About intermolecular interactions in binary and ternary solutions of some azo-benzene derivatives

Article abstract of DOI:10.1016/j.saa.2014.07.083

The nature and strength of the intermolecular interactions in the solutions of three azo-benzene derivatives (ADi, i = 1, 2, 3) were established by solvatochromic effects in solvents with different electric permittivities, refractive indices and Kamlet-Taft constants. A quantum mechanical analysis corroborated with spectral data offered information about the excited state dipole moments and polarizabilities of the studied compounds. The separation of the supply of universal and specific interactions to the total spectral shift was made based on the regression coefficients from the equations describing the solvatochromic effect. Supplementary information about the composition of the first solvation shell and the energy in the solute-solvent molecular pairs were obtained analyzing the ternary solutions of ADi, i = 1, 2, 3 compounds in solvent mixture Methanol (M) + n-Hexane (H).

Full text of DOI:10.1016/j.saa.2014.07.083

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
About intermolecular interactions in binary and ternary solutions
of some azo-benzene derivatives q
Liliana Mihaela Ivan a, Valentina Closca a, Marin Burlea b, Elena Rusu c, Anton Airinei c,
Dana Ortansa Dorohoi a,
⇑
a Faculty of Physics, Alexandru Ioan Cuza University, 11 Carol I Bvd., Iasi RO-700506, Romania
b ‘‘Gr.T. Popa’’ University of Medicine and Pharmacy, Faculty of Medicine, 16 University Street, 700115 Iasi, Romania
c ‘‘Petru Poni’’ Institute of Macromolecular Chemistry, 41 A, Aleea Grigore Ghica Voda, Iasi RO-700487, Romania
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
ꢀ
ꢀ
ꢀ
ꢀ
Solvatochromic study of
* absorption band of azo-
benzene derivatives.
Spectral data correlated with
energetic characteristics obtained by
HyperChem.
Excited state dipole moments and
polarizabilities of the studied
molecules.
p
? p
Comparison between the interaction
energy in solute–solvent molecular
pairs.
a r t i c l e i n f o
a b s t r a c t
Article history:
The nature and strength of the intermolecular interactions in the solutions of three azo-benzene deriva-
tives (ADi, i = 1, 2, 3) were established by solvatochromic effects in solvents with different electric permit-
tivities, refractive indices and Kamlet–Taft constants. A quantum mechanical analysis corroborated with
spectral data offered information about the excited state dipole moments and polarizabilities of the stud-
ied compounds. The separation of the supply of universal and specific interactions to the total spectral
shift was made based on the regression coefficients from the equations describing the solvatochromic
effect. Supplementary information about the composition of the first solvation shell and the energy in
the solute–solvent molecular pairs were obtained analyzing the ternary solutions of ADi, i = 1, 2, 3 com-
pounds in solvent mixture Methanol (M) + n-Hexane (H).
Received 3 December 2013
Received in revised form 28 July 2014
Accepted 30 July 2014
Available online xxxx
Keywords:
Azo-benzene derivatives
Electronic absorption spectra
Excited state dipole moment and
polarizability
Ó 2014 Elsevier B.V. All rights reserved.
Interaction energy in molecular pairs
Introduction
tors, as optical storage media, as photorefractive media or as non-
linear optical materials [4–9].
Azo-benzene compounds are characterized by relatively simple
procedures for obtaining [1–3] and they have a widespread range
of applications. They are used in the dye stuff industry, as photo
aligning substrates for liquid crystals, as acid-basic redox indica-
In recent years the utilization of azo compounds as food colo-
rants, as sensitizers in photodynamic therapy or as inhibitors for
tumor growth has attracted much attention [10–12]. The vast area
of their applications emphasizes the importance of understanding
the interactions between the azo-benzene compounds and solvent
molecules since in most cases dye molecules are utilized as solu-
tions and thus their optical characteristics will be determined by
the solvent nature.
q
Selected paper presented at XIIth International Conference on Molecular
spectroscopy Kraków – Białka Tatrzan´ ska, Poland, September 8–12, 2013.
⇑
Corresponding author.
http://dx.doi.org/10.1016/j.saa.2014.07.083
1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: L.M. Ivan et al., About intermolecular interactions in binary and ternary solutions of some azo-benzene derivatives, Spec-
trochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.07.083

2
L.M. Ivan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx
The optical properties of azo-benzene compounds can signifi-
chemical structure; when log P < 0, the chemical structure has
hydrophilic character, while when log P > 0, the chemical structure
has hydrophobic nature. The liophylicity of chemical compounds is
an important factor in its adsorption and distribution in organism.
