Solvent Effect on Absorption and Fluorescence Spectra of Three Biologically Active Carboxamides (C<Subscript>1</Subscript>, C<Subscript>2</Subscript> and C<Subscript>3</Subscript>). Estimation of Ground and Excited State Dipole Moment from Solvatochromic Method Using Solvent Polarity Parameters

The absorption and fluorescence spectra of three Carboxamides namely (E)-2-(4-Chlorobenzylideneamino)-N-(2-chlorophenyl)-4, 5, 6, 7-tetrahydrobenzo[b]thiophene-3-carboxamide (C₁), (E)-N-(3-Chlorophenyl)-2-(3, 4-dimethoxybenzylideneamino)-4, 5, 6, 7-tetrahydrobenzo[b]thiophene-3-carboxamide (C₂) and (E)-N-(3-Chlorophenyl)-2-(3, 4, 5-trimethoxybenzylideneamino)-4, 5, 6, 7-tetrahydrobenzo[b]thiophene-3-carboxamide (C₃) have been recorded at room temperature in solvents of different polarities using dielectric constant (ε) and refractive index (n). Experimental ground (μ_g) and excited (μ_e) state dipole moments are estimated by means of solvatochromic shift method and also the excited dipole moments are estimated in combination with ground state dipole moments. It was estimated that dipole moments of the excited state were higher than those of the ground state of all three molecules. Further, the changes in dipole moment (Dm \Delta \mu ) were calculated both from solvatochromic shift method and on the basis of microscopic empirical solvent polarity parameter (E_T^N E_T^N ) and the values are compared.     

Solvatochromic Effect on the Photophysical Properties of Two Coumarins

The absorption and emission spectra of two coumarins namely 7, 8 benzo-4-azidomethyl coumarin (C₁) and 6-methoxy-4-azidomethyl coumarin (C₂) have been recorded at room temperature in solvents of different polarities. The ground state dipole moments (μ _g ) of two coumarins were determined experimentally by Guggenheim method. The exited state (μ _e ) dipole moments were estimated from Lippert’s, Bakhshievs and Chamma-Viallet’s equations by using the variation of Stoke’s shift with the solvent dielectric constant and refractive index. The ground and excited state dipole moments were calculated by means of solvatochromic shift method and also the excited state dipole moments are determined in combination with ground state dipole moments. It was observed that dipole moments of excited state were higher than those of the ground state, indicating a substantial redistribution of the π-electron densities in a more polar excited state for two coumarins.     

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.     

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).     

Ground and excited state dipole moments of coumarin 337 laser dye

This paper reports that the effects of spectral properties of coumarin 337 laser dye have been investigated in different solvents considering solvent parameters like dielectric constant (?) and refractive index (n) of different solvent polarities. The ground state (μ_g) and excited state (μ_e) dipole moments are calculated using Lippert's, Bakhshiev's, and Kawski-Chamma-Viallet's equations. In all these three equations the variation of Stokes shift was used to calculate the excited state (μ_e) dipole moment. It is observed that the Bakhshiev method is comparatively better than the other two methods for ground state and excited state dipole moment calculations. The angle between the excited state and ground state dipole moments is also calculated.     

Experimental Determination of Ground and Excited State Dipole Moments of N,N-Bis (2, 5-di-tert-butylphenyl)-3, 4:9, 10-perylenebis (dicarboximide) (DBPI) A Photostable Laser Dye

In the present work, the absorption, emission spectra and dipole moments(μ_g, μ_e) of N, N-bis (2, 5-di-tert-butylphenyl)-3, 4:9, 10- perylenebis (dicarboximide) (DBPI) have been studied in solvents of various polarities at room temperature. Using the methods of solvatochromism, the difference between the first excited singlet state (μ_e) and ground state (μ_g) dipole moments was estimated from Lippert – Mataga,, Bakhshiev, Kawski – Chamma – Viallet equations. The change in dipole moment (Δμ) was also calculated using the variation of the Stokes shift with microscopic solvent polarity parameter (E _T ^N ). It was observed that the value of excited singlet state dipole moment is higher (3.53 Debye) than the ground state one (1.92Debye), showing that the excited state of DBPI is more polar than the ground state.     

Solvent Effects on the Spectroscopic Properties of Styrylquinolinium Dyes Series

The study on the relationship between the structure and spectroscopic properties of styrylquinolinium dyes were carried out by measuring the electronic visible absorption, steady-state and time-resolved fluorescence spectra of quinoline based hemicyanine dyes. The influence of the solvent on absorption and emission spectra and the solvatochromic properties, observed for both ground and first excited states, for all the dyes were applied for the evaluation of their excited state dipole moments. The ground state dipole moments of dyes under the study were established by applying ab initio calculations. The measured, using solvatochromic methods, excited state dipole moments of tested hemicyanines are in the range from 5.38 to 18.90 D and the change in the dipole moments caused by excitation were found to differ from 1.88 to 6.64 D. It was observed that for all tested dyes the dipole moments of the excited states were higher than those of a ground states. The fluorescence lifetime measurements with picosecond resolution was performed for entire series of hemicyanine dyes possessing different dialkylamino groups attached to the phenyl ring. The average lifetimes of the dye fluorescence, determined from the measured data by multi-order exponential decay curve fitting, were in the range from about 120 to 1200 ps at the fluorescence peak wavelength. The fluorescence lifetime measurements were performed for dyes in ethyl acetate solutions. The time-resolved fluorescence spectra measurements allowed to propose the mechanism of the dyes excited states deactivation.     

