Solvent Effects on the Absorption and Emission Spectra of the 5ABBM molecule

doi:10.21203/rs.3.rs-4084695/v1

The solvent effects on the absorption and emission spectra and dipole moments of the 5ABBM molecule have been extensively studied in a series of solvents. The dipole moments in the excited state are observed to be greater than their ground-state counterparts in all the solvents studied for the chosen molecule. The dipole moment increase in the excited singlet state ranges from 2.42 to 24.14 D. The various methods for a correct prediction of solvatochromic shifts are recalled with reference to previous conflicting theoretical interpretations using Lippert’s, Bakhshiev's, and Kawski-Chamma-Viallet’s equations. Experimentally calculated ground state and excited state dipole moments were calculated using the solvatochromatic shifts of absorption and emission spectra as a function of the dielectric constant (ɛ) and refractive index (n). These data are used to estimate the excited-state dipole moment using an experimentally determined ground-state dipole moment. A series of fifteen different organic solvents (toluene, methanol, n-butyl alcohol, ethyl acetate, DMS, acetonitril, benzene, isopropyl alcohol, water, DMF, DCM, DIO, THF, ethanol, and octonol) were investigated at constant dye concentrations. Small changes in the fluorescence spectrum were observed for the different solvents; the highest fluorescence intensity was observed for DMS and the lowest for water. The stokes shift in different solvents was studied for the 5ABBM molecule. This results in the molecule being more polar in the excited state than in the ground state for the used solvents. The ground statedipole moments, HOMO-LUMO, and molecule electrostatic potential map were also computed using ab initio calculations and evaluated using Gaussian 09 W software.

Absorption

dipole moments

fluorescence

Solvatochromic shift

Spectroscopic studies of organic dyes have created greater interest in their industrial applications. The characteristic behaviour of the dyes in various solvents reveals changes in the dipole moment and other roperties [1–4]. Researchers have shown huge attention to spectroscopic studies of various molecules for vast applications. The orientation of molecules in liquids provides insight to researchers studying solute-solvent interactions. Various molecules have been reported so far using photophysical properties [2, 5, 10]. Quantum calculations of molecules are assumed implicitly to be isolated, as if they were in the gas phase at comparatively low pressure [9, 11–13]. molecules in condensed phases, liquids, viscous liquids, and solids; the effect of these media on the absolute and relative energies of electronic states of solute molecules is, therefore, of considerable importance in photophysics and photochemistry. Molecular rotation in a liquid experiences friction due to its size, chemical property, viscosity, volume, etc. [14, 15]. The reorientation time of a solute in solvents is determined by diffusion-based theories.

The dipole moments of electronically excited species are often useful in the design of non-linear optical materials and in the elucidation of the nature of the excited states [3, 16, 17]. Obtained data on excited states is also useful in the parametrization of semi-empirical quantum chemical procedures for these states [18]. There are different methods to determine the excited state dipole moment, but the solvatochromic method is one of the most widely used [4, 17, 19, 20]. The solvatochromic method is experimentally much simpler and widely accepted [1, 3, 7, 21, 23]. It depends on the linear correlation between the wave numbers of the absorption and emission maxima and the polarity function of the solvent, which includes the relative permittivity (εr) and refractive index (n) of the medium [6, 24]. However, the linear correlation between the wavenumbers of absorption and fluorescence maxima as a function of solvent polarity was investigated. These correlations have been derived from quantum mechanical second-order perturbation and Onsager’s reaction field theories for the development of solvent polarity functions [4, 6, 10, 16, 17, 25, 26]. The Bakhshiev, Lippert-Mataga, and Kawski-Chamma functions are frequently used solvent polar functions in spectroscopic studies of dyes and reveal both an individual's dielectric constant (ε) and its refractive index (n) [1, 2, 4, 7, 23, 27]. Different techniques have been employed for experimental and theoretical studies on the ground state (µ_g) and excited state (µ_e) dipole moments of organic dyes [1, 3, 7, 21, 22, 28, 29]. In this respect, fluorescence analysis is often more informative than absorption since it is related to the energy of a relaxed, excited state [8, 30–33]. The ground and excited dipole moments of the 5ABBM molecule are estimated by analysing the impact of the solvent on its absorption and emission spectra. Geometry optimisation is an important aspect of studying the polarizibility and stability of molecules [30, 32, 34]. The experimental method to study the environmental effects is necessary, whereas a calculation gives the µ_gvalue only for a molecule in the gas phase and provides the symmetrical-asymmetrical structure of the molecule.

