Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 340–348
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Polar and low polar solvents media effect on dipole moments of some diazo Sudan dyes M.S. Zakerhamidi a,⇑, Sh. Golghasemi Sorkhabi a, A.N. Shamkhali b,c a
Research Institute for Applied Physics and Astronomy, University of Tabriz, Tabriz, Iran Department of Applied Chemistry, Faculty of Sciences, University of Mohaghegh Ardabili, P.O. Box 56199-11367, Ardabil, Iran c Department of Chemistry, Sharif University of Technology, Tehran 11155-9516, Iran b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Specific interactions in polar solvents
are main interactions in solvatochromism of Sudan. GICT, LICT and sterically hindered control Sudan dyes spectroscopic behavior. Sudan black B has highest charge individuation upon excitation in comparison to SudanIII and IV.
a r t i c l e
i n f o
Article history: Received 30 November 2013 Received in revised form 9 February 2014 Accepted 14 February 2014 Available online 27 February 2014 Keywords: Dipole moment Diazo Sudan dye Solvent–solute interaction Solvent polarity Tautomeric resonance structure Intramolecular charge-transfer
a b s t r a c t Absorption and fluorescence spectra of three Sudan dyes (SudanIII, SudanIV and Sudan black B) were recorded in various solvents with different polarity in the range of 300–800 nm, at room temperature. The solvatochromic method was used to investigate dipole moments of these dyes in ground and excited states, in different media. The solvatochromic behavior of these substances and their solvent–solute interactions were analyzed via solvent polarity parameters. Obtained results express the effects of solvation on tautomerism and molecular configuration (geometry) of Sudan dyes in solvent media with different polarity. Furthermore, analyze of solvent–solute interactions and value of ground and excited states dipole moments suggests different forms of resonance structures for Sudan dyes in polar and low-polar solvents. Ó 2014 Elsevier B.V. All rights reserved.
Introduction Aromatic azo derivatives are one of the largest and the most important classes of colorants. Their practical and theoretical importance have been reflected in textile, food, paper printing, nonlinear optical (NLO) devices and liquid crystalline displays ⇑ Corresponding author. Tel.: +98 411 3393003; fax: +98 411 3347050. E-mail address: [email protected] (M.S. Zakerhamidi). http://dx.doi.org/10.1016/j.saa.2014.02.070 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
(LCDs) [1–14]. Beside the relationship between the structure and the physical-chemical properties of these dyes, characterizations of aromatic azo dyes are also important, for practical applications [9–15]. One of the most fundamental features of azo dyes is spectroscopic capabilities. The spectroscopic behaviors of aromatic azo dyes change with parameters such as; substitution change and media effects. Changes of spectroscopic properties can be investigated via variation of dipole moment, in the studied system.
341
M.S. Zakerhamidi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 340–348
(a) Absorbance
1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
1.Diethyl ether 2.Cyclohexane 3.Acetone 4.Methanol 5.Ethanol 6.2-Propanol 7.DMF 8.1-Butanol 9.1,4-Dioxan 10.CCl4 11.1-Hexanol 12.1-Decanol 13.1-Heptanol 14.Dichloromethane 15.DMSO
λ (nm) Fig. 1. Molecular structure of the Sudan dyes.
(b) 1
v~ a þ v~ f
¼ m1 f ðe; nÞ þ const:
m2 ¼
¼ m2 ½f ðe; nÞ þ 2gðnÞ þ const:
2ðl2e l2g Þ
ð4Þ
3
Parameters m1 and m2 for difference and sum of wave numbers, which are linear functions of solvent polarity functions f(e, n) and g(n), can be determined from slopes of the straight lines. The solvent polarity parameters f(e, n) and g(n) are as followed:
gðnÞ ¼
n2 1 2n2 þ1
e1 2eþ1
1 aa2
1 aa3
480
560
600
1.Cyclohexane 2.CCl4 3.Dichloromethane 4.1,4-Dioxan 5.Diethyl ether 6.Methanol 7.Acetone 8.Ethanol 9.2-Propanol 10.1-Butanol 11.1-Hexanol 12.1-Heptanol 13.1-Decanol 14.DMF 15.DMSO
1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
0.6
0.4
0.2
0 450
500
550
600
650
700
750
800
λ (nm)
n2 1
2n2 þ1 1 2aa3
520
λ (nm)
0.8
ð3Þ
3
e1 2eþ1
440
(c) 1
hca
f ðe; nÞ ¼ 1 2aa3
0 400
1.Diethyl ether 2.Acetone 3.Cyclohexane 4.Ethanol 5.Methanol 6.DMF 7.1,4-Dioxan 8.2-Propanol 9.1-Butanol 10.DMSO 11.1-Hexanol 12.1-Decanol 13.CCl4 14.1-Heptanol 15.Dichloromethane
ð2Þ
2ðle lg Þ2
hca
0.2
ð1Þ
where
m1 ¼
0.6
0.4
Absorbance
v~ a v~ f
0.8
Absorbance
Therefore, developing quantitative measurement of dipole moment and solvation interactions has been of the highest interests [16–18]. Among several ways of determining dipole moment [19,20], the most commonly applied techniques are based on the solvent spectral shift method. In this method, employing the quantum mechanical second order perturbation method and taking into account the Onsager model of reaction field for a polarizable dipole moment ~ a and v ~f . [21–23], leads to expressions for difference and sum of v
1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
n2 1 2n2 þ1
ð5Þ
2
n2 1 2n2 þ1
ð6Þ
n2 1 2n2 þ1
Fig. 2. Absorption spectra of studied group of Sudan dyes in selected solvents with different polarities, (a) SudanIII, (b) SudanIV, (c) Sudan black B.
In these relations, e denotes the dielectric permittivity and n is the refractive index. a and a represent the spherical cavity radius of the solute and average polarizability, respectively. For an isotropic
Table 1 Spectroscopic polarity parameters, physical properties and polarity functions of employed solvents [28]. Solvents
e
a
b
p*
fBK(e, n)
gBK(n)
f(e, n) + 2g(n)
Cyclohexane 1,4-Dioxan CCl4 Diethyl ether 1-Decanol Dichloromethane 1-Heptanol 1-Hexanol 1-Butanol 2-Propanol Acetone Ethanol Methanol DMF DMSO
2.02 2.22 2.24 4.34 8.00 8.93 11.30 13.0 17.5 19.9 21.01 24.3 33.7 39.25 47.24
0.00 0.00 0.00 0.00 0.70 0.13 0.64 0.67 0.84 0.76 0.08 0.86 0.98 0.00 0.00
0.00 0.37 0.10 0.47 0.85 0.10 0.96 0.94 0.84 0.84 0.48 0.75 0.66 0.69 0.76
0.00 0.49 0.21 0.24 0.45 0.73 0.39 0.40 0.47 0.48 0.62 0.54 0.6 0.88 1.00
0.003 0.044 0.023 0.127 0.553 0.590 0.652 0.686 0.750 0.779 0.792 0.812 0.857 0.842 0.841
0.289 0.286 0.311 0.535 0.296 0.288 0.288 0.284 0.271 0.256 0.244 0.246 0.224 0.292 0.324
0.575 0.617 0.646 1.197 1.145 1.166 1.227 1.254 1.293 1.292 1.281 1.303 1.306 1.425 1.489
342
M.S. Zakerhamidi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 340–348
λ Hydrazone form(nm) 350
400
450
500
550
600
650
700
750
800
1.1,4-Dioxane Hydrazon form .................................................. 2.DMSO 4 ,5,12,3,10,13,14,1,7,8,11,9 3.DMF
Azo form ........................................................... 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
Fluorescence (a.u)
4.Acetone 5. Methanol 6.CCl4 7.Cyclohexane 8.1-Hexanol 9.Diethyl ether 10.1-Decanol 11.1-Heptanol 12.2-Propanol 13.Ethanol 14.1-Buthanol 15.Dichloromethane
0 570
620
670
720
770
Fluorescence (a.u)
Azo form ........................................................... 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
600
Hydrazon form 1.Diethyl ether .................................................. 10,3,6,1,5,9,13,2,11,4,14,12 2.1,4-Dioxane 3.CCl4 4.Dichloromethane 5.DMF 6.Acetone 7.DMSO 8.2-Propanol 9.Ethanol 10.Methanol 11.1-Buthanol 12.1-Heptanol 13.1-Decanol 14.1-Hexanol
le ¼
570
620
670
720
770
820
870
Fluorescence (a.u)
Azo form ............................................ 1,2,3,4,5,6,7,8,9,10,11,12
1.1,4-Dioxane 2.DMF 3. DMSO 4.1-Decanol 5.Dichloromethane 6.1-Heptanol 7.1-Hexanol 8.2-Propanol 9.Diethyl ether 10.Ethanol 11.Methanol 12.Acetone
0 350
400
450
500
550
λ Azo form(nm)
600
650
700
m1 þ m2 l ðm1 m2 Þ m1 m2 g
ð11Þ
tively. Onsager cavity radii (a) for investigated samples were determined theoretically according to their optimized geometry [27]. The radius of spherical cavity for each solute, used in Onsager solvation model, was calculated from its optimized gas phase geometry. First, the geometry of the molecule was optimized by B3LYP hybrid-GGA functional and 6-31G(2df, 2p)basis set in gas phase. Then, the molecular volume was computed as a volume inside a contour of 0.001 electron/Bohr3 density and the radius of this spherical’s volume is calculated. All of the calculations were performed by Gaussian 03 program [28]. In this work, the spectral features of three Sudan dyes (SudanIII, SudanIV and Sudan black B) were studied, for estimation of singlet ground and excited-state dipole moments in solvent media with different polarity. Sudan dyes’ ground and excited state dipole moments’ values and solvatochromic behaviors help understand the effects of environment’s polarity on dipole moment and structural configuration of them in ground and excited states.
