor ability (acidity) and hydrogen bond acceptor ability (basicity) and nonspecific solute-solvent interactions including electromagnetic interaction between the dipole moments of solute and polar solvents.

Effect of the π-bridge structure on the intramolecular charge transfer of push–pull 2-phenylthiophene and 2-(furan-2-yl)pyridine derivatives

Effect of the bridge structure on the photophysical properties of D-π-A of structurally similar 2,5-diphenylthiophene (cpd. I) and 2-(5-phenylfuran-2-yl)pyridine (cpd. 2) derivatives having the same electron donating and electron withdrawing groups were studied in different solvents. Solvent effect on the absorption and fluorescence emission spectra as well as their excited state decay were studied in detail. Introduction of 2,5-diphenylthiophene and 2-(5-phenylfuran-2-yl)pyridine between methoxy and carbonitrile groups lead to a shift of about 20 nm in both the absorption and fluorescence emission maxima of the former. Stokes shift of about 90 nm was observed for both compounds in protic solvents and polar aprotic solvents and decreases as the solvent polarity decreases. The solvatochromism in the fluorescence emission spectra was higher than the observed in absorption spectra, indicating higher dipole moment in the excited state than in the ground state for both compounds. DFT and TD-DFT optimized geometry calculations show that (I) is planar in the excited state while (II) is planar in both the ground and excited states reflecting the importance of the bridge structure on the geometry in the ground and excited states. Theoretical calculations of the dipole moment change from the ground to the excited states were consistent with the values obtained from Lippert-Mataga relationship and higher than values obtained from Reichardt-Ravi relationship. It has been found that the fluorescence lifetime of both compounds was found to decrease as the emission energy increases and being higher for (II) than for (I), and also was found to increase as the solvent’s dielectric constant increases. All photophysical properties were found to correlate well with Reichardt’s solvent polarity parameter, ETN. We have employed Kamlet-Taft, Catalán and Laurence et al. multi-parametric relationships to assign the contribution of the specific and non-specific solute–solvent interactions. Non-specific interactions were found to be mostly dominating in all cases.

Improvement of theoretical UV–Vis spectra calculations by empirical solvatochromic parameters: Case study of 5-arylazo-3-cyano-1-ethyl-6-hydroxy-4-methyl-2-pyridones

In order to improve the performance of theoretical UV–Vis spectra predictions, a theoretical and experimental study of solvatochromic properties of ten azo pyridone dyes has been performed. For quantitative estimation of intermolecular solvent–solute interactions, a concept of the linear solvation energy relationships has been applied using Kamlet-Taft and Catalán models. Theoretical UV–Vis spectra for all dyes have been calculated using four TD-DFT methods in nine different solvents with the aim to define the most reliable model. Finally, new polylinear equations for more accurate theoretical prediction of UV–Vis maxima are developed using empirical Kamlet-Taft and Catalán solvent parameters as additive corrections for specific and nonspecific solvent–solute interactions.

New nickel (II), cobalt (III), and iron (III) complexes with N′‐[(2‐aminochromon‐3‐yl)methylidene]benzohydrazide: Synthesis, characterization, solvatochromic shift, dipole moment, and DFT calculations