The solvent effects on the absorption and emission analysis provide useful results on physical properties such as dipole moment changes, polarizability of the molecule in the ground, and excited state. The excitation of an electron is raised to a new electronic level and is excited in much less time than it takes the whole molecule to rearrange itself with the solvent environment. In excited states, the molecule is in the same structural environment in the excited state as in the ground state. The absorption and emission spectra of the solute show variation in their chemical properties. The solvatochromism of fluorophores is usually analysed using the linear correlations of Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet, and Reichardt [1, 2, 4, 6, 7, 27, 35]. According to Lippert-Mataga,Stokes shift ($\varDelta \stackrel{-}{v}={\overline{\nu }}_{A}-{\overline{\nu }}_{F}$) of solute molecule is related to the permittivity (${\epsilon }$) and refractive index ($n$) of solvent as,

$${\overline{\nu }}_{A}-{\overline{\nu }}_{F}={m}_{1}{F}_{1}\left(\epsilon , n\right)+\text{c}\text{o}\text{n}\text{s}\text{t}\text{a}\text{n}\text{t}$$

1

Where, ${\overline{\nu }}_{A}$ and ${\overline{\nu }}_{F}$ are the absorption and fluorescence emission maxima wave numbers (cm⁻¹), ${F}_{1}\left(\epsilon ,n\right)$is the Lippert solvent polarity function (Eq. 2), and standard equation is given by

$$F\left(\epsilon ,n\right)=\frac{\epsilon -1}{2\epsilon +1}-\frac{{n}^{2}-1}{2{n}^{2}+1}$$

$${ F}_{1}\left(\epsilon ,n\right)=\frac{2{n}^{2}+1}{{n}^{2}+2}\left[\frac{\epsilon -1}{\epsilon +2}-\frac{{n}^{2}-1}{{n}^{2}+2}\right]$$

2

${m}_{1}={2\left({\mu }_{e}-{\mu }_{g}\right)}^{2}/hc{a}^{3}$ , ${\mu }_{e}$ and ${\mu }_{g}$ are the dipole moments of ground and excited state $a$ is the Onsager cavity radius of solute molecule, respectively that can be calculated using Eq. (3).

$$a= {\left(\frac{3M}{4\pi \delta {N}_{A}}\right)}^{1/3}$$

3

Here, $M$ and $\delta$ are the molecular weight and density, respectively.

Bakhshiev equation (Eq. 4) gives the dependency of the Stokes shift of solute on $\epsilon$ and $n$ of solvent as,

$${\overline{\nu }}_{A}-{\overline{\nu }}_{F}={m}_{2}{F}_{2}\left(\epsilon , n\right)+\text{c}\text{o}\text{n}\text{s}\text{t}\text{a}\text{n}\text{t}$$

4

Where, ${m}_{2}={2\left({\mu }_{e}-{\mu }_{g}\right)}^{2}/hc{a}^{3}$ and ${ F}_{2}\left(\epsilon ,n\right)$is the Bakhshiev solvent polarity function (Eq. 5),

$${ F}_{2}\left(\epsilon ,n\right)=\frac{2{n}^{2}+1}{{2(n}^{2}+2)}\left(\frac{\epsilon -1}{\epsilon +2}-\frac{{n}^{2}-1}{{n}^{2}+2}\right)+\frac{{3(n}^{4}-1)}{{2\left({n}^{2}-1\right)}^{2}}$$