So, logP plays an important role in biochemical interactions
[22,23].
Hydration energy [19,20] characterizes solution process. The
changes in enthalpy involved in solution process are related to
breaking quasi-chemical bonds by water molecules, separation of
the solvent molecules to accommodate the solute and formation
of new attractive interactions between the solute and solvent mol-
ecules. The total energy involved in these transformations is
named hydration energy [20,23].
cantly vary with the nature of electron donor or acceptor substitu-
ents in the p-positions of the aromatic rings. These substituents
can increase the molar absorptivity or can shift the absorption
maxima to longer or shorter wavelengths.
The presence of donor and/or acceptor groups in the conjugated
system of an azo-benzene derivative will determine different inter-
actions with the solvent molecules which can modify the azo-ben-
zene derivative spectral behavior in solutions. Although there are
studies regarding the solvent action on the electronic transitions
occurring in these molecules [13,14], some correlations between
the results obtained by quantum mechanical calculations and the
solvatochromic effects are also interested.
The aim of this study was to correlate the results obtained by
quantum mechanical calculations using the HyperChem Programs
with those obtained from the solvatochromic analysis. The spectral
studies of some binary and ternary solutions of the studied
4,40-substituted azo-benzene compounds (ADi, i = 1, 2, 3) offer
information about the nature and the strength of the intermolecu-
lar interactions in their liquid phase.
The electric dipole moment, polarizability, the lowest unoccu-
pied molecular orbital (LUMO) and the highest occupied molecular
orbital (HOMO) were estimated by HyperChem 8.0.6., in the limits
of AM1 method, considered as being the best for collecting quanti-
tative information [19,20].
The chemical hardness, the electronegativity, the electrophilic-
ity index and the ionization potential can be also estimated [24]
from the data of Table 1.
Experimental
Intermolecular interactions in binary solutions
Materials
The theories based on the homogeneous solutions considered as
infinite, continuous dielectric media [25,26] express the spectral
The azo-benzene derivatives (ADi, i = 1, 2, 3) were obtained by
esterification between acryloyl chlorides (namely acryloyl, meth-
acryloyl and phenylacryloyl) and azo chromophore, 4-hydroxy-4-
methylazobenzene in the presence of pyridine.
Previously, the azo-chromophore was synthesized by typical
preparation procedure via diazotization and coupling reaction
between hydroxybenzene and 4-amino-1-methylbenzene.
All solvents (Sigma Aldrich) were spectrally grade and used as
received.
ꢁ1
ꢀ
shifts
Dm
ðcm Þ of the electronic bands as functions both of the
microscopic parameters (such as dipole moment (l); electric
polarizability (
and of the macroscopic parameters (such as refractive index (n)
and electric permittivity ( )) and neglect the influence of the spe-
a); molecular radius (a); ionization potential (I))
e
cific interactions on the wavenumber in the maximum of the elec-
tronic bands [25–31].
Statistical methods must be applied to express the frequency
shifts from the electronic absorption spectra Due to the character-
istics of liquid phase [25]. In order to obtain good results in statis-
tical analysis, the aberrant points must be eliminated [32,33] from
the experimental data. In these theories, the spectral shift is sup-
posed to be due to the universal interactions (orientation, disper-
sive, inductive and polarization interactions) and the specific
interactions are neglected.
Dielectric constant – e, refractive index – n, H-bonding donor
ability – b and H-bonding acceptor ability –
taken from literature [15–18].
a of the solvents were
Electronic absorption data
The electronic absorption spectra were recorded at Specord UV
VIS Carl Zeiss Jena spectrophotometer with data acquisition sys-
tem, in 1 cm quartz cells. No concentration dependence of the
wavenumber in the absorption maxima was observed in the stud-
ied concentration ranges.
ꢀ
m
ꢀ
mor:
ꢀ
mdisp
ꢀ
mind:
ꢀ
Dmind:ꢁres
D
¼
D
þ
D
þ
D
þ
ð1Þ
Table 1
Computed by HyperChem 8.0.6 energetic parameters, surface, volume, molecular
mass, hydration energy, logP, dipole moment, polarizability and refractivity of the
studied compounds.