AbstractNew Ni (II), Co (III), and Fe (III) complexes of hydrazone (HL) derived from 2‐aminochromone‐3‐carboxaldehyde with benzoyl hydrazine were synthesized and characterized by elemental analyses, spectral (UV–Vis, IR, Mass, 1H, and 13C‐NMR) data, as well as magnetic susceptibility, molar conductivity measurements, and thermal gravimetric analysis (TGA). The ligand behaves as monobasic with ONO donor sites, forming square planar geometry with Ni (II) and octahedral geometries with both Co (III) and Fe (III) complexes. Solvent effects on the absorption and fluorescence spectra of the prepared complexes were investigated in 11 different solvents with diverse polarities. Lippert–Mataga, Bakhshiev, Kawski–Chamma–Viallet, and Reichardt‐solvatochromic methods were applied to estimate the dipole moments of the ground and excited state (μg and μe). Multiple linear regression analysis was useful to specify the extent of specific and nonspecific solute–solvent interactions using Kamlet–Taft and Catalan solvatochromic models. The Stoke's shifts of complexes were mainly controlled by the polarity/polarizability parameter of the solvent. Density function theory (DFT) at B3LYP/6‐311G(d,p) level engaged in the Gaussian 09 program was carried out to optimize the structures of the ligand and its complexes. Structural parameters data are correlated with the experimental data. Also, using Coats–Redfern techniques, the kinetic parameters were calculated for each thermal degradation stage of metal complexes. Finally, in vitro bioassays of the ligand and its complexes against Gram‐negative, Gram‐positive bacteria and the fungus strain were tested for these compounds with good results.

Effect of solvent on fluorescence and absorption spectra of fluorescent coumarin derivative: Estimation of ground and excited state dipole moments

Solvent effect on fluorescence and absorption spectra of fluorescent coumarin derivative viz, 4-[(5-amino-1,3,4-thiadiazol-2-thio)methyl]–2H-benzo[h]chromen2-one(4ATMBC) has been studied in different solvents at room temperature. The shifts in the position, intensities and shapes of the absorption and fluorescence bands have been observed. The ground and excited state dipole moment of the fluorescent molecule have been calculated from Solvatochromic shift method. The excited-state dipole moments were estimated from Lippert, Bakhshiev and Kawski-Chamma–Viallet equations by using the variation of the Stokes' shift with the solvent dielectric constant and refractive index. The Reichardt‘s microscopic solvent polarity parameter has been used to calculate change in dipole moment. It was found that the excited-state dipole moments were higher than those of the ground-state dipole moment. The large increase in dipole moment in the excited state is due to more polar excited state than in the ground state. The ratio of ground and excited state dipole moments is used to know the solubility of the fluorophore in different solvents. Further, we have calculated angle between the ground and excited state dipole moments which is found to be zero. This shows that ground and excited state dipole moments are parallel. Energy band gap values of different solvents were calculated using Tauc relation. Kamlet-Taft and Catalan methods were used to have the information of non-specific solute–solvent interactions and hydrogen bonding interactions.

Synthesis, solvatochromism and dipole moment in the ground and excited states of substitute phenol derivative fluorescent Schiff base compounds

Three new fluorescent o-hydroxyaryl Schiff base derivatives are synthesized and their structures are characterized by NMR and FTIR spectroscopies. In this study, the solvent effect on the absorption and fluorescence spectral properties, Catalán and Taft-Kamlet solvatochromism models, and electric dipole moments in the ground and excited states, are investigated for synthesized compounds. Specific and non-specific solute–solvent interactions are investigated using Catalán and Taft-Kamlet solvatochromism models in various solvents with different polarities. Taft-Kamlet and Catalán solvatochromism models derived for absorption spectra indicate that solvent dipolarity/polarizability (π*) and solvent polarity (SP) are dominant in controlling absorption spectral shifts. As a result of solute–solvent interactions, absorption spectra exhibit positive solvatochromism, while fluorescence spectra show negative solvatochromism with the increase of solvent polarity. The ground state dipole moment is determined using the Bilot–Kawski method, and the excited state dipole moment is calculated using the Bilot–Kawski, Lippert–Mataga, Bakhshiev, modified Bilot-Kawski and Reichardt correlation methods. The dipole moments estimated in both ground and excited states confirm that Schiff base compounds are more polar in the excited state. The frontier molecular orbitals (HOMO and LUMO), molecular electrostatic potential (MEP), density of states (DOS) and solvent accessibility surfaces (SAS) of these compounds have been calculated using the DFT/B3LYP/6-311++G(d,p) level of theory.