λ Azo form(nm)
(c)
ð10Þ
h is Plank’s constant and c is the velocity of light in vacuum. le and lg are the dipole moments in the excited and ground states, respec-
0 520
ð9Þ
" # m þ m hca3 1=2 2 1 2 2m1
0 470
ð8Þ
le ¼
700
Fluorescence (a.u)
(b)
500
ð7Þ
" # m m hca3 1=2 2 1 2 2m1
λ Hydrazone form(nm) 400
e 1 n2 1 e þ 2 n2 þ 2
lg ¼
820
λ Azo form(nm)
300
Considering that, the symmetry of the investigated solute molecule does not change during the electronic transition and the ground and excited state dipole moments are parallel, based on the Eqs (3) and (4) one obtains [26]:
0 520
2n2 þ 1 n2 þ 2
" # 3 n4 1 g BK ðnÞ ¼ 2 ðn2 þ 2Þ2
Fluorescence (a.u)
(a)
fBK ðe; nÞ ¼
750
Fig. 3. Fluorescence spectra of studied group of Sudan dyes in selected solvents with different polarities, (a) SudanIII, (b) SudanIV, (c) Sudan black B.
Experimental Material
polarizability of the solute, the condition 2aa3 ¼ 1 is usually satisfied [24–26] and the following relations were obtained by Bakhshiev:
Sudan dyes (Fig. 1) were obtained from Merck (pro analysis) and used without further purification as solutes. All the solvents
Table 2 Absorption and fluorescence spectral data of SudanIII in various solvents. Solvent
Cyclohexane 1,4-Dioxane CCl4 Diethyl ether 1-Decanol Dichloromethane 1-Heptanol 1-Hexanol 1-Buthanol 2-Propanol Acetone Ethanol Methanol DMF DMSO
Hydrazone form (cm1)
Azo form(cm1)
Absorption
Fluorescence
Stokes’ shift
Absorption
Fluorescence
Stokes’ shift
19,267.82 19,043.99 19,004.18 19,349.85 18,968.13 18,935.81 18,946.57 18,996.96 19,065.78 19,149.75 19,293.85 19,186.49 19,208.61 19,091.26 18,843.04
16,393.44 16,501.65 – 16,051.36 16,583.75 – 16,339.87 16,393.44 16,528.93 16,611.3 17,857.14 16,556.29 16,611.3 16,583.75 –
2874.38 2542.341 – 3298.481 2384.386 – 2606.701 2603.518 2536.851 2538.455 1436.702 2630.201 2597.31 2507.508 –
21,463.83 20,920.5 20,973.15 21,537.8 20,881.19 20,721.09 20,790.02 20,929.26 21,088.15 21,267.55 21,445.42 21,331.06 21,303.79 21,181.95 20,533.88
17,361.11 18,484.29 17,574.69 17,182.13 17,182.13 – 17,123.29 17,331.02 17,064.85 17,082.34 18,115.94 17,076.5 17,857.14 18,348.62 18,382.35
4102.722 2436.214 3398.462 4355.668 3699.055 – 3666.733 3598.237 4023.302 4185.209 3329.479 4254.555 3446.649 2833.329 2151.528
343
M.S. Zakerhamidi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 340–348 Table 3 Absorption and fluorescence spectral data of SudanIV in various solvents. Solvent
Cyclohexane 1,4-Dioxane CCl4 Diethyl ether 1-Decanol Dichloromethane 1-Heptanol 1-Hexanol 1-Buthanol 2-Propanol Acetone Ethanol Methanol DMF DMSO
Hydrazone form (cm1)
Azo form(cm1)
Absorption
Fluorescence
Stokes’ shift
Absorption
Fluorescence
Stokes’ shift
19,065.78 18,986.14 18,726.59 19,153.42 18,744.14 18,573.55 18,684.6 18,754.69 18,789.93 18,935.81 19,179.13 19,058.51 19,025.88 18,996.96 18,758.21
– 16,474.46 17,699.12 17,241.38 16,501.65 16,420.36 16,339.87 16,366.61 16,474.46 – 17,361.11 16,556.29 17,825.31 16,835.02 –
– 2511.676 1027.477 1912.04 2242.492 2153.19 2344.735 2388.077 2315.464 – 1818.022 2502.218 1200.563 2161.944 –
21,199.92 21,079.26 20,354.16 21,226.92 20,470.83 20,004 20,279.86 20,437.36 20,454.08 20,790.02 21,427.04 21,235.93 21,008.4 21,344.72 20,618.56
– 19,762.85 19,762.85 20,242.91 17,636.68 – 17,699.12 17,574.69 18,083.18 18,315.02 19,157.09 18,214.94 18,181.82 19,342.36 18,621.97
– 1316.412 591.3166 984.0007 2834.145 – 2580.747 2862.667 2370.898 2475.002 2269.953 3020.995 2826.585 2002.357 1996.583
Table 4 Absorption and fluorescence spectral data of Sudan black B in various solvents. Solvent
Cyclohexane 1,4-Dioxane CCl4 Diethyl ether 1-Decanol Dichloromethane 1-Heptanol 1-Hexanol 1-Buthanol 2-Propanol Acetone Ethanol Methanol DMF DMSO
Hydrazone form (cm1)
Azo form(cm1)
Absorption
Fluorescence
Stokes’ shift
Absorption
Fluorescence
Stokes’ shift
– – – – – – – – – – – – – – –
– – – – – – – – – – – – – – –
– – – – – – – – – – – – – – –
17,953.32 17,271.16 17,889.09 17,211.7 16,564.52 17,467.25 16,644.47 16,650.02 16,700.07 16,722.41 16,789.79 16,736.4 16,977.93 16,168.15 15,910.9
– 16,286.64 – 15,267.18 15,384.62 15,384.62 15,297.54 15,290.52 – 15,290.52 14,814.81 15,151.52 15,060.24 15,698.59 15,479.88
– 984.5122 – 1944.528 1179.903 2082.634 1346.937 1359.497 – 1431.888 1974.977 1584.887 1917.688 469.5616 431.0228
used in the study were of highest available purity from Merck. The organic solvents polarities’ range are 2.02 6 e 6 47.24.The selected empirical polarity parameters, polarity functions [29] and physical properties of the employed solvents are listed in Table 1.
1.2
Absorption spectra 1
Double beam Shimadzu UV-2450 Scan spectrophotometer was used to record the absorption spectra over a wavelength range between 300 and 800 nm, which is combined with a cell temperature controller. Fluorescences of substance’s solutions were studied with a JASCO FP-6200. Quartz cuvettes were used for measurements in solution via 1 cm optical path length. The solute concentrations were chosen 5 105 M, for all the samples. Result and discussion
Absorbance
0.8
Absorption and fluorescence spectroscopy
Hydrazone 0.6
Azo form 0.4
0.2
0 400
450
500
550
600
650
700
λ (nm) Fig. 4. Schematic spectrum decomposition into Gaussian shapes.
The solvent effect on the molecular reorientation of sudan dyes The absorption and fluorescence emission spectra of the studied Sudan dyes (5 105 M) were obtained at room temperature (22 °C), in various organic solvents with different polarities (Figs. 2 and 3). The selective spectral data are summarized in Tables 2–4. It should be noted that, the molecular structures of SudanIII and SudanIV are different than Sudan Black B. These dyes (SudanIII and SudanIV) have protic group (–OH) with naphthol part in a suitable position, as one of the azo bridges for azo-hydrazone
tautomerism. So, these two dyes can show azo-hydrazone tautomerism. Tautomerization in SudanIII and SudanIV adds hydrazone form’s absorption and fluorescence bands in higher wavelength than azo form. Due to the existence of two azo bridges in studied Sudan dyes and also, occurrence of azo-hydrazone tautomerism in one of them (naphthol part), azo-hydrazone forms of SudanIII and SudanIV show overlapping in absorption band. The position of absorption bands of azo and hydrazone forms were obtained with Gaussian fits on the overlapped absorbance spectra (Fig. 4).
344
M.S. Zakerhamidi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 340–348
(a)
and donor (HBD) abilities increase stokes shift and thus stabilize the excited state. To support this mechanism, dipole moments of the studied samples, in ground and excited state, must be calculated, using the obtained experimental data.
5000
(cm-1)
4000
Stokes’ shift of azo form
Evaluation of the dipole moments
3000
Stokes’ shift of hydrazone form
2000
Polar solvents
Low polar solvents 1000 0
10
20
30
40
50
(b) 5000 4000
(cm-1)
Stokes’ shift of azo form 3000
2000
Stokes’ shift of hydrazone form 1000
Polar solvents
Low polar solvents 0 0
(c)
10
20
30
40
50
40
50
5000
(cm-1)
4000
3000
Stokes’ shift of azo form 2000
1000
Low polar solvents
Polar solvents
0 0
10
20
30
Fig. 5. Stokes’ shift of studied Sudan dyes in selected solvents with different polarities, (a) SudanIII, (b) SudanIV, (c) Sudan black B.