Theoretical background
Quantum mechanical characterization of the studied molecules
Nr.
AD1
AD2
AD3
The energetic and electro-optical parameters of the studied
4,40-substituted azo-benzene compounds were established by
quantum-chemical software [19,20]. HyperChem 8.0.6 [21] with
the Polak Ribiere algorithm and RMS 0.001 kcal/mol was used for
optimizing the structure of the studied molecules by AM1
semi-empirical methods. The results obtained by semi empirical
methods are discussed and compared with those determined from
solvatochromic analysis.
1
2
3
4
5
6
7
Total energy (kcal/mol)
Formation energy (kcal/mol)
Bonding energy (kcal/mol)
EHOMO (eV)
ꢁ69655.81
29.348
ꢁ3779.44
ꢁ8.962
ꢁ0.824
8.138
ꢁ73109.84
18.444
ꢁ87461.66
53.610
ꢁ4988.92
ꢁ9.127
ꢁ0.891
8.236
ꢁ4065.44
ꢁ8.94
ELUMO (eV)
ꢁ0.795
8.145
D
E = |EHOMO ꢁ ELUMO| (eV)
0
518.34
560.27
623.47
Surface (AÅ2)
Volume (AÅ3)
0
8
9
838.41
4.852
896.84
4.802
1042.01
5.014
0
Molecular radius (ÅA)
The EHOMO and ELUMO with changed signs give [19] the molecular
ionization potential and electronegativity, respectively. The differ-
10 Molecular mass (u.a.m)
11 Hydration energy (kcal/mol)
12 LogP
13 Dipole moment (D)
14
266.30
ꢁ9.23
1.63
2.102
30.02
280.33
ꢁ7.97
1.98
2.452
31.86
342.40
ꢁ10.07
2.44
1.541
39.69
ence
D
E = ELUMO ꢁ EHOMO [20] characterizes the molecular reactiv-
ity of the analyzed compounds.
0
Polarizability (ÅA3)
LogP (octanol/water partition coefficient) and the refractivity
are considered as descriptors for a given chemical structure. By
0
15
89.97
95.64
119.88
Refractivity (ÅA2)
its sign, logP gives hydrophilic/hydrophobic character of
a
Please cite this article in press as: L.M. Ivan et al., About intermolecular interactions in binary and ternary solutions of some azo-benzene derivatives, Spec-
trochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.07.083

L.M. Ivan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx
3
The contribution of each type of interactions [34–36] can be
expressed as it follows:
ulate the competition between the active (from the intermolecular
interactions point of view) solvent to occupy the energetically
favored places near the spectrally active molecule [39,40].
Ternary solutions contain homogeneous mixtures of two sol-
lg
ð
lg
ꢁ
l
e cos
a3hc
u
Þ
ꢀ
D
mor:
¼
fð
e
; nÞ
ð2Þ
vents; one active (with molecules noted by
v1) and one inactive
lg2
ꢁ
l2
ag
ꢁ
a
e fð
(with molecules noted by 2) from the intermolecular interactions
v
ꢀ
mind:
D
D
¼
e fðnÞ þ 3kT
e; nÞ
ð3Þ
ð4Þ
a3hc
a3
point of view and a spectrally active molecule (noted by u) and
having the role of sensor in estimating the energy w1 and w2 of
the molecular pairs of the types u ꢁ v1 or u ꢁ v2 [42–44].
ag
ꢁ
ae IuI
v
ꢀ
mdisp
¼
fðnÞ
n2 ꢁ 1
a3
Iu þ I
v
he2f
The advantage of the ternary solutions is to have the possibility
to obtain solvents with appropriate values of macroscopic param-
ꢀ
D
mind:ꢁres ¼ ꢁ
ð5Þ
3
p2
m
v
a
2n2 þ 1
ꢀ
4
eters (n and e) in which the universal forces have appropriate val-
Let us neglect the term due to resonant – induction (ind.-res.) inter-
actions from relation (5) [36], because it is very small compared to
the terms describing the spectral shifts due to orientation (or.),
induction (ind.) and dispersion (disp.) intermolecular interactions.
ues. The specific interactions can be also evidenced in the ternary
solutions.
