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 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.     

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.     

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).     

Fluorescent properties of thiochrome in solvents of different polarity

Spectral and fluorescent properties of thiochrome in solvents of different polarity were studied. It was found that the pK_a value of the transition between the cationic and neutral forms of thiochrome in aqueous solutions increased from ∼5.5 to 9.7 upon photoexcitation. It is supposed that protonation takes place in the excited state of the molecule resulting in fluorescence quenching of the thiochrome neutral form in aqueous solutions at neutral pH values. The fluorescence quantum yield of thiochrome increased by ∼2.2 times upon the transition from aqueous solutions to alcohols or polar aprotic solvents. It was found that an increase of the solvent polarity led to an increase in the Stokes shift from 3200 to 4200 cm⁻¹ for the thiochrome neutral form emission. The change in the dipole moment upon excitation into the S1-state was estimated to be less than 3D.     

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.     

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.     

Theoretical calculation of the dipole moment function of the aΠ state of NO

The potential energy curve and theoretical dipole moment function of the a⁴Π state of NO have been determined using full-valence and first-order configuration interaction wavefunctions. Using these two different wavefunctions, the dipole moments of the a⁴Π, v = 3 level have been found equal, respectively, to 0.16 D and 0.30 D, with the polarity N⁺O⁻. These values compare well with the value of |0.20 ± 0.04| D determined by Lisy and Klemperer. The first derivative of the dipole moment has also been calculated to be equal to 1.25–1.73 D/bohr.     

π* ←π electronic transition in hydroxy-benzonitriles. I. Orthohydroxybenzonitrile

The longest wavelengthπ* ←π electronic band system of ortho-hydroxybenzonitrile vapour through the absorption technique has been reported for the first time. Assuming a planar molecular geometry in both the electronic states, the molecule is classified into aC _s point group, and the present spectrum is attributed to¹ A′ ←¹ A′ type corresponding to electric dipole forbidden transition¹ B _2u ←¹ A _1g (260 nm band system) of benzene. The most intense band at 33914 cm⁻¹ has been assigned as the 0, 0 band, and the other vibronic bands have been interpreted in terms of the excited state and a few ground state fundamentals.     

Photophysical characteristics of three novel benzanthrone derivatives: Experimental and theoretical estimation of dipole moments

The effect of solvents on absorption and fluorescence spectra and dipole moments of novel benzanthrone derivatives such as 3-N-(N′,N′-Dimethylformamidino) benzanthrone (1), 3-N-(N′,N′-Diethylacetamidino) benzanthrone (2) and 3-morpholinobenzanthrone (3) have been studied in various solvents. The fluorescence lifetime of the dyes (1-3) in chloroform were also recorded. Bathochromic shift observed in the absorption and fluorescence spectra of these molecules with increasing solvent polarity indicates that the transitions involved are π→π^?. Using the theory of solvatochromism, the difference in the excited-state (μ_e) and the ground-state (μ_e) dipole moments was estimated from Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet, and McRae equations by using the variation of Stokes shift with the solvent’s relative permittivity and refractive index. AM1 and PM6 semiempirical molecular calculations using MOPAC and ab-initio calculations at B3LYP/6-31 G^? level of theory using Gaussian 03 software were carried out to estimate the ground-state dipole moments and some other physicochemical properties. Further, the change in dipole moment value (Δμ) was also calculated by using the variation of Stokes shift with the molecular-microscopic empirical solvent polarity parameter (E_T^N). The excited-state dipole moments observed are larger than their ground-state counterparts, indicating a substantial redistribution of the π-electron densities in a more polar excited state for all the systems investigated.     

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.     

Ground- and excited-state spectroscopic studies on [1-(4-methoxyphenyl)-3-(amino)-2,4-(dicyano)-9,10-tetrahydrophenanthrene]

The effects of polar and nonpolar solvents on both the ground and the excited-state properties of [1-(4-methoxyphenyl)-3-(amino)-2,4-(dicyano)-9,10-tetrahydrophenanthrene] is examined. Light absorption results in a population of a locally excited (LE) first singlet state (S₁,n^*) which shows sensitivity to the polarity of the surrounding solvent and hydrogen-bonding ability to the quencher 4-methylpyridine. Relaxation of this state leads to an intramolecular charge-transfer state (ICT) which leads to a large Stokes shift in polar solvents and an excited-state dipole moment of _e= 10D. The quenching of the fluorescence state by 4-methylpyridine studied inn-hexane and acetonitrile at room temperature is found to be efficient and a positive deviation from linearity was observed in the Stern-Volmer plots even at concentrations of 4-methylpyridine below 0.4M. This is explained as a result of the occurrence of both a dynamic and a static quenching mechanism. The static quenching constants (K _sv) along with those obtained by visible spectroscopy (K _GS) indicate that the ground-state complex is weak and relatively solvent dependent.     

Spectral investigations on 2,3-bis(chloromethyl)-1,4- anthraquinone: solvent effects and host–guest interactions

Solvent effects on 2,3-bis(chloromethyl)-1,4-anthraquinone (DCMAQ) and the molecular recognition of DCMAQ in calix[8]arene were investigated using optical absorption and fluorescence emission techniques. Optical absorption spectra show n→π^* band in 350–500 nm region. It also indicates that the dipole–dipole interaction and solvent reorganization energies are responsible for the observed features in different solvents. The observed quantum yield of DCMAQ in different solvents is due to the formation of intermolecular hydrogen bond and reorientation of solvent molecule in the excited state of DCMAQ. Excited state dipole moment of DCMAQ is calculated by solvatochromic data and it shows a higher excited state dipole moment than ground state dipole moment. Optical absorption and fluorescence studies of DCMAQ in calix[8]arene elucidate the evidence for the formation of complex between DCMAQ and calix[8]arene. The inclusion ratios and inclusion constant of the host–guest complexes are also determined.     