Because of high sensitivity of fluorescence spectra, the emission wavelengths of azo and hydrazone forms were obtained directly from fluorescence spectrum, with corresponding excited wavelengths. Furthermore, these dyes, in both forms have low fluorescence intensity and non-radiative deactivation. Stokes shifts of Sudan dyes, Tables 2–4 and Fig. 5, in low polar solvent enhances through increasing the media polarity. But, Polar solvents show different behavior. In other words, stokes shifts value, by increasing the solvent polarity, decreases in these media. In addition, Sudans’ azo form show higher stokes shifts, as compare to hydrazone (SudanIII and SudanIV) forms. The magnitude of stokes shift indicates that the excited state geometry could be different from that of ground state. In other words, by enhancing stokes shift, excited state’s geometry shows same performance as ground states. It can be said that, azo forms in low polar solvent, with higher stokes shifts, have relatively similar configuration in ground and excited state. Furthermore, in stokes shifts of azo and hydrazone (SudanIII and SudanIV) forms, the contribution of specific solvation interactions in polar solvents are higher than general interactions (Fig. 6). In other words, in polar solvents hydrogen-bond acceptor (HBA)
To estimate the ground and excited state dipole moments of sudan azo dyes, first the solvent polarity functions, f(e, n) and f(e, n) + 2g(n), were calculated and presented in Table 1. Then, lin~a v ~ f Þ and ðv ~a þ v ~ f Þ of these ear correlation of spectral shifts ðv matters against the polarity functions f(e, n) and f(e, n) + 2g(n), respectively, were used (Figs. 7 and 8). The data were fit into a straight line using linear curve fitting approach. The slopes of these lines were taken as m1 and m2. Afterwards the ground and excited state dipole moments were calculated, using Eqs. (9) and (10). The results are summarized in Tables 5 and 6. It should be noted that, at first all the solvents were used for obtaining the dipole moments. In the second step, according to statistical factors (e.g. R2 and significance of F-test) and visual inspection, solvents were classified into two groups (polar, e > 13, and low polar, e 6 13, solvents), to increase statistical factors to an acceptable value. For all the studied Sudan dyes in polar and low polar solvents, in azo and hydrazone forms, the obtained dipole moments in excited state (le) is greater than ground state (lg). Increase in dipole moments of excited state demonstrates that compounds are more polar in excited state. The observed variations in the dipole moment values depend on the possible resonance structures1 of the dye and interactions between solvent and solute molecules. The large change in dipole moments of studied dyes in ground and excited states suggests that intramolecular charge-transfer takes place in polar and low polar solvents. Considerable change in ground and excited state’s dipole moments of Sudan dyes in polar solvents implies that the excitation of these dyes in polar and low polar solvents have dissimilar mechanisms and configurations. Increase of singlet excited state’s dipole moments, as compare to ground state, in azo forms of studied sudan dyes in polar solvents are about 16–28 Debye, and in low polar solvents is about 6–10 Debye. Moreover, in hydrazone form of SudanIII and SudanIV this increment is about 14–22 Debye in polar solvents, and about 5–7 Debye in low polar solvents. This change in dipole moment upon excitation can be explained in terms of resonance structures. The first step in explanation of the obtained data is establishing the relation between active molecular functional groups in Sudan dyes and solvation parameters. As it can be seen from Fig. 1, SudanIII and SudanIV have similar active functional groups. Furthermore, azo and hydrazone tautomerism can happen in these dyes. The solvatochromic results and obtained dipole moments indicate different forms of resonance structures for Sudan dyes (Fig. 9), in polar and low-polar solvents. In other words, SudanIII and SudanIV have two tautomeric resonance structures, azo (OH) and hydrazone (NH) form. In azo form, non-bonding electrons on the oxygen, –OH group, contribute towards the mobility of electrons on the aromatic naphthol ring, in polar and low polar solvents, in excited states. However, in Polar solvents, strong solvation effects help distribute the charge on the whole structure. But, low-polar solvents have low solvation effects and so, charge contributing in molecular structure shows local intramolecular charge-transfer. 1 Note that, resonance structures do not actually exist and the actual structure is intermediate among the resonance forms. Because of the charge or electron separation resonance’s importance to molecular geometry, in addition to symmetrically, and these parameters effects on dipole moments we related observed variations in the dipole moment values to the changes in the resonance forms’ structures.
345
M.S. Zakerhamidi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 340–348
1.2
2000
1000
Hydrazone form 500 0
0
0.3
0.2
0.6
0.4
0.6
0.8
0.2
0.4
0.6
0.8
1
2500 2000
2500
1500
2500
Low polar solvents
0
0.2
0.4
0.6
0.8
1
500 1.2
0
0.2
0.4
0.6
0.8
1
1.2 8000
3500
1000
Azo form 500 0.4
0.6
0.8
(c)
1
0
(cm-1)
(cm-1)
1500
4000 1000 3000
500
0.4
Azo form
0
2000 1.2
0.2
2000
0.6
0
0.2
0.8
1
0.6
0.8
1
6000 5000 4000 3000 2000 1000 0 1.2
1.2 6000
3000
Azo form 2500
(cm-1)
0.4
7000
2000 1500 1000
5000 4000 3000
(cm-1)
0.2
5000
2500
Polar solvents
0
6000
Low polar solvents
1500
Polar solvents
Polar solvents
2000
1500
0
3000
Low polar solvents
(cm-1)
2500
4500 3500
7000
3000
5500
1500
500
1.2
3500
6500
Hydrazone form
1
4000
1.2
1000
500 1.2
0.9
0
4500
3500 1500
(b)
5500
Low polar solvents
(cm-1)
2500
(cm-1)
1
(cm-1)
0.8
Polar solvents
0.6
(cm-1)
0.4
(cm-1)
0.2
Polar solvents
0
(a)
2000
500
1000
Low polar solvents 0 0
0.2
0.4
0.6
0.8
1
0 1.2
Fig. 6. Variation of Stokes’ shift data of the Sudan dyes as a function of the specific solvation polarity parameter, a: solvent’s hydrogen bond donor ability, b: solvent’s hydrogen bond acceptor ability, (a) SudanIII, (b) SudanIV, (c) Sudan black B.
In hydrazone form, non-bonding electrons on the nitrogen, –NH in azo group, contribute in the aromatic ring’s resonance in polar and low polar solvents, and such as azo forms, hydrazone form show global and local charge charge-transfer on molecular structure in polar and low polar solvents in excited states, respectively. So, the differences in contributing resonance structures of each tautomeric forms causes the dipole moments and solvatochromic behaviors to show dissimilar performances in polar and low polar solvents. The global intramolecular charge-transfer (GICT) of azo and hydrazone forms of SudanIII and SudanIV, in polar solvents increases the excited state dipole moments as compare to low polar solvents. Furthermore, the methyl groups, contributing in electron mobility of aromatic ring in SudanIV, increases the stability of excited states, reducing the excited state dipole moment of this dye, in comparison to SudanIII in polar solvents.
The local intramolecular charge-transfer (LICT) of these dyes upon excitation in low polar solvents leads to lowly increase of samples’ dipoles, as compared to GICT and as a result, lower dipole moments in excited state are expected. Molecular structure of Sudan black B dye does not has the potential for hydrazone tautomeric form but, different solvatochromic behavior in polar and low-polar solvents expresses different resonance structures of Sudan black B in polar and low-polar solvents. In Sudan black B’s resonance structures, nonbonding electrons on the nitrogen, –NH, in position 3 of 1,3-hydroperimidin group, contribute towards the mobility of electrons on the aromatic naphthol ring in polar solvents, and strong solvation effects help towards the distribution of charge on the whole structure, in excited state. In low polar solvents, non-bonding electrons on the nitrogen, –NH, in position 1 of 1,3-hydroperimidin
M.S. Zakerhamidi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 340–348
1
1.2
(a)
1.4
Azo form
m2 R² = 0.85
5000
m1 R² = 0.86
4000
2000
m2 R² = 0.70
1000 0
0.2
0.4
0.6
0.5
0.7
0.9
1.1
m1 R² = 0.83
2000 36000
m1 R² = 0.71
1000
35000
m2 R² = 0.82
0 0.74
(b) 3000
39500
2500
m1 R² = 0.91
0.78
1.3
1000
m2 R² = 0.80
0.82
0.84
36000
1.4
0.86
1.45
m2 R² = 0.98 m1 R² = 0.98
1500 m2 R² = 0.69
35500 1000 0.74
0.76
0.78
0.8
1.5 40500 39500 38500
m1 R² = 0.93
37500
0
0.82
0.84
0.86
37500 36500
35500 0.88
34500 0.2
0.4
0.6
(c) 1.12 2500
1.14
1.16
1.18
1.2
1.22
1.24
1.26 32500
2000
m1 R² = 0.83 32300
1000 500
1.3
1.35
1.4
1.45
1.5 32100
3500 2800 2100
Azo form
1500
1.25
31900
m2 R² = 0.80
Azo form
0
(c)
0.8
1.35
38500
36500
37000
35000 0.76
1.25
40500
39000 38000
37000
Hydrazone form
m1 R² = 0.90
1.5
m2 R² = 084
2000 2000
1.45
4000
38000
1.3
3000
1.4
40000
0.8
m2 R² = 0.92
1.35
5000
39000
Azo form
(b) 4000
1.3
3000
m1 R² = 0.72
3000
1.25
Azo form
0.8
Hydrazone form
0.6
Azo form
0.4 6000
Hydrazone form
(a)
Hydrazone form
346
31700
1400
m1 R² = 0.82
31500
700 32100
0 0.76
m2 R² = 0.91
0
0.78
0.8
0.82
0.84
0.86
31300 0.88
31900 0
0.2
0.4
0.6
0.8
~a v ~ f with fBK(e, n) ( ) and variation v ~a þ v ~ f with Fig. 8. The variation of v fBK(e, n) + 2gBK(n) ( ) for (a) SudanIII (b) SudanIV and (c) Sudan black B in polar solvents.
