The experimental studies on the determination of the ground and excited state dipole moments of some hemicyanine dyes

The ground state (mu(g)) and excited state (mu(e)) dipole moments of 15 hemicyanine dyes were studied at room temperature. They were estimated from solvatochromic shifts of the absorption and the fluorescence spectra as function of the solvent dielectric constant (varepsilon) and refractive index (n). In this paper we applied the Stokes shift phenomena not only for the determination of the difference in the dipole moment of excited state and ground state, but to determine the value of polarizability alpha as well. The obtained results show that excited state dipole moments of hemicyanine dyes are in the range from 5 to 15 Debye, and the difference between the excited and ground state dipole moments vary from 1 to 7 Debye. The excited and ground state dipole moments difference (mu(e)-mu(g)) obtained for selected dyes are positive. It means that the excited states of the dyes under the study are more polar than the ground state ones. Additionally, the value of both polarizability (alpha) and the Onsager radius (a) of each investigated hemicyanine dye molecule are determined, and the ratio of alpha/a(3) for each dye were calculated, which oscillate from 0.29 to 5.21. The increase in dipole moment has been explained in terms of the nature of excited state and its resonance structure.     

Influence of solvent and substituent on excited state characteristics of laser grade coumarin dyes

Absorption and fluorescence emission of 4 and 7 substituted coumarins viz. C 440, C 490, C 485 and C 311 have been studied in various polar and non-polar organic solvents. These coumarin dyes are substituted with alkyl, amine and fluorine groups at 4- and 7-positions. They give different absorption and emission spectra in different solvents. The study leads to a possible assignment of energy level scheme for such coumarins including the effect on ground state and excited state dipole moments due to substitutions. Excited state dipole moments of these dyes are calculated by solvetochromic data experimentally and theoretically these are calculated by PM 3 method. The dipole moments in excited state, for all molecules investigated here, are higher than the corresponding values in the ground state. The increase in dipole moment has been explained in terms of the nature of excited state and resonance structure.     

Solvent effects on the absorption and fluorescence spectra of some laser dyes: estimation of ground and excited-state dipole moments

The absorption and fluorescence spectra of three extensively used laser dyes namely 1,1,4,4-tetraphenyl-1,3-butadiene (TPB), 2-(4'-t-butylphenyl)-5-(4'-biphenylyl)-1-oxa-3,4-diazole (BPBD), 1,4-bis[2-(2-methylphenyl)ethenyl]-benzene (Bis-MSB) have been recorded at room temperature (300K) in solvents of different polarities. The effects of the solvents upon the spectral properties are discussed. The ground-state dipole moments (mu(g)) were determined experimentally by Guggenheim and Higasi method separately and were compared with theoretical values obtained using quantum chemical method. The ground-state dipole moments obtained by using Guggenheim method were then used in the estimation of excited-state dipole moments (mu(e)) by using Lippert's, Bakhshiev's and Kawski-Chamma-Viallet's equations. In all the above three equations the variation of the Stokes shift with the solvent dielectric constant and refractive index was made use of. It was observed that dipole moments of excited state were higher than those of the ground state for all the dyes.     

Experimental studies on the determination of the dipole moments of some different laser dyes

In this paper we used the Stokes shift phenomena to determine the difference in the dipole moments of the excited state micro(e) and ground state micro(g) to be (micro(e)-micro(g)), and the polarizability alpha. In this paper, we studied six different laser dyes belonging to four different classes of laser dyes which are diolefin 2,5-Distyryl pyrazine (DSB); 1,4-Bis (-pyridyl-2-vinyl) benzene (P2VB) and p-Bis-(o-methylstyryl)-benzene (Bis-MSB) with (micro(e)-micro(g)) equal to 6.40, 6.70 and 2.98 Debye, respectively; anthracene class includes 10(4-acetoxyphenyl)-2-methyl-9-acetoxy anthracene (APMAA) with (micro(e)-micro(g)) value of 7.25 Debye; Rhodamine B (RB) with (micro(e)-micro(g)) value of 5.33 Debye; and Coumarin 120 (C120) with the value 3.97 Debye for (micro(e)-micro(g)). In addition the value of both polarizability alpha and the radius r of each investigated laser dye molecule are determined. Therefore, the ratio alpha/r(3) for each dye is calculated to be 0.93, 0.79, 0.39, 0.37, 0.67 and 0.76 for DSP, P2VB, Bis-MSB, APMAA, RB and C120, respectively. The values of r are 4.83, 4.83, 4.90, 5.34, 5.75 and 4.11 A for the above consequence laser dyes. These dyes are studied in a large number of different solvents. The values obtained of (micro(e)-micro(g)) for these selected dyes are positive, which means that the excited state is more polar than the ground state.     