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.     

Solvent effect profiles of absorbance and fluorescence spectra of some indole based chalcones

The photophysical properties of a series of 3-(1′H-Indol-3′-yl)-1-phenylprop-2-en-1-one and its derivatives (indole chalcones) were studied in different solvents. Solvent effects on the absorption and fluorescence spectra were quantified using Reichardt’s and bulk solvent polarity parameters and were complemented by the results of the Kamlet-Taft treatment. The observed excited state dipole moment was found to be larger than the ground state dipole moment of these chalcones. The correlation of the solvatochromic Stokes-shifts with the microscopic solvent polarity parameter (E_T^N E_T^N ) was found to be superior to that obtained using bulk solvent polarity functions.     

Effect of positional substitution of amino group on excited state dipole moments of quinoline

The effect of positional substitution of amino group on the ground and excited state dipole moments of quinoline ring has been investigated using solvatochromic shift methods. The excited state dipole moments of 5aminoquinoline (5AQ) and 3aminoquinoline (3AQ) have been estimated from the spectral data in different non-polar, polar aprotic and polar protic solvents using Bakhshiev and Kawski-Chamma-Viallet equations. It has been observed that both grounds as well as excited state dipole moments for 5AQ are higher than those for 3AQ by approximately a factor of two. Higher values of the excited state dipole moments for both 3AQ and 5AQ as compared to corresponding ground state values have been attributed to intramolecular charge transfer processes. The role of specific solute-solvent interaction on excited state dipole moment in addition to the general solvent effects has been discussed.     

Determination of excited state electric dipole moment of the isomeric fluorophenylisocyanates from solvatochromic shift measurements

The excited state electric dipole moments of three isomeric fluorophenylisocyanates are determined using the method of solvatochromic shift measurements recently suggested from our laboratory.     

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.     

Determination of the First Excited Singlet State Dipole Moments of Coumarins by the Solvatochromic Method

The electronic absorption and fluorescence spectra of 4-hydroxycoumarin, 7-hydroxycoumarin, 7-methoxycoumarin, 7-hydroxy-4-methylcoumarin, 7-amino-4-methylcoumarin, and 7-diethylamino-4-methylcoumarin were measured at room temperature (298K) in several solvents and their first excited singlet-state dipole moments were determined by the solvatochromic shift method. The excited singlet-state dipole moments of the coumarins were compared with the ground-state values.

     

Quantitative treatment of the effect of solvent on the electronic absorption and fluorescence spectra of substituted coumarins: Evaluation of the first excited singlet-state dipole moments

The electronic absorption and fluorescence spectra of coumarin and 11 substituted coumarins were measured in several solvents (dioxane, ethyl ether, ethyl acetate, ethanol, dimethylformamide, acetonitrile, and dimethyl sulfoxide). Ground-state dipole moments were determined in dioxane at 298 K. The results were used to obtain the first excited singlet-state dipole moments of the coumarins under study by the solvatochromic shift method (Bakhshiev, Kawski-Chamma-Viallet, McRae, and Suppan correlations). Also, the ground- and the first excited singlet-state dipole moments were calculated using a combination of the PPP method (-contribution) and the vector sum of the -bond and group moments (-contribution). In general, the first excited singlet-state dipole moments of the coumarins are noticeably higher than the corresponding ground-state values, indicating a substantial redistribution of the-electron densities resulting in a more polar excited state. There is a reasonably good agreement between the calculated and the experimental dipole moments.Presented, in part, at the 2nd International Conference on Solar Energy Storage and Applied Photochemistry, Cairo, Egypt, January 6–11, 1993. For a preliminary communication, see Ref. 1.     

Dual Fluorescence and Solvatochromic Study on 3-Acyl Coumarins

Electronic absorption and emission spectra of 3-acetyl coumarin, 3-(bromoacetyl) coumarin and 3-(di bromoacetyl) coumarin have been recorded at room temperature in thirteen solvents with different polarities. Both ground and excited state dipole moments have been calculated for both locally excited and charge transfer transitions by using the solvatochromic method. Excited state dipole moments of all the three compounds are higher than their ground state values. DFT calculations have been profound to estimate their ground and excited state dipole moments. The estimated change in dipole moment by the application of microscopic solvent polarity parameter and bulk solvent polarity methods are in close agreement. Concentration dependent dual fluorescence has been observed in the emission spectra of all the three compounds.