The average relative number p1 (p2) of the solvent molecules of
types 1 (2) in the first solvation shell of the solute molecule (ADi,
i = 1, 2, 3 in our case) is expressed by:
ꢀ
Dm
ꢀ
m
ꢀ
¼
ꢁ
m0 is the total spectral shift (in electronic absorption
spectra) caused by universal interactions, expressed in cmꢁ1. In
relation (2), Iu, a, and are the ionization potential, the molecular
radius, the electric polarizability and the electric dipole moment of
the spectrally active (solute) molecule; denotes the angle
!
ꢀ
ꢁ
w1
a
l
x1 exp ꢁ kT
N1
N
N2
N
ꢀ
ꢁ
ꢀ
ꢁ
p1 ¼
¼
;
p2 ¼
¼ 1 ꢁ p1
w1
w2
x1 exp ꢁ kT þ x2 exp ꢁ kT
u
ð10Þ
between the dipole moments of the molecule in the two electronic
ꢀ
states participating to the electronic transition; m0 and f are the
In relation (10) p1 and p2 signify the average statistic weights of
the molecules of the types 1 and 2 in the first solvation shell of the
spectrally active molecule, N1 and N2 are the average numbers of
the corresponding types of molecules in the first solvation shell,
N [41–43] is a constant number of solvent molecules in the first
solvation shell of the solute molecule, x1 and x2 are the molar frac-
tions of the two solvents in the ternary solution, w1 and w2 are the
interaction energies in molecular pairs of the types: u ꢁ v1 and
wavenumber and the oscillator strength of the electronic band
for the gaseous phase of the solute; Iv is the ionization potential
of the solvent molecules; n and
electric permittivity of the solvent.
When (2)–(4) are replaced in (1) and the functions of n and
e are the refractive index and the
e
are
separated, one obtains:
ꢀ
D
m
¼ C1fð
e
l
Þ þ C2fðnÞ
e cos
a3hc
ð6Þ
ð7Þ
u ꢁ
v2, respectively, k is the Boltzmann constant and T is the abso-
lg
ð
lg
ꢁ
u
Þ
ag
ꢁ
ae
lute room temperature. Generally, the molecular pair energies are
due to the attractive forces, so, they are negative entities.
The average statistic weights of the solvent molecules in the
first solvation shell of the spectrally active molecule generally dif-
fer from their molar fractions in the binary solvent [42–44].
One can define the excess function (or index of preferential sol-
vation) [45], d(1) as being a measure of the extent of preferential
solvation of the solute molecule in the active (1) solvent.
þ 3kT
¼ C1
a3
le
ðle
ꢁ
l
g cos
a3hc
u
Þ
ag
ꢁ
ae
ag
ꢁ
ae IuI
v
ꢁ 3kT
ꢁ
þ
¼ C2
ð8Þ
a3
a3
Iu þ I
v
The relation (6) is obtained in the limits of a theory in which the
specific interactions are neglected. In order to obtain information
about the strength of the specific interactions in the studied azo-
benzenes solutions, the Kamlet–Taft solvent parameters were
introduced in the final formula describing the solvent influence
on the electronic spectra of the studied azo-derivatives [14].
d
ð1Þ
¼ p1 ꢁ x1
ð11Þ
ꢀ
ꢀ
When d(1) < 0, the solvent molecules of the type (2) prevail in the
first solvation shell of the spectrally active molecule, while d(1) > 0
shows a first solvation shell enriched in the active solvent (1). A
relation of the type (12) has been established in the cell model of
ternary solutions.
mcalc:
¼
m0 þ C1fð
e
Þ þ C2fðnÞ þ C3b þ C4
a
ð9Þ
ꢀ
In relation (9), m0 and Ci i = 1, 2, 3, 4 are coefficients (named regres-
sion coefficients) which can be determined using statistical meth-
ods [14,32,33] when the four solvent characteristics are known
e
ꢁ1
n2ꢁ1
(polarity function fð
e
Þ ¼
,
electron polarizability fðnÞ ¼
,
,
n2þ2
e
þ2
p1
1 ꢁ p1
x1
1 ꢁ x1
w2 ꢁ w1
H-bonding donor ability b and H-bonding acceptor ability
a
ln
¼ ln
þ
ð12Þ
respectively.
