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.     

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.     

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.     

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.     

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.     

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.     

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.     

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).     

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.     

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.     

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.     

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.     

Temporal dependence of the dipole moment of long-wavelength forms of n-dimethylaminobenzonitrile

The temporal dependences μ_e(t) of the dipole moment of n-dimethylaminobenzonitrile excited to different states by quanta with different energies are evaluated based on the experimental correlation functions of the shift of instantaneous spectra. It is found that, upon excitation into the maximum of absorption, the relaxation changes of the spectra are accompanied by an increase in the dipole moment from 9 D in the Franck-Condon state to 16 D in the stationary state. At the same time, the excitation of luminescence at the red absorption edge by radiation at 403 nm leads to a decrease in the range of variation of the dipole moment. In this case, the initial value of the dipole moment amounts to 14 D and, during the lifetime of the excited state, it increases to 17 D. This indicates that the nature of the radiation excited at the wavelength 403 nm is directly related to internal charge transfer states of n-dimethylaminobenzonitrile.     

High-resolution measurements of the 1 ← 0 infrared absorption band of hydrogen iodide

The ν₁ fundamental band of FNO has been studied by the technique of CO laser Stark spectroscopy. The band origin was determined to be 1844.099 cm^?1, and values for the rotational and centrifugal distortion constants of the (100) excited vibrational state were found. The ground state dipole moment components were determined to be μ_a = 1.690 and μ_b = 0.370 D, for a total dipole moment of 1.730 D, and a relatively large reduction (5%) was found in μ for the (100) state relative to the ground state.     

The hyperfine quadrupole moment of muonium in the ground state

The quadrupole moment of the ground state of the μ⁺e^? atom is calculated to be (3m_em_μ)^?1; effects in a crystal are briefly discussed.     

Conformation and dipole moment of tetrahydropyran-4-one by microwave spectroscopy

The microwave spectrum of tetrahydropyran-4-one has been studied in the frequency region 18 to 40 GHz. The rotational constants for the ground state and nine vibrationally excited states have been derived by fitting a-type R-branch transitions. The rotational constants for the ground state are (in MHz) A = 4566.882 ± 0.033, B = 2538.316 ± 0.003, C = 1805.878 ± 0.004. From information obtained from the gas-phase far-infrared spectrum and relative intensity measurements, these excited states are estimated to be ～ 100 cm^?1 above the ground state for the first excited state of the ring-bending and ～ 185 cm^?1 for the first excited state of the ring-twisting mode. Stark displacement measurements were made for several transitions and the dipole moment components determined by least-squares fitting of the displacements: (in Debye) |μ_a| = 1.693 (0.001), |μ_b| = 0.0, |μ_c| = 0.300 (0.013) yielding a total dipole moment μ_tot = 1.720 (0.003). A model calculation to reproduce the rotational parameters indicates that the data are consistent with the chair conformation.     

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.     

Spectra and structure of small ring compounds. Microwave spectrum of cyanocyclobutane

The rotational spectrum of cyanocyclobutane has been investigated in the region 18.0–40.0 GHz. Only A-type transitions were observed. R-branch assignments have been made for the ground state and the first three excited states of the ring puckering mode as well as the first two excited states of the out-of-plane cyano-bending mode. The microwave data are consistent with a bent equilibrium ground state for the ring with the cyano-group in the equatorial position. The dipole moment components were determined to be μ_a = 4.04 ± 0.09 D and μ_c = 0.92 ± 0.03 D with the total dipole moment, μ, having a value of 4.14 ± 0.09 D.     

Photophysical parameters and laser performance of 3-(4′-dimethylaminophenyl)-1-(2-furanyl)prop-2-en-1-one (DMAFP): A new laser dye

The spectral properties such as singlet absorption, molar absorptivity, emission spectra, fluorescence quantum yield and excited state lifetime of 3-(4′-dimethylaminophenyl)-1-(2-furanyl)prop-2-en-1-one (DMAFP) have been determined in different solvents. DMAFP dye exhibits a large red shift in both electronic absorption and emission spectra as the solvent polarity increases, indicating a large change in the dipole moment of molecules upon excitation. A crystalline solid of DMAFP gives an excimer like emission at 566 nm due to the excitation of molecular aggregates. This is expected from the idealized crystal structure of the dye that belongs to the B-type class of Steven's classification. The ground and excited state protonation constants of DMAFP are calculated and amounted to 1.71 and 8.3, respectively. DMAFP acts as a good laser dye upon pumping with nitrogen laser (λ_ex=337.1 nm) in chloroform, methylene chloride and dioxane and gives laser emission in the range 460–590 nm. The laser parameters such as the tuning range, gain coefficient (α), emission cross section (σ_e) and half-life energy (E_1/2) are calculated. The photoreactivity and net photochemical quantum yield of DMAFP in chloromethane solvents are also studied.     

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.