Solvent effects on the absorption and fluorescence spectra of coumarins 6 and 7 molecules: determination of ground and excited state dipole moment

Absorption and fluorescence emission spectra of coumarins 6 and 7 were recorded in solvents with different solvent parameters, viz., dielectric constant epsilon and refractive index n. The fluorescence lifetime of these dyes were measured in butanol at higher values of viscosity over temperature. Experimental ground and excited state dipole moments are determined by means of solvatochromic shift method and also the excited state dipole moments are determined in combination with ground state dipole moments. It was determined that dipole moments of the excited state were higher than those of the ground state in both the molecules.     

Ground state and excited state dipole moments of 6,8-diphenylimidazo[1,2-α]pyrazine determined from solvatochromic shifts of absorption and fluorescence spectra

Electronic absorption and dual fluorescence spectra of 6,8-diphenylimidazo[1,2-α]pyrazine (68DIP) was recorded in various solvents with different polarity at room temperature. The ground state (μg) and the excited state (μg) dipole moments of 68DIP were estimated from solvatochromic shifts of absorption and fluorescence spectra as a function of the dielectric constant (?) and refractive index (n). The results show that the value of excited state dipole moment in SE: μeSE=2.8772 D and twisted intramolecular charge transfer (TICT) excited equilibrated state dipole moment value of μeLE=2.9744 D was found. The solvent dependent spectral shifts in absorption and fluorescence spectra were analyzed by the polarizability-polarity and Kamlet-Taft parameters.     

Solvent effect on absorption and fluorescence spectra of coumarin laser dyes: evaluation of ground and excited state dipole moments

The effect of solvents on absorption and fluorescence spectra and dipole moments of coumarin 307 (C307) and coumarin 522B (C522B) have been studied extensively in various solvents, viz., general solvents, alcohols and binary mixtures (acetonitrile-benzene) at 298K. The bathchromic shift observed in absorption and fluorescence spectra of C307 and C522B with increasing solvent polarity indicates that transition involved are pi-->pi*. Solvatochromic correlations were used to obtain the ground and excited state dipole moments. The excited state dipole moments are observed to be greater than their ground state counterparts in all the solvents studied. Further, the experimentally obtained Deltamu were compared with those using normalized polarity terms E(T)(N) from Reichardt equation.     

Excited state characteristics of acridine dyes: acriflavine and acridine orange

The magnitude of the Stokes shift (frequency shifts in absorption and fluorescence spectra) is observed on changing the solvents and further has been used to calculate experimentally the dipole moments (ground state and excited state) of acriflavine and acridine orange dye molecules. Theoretically, dipole moments are calculated using PM 3 Model. The dipole moments of excited states, for both molecules investigated here, are higher than the corresponding values in the ground states. The increase in the dipole moment has been explained in terms of the nature of the excited state. Acriflavine dye overcomes the non-lasing behaviour of acridine orange due to quaternization of the central nitrogen atom.     

An experimental and theoretical study of dipole moments of N-[4-(9-acridinylamino)-3-methoxyphenyl]methanesulfonamide

The excited state (S1) dipole moment of m-AMSA (1), an acridine derivative with antitumor activity, was determined from solvatochromic shifts of the lowest energy absorption band in several organic solvents. The effect of the solute shape and the values of polarizability on the determined change of dipole moment between ground and excited state was discussed. The dipole moments in S0 and S1 state were calculated in gas phase with semiempirical quantum-chemical and DFT and CIS methods and in solvents with SM5.4A solvation model and compared with values obtained experimentally. All the results show that the dipole moment of compound 1 in the excited state is higher than that in the ground state. These methods quite well predict the values of Deltamicro between two states of an investigated compound.     

Excited-state dipole moments of some hydroxycoumarin dyes using an efficient solvatochromic method based on the solvent polarity parameter, EN(T)

Excited-state dipole moments of some hydroxycoumarins, extensively used as laser dyes, have been determined using the solvatochromic method based on the microscopic solvent polarity parameter EN(T). Agreement between experimental and Austin model 1 (AM 1) calculated dipole moment changes has been found to be close in most of the cases. Our results are expected to be quite reliable in view of the fact that the correlation of the solvatochromic Stokes shifts is superior to that obtained using bulk solvent polarity functions. The dipole moments in the excited state, for all the molecules investigated, are higher than the corresponding values in the ground state. The increase in dipole moment upon excitation has been explained in terms of the nature of emitting state and resonance structure.     

