Photophysical properties of 3MPBA: Evaluation and co-relation between solvatochromism and quantum yield in different solvents

    Photophysical properties of 3MPBA: Evaluation and co-relation between solvatochromism and quantum yield in different solvents G.V. Muddapur, R.M. Melavanki, P.G. Patil, D. Nagaraja, N.R. Patil PII: DOI: Reference:

S0167-7322(16)32269-3 doi:10.1016/j.molliq.2016.09.102 MOLLIQ 6380

To appear in:

Journal of Molecular Liquids

Received date: Revised date: Accepted date:

15 August 2016 25 September 2016 27 September 2016

Please cite this article as: G.V. Muddapur, R.M. Melavanki, P.G. Patil, D. Nagaraja, N.R. Patil, Photophysical properties of 3MPBA: Evaluation and co-relation between solvatochromism and quantum yield in different solvents, Journal of Molecular Liquids (2016), doi:10.1016/j.molliq.2016.09.102

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ACCEPTED MANUSCRIPT “Photophysical properties of 3MPBA: Evaluation and co-relation between solvatochromism and quantum yield in different solvents” G.V. Muddapur a, R.M. Melavankib*, P.G. Patilc, D. Nagarajad and N.R. Patil a*

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Department of Physics, B V B College of Engineering and Technology, Hubli 580031, Karnataka, India b Department of Physics, M S Ramaiah Institute of Technology, Bangalore 560054, Karnataka, India c Department of Physics, S.K. Arts and H.S. Kotambri Science Institute Hubli 580031, Karnataka, India d Department of Physics, Bangalore Institute of Technology, Bangalore 560004, Karnataka, India

ABSTRACT:

The present paper addresses the photophysical properties of 3-Methoxyphenyl boronic acid

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(3MPBA) by using solvatochromic shift and quantum chemical methods. The absorption and

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fluorescence spectra of newly synthesized aryl boronic acid derivative (3MPBA) have been recorded in various solvents of different polarities. The dipole moments were estimated using

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quantum chemical calculations and Solvatochromic correlations. It is observed that the

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excited state dipole moments (µe) are greater than the ground state dipole moment (µg) which confirms ππ* transition. And it is also observed that the ground state and excited state

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dipole moments are observed to be collinear to each other. The changes in dipole moment (Δµ) were also calculated both from solvatochromic shift method and microscopic solvent polarity parameter (

) and values are compared. The spectral variations were also analyzed

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by Kamlet-Taft parameters. It is found that HBA () influence is more than HBD () for  a and  f in alcohols whereas HBD () influence is more than HBA () for  a and f in non alcohols. Further, the relative quantum yield ( ), radiative and non-radiative decay constants

 Corresponding authors: Dr. N.R. Patil, Associate Professor, Dept. of Physics, B.V. Bhoomaraddi College of Engg. & Tech., Hubli-580031, Karnataka, India. Mob:+91-9902351732, e-mail: [email protected]. Dr. R.M. Melavanki, Assistant Professor, Dept. of Physics, M S Ramaiah Institute of Technology, Bangalore 560054, Karnataka, India Mob:+91- 8951478172, e-mail: [email protected],

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ACCEPTED MANUSCRIPT are estimated by single point technique which concludes that the 3MPBA is more radiative in nature and less intersystem crossing and inter conversions are observed in the excited state.

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Key words: solvatochromic shift, dipole moments, DFT, Kamlet-Taft, relative quantum yield,

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1. INTRODUCTION:

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Boronic acids have potential applications which are very important in bioorganic and medicinal chemistry as well as chemical biology [1]. Boronic acids are increasingly utilised in diverse areas of research [2]. Boronic acid containing polymers have proved

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important biomedical applications with the treatment of HIV, diabetes, obesity, and cancer

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[3]. Boronic acids also find applications in the detection and sensing of peroxides, tetraserine motif in protein and improvement of new MRI contrast agents [4].

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When a molecule is dissolved in different solvents, an effect of solvents on absorption

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and fluorescence spectra has been a subject of interesting investigation [5]. These investigations have significant importance in the field of photophysical and photochemistry.

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Photophysical properties viz fluorescence lifetime (), quantum yield ( ), excitation and emission spectral shift, etc., have been a subject of few examinations [6, 7]. Therefore

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systematic analysis on solvent effect provides useful information in studying the excited states behaviour of the molecule. A change in the solvent is accompanied by a change in polarity, polarizability or dielectric constant of the medium. Hence, a variation in solvent affects the ground and excited states differently. The understanding of dipole moments of electronically excited species is frequently useful in the design of non-linear optical materials [8] and elucidation of the nature of excited states. An intellectual capacity of excited state properties helps to aim at new molecules but also for the best execution in an investigation of the particular application. Excitation of a particle leads to the redistribution of charges and electron densities prompting to conformational changes in the excited state. Thus, the dipole moment of the excited state can increase or decrease as compared to the ground state.