~a v ~ f with fBK(e, n) ( ) and variation v ~a þ v ~ f with Fig. 7. The variation of v fBK(e, n) + 2gBK(n) ( ) for (a) SudanIII (b) SudanIV and (c) Sudan black B in low polar solvents.
group, contribute towards the mobility of electrons on the aromatic naphthol ring, and charge-transfer in molecular structure shows partial distribution.
The GICT of Sudan black B in polar solvents, with highest length of charge individuation than SudanIII and SudanIV, shows highest excited state dipole moment. Moreover, in low-polar solvents, LICT of Sudan black B, same as GICT, has greater length of charge individuation and hence the acquired excited state’s dipole moment is highest, compare to SudanIII and SudanIV.
Table 5 Dipole moments, cavity radius of Sudan dyes in azo form.
a
Sudan dyes in azo form
Radius (A°)
m1 (cm1)
m2 (cm1)
lg (D)
le (D)
Ra
In low polar solvents SudanIII SudanIV Sudan black B
7 7 7.4
940 3085 1160
909 2830 824
3.4 3.3 4.7
9.1 12.9 13.5
0.85 0.92 0.83
In polar solvents SudanIII SudanIV Sudan black B
7 7 7.4
19,007 6900 20,739
2169 1072 1517
4.6 5 6
30 20.4 34
0.83 0.98 0.80
R-Square (COD).
347
M.S. Zakerhamidi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 340–348 Table 6 Dipole moments, cavity radius of Sudan dyes in hydrazone form.
a
Sudan dyes in hydrazone form
Radius (A°)
m1 (cm1)
m2 (cm1)
lg (D)
le (D)
Ra
In low polar solvents SudanIII SudanIV Sudan black B
7 7 7.4
822 1578 –
431 1907 –
3.6 3.4 –
8.9 10.7 –
0.70 0.80 –
In polar solvents SudanIII SudanIV Sudan black B
7 7 7.4
14,366 6680 –
5904 1773 –
4.9 5.5 –
27 21 –
0.71 0.69 –
R-Square (COD).
(a) N HN O
N N N
l ow
N
po la
rs olv
en ts low
N HN
Azo form
lv so lar po
N
Hydrazon form
N N
OH
l Po s ar
s nt ve ol rs a l Po
s nt ve ol
N HN
ts en
N
N N
O
N
N N
N
O
(b)
N N
OH
N N
OH
N
N HN
N
N N
N N
OH
O
l ow
po la
rs olv
en ts
low N HN
Azo form
N
Hydrazon form
ts en lv
s ar s nt ve ol
N HN
N N
OH
l Po
o rs la Po
ts en
N
N N
O
lv so
lar po
N
N N
N
O
N N
OH
HN
(c)
HN
low
HN HN
la po
N N
N N
N
N N
ts en olv rs
N N
N N
rs la Po s nt ve ol H N HN
N
Fig. 9. Possible resonance structures of azo Sudan dyes (a) SudanIII, (b) SudanIV, (c) Sudan black B.
348
M.S. Zakerhamidi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 340–348
Conclusions SudanIII and SudanIV can show azo-hydrazone tautomerism. Molecular structure of Sudan black B does not has the potential for hydrazone tautomer form. Moreover, amin functional groups in this dye differ from SudanIII and SudanIV. But, the spectroscopic behaviors of Sudan black B, in polar and low polar solvents, are the same as SudanIII and SudanIV. The results show that, the spectroscopic behaviors of Sudan dyes in polar solvents is controlled by specific solvation interactions. The obtained dipole moments from solvent perturbation method indicate that, for all Sudan dyes, the excited state dipole moments (le) are greater than those in ground state (lg). Moreover, large changes in the dipole moment upon excitation, as compared to ground state, suggests that intramolecular charge-transfer takes place in polar and low polar solvents. Significant variation in the ground and excited state dipole moments of Sudan dyes suggests that upon excitation these dyes, in polar and low polar solvents, have dissimilar configurations. In other words, global intramolecular charge-transfer (GICT) of azo and hydrazone forms of SudanIII and SudanIV in polar solvents increases the excited state dipole moments, than low polar solvents. The local intramolecular charge-transfer (LICT) of these dyes on excitation in low polar solvents causes lowly increase of samples’ dipoles, as compare to GICT and therefore, lower dipole moments in excited state are expected. The Sudan black B in polar and low-polar solvents, with highest length of charge individuation upon excitation, in comparison to SudanIII and SudanIV, shows highest excited state dipole moments. References [1] H. Suzuki, Electronic Absorption Spectra and Geometry of Organic Molecules, Academic Press, New York, 1967. [2] R.J.H. Clark, R.E. Hester, Advances in Material Science Spectroscopy, Wiley, New York, 1991. [3] A.C. Olivieri, R.B. Wilson, I.C. Paul, D.Y. Curtin, J. Am. Chem. Soc 111 (1989) 5525–5532. [4] S. Lunak Jr., M. Nepras, R. Hrdina, H. Mustroph, Chem. Phys 184 (1994) 255– 260.
[5] N. Biswas, S. Umapathy, Chem. Phys. Lett. 236 (1995) 24–29. [6] M.M.J. Tecklenburg, D.J. Kosnak, A. Bhatnagar, D.K. Mohanty, J. Raman Spectrosc. 28 (1997) 755–764. [7] N. Biswas, S. Umapathy, J. Phys. Chem. A 101 (1997) 5555–5566. [8] S. Bell, A. Bisset, T.J. Dines, J. Raman Spectrosc. 29 (1998) 447–462. [9] M.S. Zakerhamidi, M. Keshavarz, H. Tajalli, A. Ghanadzadeh, S. Ahmadi, M. Moghadam, S.H. Hosseini, V. Hooshangi, J. Mol. Liq. 154 (2010) 94–101. [10] A. Ghanadzadeh, M.S. Zakerhamidi, H. Tajalli, J. Mol. Liq. 109 (2004) 143–148. [11] M.S. Zakerhamidi, K. Nejati, Sh. Golghasemi Sorkhabi, M. Saati, J. Mol. Liq. 180 (2013) 225–234. [12] S. Salmani, E. Safari, M.H. Majles Ara, M.S. Zakerhamidi, Opt. Mater. 35 (2013) 1619–1622. [13] M.S. Zakerhamidi, Sh. Golghasemi Sorkhabi, S. Ahmadi-Kandjani, M. Moghadam, E. Ortyl, Spectrochim. Acta A 114 (2013) 148–153. [14] H. Khan mohammadi, A. Abdollahi, Dyes. Pigm 94 (2012) 163–168. [15] S. Salmani, E. Safari, M.H. Majles Ara, M.S. Zakerhamidi, J. Mol. Liq. 182 (2013) 102–105. [16] M.J. Kamlet, J.M. Abboud, R.W. Taft, Prog. Phys. Org. Chem. 13 (1981) 485–630. [17] K. Nowak, S. Wysocki, Spectrochim. Acta A 70 (2008) 805–810. [18] J.R. Mannekutla, B.G. Mulimani, S.R. Inamdar, Spectrochim. Acta A 69 (2008) 419–426. [19] W. Liptay, Excited States, vol. 1, Academic Press, New York, 1974. pp. 129–229. [20] W. Baumann, Physical Methods of Chemistry, vol. 38, John Wiley and Sons, New York, 1989. pp. 45–131. [21] L. Bilot, A. Kawski, Z. Naturforsch 17a (1962) 621–627. [22] A. Kawski, Z. Naturforsch 57a (2002) 255–262. [23] A. Kawski, Progress in Photochemistry and Photophysics, vol. 5, CRC Press, Boston, 1992. [24] N.G. Baksiev, Opt. Skeptrosk. 16 (1964) 821–832. [25] A. Kawski, Acta. Phys. Pol. 25 (1964) 285–290. 479. [26] S.K. Patil, M.N. Wari, C. Yohannan Panicker, S.R. Inamdar, Spectrochim. Acta A 123 (2014) 117–126. [27] J. Kabatc, B. O´smiałowski, J. Paczkowski, Spectrochim. Acta A 63 (2006) 524– 531. [28] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, V.G. Zakrzewski, J.A. Montgomery Jr., R.E. Stratmann, J.C. Burant, S. Dapprich, J.M. Millam, A.D. Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski, G.A. Petersson, P.Y. Ayala, Q. Cui, K. Morokuma, N. Rega, P. Salvador, J.J. Dannenberg, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J. Cioslowski, J.V. Ortiz, A.G. Baboul, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, J.L. Andres, C. Gonzalez, M. Head-Gordon, E.S. Replogle, J.A. Pople, Gaussian 98, Revision A.11.4, Gaussian Inc., Pittsburgh, PA, 2002. [29] C. Reichardt, Solvents and Solvent Effects in Organic Chemistry, second ed., VCH, New York, 1988.