kT
ꢀ
The free term m0 signifies the extrapolated value of the wave-
The dependence of the type (12) with a slope near the unity
number in the maximum of the studied
for the gaseous phase of the azo-derivatives; Ci i = 1, 2, 3, 4 reveal
the relative contributions of the considered solvatochromic terms
from (6) [30,37,38]. The term C1f(e) gives the contribution of the
orientation-induction universal interactions, the term C2f(n) esti-
mates the contribution of the dispersion–polarization interactions
to the total spectral shift measured in the electronic spectrum of
each compound. The last two terms measure the contribution of
the specific interactions between the solvent and the spectrally
active molecules.
p ? p
* absorption band
shows the applicability of the cell model of the ternary solutions
in a concrete case. If it is applicable, relation (12) allows us to esti-
mate the difference w2 ꢁ w1 from the value of the cut at origin of
the obtained line written as [41,44]:
p1
1 ꢁ p1
x1
1 ꢁ x1
ln
¼ m ln
þ n
ð120 Þ
w2 ꢁ w1 ¼ nkT
ð13Þ
The difference w2 ꢁ w1 can be estimated by a few methods. In
the limits of the cell model, one can approximate this difference
and also can compare the energies w1 and w2 in pairs of the types
About cell model of ternary solutions
Ternary solutions allow to modify the macroscopic parameters
of the liquid by the concentrations of the two solvents and to stim-
u ꢁ v1 and u ꢁ
v2, respectively. So, when n > 0, it results |w1| > |w2|
while n < 0 indicates that |w1| < |w2|.
Please cite this article in press as: L.M. Ivan et al., About intermolecular interactions in binary and ternary solutions of some azo-benzene derivatives, Spec-
trochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.07.083

4
L.M. Ivan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx
Results and discussions
Quantum mechanical characterization of ADi, i-1, 2, 3
Three compounds were studied from the point of view of corre-
lations between the structural and spectral characteristics:
AD1 4-Methyl-40-oxyacryloyl azo-benzene
AD2 4-Methyl-40-oxymethacryloyl azo-benzene
AD3 4-Methyl-40-oxyphenylacryloyl azo-benzene
Fig. 1b. AD2 optimized structure by HyperChem 8.0.6 (red – Oxygen; blue –
Nitrogen; green – Carbon; white Hydrogen). (For interpretation of the references to
color in this figure legend, the reader is referred to the web version of this article.)
The optimized with Polak Ribiere algorithm structures of the
studied compounds are given in Figs. 1a–c.
Some energetic characteristics, molecular surface and volume,
molecular radius, hydration energy, logP, dipole moment and
polarizability in the ground state of the studied azo-benzene deriv-
atives obtained by HyperChem are listed in Table 1.
As it results from Table 1 and Figs. 1a–c, the studied azo-ben-
zene derivatives (ADi, i = 1, 2, 3) are characterized by comparable
structures with appropriate values of
DE, molecular radius, hydra-
tion energy and logP (see Table 1).
The information about the spatial extension and the molecular
surface, from which one can estimate the molecular radius, are also
listed in Table 1. The compound AD3 having as substitute a ben-
zene ring has the highest values of the surface; volume and molec-
ular radius (see Table 1). Compound AD2 has the highest electric
dipole moment; while compound AD3 is characterized by the high-
est values of polarizability and ionization potential (see Table 1).
Fig. 1c. AD3 optimized structure by HyperChem 8 0 6 (red – Oxygen; blue –
Nitrogen; green – Carbon; white Hydrogen). (For interpretation of the references to
color in this figure legend, the reader is referred to the web version of this article.)
Solvatochromic effects in binary solutions
The studied azo-benzene derivatives show individualized
p
?
p* bands in the UV range of the electronic absorption spec-
trum [14]. The aspect of these bands is illustrated in Fig. 2a and
b for binary solutions of AD1 i = 1, 2, 3 achieved in n-Hexane and
Methanol, respectively.
The electronic absorption spectrum of the compound AD3 is
more complicated due to the presence of a benzene ring in the sub-
stituent structure. The measurements were made for the band with
the higher wavelength. The wavenumber in the binary solutions of
the azo-benzene derivatives are listed in Table 2 in which the sol-
vent parameters are also given. The results of the multilinear
regression applied to the spectral data [9,27] are listed in Table 3.
The minus sign of the regression coefficients indicates a decrease of
the wavenumber (bathochromic effect), while the plus sign indi-
cates an increase (hypsochromic effect) of the wavenumber in the
Fig. 2.
p ? p
* band of the studied azo-benzene derivatives in n-Hexane (continuous
line) and Methanol (doted line).
maximum of the studied
p ? p* band.
