Excited Singlet-state Dipole Moments Research Articles

Experimental and theoretical interpretations of spectral behavior of 6-methoxyflavone

The present work emphasizes on the experimental and computational analysis of the solvatochromic behavior of 6-methoxyflavone (6MF). The steady-state absorption and fluorescence spectra were observed in certain polar protic, polar aprotic and non-polar/weakly polar solvents to examine their solvatochromism and determine the electrical dipole moment. Bathochromic shift in fluorescence spectra with solvent polarity was ascribed to intramolecular charge transfer (ICT) interaction. Calculations based on various solvent correlation techniques denote that the excited singlet-state dipole moment value is higher than the ground-state counterpart, hence indicates substantial redistribution of π-electron density in the excited state. Quantum chemical investigations were performed using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively, in vacuum and solvents. The vertical transitions, along with the bright singlet states and HOMO-LUMO, were obtained from the DFT/TD-DFT calculations. The experimentally calculated ground and excited state dipole moments and different photophysical parameters adequately reflect the values obtained from computational methods. Multiple linear regression (MLR) method based on Kamlet-Taft and Catalan solvent parameters demonstrate that the photophysical behavior of 6MF is attributed to both specific and non-specific solute-solvent interactions. Thus, the study helps to demonstrate the sensing ability of 6MF towards organic solvents and the charge transfer/hydrogen donor/acceptor properties of complex systems.

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. 40nm) with increment in the solvent's polarity, this means that BNTVB's polarity appreciates upon excitation. The dipole moment of ground state (μg) and the excited singlet state dipole moment (μe) 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 (Фc) of BNTVB was calculated in variable organic reagents such as Dioxane, CHCl3, EtOH and MeOH at room temperature. The values of φc 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 × 10-4M) in DMF, MeOH and EtOH give laser emission in the blue-green region. The green zone is excited by nitrogen pulse 337.1nm. The tuning range, gain coefficient (α) and cross - section emission (σe) 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, Ro of 40 and 32 Ả and kET equals 2.6 × 1013 and 1.06 × 1013M-1s-1 for BNTVB / R6G and BNTVB / BDP pair, respectively.

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.

Solvatochromatic shift of absorption and fluorescence spectra of 6-methoxyquinoline: Estimation of ground and excited state dipole moments

Electronic absorption and fluorescence spectra of protonated 6-methoxyquinoline (6MQ+) and neutral 6-methoxyquinoline (6MQ) have been recorded at room temperature in wide range of solvents of different polarities. The absorption maximum remains almost unchanged with the increase in solvent polarity, whereas a red shift in fluorescence emission maximum was observed. The ground-state dipole moment and the first excited singlet state dipole moment of 6MQ+ and 6MQ were obtained from Bakhshiev's and Bilot–Kawski's equations by means of solvatochromic shift method. High values of dipole moment are observed for excited state as compared to the corresponding ground state dipole moment values of 6MQ+ and 6MQ and this is attributed to the more polar excited states of 6MQ+ and 6MQ.

Ground and excited state dipole moments of quinine sulfate dication: Solvatochromic shift of absorption and fluorescence spectra

Electronic absorption and fluorescence spectra of quinine sulfate dication (QSD) have been recorded at room temperature in a wide range of solvents of different polarities. The absorption maximum remains almost unchanged with the increase in solvent polarity, whereas a red shift in fluorescence emission maximum was observed. The ground-state dipole moment of QSD was obtained from quantum mechanical calculations and the first excited singlet state dipole moment of QSD was obtained from Bakhshiev's and Bilot–Kawski's equations by means of solvatochromic shift method. Very high value of dipole moment is observed for excited state as compared to the corresponding ground state value and this is attributed to the more polar excited state of QSD. Compared to the dipole moment of quinine sulfate, both the ground and excited state dipole moments of QSD are lower.

Determination of excited singlet-state dipole moments of hydroxy and methoxy coumarins using solvatochromic method

The effects of solvents of various polarity on the electronic absorption and fluorescence spectra of 7-hydroxy-4-trifluoromethyl coumarin; 6,7-dihydroxy-4-trifluoromethyl coumarin and 7-methoxy-4-trifluoromethyl coumarin have been investigated. The singlet-state excited dipole moments ( μ e ) and ground state dipole moments ( μ g ) are estimated from Bakshiev and Kawski-Chamma-Viallet equations by using the variation of Stokes’ shift with the solvent’s dielectric constant ( e ) and refractive index ( n ). The observed singlet-state excited dipole moments are found to be larger than the ground-state ones. In addition, the geometry and other electronic properties are computed using ab-initio method with correlation functions at 6-31G basis set.

