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.     

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.     

Theoretical investigation of the ground and excited state of silylated coumarin

We present ground and excited state properties of silylated coumarin dyes. We have calculated the energies and dipole moments of ground and excited states of silylated coumarins and some coumarin derivatives. Using CIS we find a good agreement with experimental S₀→S₁ excitation energies. Silylation of dye molecules had minor effect on the transition energies. On the basis of theoretical results, we conclude that silylated dye will have improved long-term photostability compared to its unsilylated counterpart due to its covalent bonding with the host matrix.     

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).     

Molecular Stark effect spectroscopy of diflavonol and inhomogeneous broadening of its electronic spectra in erythrocyte membranes

Using spectroscopy of the molecular Stark effect and fluorescence spectroscopy, we study the characteristics of diflavonol 3,7-dihydroxy-2,8-di(4-dimethylaminophenyl)-4H,6H-pyrano[3,2-g]chromene-4,6-dione (DFME), which demonstrates intramolecular charge and proton phototransfer. In the ground state, this dye has only one form and, in the excited state, it has two forms, i.e., normal and phototautomeric. We found that, for the normal form of DFME, the transition dipole moment that is responsible for the absorption (m _a ), the dipole moment in the equilibrium ground state (μ _g ), and the change of the dipole moment upon transition of the molecule in the excited Franck-Condon state (Δ ^a μ) are parallel. In the ground equilibrium state, the dipole moments in 1,4-dioxane and cyclohexane are equal to μg = 12.2 × 10⁻³⁰ C m and μ _g = 11.0 × 10⁻³⁰ C m, respectively. Upon excitation, they increase by Δ ^a μ = 61 × 10⁻³⁰ C m and Δ ^a μ = 50.2 × 10⁻³⁰ C m in these solvents. We study the spectral characteristics of DFME in organic solvents and erythrocyte membranes. A spectral inhomogeneity of DFME in erythrocyte ghosts is found. The inhomogeneous broadening of fluorescence spectra is manifested as a long-wavelength shift of the band of the normal form of DFME by 1640 cm⁻¹ upon excitation at the red edge of the absorption spectrum.     

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.     

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.     

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.     

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.     

Dielectric relaxation of binary polar liquid mixture measured in benzene at 10 GHz frequency

The dielectric relaxation times τ _jk ’s and dipole moments μ _jk ’s of the binary (jk) polar liquid mixture of N,N-dimethyl acetamide (DMA) and acetone (Ac) dissolved in benzene (i) are estimated from the measured real σ′ _ijk and imaginary σ″ _ijk parts of complex high frequency conductivity σ* _ijk of the solution for different weight fractions w _jk ’s of 0.0, 0.3, 0.5, 0.7 and 1.0 mole fractions x _j of Ac and temperatures (25, 30, 35 and 40°C) respectively under 9.88 GHz electric field. τ _jk ’s are obtained from the ratio of slopes of σ″ _ijk -w _jk and σ′ _ijk -w _jk curves at w _jk → 0 as well as linear slope of σ″ _ijk -σ′ _ijk curves of the existing method (Murthy et al, 1989) in order to eliminate polarpolar interaction in the latter case. The calculated τ’s are in excellent agreement with the reported τ’s due to Gopalakrishna’s method. μ _jk ’s are also estimated from slopes β’s of total conductivity σ _ijk -w _jk curves at w _jk → 0 and the values agree well with the reported μ’s from G.K. method. The variation of τ _jk ’s and μ _jk ’s with x _j of Ac reveals that solute-solute molecular association occurs within 0.0–0.3x _j of Ac beyond which solute-solvent molecular association is predicted. The theoretical dipole moments μ _theo’s are calculated from bond angles and bond moments to have exact μ’s only to show the presence of inductive, mesomeric and electromeric effects in the substituent polar groups. The thermodynamic energy parameters are estimated from ln(τ _jk T) against 1/T linear curve from Eyring’s rate theory to know the molecular dynamics of the system and to establish the fact that the mixture obeys the Debye-Smyth relaxation mechanism.      