5

The equation Kawski-Chamma-Viallet gives the average of absorption and emission maximum of solute with $\epsilon$ and $n$ of solvent as,

$$\frac{{\overline{\nu }}_{A} + {\overline{\nu }}_{F}}{2}=-{{m}_{3}F}_{3}\left(\epsilon , n\right)+\text{c}\text{o}\text{n}\text{s}\text{t}\text{a}\text{n}\text{t}$$

6

Where, ${m}_{3}=2\left({{\mu }_{e}}^{2}-{{\mu }_{g}}^{2}\right)/hc{a}^{3}$and${ F}_{3}\left(\epsilon ,n\right)$ is the Kawski-Chamma-Viallet solvent polarity function as given in Eq. (7),

$${ F}_{3}\left(\epsilon ,n\right)=\frac{2(\epsilon -1)}{\epsilon +2}$$

7

${ F}_{4}\left(\epsilon \right)$ is the Suppan’s polarity parameter and given in Eq. (8)

$${ F}_{4}\left(\epsilon ,n\right)=\frac{2(\epsilon -1)}{2\epsilon +2}$$

8

The computed values of${ F}_{1}\left(\epsilon ,n\right)$,${ F}_{2}\left(\epsilon ,n\right)$,${ F}_{3}\left(\epsilon ,n\right)$and ${F}_{4}\left(\epsilon ,n\right)$ along with the values of ${E}_{T}^{N}$are given in Table.1.

Considering stable symmetry of molecule upon excitation and parallel orientation of the dipole moments, ${\mu }_{g}$,${\mu }_{e}$, and ${\mu }_{e}$/${\mu }_{g}$ can be calculated from the slopes (m₂ and m₃) of the plots of ${\overline{\nu }}_{A}-{\overline{\nu }}_{F}$versus ${ F}_{2}\left(\epsilon ,n\right)$and ${(\overline{\nu }}_{A}+ {\overline{\nu }}_{F})/2$ versus${ F}_{3}\left(\epsilon ,n\right)$as,

$${\mu }_{g}=\frac{{m}_{3}-{m}_{2}}{2}{\left(\frac{hc{a}^{3}}{2{m}_{2}}\right)}^{1/2}$$

9

$${\mu }_{e}=\frac{{m}_{3}+{m}_{2}}{2}{\left(\frac{hc{a}^{3}}{2{m}_{2}}\right)}^{1/2}$$

10

$$\frac{{\mu }_{e}}{{\mu }_{g}}=\frac{{{m}_{2}+m}_{3}}{{m}_{3}-{m}_{2}}\text{F}\text{o}\text{r}{{m}_{3}>m}_{2}$$

11

If ${\mu }_{g}$ and ${\mu }_{e}$ subtend an angle,$\varphi$

$$cos\varphi =\frac{1}{2{\mu }_{g}{\mu }_{e}}\left[\left({\mu }_{g}^{2}+{\mu }_{e}^{2}\right)-\frac{{m}_{2}}{{m}_{3}}\left({\mu }_{e}^{2}-{\mu }_{g}^{2}\right)\right]$$

12

${\mu }_{e}$ can also be determined using the empirical relation,

$${\overline{\nu }}_{A}-{\overline{\nu }}_{F}=11307.6 {\left(\frac{\varDelta \mu }{\varDelta {\mu }_{B}}\right)}^{2}{\left(\frac{{a}_{B}}{a}\right)}^{3}{E}_{T}^{N}+constant$$

13

Where, (${E}_{T}^{N}$) is themicroscopic solvent polarity function, $\varDelta \mu$ and $\varDelta {\mu }_{B}$ are the changes in the dipole moments of sample and reference (Betaine dye) molecules on excitation. ${a}_{B}$mentiontheOnsager cavity radius of reference molecule. Where $\varDelta \mu$can be determined using the slope of ${\overline{\nu }}_{A}-{\overline{\nu }}_{F}$ versus ${E}_{T}^{N}$ plot and the reported values of $\varDelta {\mu }_{B}$ and ${a}_{B}$ (9 D and 6.2 Å, respectively) for 5ABBM dye. Further, using $\varDelta \mu$ and ${\mu }_{g}$ from Eq. (9), ${\mu }_{e}$ can be determined. Eq. (13), which accounts for more intermolecular interactions, better correlates the Stokes shift and solvent polarity function than the other relations.