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ACCEPTED MANUSCRIPT This paper reports an estimation of ground and excited states of the title molecule [9-11]. In order to check the effect of the molecular shape on the dipole moments in the

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excited state and ground state, a wide range of non-polar and polar solvents have been

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selected. The quantum chemical calculations are also carried out [12] to supplement the

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experimental results. The ground state and excited state dipole moments were estimated using solvatochromic shift method. The results were analyzed using Bilot Kawaski, Lippert, Bakshiev, Chamma Viallet-Kawski and microscopic solvent polarity (

). Multiple linear

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regression technique is used to get information about individual contributions of hydrogen

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bond acceptor (HBA) and hydrogen bond donor (HBD) ability of solvents on the spectroscopic properties are correlated with Kamlet-Taft parameters [13].

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The quantum yield relates the productivity at which a fluorescent particle changes

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over absorbed photons into emitted photons. Further, it provides valuable information on the subject of excited electronic states, radiationless transitions, and the coupling of electronic to

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vibronic states. Quantum yield finds potential applications in the determination of sample purity, the appropriateness of laser media. The radiative relaxation (kr) and non-radiative

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relaxation (knr) pathways by the relative rates will determine the quantum yield which deactivates the excited state. The quantum yield can be close to unity if knr is much smaller than kr. In this study, the single point method was adopted to evaluate the relative quantum yield of 3MPBA [14-15]. 2. THEORY: 2.1. Dipole moment: By employing the simplest quantum-mechanical second order perturbation theory and taking into account Onsager’s model, Bilot and Kawski [16-17] have obtained expressions for the spectral shift given by

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=

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where

(6)

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Assuming that the symmetry of the investigated solute molecule remain unchanged upon electronic transition and the ground and excited state dipole moments are collinear,

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based on equations (3) and (4) one obtains

Generally it is assumed that dipole moments μe and μg are parallel to each other and if they are not parallel and form an angle  , then  can be calculated using equation (10) [18].

The electric dipole moment of polar solute polarizes the solvent so that the solute itself experiences an electric field, the reaction field, which is proportional to the molecule dipole moment in the ground and excited states. The three independent equations used for the evaluation of excited state dipole moment of aryl boronic acid derivatives are as follows

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ACCEPTED MANUSCRIPT Lippert’s equation [19]

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Bakshiev’s equation [20]

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Kawski-Chamma-Viallet’s equation [21]

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Where,

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And

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where F1( ,n),F2( ,n) and F3( ,n) are known as Lippert’s, Bakshiev’s and Kawski-ChammaViallet’s polarity function respectively,

is the dielectric constant and n is the refractive

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index of the solvent. Also,

And

The parameters ‘m1’, ‘m2’ and ‘m3’can be determined from absorption and fluorescence band shifts. The values of ground state dipole moment (µg) and excited state dipole moment (µe) from equations (17) and (18) can be given as. 5

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ACCEPTED MANUSCRIPT

) and

1/2(

) versus solvent polarity functions are

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The plots of (

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Or

straight lines along with their slopes ‘m1’, ‘m2’ and ‘m3’. The use of these equations is based

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on assumptions like considering both the dipole moments collinear and have same Onsager cavity radius in both dipole moments. They don’t consider the polarizability, hydrogen

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bonding effect and complex formation as well as ignores molecular aspects of solvation.

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2.2 Microscopic solvent polarity(

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For understanding hydrogen bonding effect or polarization dependence on spectral characteristics, normalized value called Molecular-Microscopic Solvent Polarity Parameter is utilised which includes not only solvent polarity but also the protic hydrogen bond

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effect. The theoretical basis for the relationship as the spectral shift with

was proposed by

Reichardt [22]

Where

and

are the Onsager cavity radius of molecule and change in dipole moment

on excitation respectively of a betaine dye and

and

are the corresponding quantities for

the present solute molecule. The change in dipole moment slope (m) of the Stoke’s shift versus

can be evaluated from the

plot and it is given by

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ACCEPTED MANUSCRIPT 2.3. Kamlet-Taft Multiple regression analysis: Kamlet and co-workers suggested multiple linear regression approach to correlate

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various spectral properties like absorption maxima ( ), emission maxima ( ) and Stoke’s ) with the indices of solvents hydrogen bond donor (HBD) strength (), Hydrogen

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shift (

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bond acceptor (HBA) strength () and solvent dipolarity/polarizability (*) through the

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equation

Where y is the desired spectral property, y0 is the corresponding spectral property in gas

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phase and A, B and C are the evaluated values of HBD ability, HBA ability and dipolarity/polarizability respectively. The magnitudes of the values of these parameters are

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evaluated using multiple linear regression method. The signs of A and B coefficients may

2.4. Quantum yield:

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vary from one compound to another [13].

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The fluorescence quantum yield ( ) is the number of photons emitted to the number of photons absorbed [5]. In other words the fluorescence quantum yield gives the probability

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of the excited state being deactivated by fluorescence rather than by another, non-radiative mechanism.

The fluorescence quantum yield  can also be represented by the relative rates of the radiative (kr) and non-radiative (knr) relaxation pathways, which deactivate the excited state.