A New Candidate Laser Dye Based 1,4-Bis[β-(2-Naphthothiazolyle)Vinyl]Benzene. Spectroscopic Behavior,Laser Parameters and Excitation Energy Transfer

A new candidate laser dye based 1,4-bis[β-(2-naphthothisolyl) vinyl] benzene (BNTVB) were prepared, and characterized in various organic solvents. The center polarity is less sensitive than electronic absorption. A red shift was noticed in the fluorescence spectra (ca. 40 nm) with increment in the solvent’s polarity, this means that BNTVB’s polarity appreciates upon excitation. The dipole moment of ground state (μ_g) and the excited singlet state dipole moment (μ_e) are determined from Kawski – Chamma and Bakshiev–Viallet equations using the disparity of Stokes shift with solvent polarity function of ε (dielectric constant) and n (refractive index) of the solvent. The result was found to be 0.019D and 5.13D for ground and exited state, in succession. DFT/TD-DFT manners were used to understand the electronic structures and geometric of BNTVB in other solvents. The experimental and theoretical results showed a good agreement. The photochemical quantum yield (Ф_c) of BNTVB was calculated in variable organic reagents such as Dioxane, CHCl₃, EtOH and MeOH at room temperature. The values of φ_c were calculated as 2.3?×?10^?4, 3.3?×?10^?3, 9.7?×?10^?5 and 6.2?×?10^?5 in Dioxane, CHCl₃, EtOH and MeOH, respectively. The dye solutions (2?×?10^?4 M) in DMF, MeOH and EtOH give laser emission in the blue-green region. The green zone is excited by nitrogen pulse 337.1 nm. The tuning range, gain coefficient (α) and cross – section emission (σ_e) of laser were also estimated. Excitation energy transfer from BNTVB to rhodamine-6G (R6G) and N,N-bis(2,6-dimethyphenyl)-3,4:9,10-perylenebis-(dicarboximide) (BDP) was also studied in EtOH to increase the laser emission output from R6G and BDP when excited by nitrogen laser. The dye-transfer power laser system (ETDL) obeys the Foster Power Transmission (FERT) mechanism with a critical transmission distance, R_o of 40 and 32 ? and k_ET equals 2.6?×?10¹³ and 1.06?×?10¹³ M^?1 s^?1 for BNTVB / R6G and BNTVB / BDP pair, respectively.     

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.     

Systematic trends in the line strengths and radial matrix elements of E1 transitions in the Be isoelectronic sequence

Line strengthS and radial matrix elementσ for the dipole allowed transitions withinn=2 complex of ions in the Be isoelectronic sequence have been fitted in the formsZ ² S=A+B/(Z − C) andZσ=A′ + B′/(Z − C′). The constantsA, B, C andA′, B′, C′ have been calculated by employing a non-linear least square method. The relevant data forS andσ have been taken from calculations which includes correlation effects. It is shown that the fitted yalues ofA andA′ are in excellent accord with their hydrogenic values (Z →α) provided that we express the zeroth-order wavefunction of the ground state 1s²2s^{2 1} S as a quantum-mechanical admixture of the Hartree-Fock (HF) state 1s²2s^{2 1} S and the near-degenerate state 1s²2p^{2 1} S.     

Calculation of radiative parameters for the $$ {A^1}\sum\nolimits_u^{+} {{X^1}} \sum\nolimits_g^{+} {} $$-transition of cesium dimer

Radiative parameters for vibrational bands (0 ≤ v′ ≤ 30, 0 ≤ v′′ ≤ 59) of the A¹?_u⁺ X¹ ?_g⁺ {A^1}\sum\nolimits_u^{+} {{X^1}} \sum\nolimits_g^{+} {} -electronic transition of a cesium dimer are calculated. These include vibronic band wavenumbers, Franck–Condon factors, Einstein coefficients for spontaneous emission, absorption band oscillator strengths, and radiative lifetimes for vibrational levels of the excited electronic state. Vibrational energies and wave functions for the ground and excited electronic states were found by a numerical solution of the radial wave equation based on potential curves plotted during the course of the study.     

Re-appraisal of the <Emphasis Type="Italic">P,T</Emphasis>-odd interaction constant <Emphasis Type="Italic">W</Emphasis><Subscript>d</Subscript> in YbF: Relativistic configuration interaction approach

Restricted active space (RAS) configuration interaction (CI) approach is employed to compute the P,T-odd interaction constant W _d for the ground (²Σ_1/2) state of YbF molecule. The present estimate of W _d = −1.164 × 10²⁵ Hz/e-cm is expected to provide a reliable limit on the electron’s electric dipole moment (EDM), d _e.     

Determination of the Dipole Moments of Excited Complexes of Polar Compounds in Proton-Donor Solvents by the Quenching of their Fluorescence

A method of determining the permanent dipole moment of polar compounds in the excited S₁ state by the dependence of the rate of radiationless conversion of the energy of this state on the polarity of the solvent (medium) is proposed. The method was used for determining the dipole moment µ_e of hydrogen-bonded complexes formed by 4-amino-, 4-methylamino-, and 4-dimethylamino-N-methylphthalimides (4AMP, 4MAMP, and 4DMAMP) in proton-donor solvents. It has been established that µ_e = 11.68 D for 4AMP in alcohols, µ_e = 11.84 D for 4MAMP in alcohols, and µ_e = 13.19 D for 4DMAMP in alcohols and water.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 2, pp. 186–191, March–April, 2005.