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.     

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.     

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.     

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.     

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.     

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.

     

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.     

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.     

Rotational Diffusion of Coumarins in Aqueous DMSO

The rotational dynamics of four structurally similar polar molecules viz., coumarin 440, coumarin 450, coumarin 466 and coumarin 151 has been studied in binary mixtures comprising of dimethyl sulphoxide and water at room temperature using the steady state fluorescence depolarization method and time correlated single photon counting technique. The binary mixtures are characterized by the fact that at a particular composition the viscosity (η) of the solution reaches a maximum value that is higher than the viscosities of either of the two co-solvents. The dielectric properties of the solution change across the composition range and the qualitative features of the solvent relaxation dynamics in complex systems are known to differ from those in simple solutions. A hook type profile of rotational reorientation time (τ _r ) vs viscosity (η) is obtained for all the solutes in dipolar aprotic mixture of dimethyl sulphoxide-water, with the rotational reorientation times being longer in organic solvent-rich zone, compared to the corresponding isoviscous point in water-rich zone due to strong hydrogen bonding. Fluorescence lifetimes as well as rotational reorientation times are sensitive to the composition of the binary solvent system under study than to the viscosity suggesting the importance of local structure. The results are discussed in the light of hydrodynamic and dielectric friction models. Dedicated to Professor M.I. Savadatti on his 77^th Birthday.     

Solvent Dependence on Structure and Electronic Properties of 7-(Diethylamino) - 2H -1- Benzopyran-2- one (C-466) Laser Dye

In this work, we studied influences on the absorption and fluorescence emission spectra of coumarin-4066 (C-466) with different solvent polarity scale. The spectral shifts reflect the effect of the equilibrium solvents association across the energized solute particle, which adjusts inertially as a result of quick charge realignment upon radiative deactivation to the lowest electronic state. The dipole moments of C-466 are determined by employing the Bakhshiev, Kawski-Chamma-Viallet, Lippert-Mataga and McRae relations. The results from all these methods are, excited state dipole moment of C-466 is higher than the ground state dipole moments and which indicates molecule is less polar in the ground state. Theoretical analysis was also carried out by Density Functional theory (DFT and TD –DFT) employing the BECKE-1998 (exchange)/STO-6G basic set in ethanol solvent and in vacuum medium. The HOMO-LUMO, Solvent Accessible Surfaces (SAS) and Molecular Electrostatic Potential (MEP) were analysed to acquire additional knowledge of the molecular arrangement and electronic properties of C-466. These photophysical properties suggest delineation can be mauled for laying out new luminescent tests for various solvents microenvironment.     

Experimental investigations on energy-transfer characteristics and performance of some laser dye mixtures

Energy transfer from both Coumarin 120 (C120) and p-Bis(o-methylstyryl)-benzene (Bis-MSB), energy donors, to coumarin 7(C7) (acceptor) individually has been studied by steady-state emission measurements in methanol. The dye laser characteristics of the above-mentioned dyes have also been studied with respect to the energy transfer mechanism in the same solvent using a pulsed nitrogen laser as a pumping source. The large values of the critical transfer distances, R₀, indicate that the dominant mechanism responsible for energy transfer is due to long-range dipole–dipole interaction between the excited donor and ground state acceptor molecule. Both photophysical and photochemical stability of the donors has been examined under the effect of N₂ laser pumping.     

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.     

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.     

SiN分子外电场情况下的发光特性

为全面分析外电场对分子发光特性的影响, 本文采用密度泛函B3P86方法6-31g(d)基组, 对SiN分子进行了基态结构的优化, 进而使用含时密度泛函方法(time dependent density functional theory, TDDFT), 计算了不同方向及大小的外电场情况下SiN分子的吸收谱、激发能、振子强度、跃迁偶极矩. 通过比较发现外电场对该分子的激发能、吸收谱、跃迁振子强度及跃迁偶极矩影响都比较明显, 说明了电场对SiN分子的激发特性影响比较复杂, 特别是在加场前后分子均有在可见光区波段的吸收谱, 这对研究分子的发光很有意义.同时对该分子所发可见光谱的产生机理进行了分析, 并与已有实验结果进行比较.     