Photoconversion of polychlorinated naphthalenes in organic solvents under simulated sunlight: Solvent effect and mechanism

In this work, the organic solvent effect on the photoconversion of polychlorinated naphthalenes (PCNs) under the simulated sunlight, as well as the mechanism and influence factor were studied. Eight organic solvents were selected to demonstrate the solvent effect on the photoconversion by the theoretical calculation method. It was found that the photoconversion rates of 1-chloronaphthalene (CN-1) in different organic solvents were in the order of dimethyl sulfoxide > methanol > acetonitrile > ethanol > dichloromethane > toluene > n-hexane > acetone. The result, obtained by the density functional theory (DFT) computation and the polarized continuum model (PCM) analysis in the framework of self-consistent reaction field (SCRF), indicated that the photoconversion was affected by the hydrogen-donating ability and electron-withdrawing potential of the solvents, as well as non-specific solute-solvent interactions. The photoconversion in acetonitrile for the five PCNs (1-chloronaphthalene, 2-chloronaphthalene, 2,3-dichloronaphthalene, 1,2,3,4-tetrachloronaphthalene, and 1,2,3,4,5,6,7,8- octachloronaphthalene) all fitted well with the first-order kinetic equation; and the reaction rate decreased with the increasing of number of chlorine atoms of the PCNs. Products analysis proved that the photoconversion process of PCNs went through two stages, namely the initial stage of dechlorination and the later stage of oxidative ring opening. It was found that inorganic ions (NO3−, Cl−, Fe3+, and Fe2+) promoted or inhibited the photoconversion by generating or quenching of the reactive oxygen species, and chlorophyll a promoted the photoconversion through the generation of singlet oxygen.

Experimental and theoretical interpretations of spectral behavior of 6-methoxyflavone

The present work emphasizes on the experimental and computational analysis of the solvatochromic behavior of 6-methoxyflavone (6MF). The steady-state absorption and fluorescence spectra were observed in certain polar protic, polar aprotic and non-polar/weakly polar solvents to examine their solvatochromism and determine the electrical dipole moment. Bathochromic shift in fluorescence spectra with solvent polarity was ascribed to intramolecular charge transfer (ICT) interaction. Calculations based on various solvent correlation techniques denote that the excited singlet-state dipole moment value is higher than the ground-state counterpart, hence indicates substantial redistribution of π-electron density in the excited state. Quantum chemical investigations were performed using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively, in vacuum and solvents. The vertical transitions, along with the bright singlet states and HOMO-LUMO, were obtained from the DFT/TD-DFT calculations. The experimentally calculated ground and excited state dipole moments and different photophysical parameters adequately reflect the values obtained from computational methods. Multiple linear regression (MLR) method based on Kamlet-Taft and Catalan solvent parameters demonstrate that the photophysical behavior of 6MF is attributed to both specific and non-specific solute-solvent interactions. Thus, the study helps to demonstrate the sensing ability of 6MF towards organic solvents and the charge transfer/hydrogen donor/acceptor properties of complex systems.

Synthesis, solvent interactions and computational study of monocarbohydrazones

Carbohydrazones are compounds that are increasingly studied due to their wide potential biological activity. Monocarbohydrazones (mCHs), as one of the carbohydrazone derivatives, so far have been poorly investigated. For a more detailed study, in this paper, eighteen compounds of monocarbohydrazones (eight known and ten newly synthesized derivatives) were synthesized and characterized using NMR and IR spectroscopy. As carbohydrazones show E/Z isomerization caused by the presence of the imino group, some of the synthesized mCHs are in the form of a mixture of these two isomers. The effects of specific and nonspecific solvent–solute interactions on the UV absorption maxima shifts were evaluated using linear free energy relationships principles, i.e., using Kamlet–Taft’s and Catalan’s models. For more information about interactions between dissolved substance and the surrounding medium, correlations have been made with Hansen’s solubility parameters. The influence of the structure on the spectral behavior of the compounds tested was interpreted using Hammett’s equation. Experimentally obtained physicochemical properties of mCHs were compared to and confirmed with computational methods that included TD-DFT calculations and MP2 geometry optimizations.