Photophysical properties and estimation of ground and excited state dipole moments of 7-diethylamino and 7-diethylamino-4-methyl coumarin dyes from absorption and emission spectra

In the present work, the effect of solvents on absorption and fluorescence spectra and dipole moments ( μ g , μ e ) of 7-diethylamino coumarin (7DEAC) and 7-diethylamino-4-methyl coumarin (7DEA4MC) have been studied in different solvents of various polarity at room temperature. The solvents have been selected in a way to cover the full range of intermolecular interactions from non-polar hexane to strongly polar formamide. Using the methods of solvatochromism, the difference in the first excited singlet-state ( μ e ) and ground state ( μ g ) dipole moments was estimated from Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet and McRae equations. The Onsager’s cavity radius of the probes has been calculated by AM1 and PM3 quantum chemical calculations and also by a direct relation. The change in dipole moment value (Δ μ ) was also calculated by using the variation of Stoke’s shift with microscopic solvent polarity parameter ( E T N ). The calculated dipole moments represent new results, as well as some of the solvatochromic results that were not studied earlier in such large number of solvents. It is observed that the values of excited singlet-state dipole moments are higher than the ground state ones in both the molecules, which shows that excited states are more polar than the ground states.

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.

Revisiting the photophysical properties and excited singlet-state dipole moments of several coumarin derivatives

The solvent effects on the electronic absorption and fluorescence emission spectra of several coumarins derivatives, containing amino, N,N-dimethyl-amino, N,N-diethyl-amino, hydroxyl, methyl, carboxyl, or halogen substituents at the positions 7, 4, or 3, were investigated in eight solvents with various polarities. The first excited singlet-state dipole moments of these coumarins were determined by various solvatochromic methods, using the theoretical ground-state dipole moments which were calculated by the AM1 method. The first excited singlet-state dipole moment values were obtained by the Bakhshiev, Kawski–Chamma–Viallet, Lippert–Mataga, and Reichardt–Dimroth equations, and were compared to the ground-state dipole moments. In all cases, the dipole moments were found to be higher in the excited singlet-state than in the ground state because of the different electron densities in both states. The red-shifts of the absorption and fluorescence emission bands, observed for most compounds upon increasing the solvent polarity, indicated that the electronic transitions were of π–π* nature.

Extremely Large Dipole Moment in the Excited Singlet State of Tris{[p-(N,N-dimethylamino)phenylethynyl]duryl}borane

Solvent effects on the spectroscopic and photophysical properties of tris{[p-(N,N-dimethylamino)phenylethynyl]duryl}borane (TMAB) and tris[(phenylethynyl)duryl]borane (TPhB) were studied in detail. Both TMAB and TPhB exhibited broad and structureless absorption and fluorescence bands ascribed to the charge transfer (CT) transition between the pi-orbital of the aryl group (pi(aryl)) and the vacant p-orbital on the boron atom (p(B)): pi(aryl)-p(B) CT. The fluorescence spectra of TMAB and TPhB were dependent on a solvent polarity, and the Stokes shifts of the compounds (Deltanu(S)) were shown to correlate linearly with a solvent polarity parameter: f(X) = (D(s) - 1)/(2D(s) + 1) - (n(2) - 1)/(2n(2) + 1) where D(s) and n are the dielectric constant and refractive index of a solvent, respectively. The slope value of the Deltanu(S) versus f(X) plot gave the excited singlet state dipole moment of TMAB or TPhB to be approximately 60 or approximately 30 D, respectively, demonstrating that the excited singlet state of TMAB possessed an extremely large dipole moment. The fluorescence quantum yields (Phi(f)) and lifetimes (tau(f)) of the compounds were also dependent on f(X). Detailed analysis of the present results demonstrated that the photophysical properties of TMAB were governed by the magnitude of the fluorescence rate constant (k(f)) and the k(f) value decreased almost one-tenth with an increase in f(X), which was the primary origin of the f(X) dependences of Phi(f) and tau(f). The results were discussed in terms of the characteristic pi(aryl)-p(B) CT excited states of the derivatives.

Solvatochromic study of 2-hydroxy-4-methylquinoline for the determination of dipole moments and solute–solvent interactions

The electronic absorption and fluorescence spectra of 2-hydroxy-4-methylquinoline (HMQ) have been recorded at room temperature (298 K) in solvents of different polarities. The spectral data have been used to evaluate the ground and first excited singlet state dipole moment using the solvatochromic shift method (Bakhshiev [31] and Kawski–Chamma–Viallet [32,33]). The validity of these methods in the light of proper choice of solvents is discussed.