The [5-amino-1-(bromomethyl)indolizin-3-yl](4-bromophenyl)methanone (5ABBM) was synthesized using standard method.. The solvents used in the present study namely water, dimethyl formamide (dmf), acetonitrile, ethyl acetate, toluene, 1–4 dioxane etc. purchased from S-D FINE Chemicals Ltd., India and of spectroscopic quality.The molecular structure of molecule is shown in Fig. 1.

5ABBM absorption spectra were captured on a Hitachi UH5300 UV/VIS(all wavelengths 200-700nm700 nm) spectrophotometer, and fluorescence spectral photometer was recorded on the Hitachi F-7000 FL (All Frequency of biological absorbance) Room temperature was used for all of these measurements. The uncertainty in the measured wavelength of absorption and emission maxima is ± 1 nm. The concentrations of all organic solvents were chosen to be 1×10^− 5 M. Every time fresh homogeneous solutions were prepared to record both absorption and fluorescence spectra.The absorption and fluorescence spectra of 5ABBM have a considerable vibrational structure and have a mirrorimage relation.

Solvent effect on Absorption and emission Spectra:

The absorption and emission spectra of 5ABBM in differentsolvents are recorded.The solvent polarity functions F(ε,n), F₁(ε,n), F₂(ε,n),F₃(ε), F₄(ε) werecalculated using Eq. (2), (5), (7) and (8) respectively for series of different solvents of various polarities (given inTable.1)[25, 31, 32, 36].

Table.1. Calculated values ofF (ε,n), F ₁ (ε,n), F ₂ (ε,n),F ₃ (ε), F ₄ (ε)for various solvents.

Solvent	F(ε,n)	F₁(ε,n)	F₂(ε,n)	F₃(ε)	F₄(ε)
TOLUENE	0.013	0.029	0.349	0.630	0.479
METHANOL	0.309	0.857	0.652	1.831	0.956
N BUTYL ALCOHOL	0.263	0.749	0.646	1.690	0.916
ETHYL ACETATE	0.200	0.492	0.499	1.257	0.772
DMS	0.263	0.841	0.744	1.878	0.968
ACETONITRIL	0.304	0.861	0.664	1.844	0.959
BENZENE	0.003	0.007	0.340	0.598	0.460
ISOPROPYL ALCOHOL	0.276	0.780	0.646	1.729	0.927
WATER	0.320	0.913	0.683	1.927	0.981
DMF	0.275	0.839	0.711	1.850	0.961
DCM	0.216	0.589	0.582	1.449	0.840
DIO	0.029	0.061	0.316	0.604	0.464
THF	0.209	0.547	0.548	1.368	0.812
ETHANOL	0.288	0.811	0.651	1.771	0.939
OCTONOL	0.225	0.626	0.604	1.512	0.861

The numerical value of solubility parameter indicates the relative solvency behaviour of a specific solvent. The cohesive energy density of the solvent, which in turn is derived from the heat of vaporization.The solubility is that which the molecules or a material dissolves. In other words, polar solvents dissolve polar materials, and non-polar solvents dissolve non-polar materials.The solvent parameters respect to fluorophore 5ABBM in series of solvents with dielectric constant (ε), refractive index (n) and ${\varvec{E}}_{\varvec{T}}^{\varvec{N}}$is shown in Table.2.