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Polar and low polar solvents media effect on dipole moments of some diazo Sudan dyes M.S. Zakerhamidi a,⇑, Sh. Golghasemi Sorkhabi a, A.N. Shamkhali b,c a
Research Institute for Applied Physics and Astronomy, University of Tabriz, Tabriz, Iran Department of Applied Chemistry, Faculty of Sciences, University of Mohaghegh Ardabili, P.O. Box 56199-11367, Ardabil, Iran c Department of Chemistry, Sharif University of Technology, Tehran 11155-9516, Iran b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Specific interactions in polar solvents
are main interactions in solvatochromism of Sudan. GICT, LICT and sterically hindered control Sudan dyes spectroscopic behavior. Sudan black B has highest charge individuation upon excitation in comparison to SudanIII and IV.
a r t i c l e
i n f o
Article history: Received 30 November 2013 Received in revised form 9 February 2014 Accepted 14 February 2014 Available online 27 February 2014 Keywords: Dipole moment Diazo Sudan dye Solvent–solute interaction Solvent polarity Tautomeric resonance structure Intramolecular charge-transfer
a b s t r a c t Absorption and fluorescence spectra of three Sudan dyes (SudanIII, SudanIV and Sudan black B) were recorded in various solvents with different polarity in the range of 300–800 nm, at room temperature. The solvatochromic method was used to investigate dipole moments of these dyes in ground and excited states, in different media. The solvatochromic behavior of these substances and their solvent–solute interactions were analyzed via solvent polarity parameters. Obtained results express the effects of solvation on tautomerism and molecular configuration (geometry) of Sudan dyes in solvent media with different polarity. Furthermore, analyze of solvent–solute interactions and value of ground and excited states dipole moments suggests different forms of resonance structures for Sudan dyes in polar and low-polar solvents. Ó 2014 Elsevier B.V. All rights reserved.
Introduction Aromatic azo derivatives are one of the largest and the most important classes of colorants. Their practical and theoretical importance have been reflected in textile, food, paper printing, nonlinear optical (NLO) devices and liquid crystalline displays ⇑ Corresponding author. Tel.: +98 411 3393003; fax: +98 411 3347050. E-mail address: [email protected] (M.S. Zakerhamidi). http://dx.doi.org/10.1016/j.saa.2014.02.070 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
(LCDs) [1–14]. Beside the relationship between the structure and the physical-chemical properties of these dyes, characterizations of aromatic azo dyes are also important, for practical applications [9–15]. One of the most fundamental features of azo dyes is spectroscopic capabilities. The spectroscopic behaviors of aromatic azo dyes change with parameters such as; substitution change and media effects. Changes of spectroscopic properties can be investigated via variation of dipole moment, in the studied system.
341
M.S. Zakerhamidi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 340–348
(a) Absorbance
1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
1.Diethyl ether 2.Cyclohexane 3.Acetone 4.Methanol 5.Ethanol 6.2-Propanol 7.DMF 8.1-Butanol 9.1,4-Dioxan 10.CCl4 11.1-Hexanol 12.1-Decanol 13.1-Heptanol 14.Dichloromethane 15.DMSO
λ (nm) Fig. 1. Molecular structure of the Sudan dyes.
(b) 1
v~ a þ v~ f
¼ m1 f ðe; nÞ þ const:
m2 ¼
¼ m2 ½f ðe; nÞ þ 2gðnÞ þ const:
2ðl2e l2g Þ
ð4Þ
3
Parameters m1 and m2 for difference and sum of wave numbers, which are linear functions of solvent polarity functions f(e, n) and g(n), can be determined from slopes of the straight lines. The solvent polarity parameters f(e, n) and g(n) are as followed:
gðnÞ ¼
n2 1 2n2 þ1
e1 2eþ1
1 aa2
1 aa3
480
560
600
1.Cyclohexane 2.CCl4 3.Dichloromethane 4.1,4-Dioxan 5.Diethyl ether 6.Methanol 7.Acetone 8.Ethanol 9.2-Propanol 10.1-Butanol 11.1-Hexanol 12.1-Heptanol 13.1-Decanol 14.DMF 15.DMSO
1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
0.6
0.4
0.2
0 450
500
550
600
650
700
750
800
λ (nm)
n2 1
2n2 þ1 1 2aa3
520
λ (nm)
0.8
ð3Þ
3
e1 2eþ1
440
(c) 1
hca
f ðe; nÞ ¼ 1 2aa3
0 400
1.Diethyl ether 2.Acetone 3.Cyclohexane 4.Ethanol 5.Methanol 6.DMF 7.1,4-Dioxan 8.2-Propanol 9.1-Butanol 10.DMSO 11.1-Hexanol 12.1-Decanol 13.CCl4 14.1-Heptanol 15.Dichloromethane
ð2Þ
2ðle lg Þ2
hca
0.2
ð1Þ
where
m1 ¼
0.6
0.4
Absorbance
v~ a v~ f
0.8
Absorbance
Therefore, developing quantitative measurement of dipole moment and solvation interactions has been of the highest interests [16–18]. Among several ways of determining dipole moment [19,20], the most commonly applied techniques are based on the solvent spectral shift method. In this method, employing the quantum mechanical second order perturbation method and taking into account the Onsager model of reaction field for a polarizable dipole moment ~ a and v ~f . [21–23], leads to expressions for difference and sum of v
1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
n2 1 2n2 þ1
ð5Þ
2
n2 1 2n2 þ1
ð6Þ
n2 1 2n2 þ1
Fig. 2. Absorption spectra of studied group of Sudan dyes in selected solvents with different polarities, (a) SudanIII, (b) SudanIV, (c) Sudan black B.
In these relations, e denotes the dielectric permittivity and n is the refractive index. a and a represent the spherical cavity radius of the solute and average polarizability, respectively. For an isotropic
Table 1 Spectroscopic polarity parameters, physical properties and polarity functions of employed solvents [28]. Solvents
e
a
b
p*
fBK(e, n)
gBK(n)
f(e, n) + 2g(n)
Cyclohexane 1,4-Dioxan CCl4 Diethyl ether 1-Decanol Dichloromethane 1-Heptanol 1-Hexanol 1-Butanol 2-Propanol Acetone Ethanol Methanol DMF DMSO
2.02 2.22 2.24 4.34 8.00 8.93 11.30 13.0 17.5 19.9 21.01 24.3 33.7 39.25 47.24
0.00 0.00 0.00 0.00 0.70 0.13 0.64 0.67 0.84 0.76 0.08 0.86 0.98 0.00 0.00
0.00 0.37 0.10 0.47 0.85 0.10 0.96 0.94 0.84 0.84 0.48 0.75 0.66 0.69 0.76
0.00 0.49 0.21 0.24 0.45 0.73 0.39 0.40 0.47 0.48 0.62 0.54 0.6 0.88 1.00
0.003 0.044 0.023 0.127 0.553 0.590 0.652 0.686 0.750 0.779 0.792 0.812 0.857 0.842 0.841
0.289 0.286 0.311 0.535 0.296 0.288 0.288 0.284 0.271 0.256 0.244 0.246 0.224 0.292 0.324
0.575 0.617 0.646 1.197 1.145 1.166 1.227 1.254 1.293 1.292 1.281 1.303 1.306 1.425 1.489
342
M.S. Zakerhamidi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 340–348
λ Hydrazone form(nm) 350
400
450
500
550
600
650
700
750
800
1.1,4-Dioxane Hydrazon form .................................................. 2.DMSO 4 ,5,12,3,10,13,14,1,7,8,11,9 3.DMF
Azo form ........................................................... 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
Fluorescence (a.u)
4.Acetone 5. Methanol 6.CCl4 7.Cyclohexane 8.1-Hexanol 9.Diethyl ether 10.1-Decanol 11.1-Heptanol 12.2-Propanol 13.Ethanol 14.1-Buthanol 15.Dichloromethane
0 570
620
670
720
770
Fluorescence (a.u)
Azo form ........................................................... 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
600
Hydrazon form 1.Diethyl ether .................................................. 10,3,6,1,5,9,13,2,11,4,14,12 2.1,4-Dioxane 3.CCl4 4.Dichloromethane 5.DMF 6.Acetone 7.DMSO 8.2-Propanol 9.Ethanol 10.Methanol 11.1-Buthanol 12.1-Heptanol 13.1-Decanol 14.1-Hexanol
le ¼
570
620
670
720
770
820
870
Fluorescence (a.u)
Azo form ............................................ 1,2,3,4,5,6,7,8,9,10,11,12
1.1,4-Dioxane 2.DMF 3. DMSO 4.1-Decanol 5.Dichloromethane 6.1-Heptanol 7.1-Hexanol 8.2-Propanol 9.Diethyl ether 10.Ethanol 11.Methanol 12.Acetone
0 350
400
450
500
550
λ Azo form(nm)
600
650
700
m1 þ m2 l ðm1 m2 Þ m1 m2 g
ð11Þ
tively. Onsager cavity radii (a) for investigated samples were determined theoretically according to their optimized geometry [27]. The radius of spherical cavity for each solute, used in Onsager solvation model, was calculated from its optimized gas phase geometry. First, the geometry of the molecule was optimized by B3LYP hybrid-GGA functional and 6-31G(2df, 2p)basis set in gas phase. Then, the molecular volume was computed as a volume inside a contour of 0.001 electron/Bohr3 density and the radius of this spherical’s volume is calculated. All of the calculations were performed by Gaussian 03 program [28]. In this work, the spectral features of three Sudan dyes (SudanIII, SudanIV and Sudan black B) were studied, for estimation of singlet ground and excited-state dipole moments in solvent media with different polarity. Sudan dyes’ ground and excited state dipole moments’ values and solvatochromic behaviors help understand the effects of environment’s polarity on dipole moment and structural configuration of them in ground and excited states.