The study of dipole moment of some substituted acetic acids in an electronically excited state

The electronic absorption spectra of eight substituted acetic acids have been measured at room temperature in several solvents. The ground state dipole moments are evaluated experimentally for these molecules. These ground state values are used in conjunction with the spectral results to evaluate their first electronically excited state dipole moments. For all the molecules investigated here the dipole moments in the excited state are higher than their ground state values.     

Bischromophoric styrylpyridinium dyes. Spectroscopic properties of 1,3-bis-[4-(p-N,N-dialkylaminostyryl)pyridinyl]propane dibromides

The photophysical properties of newly synthesized bischromophoric solvatochromic stilbazolium dyes, 1,3-bis-[4-(p-N,N-dialkylaminostyryl)pyridinyl]propane dibromides (C1-C9), were studied in a series of solvents and their spectroscopic properties were compared with structurally related, monochromophoric styrylpyridinium dyes (SP1-SP9). The position of the UV-vis absorption spectra maximum of novel dyes is only slightly solvent polarity dependent in contrast to the fluorescence spectra that show pronounced solvatochromic effect demonstrated by a large Stokes shifts. 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 used for the evaluation of their excited state dipole moments. The ground state dipole moments of both mono- and bischromophoric dyes were established by applying ab initio calculations. The calculations and measurements unexpectedly show that the bischromophoric dyes are characterized by ground state dipole moments being equal to about half of that characterizing their monomeric equivalents, while the excited state dipole moments of bischromophoric dyes are about 10-25% higher in comparison to their monomeric equivalents.     

Dipole moments studies of fluorenone and 4-hydroxyfluorenone

Electronic absorption, excitation and fluorescence spectra of fluorenone and 4-hydroxyfluorenone were recorded at room temperature in several aprotic solvent of varying polarities. The ground (mu(g)) and excited (mu(e)) state dipole moments of both molecules were estimated from solvatochromic shifts of absorption and fluorescence spectra as a function of the dielectric constant (epsilon) and refractive index (n). These experimental results were completed with theoretical results of quantum chemical calculations (AM1). The experimental and theoretical dipole moments in the ground state were compared. It was determined that dipole moments of excited state were higher than those of the ground state for both molecules.     

Determination of the ground state,excited state and change in dipole moments of magnesium and zinc chlorin

High-resolution Stark effect measurements on the S1 <-- S0 (pi pi*) origin of magnesium chlorin (MgCh) and zinc chlorin (ZnCh) in single crystals of n-octane at 4.2 K are reported. The corresponding change in dipole moment (absolute value(delta mu(ge))) associated with each transition was estimated to be 0.23 +/- 0.04 and 0.27 +/- 0.05 debye, respectively. Each molecule's orientation in the n-octane crystal was also determined. The change in dipole moment of MgCh was also found using solvatochromic shift data (absolute value(delta mu(ge))) = 0.33 +/- 0.08 debye). The ground state dipole moment (mu(g)) of MgCh was determined by dielectric constant measurement of MgCh/benzene solutions (mu(g) = 2.26 +/- 0.08 debye). These were combined to calculate the average excited state dipole moment of MgCh (mu(e) = 2.51 +/- 0.08 debye). The ground state dipole moment of ZnCh was also determined using solvatochromic shift data (mu(g) = 3.17 +/- 0.08 debye). This was combined with its measured absolute value(delta mu(ge)) to calculate the excited state dipole moment of ZnCh (mu(e) = 3.44 +/- 0.08 debye); the S1 <-- S0 (pi pi*) origin band of both complexes was red-shifted at room temperature as the polarity of the solvents was increased, which implies that delta mu(ge) is positive.     

Bichromophoric hemicyanine dyes as fluorescence probes applied for monitoring of the photochemically initiated polymerization