Table.2.Solvent parameters in series of solvents

Solvent	DielectricConstant(ε)	Refractive index(n)	${\varvec{E}}_{\varvec{T}}^{\varvec{N}}$
TOLUENE	2.38	1.497	0.099
METHANOL	33.7	1.329	0.762
N BUTYL ALCOHOL	17.4	1.399	0.586
ETHYL ACETATE	6.08	1.372	0.228
DMS	47.2	1.479	0.444
ACETONITRIL	36.64	1.344	0.46
BENZENE	2.28	1.499	0.111
ISOPROPYL ALCOHOL	20.2	1.377	0.617
WATER	80.4	1.333	1
DMF	38.25	1.430	0.386
DCM	8.9	1.424	0.321
DIO	2.3	1.421	0.164
THF	7.5	1.404	0.207
ETHANOL	24.3	1.361	0.654
OCTONOL	10.3	1.429	0.537

The electronic absorption and fluorescence spectra of 5ABBMwere recorded in different solventswith variation in polarities in specific concentration. The solvent parameters like polarity, dielectric constant and polarizability play an important role to in inducing changes in intensity, position and size of absorption and fluorescence spectra.

From Fig. 2shows that fluorescence maxima of the fluorophore show bathochromic shift of 365 nm to 385 nm for 5ABBM and the charge distribution in the excited state may be are influenced by the interactions between solutes and solvents.However, the absorption transition is dominated by the emission transition, which means that this increases the excited state's dipole moment. In addition, the changes in the fine spectral band and the Stokes shifts indicate the intramolecular charge transfer (ICT) caused by the π → π* transition of singlets in the excited state.Value of absorption maximum ($\overline{\varvec{\upsilon }}$_a), fluorescence emission maximum ($\overline{\varvec{\upsilon }}$_f) and Stokes shift (Δ$\overline{\varvec{\upsilon }}$) determined from absorption and emission spectra.(Table.3).

Table.3. Absorptionmaxima,FluorescencemaximaandStokesShiftsfor5ABBM

Solvent	AbsorptionMaximum ($\overline{\varvec{\upsilon }}$_a) (nm)	FluorescenceMaximum ($\overline{\varvec{\upsilon }}$_f) (nm)	StokesShift (Δ$\overline{\varvec{\upsilon }}$)(cm^− 1)
TOLUENE	240	384	15638
METHANOL	250	376	13404
N BUTYL ALCOHOL	215	376	19944
ETHYL ACETATE	238	380	15701
DMS	240	384	15679
ACETONITRIL	254	380	13095
BENZENE	240	383	15570
ISOPROPYL ALCOHOL	250	381	13753
WATER	264	374	11197
DMF	240	381	15461
DCM	260	379	12090
DIO	225	365	17107
THF	250	381	13753
ETHANOL	250	376	13418
OCTONOL	240	377	15155

The excited state dipole moments of the synthesized compounds were determined by correlating their spectroscopic properties with Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet and Reichardt. The solvatochromic plots for 5ABBM are presented in Fig. 3 and Fig. 4 and the slopes, intercepts and correlation coefficients are given in Table.4.

Table.4.Slope,Interceptandcorrelationcoefficientdata’sof 5ABBM

Method	Slope	Intercept	Correlationcoefficient	No.ofdata
Lippert’s	69286	-2653	0.95	6
Bakhshiev’s	21184	250.41	0.97	6
KawskiChammaViallet’s	-9337	39311	0.95	9
${\varvec{E}}_{\varvec{T}}^{\varvec{N}}$	3081	11418	0.85	6

The ground state (µ_g), excited state (µ_e), the ratio of the excited to ground state dipole moment (µ_e/µ_g) and the change in dipole moments (Δµ) of the 5ABBM is determined using the from various methods and are given in Tables.5 and 3. The significant difference between the ground and excited state dipole moment of the fluorophore indicates that the significant charge distribution in the single excited state is due to an internal charge transfer process. Table 2 shows that the dipole moment of the excited state is greater than that of the ground state, indicating the synthesized compounds are more polar in the excited state and also more sensitive to solvents. The variation of the dipole moment of the excited state obtained by different solvatochromic methods is due to the different assumptions of the methods. The Lippert technique, does not consider polarizability, gives the highest value of µe, and the solvent polarity parameter method, which takes into account certain solvent-solvent interactions, gives the lowest value[27]. 5ABBM is also found to be more sensitive to the solvent environment. The angle between the dipoles in Table 3 shows that µe and µg are parallel and the electronic transition does not affect the molecular symmetry..