If the rate of non-radiative decays constant (knr) is much smaller than a rate of the radiative decay constant (kr) then quantum yield can be nearer to unity.

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ACCEPTED MANUSCRIPT Quantum yield gives important information about excited electronic states, radiation less transitions, and coupling of electronic to vibronic states. Also, they are used in the

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determination of chemical structure, sample purity and appropriateness of laser media. An

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estimation of absolute quantum yield requires sophisticated instrumentation [23]. It is easier

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to estimate the relative quantum yield by comparing to a standard with a known fluorescence quantum yield. The relative quantum yield measurements of samples using single point technique include a standard reference. There are many standard references available in

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literature [24]. The standard should be chosen to provide maximum overlap of the excitation

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and emission between sample and reference. we have chosen Tryptophan in double distilled water at 200 C as standard reference whose excitation maxima is 280 nm and fluorescence

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quantum yield is 0.13 and measured the relative quantum yield of 3MPBA in different

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solvents particularly in alcohols and non alcohols. The determination of relative quantum

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yields from previous research is given in equation (26)[25].

where - quantum yield, F- integrated area under the corrected emission spectrum (in Ep

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units), OD- absorbance at the excitation wavelength, n- the refractive index of the solvent used and the subscripts u refer to the unknown and s refers to standard. Quantum yield is also specified in terms of average life time (0) and radiative decay rate constant (kr) as given in equation (27)[26].

And the non-radiative decay rate constant is given by the equation

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ACCEPTED MANUSCRIPT 3. MATERIALS AND METHODS Materials:

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The molecule 3-Methoxyphenyl boronic acid (3MPBA) was synthesized by standard

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methods [27]. The molecular structure of 3MPBA is given in Fig.1. Spectroscopic graded

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solvents supplied by S-D Fine Chemicals Ltd., India have been used without further purification. The concentration of the solution maintained at 110- 4 M to avoid aggregation and dimer formation. Tryptophan was purchased from Sigma Aldrich and used without

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further modifications. A standard reference solution was prepared by dissolving tryptophan in

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double distilled water with a concentration of 1X10-4 M for the measurement of relative quantum yield.

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Spectroscopic Methods:

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The absorption spectra were measured at room temperature using a UV-VIS Spectrophotometer (Model: Shimadzu UV-1800, Kyoto, Japan) with wavelength accuracy of

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0.5nm. The absorbance (OD) of the solutions at the excited wavelength is less than 0.2. The absorption spectra were recorded over a range of 200 - 600 nm. The fluorescence spectra of

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the molecule were measured using a Fluorescence spectrophotometer (Model: Hitachi F-2700, Tokyo, Japan) at room temperature with perpendicular geometry. Florescence lifetime (o) measurements were carried out using TCSPC nanosecond fluorescence lifetime spectrometer, (Model: ChronosBH, USA) . 4. RESULTS AND DISCUSSION: 4.1 Solvent effects on absorption and fluorescence spectra: Absorption and fluorescence spectra were measured in alcohols and non alcohol solvents of different polarities. Typical normalized absorption and emission spectra of 3MPBA in propanol and acetonitrile are given in Fig. 2. The dielectric constant (ε), refractive index (n), solvent polarity functions, microscopic solvent polarity parameter (

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ACCEPTED MANUSCRIPT and Kamlet-Taft parameters (α, , *) for alcohol and non alcohol solvents are listed in Table 1. The maximum excitation and emission wavelength, stokes shift, and the average

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absorption and emission maximum of 3MPBA are given in Table 2. It is clear from Table 2

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that Stokes shift increases with varying solvent polarity. The magnitude of Stokes

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shift shows that the excited state geometry could be significantly unlike from that of the ground state and thus large values of excited state dipole moments are expected. With an increase in solvent polarity, the magnitude of Stokes shift varies

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3014.81 cm-1 to 3238.26 cm-1 and 3001.57 cm-1 to 3689.26 cm-1 in alcohols and non

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alcohols respectively.

4.2 Estimation of ground and excited state dipole moments: 4.2.1 Analysis of Bilot Kawaski equation:

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In order to determine the ground state and excited state dipole moments of 3MPBA, we employed solvent polarity functions like

ε

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solvatochromic shift methods. We plotted

and

ε

based on the various

versus f(ε, n) and

versus

, using Bilot-Kawski equations shown in Fig. 3. The correspondent statistical values

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are given in Table 3. The Onsager cavity radius is approximately equal to the radius of the solute molecule and was calculated from the molecular volume of the molecule [28]. Using Eqns. (7 & 8) the ground state and excited state dipole moments are estimated and it is observed that the ground state dipole moment of the molecule is about 0.686 D and 0.608 D for alcohols and non alcohols. Whereas, the excited state dipole moment of the molecule is found to be 1.594 D and 2.336 D for alcohols and non alcohols respectively. All the data are listed in Table 4. It can be observed that, the excited state dipole moment is more prominent than ground state dipole moment for all the solvents studied. Many authors [29-31] assumed that excited state dipole moment is collinear with the ground state. The angle between ground and excited state dipole moments is calculated using 10

ACCEPTED MANUSCRIPT equation (10) and it is found to be 00 which confirms that, the ground and excited state dipole moments are parallel to each other. Direction of the dipole moment in a molecule

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depends on the centers of positive and negative charges. The collinear between the ground

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molecule in the excited state than those of ground state.