Photophysical properties and fluorosolvatochromism of D-π-A thiophene based derivatives.

Solvation-dependent photophysical properties of two push–pull thiophene-based compounds with donor–π–acceptor (D–π–A) structures were investigated using absorption, fluorescence emission and time resolved spectroscopy, and supported by different solvation models. Intramolecular charge transfer characteristics of the structurally similar 2-fluoro-4-(5-(4-methoxyphenyl)thiophen-2-yl)benzonitrile (MOT) and 4-(5-(4-(dimethylamino)phenyl)thiophen-2-yl)-2-fluorobenzonitrile (DMAT) were investigated. Significant enhancement of intramolecular charge transfer strength has been observed through molecular structure modification of the electron donating group from a methoxy to dimethylamine group. Ground state absorption spectra show a small red shift of about 10 nm and 18 nm while the fluorescence emission spectra show a large red shift of about 66 nm and 162 nm on changing from the nonpolar cyclohexane to the aprotic polar DMSO for MOT and DMAT, respectively. Dipole moment change from the ground state to the charge transfer excited state is calculated to be 6.6 D in MOT and 9.0 D in DMAT. The fluorescence quantum yield, fluorescence lifetime and the derived radiative and non-radiative rate constants were found to be better correlated to the emission energy rather than any of the solvent properties. Three multi-parametric relationships were used in the interpretation of the specific versus non-specific solute–solvent interactions, namely, Kamlet–Taft, Catalán and Laurence et al. models. The findings of these approaches are used to extract useful information about different aspects of solvent effects on the photophysical properties of the two studied compounds. Kamlet–Taft solvatochromic model indicates that non-specific interactions are dominant in controlling the photophysical properties. Catalán's solvent dipolarity/polarizability parameter is found to play a significant role in solvatochromic behaviour which is also designated by the Laurence model.

Solvatochromic analysis and DFT computational study of N-(hexyl)-N-(5-(3-hydroxynaphthyl-2-yl)-1,3,4-oxadiazol-2-yl)amine

A detailed analysis of the molecular orbitals contained in the electronic transitions in the UV-spectra and a detailed synthesis and conformational study of N-(hexyl)-N-(5-(3-hydroxynaphthyl-2-yl)-1,3,4-oxadiazol-2-yl)amine (NOH) were conducted using the method of TD-DFT (B3LYP/6-311 + G (d,p)). All the theoretical results were found to be in line with the experimental values. For the most stable conformer, the optimized structure parameters (bond lengths, bond angles), vibrational modes and their assignments and were calculated using DFT/B3LYP functional and 6-311 +G(d,p) basis set. The basic vibrational modes were determined by PED, the experimental and computed values were found to support each other. The chemical shifts of 1H-NMR and 13C-NMR were specified using the method of GIAO and compared with the experimental chemical shifts. The frontier orbital energy gap, global chemical reactivity restrictive such as the chemical potential, global hardness, electronegativity, index of electrophilicity, global softness of the molecule were also studied. The Natural Bond Orbital (NBO) analysis was performed to find out the stability and strength of the molecule. Based upon the experimental solvent influence and the theoretical examinations, the long wavelength bands were attributed to π → π* transitions induced by HOMO–LUMO intra-molecular charge transfer from the naphthyl ring to the 1,3,4-oxadiazole. Beside these, electrophilic index, EHOMO (− 5.88 eV), ELUMO (1.89 eV) and energy gap (3.99 eV) were computed to investigate the bio activity, reactivity and stability of the NOH. Kamlet–Taft and Catalan solvatochromism of synthesized 1,3,4-oxadiazole derivative were discussed. The Kamlet–Taft and Catalan solvent parameter sets were used to determine the effect of specific and non-specific solvent–solute interactions on the shifts of UV–Vis absorption maxima.