The spectroscopic properties of series homodimmeric hemicyanine dyes based on (p-N,N-dimethylaminostyryl)benzothiazolium, (p-N,N-dimethylaminostyryl)benzoxazolium, (p-N,N-dimethylaminostyryl)-2,3,3-trimethyl-3H-indolium residues were determined. The absorption and fluorescence spectra of the dyes under study were measured in different polarity solvents at room temperature. On the basis of the solvatochromic behavior the ground state (μ_g) and excited state (μ_e) dipole moments of bis-(N,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 dielectric constant (ε) and refractive index (n) of applied solvents. The absorption and fluorescence spectra are only slightly affected by the solvent polarity. The analysis of solvatochromic behavior of the fluorescence spectra as a function of Δf (ε, n) revealed that the emission occurs from a high polarity excited state. The large dipole moment changes along with the red-shifted fluorescence, as the solvent polarity is increased, demonstrates the formation of an intramolecular charge transfer state (ICT). Six bichromophoric hemicyanine dyes, possessing benzothiazole, benzoxazole or indolinium group linked by 5 or 10 methylene groups were evaluated as fluorescence probes applied for monitoring of the polymerization process. The study on the changes in fluorescence intensity and spectroscopic shift of studied compounds were carried out during photochemically initiated polymerization of 2-ethyl-2-(hydroxymethyl)-propane-1,3-diol triacrylate (TMPTA).     

Experimental measurement of the induced dipole moment of an isolated molecule in its ground and electronically excited states: indole and indole-H2O

Reported here are measurements of the magnitude and orientation of the induced dipole moment that is produced when an indole molecule in its ground S(0) and electronically excited S(1) states is polarized by the attachment of a hydrogen bonded water molecule in the gas phase complex indole-H(2)O. For the complex, we find the permanent dipole moment values mu(IW)(S(0)) = 4.4 D and mu(IW)(S(1)) = 4.0 D, values that are substantially different from calculated values based on vector sums of the dipole moments of the component parts. From this result, we derive the induced dipole moment values mu(I) (*)(S(0)) = 0.7 D and mu(I) (*)(S(1)) = 0.5 D. The orientation of the induced moment also is significantly different in the two electronic states. These results are quantitatively reproduced by a purely electrostatic calculation based on ab initio values of multipole moments.     

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.     

Solvatochromic behavior on the absorption and fluorescence spectra of Rose Bengal dye in various solvents

The absorption and fluorescence spectra of Rose Bengal dye were studied in various solvents. It was found that solvent effects on the absorption wavelength are consistent with the solvatochromic model of Kamlet, Abboud and Taft. The solvent polarizability value pi* was found to have a linear relationship with the absorption wavelength of the dye in various solvents. Additionally, the normalized transition energy value (E(T)(N)) showed some scattering when plotted versus Deltanu(af). Density functional calculations were used to assign the absorption in the region 540-570 nm to a pi-pi* transition between the HOMO and LUMO of the anion. Experimental ground state and excited state dipole moments were calculated by using the solvatochromatic shifts of absorption and fluorescence spectra as a function of the dielectric constant (epsilon) and refractive index (n). The dipole moment for Rose Bengal was found to be 1.72 Debye in the ground state, whereas this value was 2.33 Debye in the excited state.     

Solvatochromism of a novel betaine dye derived from purine

A novel solvatochromic betaine dye has been synthesized from xanthosine and characterized spectroscopically by UV-vis in a broad range of solvents. The dye 9-(2',3',5'-tri-O-acetyl-beta-d-ribofuranosyl)-2-(pyridinium-1-yl)-9H-purin-6-olate, 1a, exhibits solvent-induced spectral band shifts that are (2)/(3) as large as that of the betaine known as Reichardt's dye, which forms the basis of the E(T)(30) solvent polarity scale. Moreover, the dye 1a is a ribonucleoside and hence has the potential application as a polarity probe for application in RNA oligonucleotides. The isomeric dye 6-(pyridinium-1)-yl-9H-purin-2-olate, 2a, has also been synthesized and exhibits slightly smaller solvatochromic band shifts. The new betaine dyes have also been studied by comparing the experimental and calculated solvatochromic shifts based on the calculation of the UV/vis absorption spectra, using a combination of methods with density functional theory (DFT). The COSMO continuum dielectric method, an applied electric field term in the Hamiltonian, and time-dependent density functional theory (TD-DFT) methods were used to obtain absorption energies, ground-state dipole moments, and the difference dipole moment between the ground and excited states. The calculations predict a lower energy absorption band of charge-transfer character that is highly solvatochromic, and a higher energy absorption band that has pi-pi character which is not solvatochromic, in agreement with the experimental data. For Reichardt's dye the difference dipole moment between the ground and excited state (Deltamu = mu(e) - mu(g)) was also calculated and compared to experiment: Deltamu(calcd) = -6 D and Deltamu(exptl) = -9 +/- 1 D.(1) The ground-state dipole moment was found to be mu(g)(calcd) = 18 D and mu(g)(exptl) = 14.8 +/- 1.2 D.(1).