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and excited state dipole moments demonstrates the more charge kineticism across the

4.2.2 Analysis of Lippert Mataga, Bakhshiev, Kawski Chamma Viallet equations: We have employed different solvent polarity functions

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ε

ε

and

ε

plotted

versus

ε

,

versus

ε

,

versus

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are

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to estimate the ground state (µg) and excited state (µe) dipole moments of 3MPBA. Graphs

ε

for Lippert Mataga, Bakhshiev and Kawski-Chamma-Viallet respectively. The

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graphs are given in Figs. 4-6. The corresponding values of the slopes and correlations are

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given in the respective plots and listed in Table 3. The ground state (µg) and excited state (µe) dipole moments are estimated by using Eqs. (20) and (21). The excited state dipole

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moments (µe) are also determined from the slopes (m1, m2, and m3) of Lippert Mataga, Bakhshiev, and Kawski-Chamma-Viallet correlations. All of the results are presented in

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Table 4.

It can be noted that, the excited state dipole moment is found to be greater than ground state dipole moment in both alcohol and non alcohol solvents, which indicates that the molecule is significantly more polar in excited state than in ground state. Consequently, the solvent solute interactions should be more vigorous in the excited state than in the ground state, denoting a consequential redistribution of charge densities between both electronic states. We have observed a good agreement between the excited state dipole moments except Lippert Mataga method. It can be noticed that Lippert Mataga method is quite larger compared to value obtained by the alternative methods, since it doesn’t consider polarizability impact of the solute. The nature of emitting state and charge transfer may be due to the 11

ACCEPTED MANUSCRIPT change in dipole moment by excitation. The estimated values of the ground state and excited state dipole moments of 3MPBA are higher in alcohols as compared with non alcohols. This

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may be due to the reason that, the molecule is more polar in alcohols. From Table 4 it may be

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noted that, the change in dipole moment of the 3MPBA is about 0.908 D (from Bilot

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Kawaski) and 1.941 D (from experimental) for alcohols. Whereas, 1.728D (from Bilot Kawaski) and 1.729 D (from experimental) for non alcohols. This increase in excited state dipole moments for both alcohols and non alcohols gives a confirmation to the character of

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the ICT. In the emitting singlet state of 3MPBA this clearly confirms that the molecule

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undergoes ππ* transition in the excited state.

4.2.3 Molecular-Microscopic Solvent Polarity Parameter (

of the 3MPBA is given in Fig. 7 for

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The plot of Stoke’s shift as a function of

):

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alcohols and non alcohols. The dependence of Stoke’s shift over linear molecular microscopic solvent polarity parameter (

) indicates the existence of a general type of

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solute-solvent interaction in which the Stoke’s shift depends on the dielectric constant (ε) and refractive index (n) of the solvents. The excited state dipole moment is calculated using according to Eqn. (24). The value of excited

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microscopic solvent polarity parameter (

state dipole moment estimated from this method is represented as μei and is listed in Table 4. It is observed that, the value of excited state dipole moment estimated using

parameter is

slightly smaller than Lippert’s, Bakshiev’s and Kawaski-Chamma-Viallet equations. This could be due to the fact that the techniques based on Lippert’s, Bakshiev’s and KawaskiChamma-Viallet equations don’t consider particular solute-solvent interactions such as hydrogen bonding effect and complex formation whereas ignore molecular aspects of salvation, but these aspects are included in the technique based on

[32]. Absorption and

emission bands undergo a bathochromic shift with an increasing solvent polarity. This denotes ICT (intermolecular charge transfer) absorption of the less dipolar ground-state 12

ACCEPTED MANUSCRIPT particle with predominant mesomeric structure, leading to exceedingly dipolar-excited state and with the prominent structure of boronic acids. Hence, the molecule is more polar in

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excited state than the ground state due to intermolecular charge transfer.

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The change in dipole moment (µ=µe-µg) is calculated using experimentally estimated

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values of µg and µe. and using equation (24) are presented in Table 4. A fair agreement can be observed in change in dipole moment between two methods. 4.3 Quantum chemical calculations:

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ab initio [33] calculations were used to estimate the ground state dipole moment in

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order to support and explain the experimental observations. The quantum chemical calculations were carried out using DFT/B3LYP level of theory 6-31 G(d, p) basis set. The

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(optimized) geometry of the molecule is shown in Fig. 8a. The ground state dipole moment

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calculated using this method is 1.636D and is listed in Table 4. Discrepancies between experimental and theoretically obtained results can be recognized to the fact that,

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theoretical calculations belong to the gas phase and exclude solvent interactions [34]. The Fig. 8b indicates the geometry of the molecule in the ground state and the arrow mark