CASPT2 and CCSD(T) calculations of dipole moments and polarizabilities of acetone in excited states

The acetone molecule is investigated in its ground state and valence ^1,3n-π*, ^1,3π-π*, and ^1,3σ-π* excited states and Rydberg ^1,3n-3s, ^1,3π-3?, ^1,3n-3p_y and ^1,3π-3p_y states using the CASSCF, CASPT2, and CCSD(T) methods. Equilibrium geometries of excited states are obtained and their changes with respect to the ground state are discussed. For most excited states the C_2v symmetry of the ground state is lowered to the C_s symmetry. A series of valence vertical and adiabatic excitation energies is presented along with excitation energies for Rydberg states. The main body of the paper contains Finite-Field Perturbation Theory (FFPT) calculations of electric properties of the vertically as well as geometry relaxed excited states. Dipole moments of valence excited states decrease significantly upon excitation, being about one half of the ground state dipole moment. Polarizabilities usually change upon excitation much less (increase by about 30%) but hyperpolarizabilities are enhanced up to one or two orders of magnitude. The orientation of the dipole moment is reversed in some vertically excited Rydberg states. Properties of the ground and excited states are discussed considering alterations of the electronic structure and shifts in the geometry.     

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.     

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.     

Microwave spectrum and conformation of 6-thiabicyclo[3.1.0]hexane

The microwave spectrum of 6-thiabicyclo[3.1.0]hexane (cyclopentene sulfide) has been measured in the region 26,500-40,000 MHz. The experimental data are consistent with a single stable conformation. Furthermore, these data can only be satisfactorily explained by assuming that this conformation is the boat form. Rotational constants were obtained, both for the ground state and two excited vibrational states, while centrifugal distortion coefficients were obtained for the ground state and one excited vibrational state. The ground state rotational constants found were A₀ = 5026.243 ± 0.003 MHz, B₀ = 2833.813 ± 0.003 MHz, and C₀ = 2411.679 ± 0.03 MHz. For the ground state of the molecule, the electric dipole moment components were found to be μ_a = 1.800 ± 0.012 D and μ_c = 1.155 ± 0.024 D, yielding a total dipole moment μ = 2.139 ± 0.027 D.     

Influence of local excitation of octupolar Oligophenylenevinylenes on their dipole moments

Absorption and fluorescence spectra of octupolar centrosymmetric oligophenylenevinylene dyes (E,E)-bis[2-(4-hexyloxyphenyl)ethenyl]-(E,E)-3,6-bis-[2-(4-N,N-dipropylaminophenyl)ethenyl]pyrazine and (E,E,E,E)-2,3,5,6- tetra-[2-(4-hexyloxyphenyl)ethenyl]pyrazine were measured in various solvents. An electro-optical absorption method was used to determine their dipole moments as μ _g  = 6.1∙10^–30 and 3.4∙10^–30 C∙m in the equilibrium ground state and the increased values ∆ ^a μ = 11.9∙10^–30 and 8.2∙10^–30 C∙m upon excitation into a Franck–Condon state. Quantum-chemical calculations showed that the molecules had non-planar configurations. The π,π-conjugated system was localized on the most planar part of the molecule that was responsible for light absorption in the range 300–450 nm due to a change in the geometry of the molecules in the ground state. Localized excitation of the molecules caused their dipole moments ∆ ^a μ to change significantly.     