λ Azo form(nm)
(c)
ð10Þ
h is Plank’s constant and c is the velocity of light in vacuum. le and lg are the dipole moments in the excited and ground states, respec-
0 520
ð9Þ
" # m þ m hca3 1=2 2 1 2 2m1
0 470
ð8Þ
le ¼
700
Fluorescence (a.u)
(b)
500
ð7Þ
" # m m hca3 1=2 2 1 2 2m1
λ Hydrazone form(nm) 400
e 1 n2 1 e þ 2 n2 þ 2
lg ¼
820
λ Azo form(nm)
300
Considering that, the symmetry of the investigated solute molecule does not change during the electronic transition and the ground and excited state dipole moments are parallel, based on the Eqs (3) and (4) one obtains [26]:
0 520
2n2 þ 1 n2 þ 2
" # 3 n4 1 g BK ðnÞ ¼ 2 ðn2 þ 2Þ2
Fluorescence (a.u)
(a)
fBK ðe; nÞ ¼
750
Fig. 3. Fluorescence spectra of studied group of Sudan dyes in selected solvents with different polarities, (a) SudanIII, (b) SudanIV, (c) Sudan black B.
Experimental Material
polarizability of the solute, the condition 2aa3 ¼ 1 is usually satisfied [24–26] and the following relations were obtained by Bakhshiev:
Sudan dyes (Fig. 1) were obtained from Merck (pro analysis) and used without further purification as solutes. All the solvents
Table 2 Absorption and fluorescence spectral data of SudanIII in various solvents. Solvent
Cyclohexane 1,4-Dioxane CCl4 Diethyl ether 1-Decanol Dichloromethane 1-Heptanol 1-Hexanol 1-Buthanol 2-Propanol Acetone Ethanol Methanol DMF DMSO
Hydrazone form (cm1)
Azo form(cm1)
Absorption
Fluorescence
Stokes’ shift
Absorption
Fluorescence
Stokes’ shift
19,267.82 19,043.99 19,004.18 19,349.85 18,968.13 18,935.81 18,946.57 18,996.96 19,065.78 19,149.75 19,293.85 19,186.49 19,208.61 19,091.26 18,843.04
16,393.44 16,501.65 – 16,051.36 16,583.75 – 16,339.87 16,393.44 16,528.93 16,611.3 17,857.14 16,556.29 16,611.3 16,583.75 –
2874.38 2542.341 – 3298.481 2384.386 – 2606.701 2603.518 2536.851 2538.455 1436.702 2630.201 2597.31 2507.508 –
21,463.83 20,920.5 20,973.15 21,537.8 20,881.19 20,721.09 20,790.02 20,929.26 21,088.15 21,267.55 21,445.42 21,331.06 21,303.79 21,181.95 20,533.88
17,361.11 18,484.29 17,574.69 17,182.13 17,182.13 – 17,123.29 17,331.02 17,064.85 17,082.34 18,115.94 17,076.5 17,857.14 18,348.62 18,382.35
4102.722 2436.214 3398.462 4355.668 3699.055 – 3666.733 3598.237 4023.302 4185.209 3329.479 4254.555 3446.649 2833.329 2151.528
343
M.S. Zakerhamidi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 340–348 Table 3 Absorption and fluorescence spectral data of SudanIV in various solvents. Solvent
Cyclohexane 1,4-Dioxane CCl4 Diethyl ether 1-Decanol Dichloromethane 1-Heptanol 1-Hexanol 1-Buthanol 2-Propanol Acetone Ethanol Methanol DMF DMSO
Hydrazone form (cm1)
Azo form(cm1)
Absorption
Fluorescence
Stokes’ shift
Absorption
Fluorescence
Stokes’ shift
19,065.78 18,986.14 18,726.59 19,153.42 18,744.14 18,573.55 18,684.6 18,754.69 18,789.93 18,935.81 19,179.13 19,058.51 19,025.88 18,996.96 18,758.21
– 16,474.46 17,699.12 17,241.38 16,501.65 16,420.36 16,339.87 16,366.61 16,474.46 – 17,361.11 16,556.29 17,825.31 16,835.02 –
– 2511.676 1027.477 1912.04 2242.492 2153.19 2344.735 2388.077 2315.464 – 1818.022 2502.218 1200.563 2161.944 –
21,199.92 21,079.26 20,354.16 21,226.92 20,470.83 20,004 20,279.86 20,437.36 20,454.08 20,790.02 21,427.04 21,235.93 21,008.4 21,344.72 20,618.56
– 19,762.85 19,762.85 20,242.91 17,636.68 – 17,699.12 17,574.69 18,083.18 18,315.02 19,157.09 18,214.94 18,181.82 19,342.36 18,621.97
– 1316.412 591.3166 984.0007 2834.145 – 2580.747 2862.667 2370.898 2475.002 2269.953 3020.995 2826.585 2002.357 1996.583
Table 4 Absorption and fluorescence spectral data of Sudan black B in various solvents. Solvent
Cyclohexane 1,4-Dioxane CCl4 Diethyl ether 1-Decanol Dichloromethane 1-Heptanol 1-Hexanol 1-Buthanol 2-Propanol Acetone Ethanol Methanol DMF DMSO
Hydrazone form (cm1)
Azo form(cm1)
Absorption
Fluorescence
Stokes’ shift
Absorption
Fluorescence
Stokes’ shift
– – – – – – – – – – – – – – –
– – – – – – – – – – – – – – –
– – – – – – – – – – – – – – –
17,953.32 17,271.16 17,889.09 17,211.7 16,564.52 17,467.25 16,644.47 16,650.02 16,700.07 16,722.41 16,789.79 16,736.4 16,977.93 16,168.15 15,910.9
– 16,286.64 – 15,267.18 15,384.62 15,384.62 15,297.54 15,290.52 – 15,290.52 14,814.81 15,151.52 15,060.24 15,698.59 15,479.88
– 984.5122 – 1944.528 1179.903 2082.634 1346.937 1359.497 – 1431.888 1974.977 1584.887 1917.688 469.5616 431.0228
used in the study were of highest available purity from Merck. The organic solvents polarities’ range are 2.02 6 e 6 47.24.The selected empirical polarity parameters, polarity functions [29] and physical properties of the employed solvents are listed in Table 1.
1.2
Absorption spectra 1
Double beam Shimadzu UV-2450 Scan spectrophotometer was used to record the absorption spectra over a wavelength range between 300 and 800 nm, which is combined with a cell temperature controller. Fluorescences of substance’s solutions were studied with a JASCO FP-6200. Quartz cuvettes were used for measurements in solution via 1 cm optical path length. The solute concentrations were chosen 5 105 M, for all the samples. Result and discussion
Absorbance
0.8
Absorption and fluorescence spectroscopy
Hydrazone 0.6
Azo form 0.4
0.2
0 400
450
500
550
600
650
700
λ (nm) Fig. 4. Schematic spectrum decomposition into Gaussian shapes.
The solvent effect on the molecular reorientation of sudan dyes The absorption and fluorescence emission spectra of the studied Sudan dyes (5 105 M) were obtained at room temperature (22 °C), in various organic solvents with different polarities (Figs. 2 and 3). The selective spectral data are summarized in Tables 2–4. It should be noted that, the molecular structures of SudanIII and SudanIV are different than Sudan Black B. These dyes (SudanIII and SudanIV) have protic group (–OH) with naphthol part in a suitable position, as one of the azo bridges for azo-hydrazone
tautomerism. So, these two dyes can show azo-hydrazone tautomerism. Tautomerization in SudanIII and SudanIV adds hydrazone form’s absorption and fluorescence bands in higher wavelength than azo form. Due to the existence of two azo bridges in studied Sudan dyes and also, occurrence of azo-hydrazone tautomerism in one of them (naphthol part), azo-hydrazone forms of SudanIII and SudanIV show overlapping in absorption band. The position of absorption bands of azo and hydrazone forms were obtained with Gaussian fits on the overlapped absorbance spectra (Fig. 4).
344
M.S. Zakerhamidi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 340–348
(a)
and donor (HBD) abilities increase stokes shift and thus stabilize the excited state. To support this mechanism, dipole moments of the studied samples, in ground and excited state, must be calculated, using the obtained experimental data.
5000
(cm-1)
4000
Stokes’ shift of azo form
Evaluation of the dipole moments
3000
Stokes’ shift of hydrazone form
2000
Polar solvents
Low polar solvents 1000 0
10
20
30
40
50
(b) 5000 4000
(cm-1)
Stokes’ shift of azo form 3000
2000
Stokes’ shift of hydrazone form 1000
Polar solvents
Low polar solvents 0 0
(c)
10
20
30
40
50
40
50
5000
(cm-1)
4000
3000
Stokes’ shift of azo form 2000
1000
Low polar solvents
Polar solvents
0 0
10
20
30
Fig. 5. Stokes’ shift of studied Sudan dyes in selected solvents with different polarities, (a) SudanIII, (b) SudanIV, (c) Sudan black B.