Preferential Solvation of Mordant Black and Solochrome Dark Blue in Mixed Solvent Systems

In this study, the preferential solvation of Mordant Black and Solochrome Dark Blue were investigated in mixed solvent systems of aqueous methanol, ethanol, propan-1-ol, propan-2-ol, methanol: ethanol, methanol:propan-1-ol, methanol:propan-2-ol, ethanol:propan-1-ol, ethanol:propan-2-ol, propan-1-ol:propan-2-ol and carbon tetrachloride: dimethylformamide. Results showed a deviation of solvation data from ideality over the majority of composition ranges in all the solvent mixtures. The type and contribution of specific and non-specific solute-solvent interactions were analyzed in the framework of the linear solvation energy relationships. Statistical analysis of single, dual, and multiparametric equations revealed that in pure solvents, spectral behaviours of MB and SDB were affected by the polarity and basicity of the solvent milieu respectively. However in aqueous alcohols, polarity of the solvent milieu was the most significant determinant of spectral patterns with α and β parameters playing secondary contributory roles in the spectral changes of MB and SDB, respectively. Multiparametric equations generally yielded the best fitted model in mixed alcohol systems with polarity remaining the largest contributor, followed by β and α of the solvent milieu in that order. Spectral-structure relationships identified ion-dipole interactions involving the charged sulphonate and hydrazone moieties as well as proton-donor-acceptor interactions of the common labile hydroxyl groups as mechanisms for the observed solvation data.

Substituted benzylideneanilines: A family of solvatochromic probes.

The solvatochromic behaviour of ten tailor-made structurally-related substituted N-benzylidineanilines was investigated in presence of solvents of varying polarities through inspection of UV-visible absorption spectra in the range 200 to 600 nm. The spectral bands were found to be significantly influenced by altering the polarity of the solvents. The o-hydroxy substituted N-benzylideneanilines were found to be less sensitive towards solvents in comparison to p-hydroxy substituted N-benzylideneanilines because of intramolecular hydrogen bonding between o-hydroxy group with the nitrogen atom of azomethine unit. The electronic transitions of these N-benzylideneanilines are observed to depend on specific as well as non-specific solute-solvent interactions arising out of the variation in nature and position of the substituent in the phenyl rings. The energy of interactions could very well discriminate the characteristics of solvents such as polar protic, polar aprotic and aprotic solvents. The solvatochromic behaviour and solvent-solute interactions were analyzed by means of well-studied multiparametric linear-solvation energy- relationship involving fourteen different solvent parameters. Optimization of multiparametric regression model was achieved by successive exclusion of variable technique. The validity of the regression model was established from the linearity of the plot of calculated and observed transition energy of the absorption. The overall studies divulge that the solvatochromism behaviour of the substituted N-benzylideneanilines under consideration could be exploited to classify solvents for desired applications.

Influence of solvents on the spectra of benzylidene malonitrile derivative and DFT calculations

The spectroscopic behavior of benzylidene malonitrile (BZM), a donor-π-conjugate-electron acceptor compound, is reported in various solvents. Kamlet–Taft and Catalan models were used to evaluate specific and non-specific solute-solvent interactions. Solvent polarizability (SP) was found to be the dominant factor affecting the absorption and fluorescence spectral shifts. The π →π* transitions was assigned between HOMO and LUMO, based on time-dependent density functional theoretical calculations. The dipole moment of BZM in the ground and excited states were calculated using Stokes shift and solvent polarity functions. The experimental ground state dipole moment (μg = 1.7 D) was found to be lower than that in the excited state (μe = 5.5 D). In binary solvent mixtures, BZM showed both ideal (DMSO/ethanol) and non-ideal (DMSO/acetone and DMSO/dioxane) behaviors. The formation constants in DMSO/ethanol was much lower as compared to the other two mixtures. BZM also exhibited self-quenching fluorescence which is attributed to the primary inner filter effect.