Estimation of the ground and the first excited singlet-state dipole moments of 1,4-disubstituted anthraquinone dyes by the solvatochromic method

The both, ground-state ( μ g ) and the excited-state ( μ e ) dipole moments of three 1,4-disubstituted anthraquinones, namely 1,4-diaminoanthracene-9,10-dione (1,4-DAAQ), 1-amino-4-hydroxyanthracene-9,10-dione (1,4-AHAQ), and 1,4-dihydroxyanthracene-9,10-dione (1,4-DHAQ) were estimated in binary solvent mixtures (methylcyclohexane–ethyl acetate and ethyl acetate–acetonitrile). The dipole moments ( μ g and μ e ) were estimated from Lippert–Mataga, Bakhshiev, Kawski–Chamma–Viallet, McRae, and Suppan equations by using the variation of Stokes shift with the solvent's relative permittivity and refractive index. The ground-state dipole moments were also calculated theoretically by Gaussian 03 software using B3LYP/6-31 G* level of theory. Further, the change in dipole moment values Δ μ were 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 molecules investigated.

Estimation of first excited singlet-state dipole moments of aminoanthraquinones by solvatochromic method

The ground state ( μ g) and the excited state ( μ e) dipole moments of three substituted anthraquinones, namely 1-aminoanthracene-9,10-dione (AAQ), 1-(methylamino)anthracence-9,10-dione (MAQ) and 1,5-diaminoanthracene-9,10-dione (DAQ) were estimated in various solvents. The dipole moments ( μ g and μ e) were estimated from Lippert, Bakhshiev, Kawski-Chamma-Viallet, McRae and Suppan equations by using the variation of Stokes shift with the solvent dielectric constant and refractive index. The excited state dipole moments were also calculated by using the variation of Stokes shift with microscopic solvent polarity parameter ( E T N ). It was observed that dipole moment values of excited states ( μ e) were higher than corresponding ground state values ( μ g), indicating a substantial redistribution of the π-electron densities in a more polar excited state for all the molecules investigated.

Theoretical predictions for occurrence of charge transfer complex within the two synthesized bichromophores considering the role of their spacers in interactions with the π-orbitals of the redox centers

Computational work has been done for the bichromophores comprising a donor molecule 4 methoxy-benzo[ b]thiophene (4MBT) and an acceptor molecule p-chloro-acetophenone (PCA) linked together by unsaturated and saturated olefinic spacers, HC CH and H 2C CH 2. The difference between the ground and excited singlet state dipole moments confirmed the electron transfer probability. The possibility of formation of ground state charge transfer complex in case of the bichromophoric systems is indicated by time dependent density functional theory (TD-DFT) with B3LYP/6-311G(d,p) theoretical and semi-empirical RHF-SCF-PM3 calculation and confirmed experimentally by electronic absorption (UV–Vis) spectroscopic measurements.

Solvatochromic correlations and ground- and excited-state dipole moments of curcuminoid dyes

Experimental dipole moments of curcumin ( 1) and of its parent compound dicinnamoylmethane ( 2) were determined in dioxane and benzene, respectively. Theoretical dipole moments were calculated using a combination of the PPP method (π-moment) and a vector sum of the σ-bond moments (σ-moment) as well as by the ZINDO/1 method. Solvatochromic correlations were used to obtain the experimental first excited singlet-state dipole moments. The experimental electronic absorption spectra were compared with the calculated transitions.

Theoretical and Experimental Dipole Moments of Purines

As a follow-up on our previous study of a series of purines (purine, 6-chloropurine, purine-6-thiol, hypoxanthine, theobromine, theophylline, caffeine, and uric acid), we have investigated six additional biologically important purines (adenine, guanine, isoguanine, thioguanine, xanthine, and kinetin). Their ground-state dipole moments were measured in dioxane at 293 K. The first excited singlet-state dipole moments were obtained using the solvatochromic shift equations (McRae, Suppan, Bakhshiev, and Kawski-Chamma-Viallet). The theoretical dipole moments were calculated as a combination of the π-moment (PPP method) and the σ-moment (vector sum of the σ-bond and σ-group moments). The same approach was used to obtain their first excited singlet-state dipole moments (excited state π-moment; σ-moment assumed to be the same as in the ground state). Ab initio HF 6-31G** calculations were also used to obtain ground-state dipole moments for all the fourteen purines under study. In addition, a DFT/B3PW91/6311++(2df,2p) calculation has been carried out for purine for comparison. The different sets of theoretical dipole moments were compared with the respective experimental values. There is an approximately equally good agreement among the experimental dipole moments and the PPP + σ dipole moments (±6.9%) and the ab initio dipole moments (±7.4%). The effect of structure on the dipole moments is discussed.