Because of high sensitivity of fluorescence spectra, the emission wavelengths of azo and hydrazone forms were obtained directly from fluorescence spectrum, with corresponding excited wavelengths. Furthermore, these dyes, in both forms have low fluorescence intensity and non-radiative deactivation. Stokes shifts of Sudan dyes, Tables 2–4 and Fig. 5, in low polar solvent enhances through increasing the media polarity. But, Polar solvents show different behavior. In other words, stokes shifts value, by increasing the solvent polarity, decreases in these media. In addition, Sudans’ azo form show higher stokes shifts, as compare to hydrazone (SudanIII and SudanIV) forms. The magnitude of stokes shift indicates that the excited state geometry could be different from that of ground state. In other words, by enhancing stokes shift, excited state’s geometry shows same performance as ground states. It can be said that, azo forms in low polar solvent, with higher stokes shifts, have relatively similar configuration in ground and excited state. Furthermore, in stokes shifts of azo and hydrazone (SudanIII and SudanIV) forms, the contribution of specific solvation interactions in polar solvents are higher than general interactions (Fig. 6). In other words, in polar solvents hydrogen-bond acceptor (HBA)
To estimate the ground and excited state dipole moments of sudan azo dyes, first the solvent polarity functions, f(e, n) and f(e, n) + 2g(n), were calculated and presented in Table 1. Then, lin~a v ~ f Þ and ðv ~a þ v ~ f Þ of these ear correlation of spectral shifts ðv matters against the polarity functions f(e, n) and f(e, n) + 2g(n), respectively, were used (Figs. 7 and 8). The data were fit into a straight line using linear curve fitting approach. The slopes of these lines were taken as m1 and m2. Afterwards the ground and excited state dipole moments were calculated, using Eqs. (9) and (10). The results are summarized in Tables 5 and 6. It should be noted that, at first all the solvents were used for obtaining the dipole moments. In the second step, according to statistical factors (e.g. R2 and significance of F-test) and visual inspection, solvents were classified into two groups (polar, e > 13, and low polar, e 6 13, solvents), to increase statistical factors to an acceptable value. For all the studied Sudan dyes in polar and low polar solvents, in azo and hydrazone forms, the obtained dipole moments in excited state (le) is greater than ground state (lg). Increase in dipole moments of excited state demonstrates that compounds are more polar in excited state. The observed variations in the dipole moment values depend on the possible resonance structures1 of the dye and interactions between solvent and solute molecules. The large change in dipole moments of studied dyes in ground and excited states suggests that intramolecular charge-transfer takes place in polar and low polar solvents. Considerable change in ground and excited state’s dipole moments of Sudan dyes in polar solvents implies that the excitation of these dyes in polar and low polar solvents have dissimilar mechanisms and configurations. Increase of singlet excited state’s dipole moments, as compare to ground state, in azo forms of studied sudan dyes in polar solvents are about 16–28 Debye, and in low polar solvents is about 6–10 Debye. Moreover, in hydrazone form of SudanIII and SudanIV this increment is about 14–22 Debye in polar solvents, and about 5–7 Debye in low polar solvents. This change in dipole moment upon excitation can be explained in terms of resonance structures. The first step in explanation of the obtained data is establishing the relation between active molecular functional groups in Sudan dyes and solvation parameters. As it can be seen from Fig. 1, SudanIII and SudanIV have similar active functional groups. Furthermore, azo and hydrazone tautomerism can happen in these dyes. The solvatochromic results and obtained dipole moments indicate different forms of resonance structures for Sudan dyes (Fig. 9), in polar and low-polar solvents. In other words, SudanIII and SudanIV have two tautomeric resonance structures, azo (OH) and hydrazone (NH) form. In azo form, non-bonding electrons on the oxygen, –OH group, contribute towards the mobility of electrons on the aromatic naphthol ring, in polar and low polar solvents, in excited states. However, in Polar solvents, strong solvation effects help distribute the charge on the whole structure. But, low-polar solvents have low solvation effects and so, charge contributing in molecular structure shows local intramolecular charge-transfer. 1 Note that, resonance structures do not actually exist and the actual structure is intermediate among the resonance forms. Because of the charge or electron separation resonance’s importance to molecular geometry, in addition to symmetrically, and these parameters effects on dipole moments we related observed variations in the dipole moment values to the changes in the resonance forms’ structures.
345
M.S. Zakerhamidi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 340–348
1.2
2000
1000
Hydrazone form 500 0
0
0.3
0.2
0.6
0.4
0.6
0.8
0.2
0.4
0.6
0.8
1
2500 2000
2500
1500
2500
Low polar solvents
0
0.2
0.4
0.6
0.8
1
500 1.2
0
0.2
0.4
0.6
0.8
1
1.2 8000
3500
1000
Azo form 500 0.4
0.6
0.8
(c)
1
0
(cm-1)
(cm-1)
1500
4000 1000 3000
500
0.4
Azo form
0
2000 1.2
0.2
2000
0.6
0
0.2
0.8
1
0.6
0.8
1
6000 5000 4000 3000 2000 1000 0 1.2
1.2 6000
3000
Azo form 2500
(cm-1)
0.4
7000
2000 1500 1000
5000 4000 3000
(cm-1)
0.2
5000
2500
Polar solvents
0
6000
Low polar solvents
1500
Polar solvents
Polar solvents
2000
1500
0
3000
Low polar solvents
(cm-1)
2500
4500 3500
7000
3000
5500
1500
500
1.2
3500
6500
Hydrazone form
1
4000
1.2
1000
500 1.2
0.9
0
4500
3500 1500
(b)
5500
Low polar solvents
(cm-1)
2500
(cm-1)
1
(cm-1)
0.8
Polar solvents
0.6
(cm-1)
0.4
(cm-1)
0.2
Polar solvents
0
(a)
2000
500
1000
Low polar solvents 0 0
0.2
0.4
0.6
0.8
1
0 1.2
Fig. 6. Variation of Stokes’ shift data of the Sudan dyes as a function of the specific solvation polarity parameter, a: solvent’s hydrogen bond donor ability, b: solvent’s hydrogen bond acceptor ability, (a) SudanIII, (b) SudanIV, (c) Sudan black B.
In hydrazone form, non-bonding electrons on the nitrogen, –NH in azo group, contribute in the aromatic ring’s resonance in polar and low polar solvents, and such as azo forms, hydrazone form show global and local charge charge-transfer on molecular structure in polar and low polar solvents in excited states, respectively. So, the differences in contributing resonance structures of each tautomeric forms causes the dipole moments and solvatochromic behaviors to show dissimilar performances in polar and low polar solvents. The global intramolecular charge-transfer (GICT) of azo and hydrazone forms of SudanIII and SudanIV, in polar solvents increases the excited state dipole moments as compare to low polar solvents. Furthermore, the methyl groups, contributing in electron mobility of aromatic ring in SudanIV, increases the stability of excited states, reducing the excited state dipole moment of this dye, in comparison to SudanIII in polar solvents.
The local intramolecular charge-transfer (LICT) of these dyes upon excitation in low polar solvents leads to lowly increase of samples’ dipoles, as compared to GICT and as a result, lower dipole moments in excited state are expected. Molecular structure of Sudan black B dye does not has the potential for hydrazone tautomeric form but, different solvatochromic behavior in polar and low-polar solvents expresses different resonance structures of Sudan black B in polar and low-polar solvents. In Sudan black B’s resonance structures, nonbonding electrons on the nitrogen, –NH, in position 3 of 1,3-hydroperimidin group, contribute towards the mobility of electrons on the aromatic naphthol ring in polar solvents, and strong solvation effects help towards the distribution of charge on the whole structure, in excited state. In low polar solvents, non-bonding electrons on the nitrogen, –NH, in position 1 of 1,3-hydroperimidin
M.S. Zakerhamidi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 340–348
1
1.2
(a)
1.4
Azo form
m2 R² = 0.85
5000
m1 R² = 0.86
4000
2000
m2 R² = 0.70
1000 0
0.2
0.4
0.6
0.5
0.7
0.9
1.1
m1 R² = 0.83
2000 36000
m1 R² = 0.71
1000
35000
m2 R² = 0.82
0 0.74
(b) 3000
39500
2500
m1 R² = 0.91
0.78
1.3
1000
m2 R² = 0.80
0.82
0.84
36000
1.4
0.86
1.45
m2 R² = 0.98 m1 R² = 0.98
1500 m2 R² = 0.69
35500 1000 0.74
0.76
0.78
0.8
1.5 40500 39500 38500
m1 R² = 0.93
37500
0
0.82
0.84
0.86
37500 36500
35500 0.88
34500 0.2
0.4
0.6
(c) 1.12 2500
1.14
1.16
1.18
1.2
1.22
1.24
1.26 32500
2000
m1 R² = 0.83 32300
1000 500
1.3
1.35
1.4
1.45
1.5 32100
3500 2800 2100
Azo form
1500
1.25
31900
m2 R² = 0.80
Azo form
0
(c)
0.8
1.35
38500
36500
37000
35000 0.76
1.25
40500
39000 38000
37000
Hydrazone form
m1 R² = 0.90
1.5
m2 R² = 084
2000 2000
1.45
4000
38000
1.3
3000
1.4
40000
0.8
m2 R² = 0.92
1.35
5000
39000
Azo form
(b) 4000
1.3
3000
m1 R² = 0.72
3000
1.25
Azo form
0.8
Hydrazone form
0.6
Azo form
0.4 6000
Hydrazone form
(a)
Hydrazone form
346
31700
1400
m1 R² = 0.82
31500
700 32100
0 0.76
m2 R² = 0.91
0
0.78
0.8
0.82
0.84
0.86
31300 0.88
31900 0
0.2
0.4
0.6
0.8
~a v ~ f with fBK(e, n) ( ) and variation v ~a þ v ~ f with Fig. 8. The variation of v fBK(e, n) + 2gBK(n) ( ) for (a) SudanIII (b) SudanIV and (c) Sudan black B in polar solvents.