Solvatochromism of a highly conjugated novel donor-π-acceptor dipolar fluorescent probe and its application in surface-energy transfer with gold nanoparticles

A novel highly conjugated donor-π-acceptor (D-π-A) fluorescent probe 4-((1E,3E)-4-(4-(5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl)phenyl)buta-1,3-dienyl)-N,N-dimethylbenzenamine (3TVPO) is synthesized using a Wittig reaction and characterized by 1H, 13C NMR, FT-IR spectroscopy and high-resolution mass spectrometry (HR-MS). The photophysical properties have been studied to understand the intramolecular charge-transfer (ICT) character of the compound. The solvatochromism of 3TVPO has been explored in polar protic/aprotic/weakly polar solvents. Various solvent correlation techniques such as Lippert–Mataga, Bilot–Kawski, Kawski–Chamma–Viallet, Bakhshiev, and Reichardt methods were employed to estimate the singlet ground- and excited-state dipole moment and are compared and discussed with those obtained computationally. The specific and non-specific solute-solvent interactions were analyzed using Kamlet–Taft and Catalán solvent parameters by means of a multiple-linear-regressions (MLR) method. In addition, surface-energy transfer (SET) has been studied using this optoelectronically important 3TVPO molecule as efficient donor and gold nanoparticles (Au MNPs) as excellent acceptors employing steady-state and time-resolved spectroscopic techniques. The size- and distance-dependent SET between 3TVPO and Au MNPs was explored. It is demonstrated that the quenching efficiency increases as the size of Au MNPs increases from 40 to 53 nm. The super-quenching effect and nonradiative energy transfer were analyzed using Stern–Volmer plots. The impact of the present investigation about the super-quenching effect of the Au MNPs can be exploited for biosensing applications owing to its acute sensitivity.

Solvent, structural, quantum chemical study and antioxidative activity of symmetrical 1-methyl-2,6-bis[2-(substituted phenyl)ethenyl]pyridinium iodides

15 symmetric 1-methyl-2,6-bis[2-(substituted phenyl)ethenyl]pyridinium iodides were synthesized in this work. Their structures were characterized using IR, 1H and 13C NMR, and UV–Vis spectroscopy. DFT calculations indicated that s-trans/s-trans conformation prevail in all compounds. The effects of specific and non-specific solvent–solute interactions on the UV–Vis absorption maxima shifts were evaluated using linear solvation-free energy relationships (LSER), i.e., Kamlet–Taft and Catalan models. A linear free energy relationship (LFER) in the form of single substituent parameter equations (SSP) was used to postulate quantitative structure–property relations of substituent effect on NMR data. TD-DFT results showed dependence of electronic transition on the substituent effects. The push–pull character of these compounds was analyzed by differences in 13C chemical shift of the ethylenic double bond in 2- and 6-positions of cross-conjugated with pyridinum central ring. Also, the quotient of the occupations for the bonding π and anti-bonding π* orbitals of this bond was considered. Good correlations of the selected parameter between double bond lengths with π*/π and 13C chemical shift differences of the bridging group proved them to be adequate descriptor of push–pull character. Synthesized compounds were screened for the antioxidant activity, using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical methods, and results demonstrated moderate antioxidant potential.

Investigation on the interactions of E-4-methoxycinnamic acid with solvent: Solvatochromism, electric dipole moment and pH effect