The electronic absorption spectra of azo-benzene derivatives
were recorded in some solvents (Table 2) and the wavenumbers
The regression parameters Ci i = 1, 2, 3, 4 are dependent on the
chemical structure of the spectrally active compounds. The nega-
tive sign of these coefficients shows the bathochromic contribution
in the maximum of the
p ? p* band were similar with those listed
of the corresponding terms to the spectral shift. Only the C4(cmꢁ1
)
in Table 1 from [14]. So, the values of the regression coefficients of
Eq. (9) are those from [14] and are listed in Table 3. They are used
in the following assertions.
regression coefficient is positive for all studied compounds, show-
ing that when spectrally active molecules donate hydrogen bonds,
their electronic band shifts to higher wavelengths.
The regression coefficient C2(cmꢁ1) characterizes the dispersive
forces in ADi, i = 1, 2, 3 solutions and the product C2f(n) is propor-
tional with the strength of the dispersive forces.
The regression coefficient C4(cmꢁ1) is proportional with the
energy implied in the hydrogen bond realized by an acceptor sol-
vent. The higher the spectral shifts caused by the dispersive forces,
the higher are the energies of the specific interactions of ADi, i = 1,
2, 3 compounds with the solvent molecules. The specific interac-
tions realized by the proton transfer from the ADi, i = 1, 2, 3
towards the solvent molecules cause a hypsochromic effect in elec-
tronic absorption spectra.
Fig. 1a. AD1 optimized structure by HyperChem 8.0.6 (red – Oxygen; blue –
Nitrogen; green – Carbon; white Hydrogen). (For interpretation of the references to
color in this figure legend, the reader is referred to the web version of this article.)
Please cite this article in press as: L.M. Ivan et al., About intermolecular interactions in binary and ternary solutions of some azo-benzene derivatives, Spec-
trochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.07.083

L.M. Ivan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx
5
Table 2
Solvent parameters and the wavenumbers mðcm Þ in the maximum of the
?
p * absorption band of the studied azo-benzene compounds.
ꢁ1
ꢀ
p
Nr.
Solvent
e
an
a
b
AD1
AD2
AD3
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
n-Hexane
1.89
2.02
2.22
2.24
2.38
9.08
10.42
15.13
17.84
17.93
18.56
20.18
20.80
25.30
33
1.3748
1.4266
1.4224
1.4601
1.4961
1.4242
1.4448
1.4101
1.3993
1.3955
1.3788
1.3776
1.3855
1.3611
1.3288
1.4318
0.00
0.00
0.37
0.00
0.11
0.00
0.00
0.92
0.88
0.84
0.48
0.95
0.85
0.77
0.62
0.52
0.00
0.00
0.00
0.00
0.00
0.30
0.00
0.70
0.79
0.79
0.06
0.76
0.78
0.83
0.93
0.90
30490
30,300
29,990
30,170
29,810
30,080
29,900
30,080
30,080
30,300
29,850
29,810
30,120
29,940
30,210
29,630
30,210
31,120
29,830
29,850
29,630
29,880
29,760
29,760
29,850
29,940
29,670
29,990
29,880
29,910
29,990
29,150
30,410
30,330
30,940
30,940
30,900
30,300
30,120
30,400
30,400
31,060
29,850
30,490
30,860
30,490
30,630
30,300
Cyclohexane
1.4 Dioxane
CCl4
Toluene
Dichloromethane
Dichloroethane
1-Pentanol
1-Butanol
iso-Butanol
2-Butanone
2-Propanol
1-Propanol
Ethanol
Methanol
Ethylene glycol
41.40
Table 3
Regression parameters in relation (9) for ADi, i = 1, 2, 3.
C1 (cmꢁ1
)
C2 (cmꢁ1
)
C3 (cmꢁ1
)
C4 (cmꢁ1
)
R
SD
CP
m0ðcmꢁ1
ꢀ
Þ
AD1
AD2
AD3
31,830
31,860
31,970
ꢁ771.8
ꢁ319.9
285.0
ꢁ5121.9
ꢁ7087.1
ꢁ6143.9
ꢁ54.6
ꢁ243.5
ꢁ59.7
238.7
268.3
257.9
0.99
0.98
0.99
44
43
36
4.9
5.1
5.1
ae ¼ 51:6010ꢁ24 cm3
The solutions of these equations are listed in Table 4. The data
in Table 4 were obtained from systems of equations written above
and by using HyperChem Programs (I, a, lg, ag) and solvatochromic
effects (C1, C2). The system of two equations obtained in the solva-
ð4AD3
Þ
HyperChem calculations indicate positive values for logP and
so, a hydrophobic nature of the studied compounds. The dispersive
interactions are dominant in binary solutions of ADi, i = 1, 2, 3, due
to their hydrophobic nature and to the small values of the electric
dipole moment (see Table 1).