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represents direction of the dipole moment. 4.4 Multiple linear regression analysis: The 3MPBA is examined for individual contributions of hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD) ability of solvents on the spectroscopic properties  a ,

and  are correlated with Kamlet-Taft parameters ,  and * using multiple linear

regression analysis. The analyzed data and correlation co-efficients (r) are given in the following equation. -1  a (cm )=36844.83 - 265.00 - 185.67 + 130.64 (r=0.76) -1  f (cm )=35107.10 - 327.48 - 252.15 - 329.23 (r=0.86)

Alcohols

 (cm-1)=2559.28+881.18+531.47+1053.15 (r=0.91) 13

ACCEPTED MANUSCRIPT -1  a (cm )=35781.423 + 133.770 + 24.639 -114.819 (r=0.732) -1  f (cm )=32910.756 + 44.109 - 171.179 - 309.114 (r=0.834)

Non alcohols

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 (cm-1)=2976.685 + 361.381 + 630.465 + 512.789 (r=0.846)

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From the above analysis it can be observed that HBA () influence is more than HBD

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() for  a and  f , whereas HBD () influence is more than HBA () for  in alcohols. Whereas, HBD () influence is more than HBA () for  a and  f , and HBA () influence is for 

in non alcohols. However, the contribution of

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more than HBD ()

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(dipolarity/polarizability) nonspecific dielectric interactions cannot be neglected. 4.5 Estimation of relative quantum yield:

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The determination of the relative quantum yield of 3MPBA, we have adopted single

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point method. The solvents used for the study are pentane, heptane, nonane, 1, 4 dioxane, octanol, 1-propanol, acetonitrile and water. The possibility of self-quenching can be ruled out

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for low concentration. The standard reference solution is used as tryptophan by dissolving in double distilled water. All the solutions inclusive of reference are excited at 280nm. The slit

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width, PMT voltage and scanning range are respectively 5 nm, 400 V and 280–500 nm. It is found that the optical density varies between 0.028 (in water) to 0.181 (in octanol). The absorption and emission spectra of the Tryptophan in water and 3MPBA in 1-propanol are given in Figs. 9 and 10. Fluorescence integrated intensity (Fint) of 3MPBA is calculated for all the solvents studied and it is observed that the fluorescence integrated intensity (Fint) is more in 1-propanol. The relative quantum yield (ϕ), radiative decay constant (kr) and non-radiative decay constant (knr) are estimated using Eqs. (26-28). Values of life time (τ0) of 3MPBA in different solvents, (ϕ), (kr) and (knr) are listed in Table 5. The typical decay profile of 3MPBA in 1-propanol is shown in Fig. 11. From the Table 5 it can be noted that, the quantum yield of 3MPBA is more in 1,4dioxane, though its OD is less than octanol, heptane, 1-propanol and

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ACCEPTED MANUSCRIPT nonane. Further it can also be noted that the rate of radiative decay (Kr) is higher than non radiative decay (Knr) for all the solvents. This confirms that, the molecule is more radiative in

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nature and less intersystem crossing in the excited state.

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In order to study the variation of quantum yield versus dielectric constant and

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quantum yield versus viscosity graphs are plotted and given in Fig. (12 a, b). It is observed that, there is a decrease in the value of quantum yield with an increase of dielectric constant, which is possibly due to red shift and intermolecular charge transfer (ICT) [35].Whereas

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quantum yield increases with increase in viscosity which is in accordance with ForsterHoffmann expression [36] as specified in equation (29).

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log   log C  x.(log )

(29)

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where η is the viscosity, C is a constant, and x is a free volume term that depends on the

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structural parameters of the fluorophore and represents the fraction of the total critical free volume for solvent motion that is required by the fluorophore in order to undergo torsional

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rearrangement [37]. It may be due to the reason that, the capability of the solvent to form hydrogen bonds has a major influence on the correlation between quantum yield and

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viscosity.

CONCLUSIONS:

It is observed that, the excited state dipole moment (µe) of 3MPBA is greater than the ground state dipole moment (µg). The boronic acid derivative 3MPBA exhibits a bathochromic shift. The bathochromic shift of the emission spectra and the increase in the excited state dipole moment illustrates * transitions with the possibility of intermolecular charge transfer (ICT) nature in the emitting singlet state. HBA () influence is more than HBD () for  a and  f for alcohol solvents whereas HBD () influence is more than HBA () for  a and  f , for non alcohols solvents. An estimation of the relative quantum yield in different solvents has noticed that there is a variation of quantum yield from 0.508 to 0.957 15

ACCEPTED MANUSCRIPT with the change in the solvent surroundings. This strongly suggests that, the excited state energy levels of 3MPBA are perturbed by the solvent polarity.

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ACKNOWLEDGEMENT:

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This work is fully supported by BVB CET under “Capacity Building Projects” grants. The

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author (G V M) thanks KLE Society and BVB CET, Hubli for financial support. The authors acknowledge Principal, H.O. D. Physics of M.S.R.I.T Bangalore and also USIC, Karnataka

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University Dharwad for Instrumental facility. REFERENCES

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[18] A. Kawski, Z. Naturforsch, 57a (2002) 255-262.