Solvent effects of the electronic absorption and photophysical properties of poly(3-methoxythiophene), a conducting oligomer: evaluation of the dipole moment and specific solute–solvent interactions in the first excited singlet-state

The electronic absorption and fluorescence spectra, and fluorescence quantum yields ( φ F) of poly(3-methoxythiophene) (PMOT) were determined at room temperature (298 K) in a variety of solvents with different polarities (hexane, cyclohexane, 2-propanol, ethyl acetate, methanol, ethanol, acetonitrile, ethylene glycol, dioxane, propylene carbonate, dimethylformamide, and dimethyl sulfoxide). The solvent effects on the PMOT spectral and photophysical characteristics (absorption and fluorescence wavenumbers) were studied quantitatively, using the Kamlet–Abboud–Taft solvation relationships. The spectral data were used, in combination with the PMOT ground-state dipole moment ( μ g), to evaluate its first excited singlet-state dipole moment ( μ e). A μ e/ μ g ratio of 5.8 was obtained by means of the solvatochromic shift method (Bakhshiev's and Kawski–Chamma–Viallet's correlations). The Kamlet–Abboud–Taft solvatochromic parameters were applied to determine the solute–solvent interactions in the PMOT ground and excited singlet states.

An Experimental and Theoretical Study of the Photophysical Properties and the Dipole Moments of Methoxynitronaphthalenes

Isomeric methoxynitronaphthalenes (MNN, 14 possible isomers, cf. Scheme 1) were studied theoretically and experimentally. PPP calculations were carried out for all possible isomers and the results were compared with the experimental electronic absorption, fluorescence, and phosphorence spectra of selected isomers. Also the phosphorescence lifetimes were determined. Theoretical ground-state dipole moments of MNN were obtained as a combination of the π-component (PPP method) and the [sgrave]-component (a vector sum of à-bond and group moments). The experimental groundstate dipole moments were measured for a series of MNN (on a dipole meter) and compared with the theoretical values. The effect of solvent polarity upon the electronic absorption and fluorescence spectra of selected MNN was studied and the solvatochromic method using the Bakhshiev and Kawski-Chamma-Viallet equations and the ground-state dipole moments was employed to obtain the experimental first excited singlet-state dipole moments.

Solvent effects on the absorption and fluorescence spectra of some acridinedione dyes: determination of ground and excited state dipole moments

The acridinediones have been reported earlier as a new class of the laser dyes. The absorption and fluorescence spectra of the different substituted acridinediones have been recorded in different solvents and the difference in the dipole moment between the ground and excited state has been obtained. The value of the Onsager cavity radius was calculated from the radius obtained from the surface area using the software PCMODEL. The ground state dipole moment has been obtained using Guggenheim's method. The results were used to obtain the first excited singlet state dipole moment of the acridinedione dyes by the solvatochromic shift method.

A solvatochromic study of new benzo[a]phenothiazines for the determination of dipole moments and specific solute—solvent interactions in the first excited singlet state

The electronic absorption and fluorescence excitation and emission spectra of seven benzo[a]phenothiazines, including 12H-benzo[a]phenothiazine, 9-methyl-benzo[a]phenothiazine, 10-methyl-benzo[a]phenothiazine, 11-methyl-benzo[a]phenothiazine, 5-oxo-5H-benzo[a]phenothiazine, 5-oxo-6-methyl-benzo[a]phenothiazine and 5-oxo-6-hydroxy-benzo[a]phenothiazine, were determined at room temperature (298 K) in solvents of various polarity (cyclohexane, ethyl ether, ethyl acetate, tetrahydrofuran, ethanol, dimethylformamide, acetonitrile and dimethylsulphoxide). The effect of the solvent on the spectral characteristics was studied quantitatively. In combination with the ground state dipole moments of these compounds, the spectral data of the benzo[a]phenothiazines were used to evaluate their first excited singlet state dipole moments using the solvatochromic shift method (Bakhshiev and Kawski—Chamma—Viallet correlations). The theoretical ground and excited singlet state dipole moments of the benzo[a]phenothiazines were also calculated as the vector sum of the π component (obtained by the Pariser—Parr—Pople method) and the σ component (obtained from σ bond moments). In most cases, a satisfactory agreement was found between the experimental and calculated values of the dipole moments. For most benzo[a]phenothiazine derivatives under study, the experimental excited singlet state dipole moments were higher than their ground state counterparts. The application of the Kamlet—Abboud—Taft solvatochromic parameters to explain the effect of the solvent on the spectral properties of benzo[a]phenothiazines is discussed.