Dipole Moments of 4′-Aminoflavonol Fluorescent Probes in Different Solvents

Electrooptical absorption measurements (EOAM) were used to measure the dipole moments of the normal form of 4-(dimethylamino)-3-hydroxyflavone (FME), and 4 N-(15-azacrown-5)-3-hydroxyflavone (FCR) in 1,4-dioxane, toluene, and cyclohexane. With these probes excited-state intramolecular proton transfer (ESIPT) takes place. For comparison, the dipole moments of 4-(dimethylamino)-3-metoxyflavone (FME3ME), for which ESIPT is lacking, were measured, too. For all three probes the ground (_g) and excited Franck-Condon state (_e^FC) electrical dipole moments are parallel to each other and also parallel to the transition dipole moment. The electrical dipole moments of FCR, FME, and FME3ME in their ground state have values within the range (12.0–17.7) × 10^–30 C m. Upon optical excitation, the dipole moments increase by (41.9–52.9) ×10^–30 C m. The value of the change of the dipole moment vector ^a with excitation to the Franck-Condon state and the value of the vector _e^FC for FCR and FME are practically independent on the solvent polarity. From this point of view and due to large values of the dipole moments FCR and FME are very promising probes for the investigation of the distribution of the local polarity in biological systems using site-selective excitation of the different sites. Our steady-state fluorescence studies on FME and FCR have demonstrated a high spectral sensitivity of the normal form to such solvent characteristics as polarity.     

Microwave and far-infra-red dielectric absorption inn-alkanes

Summary The power absorption coefficient (α) forn-hexane (C₆),n-heptane (C₇),n-dodecane (C₁₂) andn-tetradecane (C₁₄), benzene and cyclohexane has been studied at 20 °C, in the wave number range 20 to 300 cm⁻¹ within an accuracy of 2%. The power absorption measurements onn-alkanes (C₅−C₁₄ except for C₈, C₁₁ and C₁₃) are discussed in conjunction with the dielectric loss in the frequency range (9⋎140) GHz. The results indicate that, unlike other nonpolar liquids,n-alkanes show a broad dielectric dispersion in the microwave frequency range followed by a second dispersion in the far infra-red. The results are interpreted in terms of a dipole moment of 0.09 D in alkanes. A possible explanation for the origin of the dipole moment is discussed. A reference is also made to measurements of the dielectric loss and the Stark effect on the lower-series alkanes in the gas phase.

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Riassunto Si è studiato il coefficiente di assorbimento di potenza (α) pern-esano (C₆),n-eptano (C₇),n-dodecano (C₁₂) en-tetradecano (C₁₄), nel benzene e nel cicloensano a 20 °C nell’intervallo di numeri d’onda da 20 a 300 cm⁻¹ con un’accuratezza del 2%. Le misurazioni dell’assorbimento di potenza neglin-alcani (C₅−C₁₄, eccetto che per C₈, C₁₁ e C₁₃) sono discusse insieme alla perdita dielettrica nell’intervallo di frequenza (9⋎140) GHz. I risultati indicano che, diversamente da altri liquidi non polari, glin-alcani mostrano un’ampia dispersione dielettrica nell’intervallo di frequenza delle microonde, seguíta da una seconda dispersione nel lontano infrarosso. I risultati sono interpretati in termini di un momento dipolare di 0.09 D negli alcani. Si discute una possibile spiegazione dell’origine del momento dipolare. Si fa anche un accenno alle misurazioni della perdita dielettrica e dell’effetto di Stark sugli alcani della serie inferiore in fase gassosa.

     

Magnetic dipole,electric quadrupole and magnetic octupole moments of the <Emphasis Type="Italic">Δ</Emphasis> baryons in light cone QCD sum rules

Due to the very short life time of the Δ baryons, a direct measurement on the electromagnetic moments of these systems is almost impossible in the experiment and can only be done indirectly. Although only for the magnetic dipole moments of Δ ⁺⁺ and Δ ⁺ systems there are some experimental data, the theoretical, phenomenological and lattice calculations could play crucial role. In the present work, the magnetic dipole (μ _Δ ), electric quadrupole (Q _Δ ) and magnetic octupole (O _Δ ) moments of these baryons are computed within the light cone QCD sum rules. The results are compared with the predictions of the other phenomenological approaches, lattice QCD and existing experimental data.     

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.