Electrooptical Absorption Measurements (EOAM) Testify Existence of two Conformers of Prodan and Laurdan with Different Dipole Moments in Equilibrium Ground and Franck-Condon Excited State

The results from the electrooptical absorption measurements (EOAM) on the equilibrium ground and excited Franck-Condon state dipole moments of Prodan and Laurdan in 1,4-dioxane are presented. As follows from experiments Prodan and Laurdan in the equilibrium ground and excited Franck-Condon state have two conformers with considerably different dipole moments. The electrical dipole moments and the transition dipole moment, obtained from the short-wavelength region of the absorption spectrum are parallel. The electrical dipole moments measured at the long-wavelength spectral region are parallel to each other but not parallel to the transition dipole moment m _a. The angle θ between the transition dipole moment m _a and the dipole moment in the equilibrium ground state μ _g of the long-wavelength conformer is about 30⁰ for both probes. Obtained results evidence that donor-acceptor pairs of the short-wavelength and long-wavelength conformers are not located on the same axis. Two low-energy conformers of Prodan have been found by density functional theory (DFT) calculations, differing in the orientation of the carbonyl group towards the naphthalene system.     

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.     

The microwave spectrum of cyanogen isocyanate (NCNCO)

The microwave spectrum of cyanogen isocyanate has been measured in the ground state and first three excited states of the lowest frequency vibration. Rotational constants, centrifugal distortion constants, and moments of inertia have been obtained. The molecule is a planar asymmetric rotor in its ground state, but shows considerable evidence of quasilinearity. The dipole moment has been measured, and, along with the structure, is compared with that of related molecules.     

Rotational diffusion of coumarin laser dye studied by fluorescence depolarization technique

Solute-solvent interactions play a major role in determining the physiochemical properties of solutions. Yet our understanding of this subject is far from complete. Rotational diffusion studies of medium-sized molecules provide a useful means to probe these interactions. The rate of diffusion is sensitive to the shape of the molecule and interaction between the solute and solvent molecules. Because of continuous interactions with their neighbours, molecules rotating in liquid, experience friction. By modeling this friction using various continuum-based theories, we can get better insight into the nature of the solute-solvent interactions. In the present work steady-state and time-resolved fluorescence polarization studies have been carried out with coumarin 30. The rotational reorientation of this probe has been measured in butanol at higher values of viscosity over temperature. However, it was found that coumarin 30 rotates faster in butanol compared to n-octanenitrile.     

Time-resolved study of intramolecular charge transfer fluorescence in 1,2,3,4-tetrachloro-11H-isoindolo-[2, 1-a]-benzimidazol-11-one

Fluorescent properties of 1,2,3,4-tetrachloro-11H-isoindolo-[2,1-a]-benzimidazol-11-one (TCIB) in various organic solutions are described. Detailed investigation of the fluorescence from the solutions revealed that it was ascribable to the electronic transition from the lowest singlet excited state of an isolated molecule to its ground state, though the fluorescence spectrum was broad and structureless and the Stokes’ shift was about 1 eV. The absorption peak of TCIB was relatively insensitive to change in solvent polarity, whereas its fluorescence peak shifted to the red with an increase in the polarity. This finding suggests that the dipole moment of the molecule in the ground state is almost zero, and that the excited state has a non-zero dipole moment, which coincides with the predicted semiempirical molecular orbital calculation. Fluorescence quantum efficiency decreased with increase of solvent polarity. The efficiency was reduced by a factor of 39 in going from n-hexane solution to acetonitrile solution. The radiative rate constant also decreased with increase of solvent polarity. However, its reduction was very moderate; the reduction factor was only 2.5 for acetonitrile solution as compared with n-hexane solution. This finding indicates that the emitting state of the title compound is influenced by a solvent-dependent non-radiative mechanism, for which solvent-sensitive intersystem-crossing deactivation is tentatively proposed.     

Solvent Effect on the Electronic States Properties of Benzodiazepine-2,4-dione Using the Dielectric Continuum Model

The molecular properties of benzodiazepine-2,4-dione that depend on the nature of the solvent have been investigated using the dielectric continuum model and the Dimroth polarity parameter E_T(30). The difference of dipole moments between the ground and excited states has been evaluated. The results indicate that the stabilization of the first excited state S₁ is less marked than the destabilization of the ground state, and the solute–solvent interactions are more important in the ground state than in the excited state.