Table.5Ground-state,ExcitedstateDipolemomentof 5ABBM

Molecule

OnsagerCavity

radius‘a’(Å)

µga

(D)

µeb

(D)

µec

(D)

µed

(D)

µee

(D)

µef

(D)

µ_e/µg^g

Φ^h

TP 3

3.9977

3.23

8.33

24.14

14.8

10.91

2.42

2.57

0

Debye (D) = 3.33564X10-30cm = 10–18 esu cm

^aGroundstatedipolemomentcalculatedfromEquation8

^bExcitedstatedipolemomentcalculatedfromEquation 9

^cExcitedstatedipolemomentcalculatedfromLippert’sEquation

^dExcitedstatedipolemomentcalculatedfromBakshievEquation

^eExcitedstatedipolemomentcalculatedfromKawaski-Chamma-Viallet equation

^fExcitedstatedipolemomentcalculatedfrommicroscopicsolventpolarityfunction E_T^N

^gRatioofexcitedtogroundstatedipolemoment

^hAnglebetweenexcitedstatetogroundstatedipolemomentwithsolvatochromic

The ground state dipole moment of 5ABBM was obtained using quantum chemical calculation following geometry optimization Table.6. The assumption that molecules are in gas phase and does not include solvent interactions calculated. This could be due to the overestimation by quantum chemical method, in which solvent interactions are neglected. Thestokes shift, arithmetic mean of stokes values of 5ABBM in series of solvents is provided in Table.4.This indicates that Stokes' shift value increases with increase in solvent polarity. The values of Stokes shift indicates a higher amount of interaction between solute and solvent in the excited state. Resulting pointing out that solute-solvent interaction in the excited state is differentfrom that of the ground state, which may increase the excited state dipole moment.

Table.4StokesShift,arithmeticmeanofStokesvaluesof 5ABBM

Solvent	$\overline{\varvec{\upsilon }}$_a	$\overline{\varvec{\upsilon }}$_f	$\overline{\varvec{\upsilon }}\mathbf{a}-\overline{\varvec{\upsilon }}\mathbf{f}$	$(\overline{\varvec{\upsilon }}\mathbf{a}-\overline{\varvec{\upsilon }}\mathbf{f})/2$
TOLUENE	41666	26028	15638	33847
METHANOL	40000	26595	13404	33297
N BUTYL ALCOHOL	46511	26567	19944	36539
ETHYL ACETATE	42016	26315	15701	34166
DMS	41666	25987	15679	33827
ACETONITRIL	39370	26274	13095	32822
BENZENE	41666	26096	15570	33881
ISOPROPYL ALCOHOL	40000	26246	13753	33123
WATER	37878	26680	11197	32279
DMF	41666	26205	15461	33936
DCM	38461	26371	12090	32416
DIO	44444	27337	17107	35890
THF	40000	26246	13753	33123
ETHANOL	40000	26581	13418	33290
OCTONOL	41666	26511	15155	34088

Analysis of Global Chemical Reactivity Descriptor (GCRD) Parameters:

The geometry optimisation has been carried out in vacuum using a semi-empirical method for the PM6 basis set on an Intel i7/2.11GHz personal computer using the Gaussian 09 W program package[4]. The optimised geometry of the title molecule and the optimised ground-state molecular geometry are shown in Fig. 5. The theoretical ground state dipole moment is 3.02 D using Gaussian software in the gas phase, and the experimental ground state dipole moment is estimated from the solvatochromic shift method. There exists a slight discrepancy between the theoretical value and the experimental value of the ground-state dipole moments. Here we observed from Fig. 1 that the 5ABBM molecule looks symmetrical (in two- dimensions), and in Fig. 5, the three-dimensional structure shows asymmetry. The variation in values may be attributed to variations in the experimental and theoretical values of the dipole moments [6, 7, 23, 26, and 30]. A measurement of the solute molecule's radius is necessary for the ground-state dipole moment to differ. As compared to experimental and theoretical values obtained from ab initio calculations, they are based on the gaseous phase.