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Graphical Abstract Dual fluorescence of 3-acetyl coumarin (I) in different solvents.

     

Further Solvatochromic, Thermochromic, and Theoretical Studies on Nile Red

Experimental steady-state solvatochromic and thermochromic studies of Nile Red absorption and emission in nine dipolar solvents are reported, as well as theoretical modeling results concerning the ground and excited states of Nile Red in solution. Solvatochromic absorption and emission data analyzed according to conventional methods yield ground- and excited-state dipole moments of 8.9 ± 0.5 and 14.4 ± 0.5 D. Application of this conventional model to thermochromic shift data gave dipole moments of 8.4 ± 1.0 and 13.4 ± 1.0 D. The thermochromic data were also analyzed using a novel solute monopole–solvent dipole model; this model did not appear to reproduce trends in the thermochromic shift data as well as the conventional model. Results of semiempirical ZINDO/S calculations on Nile Red combined with an Onsager model for solvation were also used to examine the energetics of the excited states of Nile Red in solution. These calculations suggest the presence of a TICT state in Nile Red comparable in energy to an emitting excited state at high solvent polarity. Conventional models for solvatochromic and thermochromic response, however, appear to explain the experimental results independently of any emission from this TICT state in the present solvents.     

Fully conjugated push–pull dendrons with high dipole moments in excited state; synthesis and theoretical rationalization

Novel fully conjugated push–pull dendrons were synthesized by a divergent approach to evaluate the performance of non‐conventional architectures like dendritic one in charge separation processes associated with photovoltaic events. The dipole moments in excited state were estimated by the solvatochromic method, to be related to the charge separation efficiency. A 1:2 ratio of donor–acceptor groups (methoxy and nitro groups respectively) promotes the largest dipole moment in both ground and excited state (up to 17 D), due to the efficient electron density transfer over the entire molecule, through the π‐electron system. The synthesized dendrons induce charge transfer on excitation as follows from UV–vis absorption–emission analysis and theoretical calculations. Copyright © 2015 John Wiley & Sons, Ltd.     

Spectroscopic Study of Solvent Polarity on the Optical and Photo-Physical Properties of Novel 9,10-bis(coumarinyl)anthracene

Novel 7,7′-((anthracene-9,10-diylbis(methylene))bis(oxy))bis(4-methyl-2H-chromen-2-one) (BisCA) was prepared as fluorescent probe. The chemical structure of the novel BisCA was confirmed by spectroscopic data as well as elemental analyses. The solvatochromic characteristics of the new proble and its precursors were investigated in different solvents including, ethanol, DMF and toluene as protic polar, aprotic polar and non-polar solvents, respectively. Photo-physical parameters of probes, such as fluorescence quantum yields, fluorescence lifetime of excited state, radiative and non-radiative decay, were assessed in different media. The intermolecular H-bond effect on absorption and excitation spectra of the novel probe was reported in different solvents. Also, Onsager cavity radius and dipole moment of ground state and excited state of the probe were calculated as described by Bakhshiev and Reichardt methods.     

Influence of the polarity of a medium on the photonics of a merocyanine dye with a high quadratic polarizability

The influence of the polarity of a medium on the spectral and luminescent properties of 2-[(2E,4E)-6-(1,3,3-trimethyl-2,3-dihydro-1H-2-indolyliden)-2,4-hexadienyliden]malononitrile (THDM) in solutions and polymer matrices is studied at room temperature under conditions of steady-state and pulsed laser excitation. A large bathochromic shift of the absorption spectra observed upon an increase in the polarity of a solvent is caused by a strong increase in the molecular dipole moment μ due to a transition of molecules from the ground state (μ_g = 7.6 D) to an excited Franck-Condon state (μ^FC = 33.5 D). Based on the solvatochromic data, the quadratic polarizability was calculated to be β = (3.2 ± 0.6) × 10^?28 esu, which is close to the experimentally determined value β_ex = (3.9 ± 0.2) × 10^?28 esu. A strong narrowing of the fluorescence spectra in comparison with the absorption spectra is observed upon an increase in the solvent polarity. This narrowing is explained by a decrease in the bond length alternation parameter and by weakening of vibronic interactions in the singlet excited state. The dynamic solvatofluorochromism of THDM in the picosecond range is caused by reorientations of molecules of the polar environment occurring during a time period consistent with the dielectric relaxation time of these molecules.     

Kinetics of dipole moments of polyatomic molecules

The relations that link the time dependences of the dipole moments of the ground and excited states of a molecular system whose charge distribution is nonstationary with the correlation functions of the shift of the absorption and emission spectra of this system are derived on the basis of of the well-known equations of solvatochromism. The calculated dependences of the kinetics of the dipole moments of the excited singlet states of dimethylaminobenzonitrile and 4-dimethylamino-4′-cyanostilbene in some polar solvents are presented.