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[19] E. Lippert, Z. Eleckchem, 61 (1957) 962-975. [20] N.G. Bakshiev, Opt. Spektrosk., 16 (1964) 821-832.

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[21] A. Chamma, P. Viallet. C.R. Acad, Sci. Paris, Ser. C., 270 (1970) 1901-1904. [22] C. Reichardt, Wiley VCH, Solvents and solvents effects in organic chemistry, third

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ed.,Weinheim, (2003).

[23] C.V Bindhu, S.S. Harilal, G.K. Varier, R.C. Issac, V.P.N. Nampoori, C.P.G. Vallabhan, J. Phys. D: Appl. Phys., 29 (1996) 1074-1079. [24] Rance A. Velapoldi, Hanne H. Tønnesen. J. Fluoresc. 14(4) (2004) 465-472. [25] G. K. Turner, Science, 146 (1964) 183-189. [26] J.B. Bricks, Photophysics of aromatic molecules,Wiley-Interscience, New york (1970). [27] Gary A. Molander, Sarah L. J. Trice, Spencer D. Dreher, J. Am. Chem. Soc., 132 (2010) 17701-17703. [28] http://www.molinspiration.com/cgi-bin/properties.

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Sanningannavar, B.S. Navati,

N.R.

Patil,

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Kusanur,

R.M. Melavanki, Can. J. of Phy., 92(11) (2014) 1330-1336.

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[30] R.M. Melavanki, N.R. Patil, S.B. Kapatkar, N.H. Ayachit, Siva Umapathy,

Kadadevarmath,

G.H.

Malimath, N.R.

Patil,

H.S.

Geethanjali,

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[31] J.S.

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J. Thipperudrappa, A.R. Nataraju. J. Mol. Liq. 158(2) (2011) 105-110.

R.M. Melavanki. Can. J. Phy., 91(12) (2013) 1107-1113. [32] S. Joshi, D.D. Pant, J. Mol. Liq., 166 (2012) 49-52.

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[33] A.D. Becke, J. Chem. Phys., 98 (1993) 5648-5652.

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[34] Bilal A, Mustafa A, Hasan E, J. Mol. Struct. (Theochem.), 548 (2001) 165-171. [35] J. M. Petit, M. Denis-Gay, Marie-Hélène Ratinaud, Biol Cell, 78 (1993)

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[36] Förster T, Hoffmann G. Z Phys. Chem., 75 (1971) 63-76.

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[37] Kung, C.E. & Reed, J.K. Biochemistry, 28 (1989) 6678-6686.

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Fig. 1 Molecular structure of 3MPBA

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Fig. 2 Typical Normalized Absorption and emission spectra of 3MPBA in acetonitrile and propanol solvents

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Fig. 3 The variation of Stoke’s shift with f (, n)and (n) using Bilot Kawaski equation for 3MPBA in alcohols and non alcohols solvent

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Fig. 4 The variation of Stoke’s shift with F1 (,n) using Lippert equation for 3MPBA in alcohols and non alcohols solvents

Fig. 5 The variation of Stoke’s shift with F2 (, n) using Bakshiev’s equation for 3MPBA in alcohols and non alcohols

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Fig. 6 The variation of arithmetic means of absorption and emission wave number with F3 (, n) using Kawski- Chamma-Viallet’s equation for 3MPBA in alcohols and non alcohols

Fig. 7 The variation of Stoke’s shift with ETN for 3MPBA in alcohols and non alcohols

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Fig.8 Optimized diagram and Ground state optimized molecular geometries of 3MPBA The arrow indicates the direction of the dipole moment.

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Fig. 9 Absorption and emission spectra of standard reference (tryptophan in water) with fluorescence integrated intensity

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Fig. 10 Absorption and emission spectra of 3MPBA in 1-Propanol with fluorescence integrated intensity.

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Fig.11 Life time decay profile of 3MPBA in propanol

Fig. 12 Plot of (a) relative quantum yield vs dielectric constant ( ε) and (b) logarithm of quantum yield vs logarithm of viscosity (η) of solvents.

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ACCEPTED MANUSCRIPT Table1. Dielectric constant (ε), refractive index (n), solvent polarity functions, microscopic solvent polarity parameter ( ), Kamlet Taft parameters (α, ,*) F1

F2

F3

0.47 1

0.00 3

0.00 56

0.23 55

0.0 09

1.89 0

1.3 75

0.00 1

0.51 0

0.00 01

0.00 02

0.25 50

0.0 09

Heptane

1.90 0

1.3 88

0.00 6

0.52 1

0.00 34

0.00 64

0.26 06

0.0 12

Decane

2.00 0 2.00 0 2.02 0 2.22 0 2.40 0 3.42 0 7.58 0 8.93 0 37.5 00 38.2 50 47.2 40 80.4 00