The reason may be that the experimental method considers solvent and environmental effects, while ab initio calculations only give a value of µ_g for the gas phase molecule. The HOMO-LUMO values were found to be -8.404 and − 1.089, respectively, with the ΔE value being − 7.315. The negative chemical potential of HOMO-LUMO shows that the molecule 5ABBM is highly stable. This shows optimization in the geometrical structure of 5ABBM with the GCRD parameter Table 5 [7, 37]. This shows a wider gap in HOMO-LUMO with stability and hardness, which signifies a more reactive soft molecule with high polarization [4, 6, 7, 34, 38].

Table.5: Global Chemical Reactivity Descriptor (GCRD) Parameter

E_HOMO eV

E_LUMOeV

Ionisation Potential I eV

Electron affinity

A eV

Electronegativity

χ eV

Chemical hardness

η eV

Chemical potential

µ eV

Chemical softness

S eV

Electrophilici index ω eV

-8.404

-1.089

8.404

1.089

4.746

3.657

-4.746

0.136

3.080

The calculated GCRD parameters such as E_HOMO, E_LUMO, ionisation potential (I), electron affinity (A), electronegativity (χ), chemical hardness (η), chemical potential (µ), chemical softness (σ), and electrophilic index (ω) predict the material having good chemical strength and kinetic stability. Hence, it favours the suitability of the material for optoelectronic applications. The electrophilic index is an indicator of the ability of a molecule to add electron density and is found to be 3.080 eV. The literature did not present any additional experimental data on µ_g for comparison purposes.

We studied the spectroscopic behaviour of 5ABBM. It was found that the dipole moment (µ_e) of the excited state is greater than the dipole moment (µg) of the ground state of the molecule. The dipole moment increase in the excited singlet state ranges from 2.42 to 24.14 D. In the excited state of each studied solvent, the molecule is more polar than in the ground. It is noticeable that there is a difference between the dipole moments of the ground state and the excited state, as estimated by Eqs. (8) and (9). It should be emphasized that the observed differences may arise from the approximations made by both methods to estimate the dipole moments of the ground state and excited singlet state of the title molecule. Also, Eq. (13) can be used to estimate the value of the dipole moment of the excited state, knowing the value of the dipole moment of the ground state without the need to know the radius of the solute. The ground and excited state dipole moments are parallel to each other and bounded by an angle of 0⁰. The geometry optimisation has been carried out in vacuum using the semi-empirical method. The experimental method takes solvent and environmental effects into account, whereas ab initio a calculation gives µ_g value only for molecules in the gas phase and finds the asymmetrical structure.

Acknowledgement:

D.S. Lalasangi is thankful to the Principal, Government First Grade College, Dharwad, and Commissioner, Department of Collegiate and Technical Education, Government of Karnataka, Bengaluru, for providing anopportunity to carry out research.

Ethical Approval: Not applicable.

Competing Interests: Declared that no competing Interest.

Author’s contribution:

Dayanand Lalasangi : Conceptualization; Data curation; Formal analysis; Investigation; Methodology; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; Writing - review & editing.

Dr. S.M. Hanagodimath : Conceptualization; Data curation; Formal analysis; Investigation; Methodology; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; Writing - review & editing.

Tairabi Khanadal : Provided synthesized organic dyes

Dr.Basavaraj Padmasshali: Provided synthesized organic dyes

Dr. Mangeh Jadav : Resources; Software; Validation; Visualization; Roles/Writing

Original draft; Writing - review & editing

Funding: Not applicable

Availability of data and materials: All data can be accessed.

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No competing interests reported.

Solvent Effects on the Absorption and Emission Spectra of the 5ABBM molecule

Status:

Journal Publication

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Abstract

Figures

Introduction

Theory

Materials and Methods

Results and discussion

Solvent effect on Absorption and emission Spectra:

Analysis of Global Chemical Reactivity Descriptor (GCRD) Parameters:

Conclusions

Declarations

References

Additional Declarations

Status:

Journal Publication

Version 1