The UV–vis absorption and steady state fluorescence spectra of E-4-methoxycinnamic acid (abbreviated as E-4mCinA) have been recorded in serial solvents with different properties. Specific and non-specific solute-solvent interactions are evaluated by the way of spectral changes. The ground state and excited state dipole moments are determined by using Lippert–Mataga, Bakhshiev, Bilot–Kawski and Reichardt solvatochromic shift methods as a function of solvents parameters and spectral shifts in the absorption and fluorescence spectra. The relatively large excited state dipole moment value indicates that E-4mCinA is more polar in the excited state. Solvatochromism of E-4mCinA is investigated by using Kamlet–Taft and Catalan models. Kamlet–Taft solvatochromic model indicates that specific interactions are dominant in controlling the absorption and fluorescence spectral shifts. Solvent dipolarity/polarizability is found to play significant role in solvatochromic behavior of fluorescence spectral shifts. Catalan solvatochromic model designates that solute-solvent interactions are predominantly governed by solvent dipolarity. Molarity, water and pH effects on the spectral and solvatochromic behaviors are investigated. It is confirmed that E-4mCinA acid displays aggregation depended spectral changes. Nonetheless, adding water to methanolic solution of E-4mCinA leads to forming new charge transfer channels by the way of interaction between one molecule water and two molecule methanol. Acidic and basic media give rise to protonation and deprotonation process for E-4mCinA. Theoretical UV spectra and HOMO, LUMO plots and energy values have been calculated both in gas phase and methanol by B3LYP/6-31G(d) and TD- B3LYP/6-31G(d) level of theory. Ground state molecular electrostatic potential (MEP) and solvent accessible surface (SAS) are computed in gas phase by using B3LYP/6-31G(d) method.

A detailed experimental and computational study of monocarbohydrazones

The substituent and solvent effect on intramolecular charge transfer (ICT) of twelve monocarbohydrazones (mCHs) were studied using experimental and theoretical methodology. The effects of specific and non-specific solvent–solute interactions on the UV–Vis absorption maxima shifts were evaluated using linear free energy relationships (LFERs) principles, i.e. using the Kamlet-Taft and Catalán models. Linear free energy relationships in the form of single substituent parameter equation (SSP) was used to analyze substituent effect on UV–Vis, NMR and pKa change. According to crystallographic data and quantum chemical calculations, the trans (E) form was found to be more stable. A photochromism of compounds with 2-hydroxyphenyl and 2-pyridylimino groups substituted at imine carbon atom results in E/Z isomerization due to creation of intermolecular hydrogen bond in E and Z form, respectively. Multiple stage mass spectrometry (MS-MSn) analysis was applied to define main fragmentation pathways. Furthermore, the experimental findings were interpreted with the aid of ab initio MP2/6–311G(d,p) and time-dependent density functional (TD-DFT) methods. TD-DFT calculations were performed to quantify the efficiency of intramolecular charge transfer (ICT) with the aid of the charge-transfer distance (DCT) and the amount of transferred charge (QCT) calculation. It was found that both substituents and solvents influence electron density shift i.e. extent of conjugation, and affect ICT character in the course of excitation.

A combined experimental and computational investigation of solvatochromism of nonpolar laser dyes: Evaluation of ground and singlet excited-state dipole moments

In the present work, the solvatochromism of two large nonpolar laser dyes Exalite 384 (E384) and Exalite 416 (E416) has been studied both experimentally and computationally. The steady state absorption and fluorescence spectra have been measured in a series of polar protic, polar aprotic and non-polar/weakly polar solvents to investigate their solvatochromism and determine dipole moments. Various solvent correlation techniques, like Lippert–Mataga, Bilot–Kawski, Kawski–Chamma–Viallet, Bakhshiev and Reichardt methods were used to evaluate the singlet excited and ground state dipole moments. Kamlet–Taft and Catalan solvent parameters were used by means of multiple linear regression (MLR) method to analyze specific and non-specific solute-solvent interactions. Computational studies were carried out to optimize ground and excited state geometries using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively, in vacuum. This study also extends to evaluate the electronic transition energies from ground to first electronic excited state of solvated laser dyes employing semiempirical wave function model. In particular, the semiempirical method ZINDO has been combined with integral equation formalism of polarizable continuum model (IEF-PCM) to calculate solute-solvent interaction potential which is comparatively studied with ET(30) polarity scale along with experimental. The intramolecular charge transfer and hybridization is demonstrated by natural bond orbital analysis (NBO). The ground (μg) and excited state dipole moments (μe) of these dyes computed and those determined experimentally are compared and the results are discussed.