~a v ~ f with fBK(e, n) ( ) and variation v ~a þ v ~ f with Fig. 7. The variation of v fBK(e, n) + 2gBK(n) ( ) for (a) SudanIII (b) SudanIV and (c) Sudan black B in low polar solvents.
group, contribute towards the mobility of electrons on the aromatic naphthol ring, and charge-transfer in molecular structure shows partial distribution.
The GICT of Sudan black B in polar solvents, with highest length of charge individuation than SudanIII and SudanIV, shows highest excited state dipole moment. Moreover, in low-polar solvents, LICT of Sudan black B, same as GICT, has greater length of charge individuation and hence the acquired excited state’s dipole moment is highest, compare to SudanIII and SudanIV.
Table 5 Dipole moments, cavity radius of Sudan dyes in azo form.
a
Sudan dyes in azo form
Radius (A°)
m1 (cm1)
m2 (cm1)
lg (D)
le (D)
Ra
In low polar solvents SudanIII SudanIV Sudan black B
7 7 7.4
940 3085 1160
909 2830 824
3.4 3.3 4.7
9.1 12.9 13.5
0.85 0.92 0.83
In polar solvents SudanIII SudanIV Sudan black B
7 7 7.4
19,007 6900 20,739
2169 1072 1517
4.6 5 6
30 20.4 34
0.83 0.98 0.80
R-Square (COD).
347
M.S. Zakerhamidi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 340–348 Table 6 Dipole moments, cavity radius of Sudan dyes in hydrazone form.
a
Sudan dyes in hydrazone form
Radius (A°)
m1 (cm1)
m2 (cm1)
lg (D)
le (D)
Ra
In low polar solvents SudanIII SudanIV Sudan black B
7 7 7.4
822 1578 –
431 1907 –
3.6 3.4 –
8.9 10.7 –
0.70 0.80 –
In polar solvents SudanIII SudanIV Sudan black B
7 7 7.4
14,366 6680 –
5904 1773 –
4.9 5.5 –
27 21 –
0.71 0.69 –
R-Square (COD).
(a) N HN O
N N N
l ow
N
po la
rs olv
en ts low
N HN
Azo form
lv so lar po
N
Hydrazon form
N N
OH
l Po s ar
s nt ve ol rs a l Po
s nt ve ol
N HN
ts en
N
N N
O
N
N N
N
O
(b)
N N
OH
N N
OH
N
N HN
N
N N
N N
OH
O
l ow
po la
rs olv
en ts
low N HN
Azo form
N
Hydrazon form
ts en lv
s ar s nt ve ol
N HN
N N
OH
l Po
o rs la Po
ts en
N
N N
O
lv so
lar po
N
N N
N
O
N N
OH
HN
(c)
HN
low
HN HN
la po
N N
N N
N
N N
ts en olv rs
N N
N N
rs la Po s nt ve ol H N HN
N
Fig. 9. Possible resonance structures of azo Sudan dyes (a) SudanIII, (b) SudanIV, (c) Sudan black B.
348
M.S. Zakerhamidi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 340–348
Conclusions SudanIII and SudanIV can show azo-hydrazone tautomerism. Molecular structure of Sudan black B does not has the potential for hydrazone tautomer form. Moreover, amin functional groups in this dye differ from SudanIII and SudanIV. But, the spectroscopic behaviors of Sudan black B, in polar and low polar solvents, are the same as SudanIII and SudanIV. The results show that, the spectroscopic behaviors of Sudan dyes in polar solvents is controlled by specific solvation interactions. The obtained dipole moments from solvent perturbation method indicate that, for all Sudan dyes, the excited state dipole moments (le) are greater than those in ground state (lg). Moreover, large changes in the dipole moment upon excitation, as compared to ground state, suggests that intramolecular charge-transfer takes place in polar and low polar solvents. Significant variation in the ground and excited state dipole moments of Sudan dyes suggests that upon excitation these dyes, in polar and low polar solvents, have dissimilar configurations. In other words, global intramolecular charge-transfer (GICT) of azo and hydrazone forms of SudanIII and SudanIV in polar solvents increases the excited state dipole moments, than low polar solvents. The local intramolecular charge-transfer (LICT) of these dyes on excitation in low polar solvents causes lowly increase of samples’ dipoles, as compare to GICT and therefore, lower dipole moments in excited state are expected. The Sudan black B in polar and low-polar solvents, with highest length of charge individuation upon excitation, in comparison to SudanIII and SudanIV, shows highest excited state dipole moments. References [1] H. Suzuki, Electronic Absorption Spectra and Geometry of Organic Molecules, Academic Press, New York, 1967. [2] R.J.H. Clark, R.E. Hester, Advances in Material Science Spectroscopy, Wiley, New York, 1991. [3] A.C. Olivieri, R.B. Wilson, I.C. Paul, D.Y. Curtin, J. Am. Chem. Soc 111 (1989) 5525–5532. [4] S. Lunak Jr., M. Nepras, R. Hrdina, H. Mustroph, Chem. Phys 184 (1994) 255– 260.
[5] N. Biswas, S. Umapathy, Chem. Phys. Lett. 236 (1995) 24–29. [6] M.M.J. Tecklenburg, D.J. Kosnak, A. Bhatnagar, D.K. Mohanty, J. Raman Spectrosc. 28 (1997) 755–764. [7] N. Biswas, S. Umapathy, J. Phys. Chem. A 101 (1997) 5555–5566. [8] S. Bell, A. Bisset, T.J. Dines, J. Raman Spectrosc. 29 (1998) 447–462. [9] M.S. Zakerhamidi, M. Keshavarz, H. Tajalli, A. Ghanadzadeh, S. Ahmadi, M. Moghadam, S.H. Hosseini, V. Hooshangi, J. Mol. Liq. 154 (2010) 94–101. [10] A. Ghanadzadeh, M.S. Zakerhamidi, H. Tajalli, J. Mol. Liq. 109 (2004) 143–148. [11] M.S. Zakerhamidi, K. Nejati, Sh. Golghasemi Sorkhabi, M. Saati, J. Mol. Liq. 180 (2013) 225–234. [12] S. Salmani, E. Safari, M.H. Majles Ara, M.S. Zakerhamidi, Opt. Mater. 35 (2013) 1619–1622. [13] M.S. Zakerhamidi, Sh. Golghasemi Sorkhabi, S. Ahmadi-Kandjani, M. Moghadam, E. Ortyl, Spectrochim. Acta A 114 (2013) 148–153. [14] H. Khan mohammadi, A. Abdollahi, Dyes. Pigm 94 (2012) 163–168. [15] S. Salmani, E. Safari, M.H. Majles Ara, M.S. Zakerhamidi, J. Mol. Liq. 182 (2013) 102–105. [16] M.J. Kamlet, J.M. Abboud, R.W. Taft, Prog. Phys. Org. Chem. 13 (1981) 485–630. [17] K. Nowak, S. Wysocki, Spectrochim. Acta A 70 (2008) 805–810. [18] J.R. Mannekutla, B.G. Mulimani, S.R. Inamdar, Spectrochim. Acta A 69 (2008) 419–426. [19] W. Liptay, Excited States, vol. 1, Academic Press, New York, 1974. pp. 129–229. [20] W. Baumann, Physical Methods of Chemistry, vol. 38, John Wiley and Sons, New York, 1989. pp. 45–131. [21] L. Bilot, A. Kawski, Z. Naturforsch 17a (1962) 621–627. [22] A. Kawski, Z. Naturforsch 57a (2002) 255–262. [23] A. Kawski, Progress in Photochemistry and Photophysics, vol. 5, CRC Press, Boston, 1992. [24] N.G. Baksiev, Opt. Skeptrosk. 16 (1964) 821–832. [25] A. Kawski, Acta. Phys. Pol. 25 (1964) 285–290. 479. [26] S.K. Patil, M.N. Wari, C. Yohannan Panicker, S.R. Inamdar, Spectrochim. Acta A 123 (2014) 117–126. [27] J. Kabatc, B. O´smiałowski, J. Paczkowski, Spectrochim. Acta A 63 (2006) 524– 531. [28] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, V.G. Zakrzewski, J.A. Montgomery Jr., R.E. Stratmann, J.C. Burant, S. Dapprich, J.M. Millam, A.D. Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski, G.A. Petersson, P.Y. Ayala, Q. Cui, K. Morokuma, N. Rega, P. Salvador, J.J. Dannenberg, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J. Cioslowski, J.V. Ortiz, A.G. Baboul, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, J.L. Andres, C. Gonzalez, M. Head-Gordon, E.S. Replogle, J.A. Pople, Gaussian 98, Revision A.11.4, Gaussian Inc., Pittsburgh, PA, 2002. [29] C. Reichardt, Solvents and Solvent Effects in Organic Chemistry, second ed., VCH, New York, 1988.