1.4 08 1.4 05 1.4 26 1.4 21 1.4 96 1.4 77 1.4 07 1.4 24 1.3 46 1.4 30 1.4 79 1.3 33

0.00 4 0.00 6 0.00 3 0.04 5 0.03 4 0.21 0 0.54 9 0.59 0 0.86 3 0.84 0 0.84 1 0.91 4

0.55 8 0.55 6 0.57 5 0.61 6 0.70 3 0.85 5 1.10 2 1.16 6 1.33 4 1.42 3 1.48 9 1.36 8

0.00 21 0.00 31 0.00 16 0.02 20 0.01 53 0.08 84 0.20 96 0.21 72 0.30 47 0.27 54 0.26 34 0.32 01

0.00 41 0.00 61 0.00 31 0.04 45 0.03 37 0.21 03 0.54 92 0.59 04 0.86 25 0.83 95 0.84 14 0.91 38

0.27 92 0.27 82 0.28 75 0.30 80 0.35 16 0.42 76 0.55 10 0.58 29 0.66 69 0.71 14 0.74 45 0.68 37

0.0 09 0.0 09 0.0 06 0.1 64 0.0 99 0.1 60 0.2 07 0.3 09 0.4 60 0.4 04 0.4 44 1.0 00

2.23 99 2.48 22 2.54 05 2.72 22

2.82 06 3.04 97 3.09 61 3.26 45

0.22 59 0.24 44 0.24 97 0.26 33

0.62 72 0.69 1 0.70 36 0.74 94

0.60 39 0.62 93 0.62 96 0.64 59

0.5 37 0.5 59 0.5 68 0.5 86

Nonane Cyclohex ane 1,4 dioxane Toluene

THF DCM

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TCE

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Acetonitr ile DMF DMSO Water

Octanol Hexanol Alcoh ols

Pentanol Butanol

10.3 0 13.3 0 13.9 0 17.4 0

1.4 28 1.4 18 1.4 09 1.3 99

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1.80 0

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α

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φ(n)

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f (ε,n) 0.00 6

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ε

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Solvents



*

0.0 0.0 0 0 0.0 8 0.0 0.0 0 0 0.0 4 0.0 0.0 0 0 0.0 8 0.0 0.0 0.0 0 0 3 0.0 0 0.0 0 0.0 0 0.0 0 0.0 0 0.1 3 0.1 9 0.0 0 0.0 0 1.1 7

0.0 0 0.3 7 0.1 1 0.0 5 0.5 5 0.1 0 0.4 0 0.6 9 0.7 6 0.4 7

0.0 0 0.5 5 0.5 4 0.5 3 0.5 8 0.8 2 0.7 5 0.8 8 1.0 0 1.0 9

0.7 7 0.8 0 0.8 4 0.8 4

0.8 1 0.8 4 0.8 6 0.8 4

0.4 0 0.4 0 0.4 0 0.4 7 24

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2.87 22 3.01 76 3.25 67

3.38 92 3.50 90 3.70 36

0.27 61 0.28 86 0.30 94

0.78 18 0.81 17 0.85 78

0.64 93 0.65 16 0.65 23

0.6 17 0.6 54 0.7 62

0.8 0.9 0.5 4 0 2 0.8 0.7 0.5 6 5 4 0.9 0.6 0.6 8 6 0

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20.4 5 24.3 0 33.7 0

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1Propanol Ethanol

Table2. Solvatochromic data of 3MPBA in different solvents λa(nm)

λe(nm)

(cm-1)

cm-1)

(

) -1

(cm )

304.50 304.70 304.50 304.90 305.10 304.90 305.10 306.40 306.50 310.60 311.00 313.70 312.80 313.40 313.50

35842.29 35714.29 35752.59 35727.05 35739.81 35701.54 35752.59 35676.06 35688.79 35561.88 35536.60 35498.76 35523.98 35460.99 35587.19

32840.72 32819.17 32840.72 32797.64 32776.14 32797.64 32776.14 32637.08 32626.43 32195.75 32154.34 31877.59 31969.31 31908.10 31897.93

3001.57 2895.12 2911.87 2929.41 2963.68 2903.9 2976.45 3038.99 3062.37 3366.13 3382.26 3621.17 3554.67 3552.89 3689.26

(cm-1) 34341.51 34266.73 34296.66 34262.34 34257.98 34249.59 34264.37 34156.57 34157.61 33878.81 33845.47 33688.17 33746.64 33684.55 33742.56

282.50 283.30 283.40 283.50 283.60 283.60 283.70

308.80 310.50 310.60 311.40 311.70 311.90 312.40

35398.23 35298.27 35285.82 35273.37 35260.93 35260.93 35248.50

32383.42 32206.12 32195.75 32113.04 32082.13 32061.56 32010.24

3014.81 3092.15 3090.06 3160.33 3178.80 3199.37 3238.26

33890.82 33752.19 33740.78 33693.20 33671.53 33661.24 33629.37

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Alcohols

Octanol Hexanol Pentanol Butanol 1-Propanol Ethanol Methanol

279.00 280.00 279.70 279.90 279.80 280.10 279.70 280.30 280.20 281.20 281.40 281.70 281.50 282.00 281.00

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Non alcohols

Pentane Hexane Heptane Decane Nonane Cyclohexane 1,4 dioxane Toluene TCE THF DCM Acetonitrile DMF DMSO Water

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Slope

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m(1)

Bilot Kawaski Correlation

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m(2)

Lippert Correlation

Bakhshiev‟s correlation Kawski-ChammaViallet‟s correlation correlation

Correlation factor „r‟

Number of data

769.72

0.99

15

212.70

0.98

07

1310.97

0.98

15

533.95

0.95

07

2260.76

0.99

15

2645.58

0.98

07

769.22

0.99

15

970.88

0.99

07

1311.02

0.98

15

4842.87

0.98

07

1091.47

0.97

15

868.18

0.94

07

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Correlations

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Table 3 Statistical treatment of the correlations of solvents spectral shifts of 3MPBA

m1

m2

m3

m

Solvent type Non alcohols Alcohols Non alcohols Alcohols Non alcohols Alcohols Non alcohols Alcohols Non alcohols Alcohols Non alcohols Alcohols

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Table 4. Ground state and excited state dipole moments of 3MPBA

3.39 3

Solv ents

µg2 (D )

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3MPB A

Rad µg1 ius (D „a‟( ) o A)

1.6 36

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Alco hols Non Alco hols

0.6 86 0.6 08

µg3 (D ) 3.8 71 0.6 07

µ e4 (D ) 1.5 94 2.3 36

µ e5 (D ) 5.8 12 2.3 36

µ e6 (D ) 7.0 75 4.7 96

µ e7 (D ) 5.8 12 2.3 34

µ e8 (D ) 5.8 12 2.3 36

µ e9 (D ) 4.8 80 1.7 39

Δµ

Δµ

10

11

(D ) 1.9 41 1.7 29

(D ) 1.0 09 1.1 32

(µe / µg)

ϕ 13

12

1.5 01 3.8 48

0 0

0 0

Debye (D) = 3.33564X10-30cm = 10-18 esu cm. 1 The ground states dipole moments calculated using Gaussian software 2 The ground states dipole moments calculated using Bilot Kawaski Eq. 7 3 The ground states dipole moments calculated using Eq.20 4 The excited states dipole moments calculated using Bilot Kawaski Eq. 8. 5 The excited states dipole moments calculated using Eq. 21. 6 The experimental excited state dipole moments calculated from Lippert’s equation. 7 The experimental excited state dipole moments calculated from Bakshiev equation. 8 The experimental excited state dipole moments calculated from Kawaski-Chamma-Viallet equation. 9 The excited state dipole moments calculated from equation 10 The change in dipole moments for μe and μg 11 The change in dipole moments calculated from Eq. 24 12 The ratio of excited state and ground state dipole moment

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The angle between ground and excited state dipole moments calculated using Eq.10.

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η

ε

n

OD

Pentane

1.800

2

Heptane

3

Nonane

4 5

1, 4 Dioxane Octanol

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1-Propanol

7

Acetonitril e Water

0.23 0 0.41 0 0.66 0 1.18 0 7.63 0 1.96 0 0.37 0 0.89 0

1.35 0 1.38 8 1.40 5 1.42 1 1.42 8 1.38 0 1.34 6 1.33 3

0.09 4 0.13 9 0.10 8 0.09 2 0.18 1 0.12 7 0.09 0 0.02 8

2.220

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10.30 0 20.45 0 37.50 0 80.40 0

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2.000



0 (ns)

45927.09 8 88294.73 1 72614.10 5 75679.62 3 78659.44 3 91952.29 6 63935.93 0 13896.04 3

0.51 3 0.70 5 0.76 5 0.95 7 0.51 1 0.79 5 0.74 2 0.50 8

3.17 0 2.02 0 1.76 0 2.97 0 3.54 0 3.92 0 2.96 0 2.50 0

kr 109(s -1 ) 0.16 2 0.34 9 0.43 5 0.32 2 0.14 4 0.20 3 0.25 1 0.20 3

knr 109(s -1 ) 0.15 3 0.14 6 0.13 3 0.01 5 0.13 8 0.05 2 0.08 7 0.19 7

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Table 5.Viscosity(η), dielectric constant(ε), refractive index(n), absorbance(OD), fluorescence integrated intensity(Fint), excited state life time(0), relative quantum yield(), kr and knr of 3MPBA

(OD)s=0.13, (Fint)s=20435.159

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Graphical abstract

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ACCEPTED MANUSCRIPT HIGHLIGHTS

 A bathochromic shift is observed.

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 The ground and excited state is dipole moments are collinear.

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 HBA influence is more than HBD for alcohol whereas HBD influence is more than HBA for non alcohols.

state.

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 The molecule is more radiative in nature and less intersystem crossing in the excited

 Quantum yield decreases with an increase of dielectric constant and quantum yield

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increases with increase in viscosity

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