Let us utilise the values of the regression coefficients from
Table 3 and the Eqs. (7) and (8) which express these coefficients
versus the solvent macroscopic and solute microscopic parameters.
One obtains:
tochromic study does not allow estimating the three unknown
molecular parameters le
and polarizability and the angle between the dipole moments in
the electronic states participating to the
p* transition. In
absence of supplementary information for the third equation, the
system was solved in the approximation = 0 for AD1 and AD2
and = 180° for AD3. Our results indicate that the excitation
, ae, u: excited states dipole moment
p
?
ꢁ92:576
le cos
u
þ 5:311
D
a
þ 965:578 ¼ 0
ð1AD1
Þ
u
ꢁ44:042l2e þ92:576
l
e cos
u
ꢁ5:311 þ333:687
D
a
Da
þ5121:89¼0
u
increases the electric dipole moment and the polarizability of the
azo-derivatives under the study.
ð2AD1
u = 1, the solutions of the system (1AD1)–(2AD1) are:
Þ
Þ
For cos
le ¼ 121:891 D and le ¼ 10:166 D
ae ¼ 34:2410ꢁ24 cm3
ð3AD1
Electronic absorption spectra of azo-benzenes derivatives in ternary
solutions
ð4AD1
ð1AD2
Þ
Þ
The electronic absorption spectra of the studied compounds in
binary solvent: Methanol (M) + n-Hexane (H) was studied in order
to obtain more information regarding the intermolecular forces in
azo-benzene solutions we studied.
By using the values of the regression coefficients from Table 3
and the solvent macroscopic parameters of n-Hexane and Metha-
nol (Table 5), the supply of each type of interactions to the total
spectral shift measured in each component of the binary solvent
has been evaluated and the results are given in Table 6.
ꢁ111:490
le cos
u
þ 5:499
D
a
þ 593:496 ¼ 0
ꢁ45:432l2e þ111:490
l
e cos
u
ꢁ5:499 þ 515:721
D
a
D
a
þ7087:1¼0
ð2AD2
u = 1, the solutions of the system (1AD2)–(2AD2) are:
Þ
For cos
le ¼ 225:457 D and le ¼ 4:684 D
ae ¼ 44:82110ꢁ24 cm3
ð3AD2
Þ
ð4AD2
ð1AD3
Þ
Þ
The pair of solvents contains liquids with appropriate values of
refractive indices (nM = 1.331 and nH = 1.375) and different electric
permittivities (eM = 1.89 and nH = 31.0), as it results from Table 5.
ꢁ61:500
l
e cos
u
þ 4:831
D
a
ꢁ 190:229 ¼ 0
ꢁ4:831 þ 458:063
ꢁ39:909l2e þ61:500
le cos
u
D
a
D
a
þ6143:9¼0
ð2AD3
= ꢁ1. The solutions of the system (1AD2)–
Table 4
Data regarding the studied azo-benzene molecules.
Þ
Compound
Iu (eV)
lg (D)
ag (A3)
a (A)
le (D)
ae (A3)
Let us consider cos
(2AD2) are:
u
AD1
AD2
AD3
8.96
8.94
9.13
2.102
2.454
1.541
30.02
31.86
39.69
4.852
4.802
5.014
10.167
4.684
4.005
34.24
44.82
51.60
le ¼ ꢁ150:119 D and le ¼ 4:005 D
ð3AD3Þ
Please cite this article in press as: L.M. Ivan et al., About intermolecular interactions in binary and ternary solutions of some azo-benzene derivatives, Spec-
trochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.07.083

6
L.M. Ivan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx
Table 5
Table 8
x1
p1
1ꢁp1
Solvent parameters for ternary solutions.
ln 1ꢁx , d(1) and ln
for ternary solution ADi + M + H (i = 1, 2, 3).
1
x1
1ꢁx1
ðg=cm3Þ
Solvent
n
e
M (g/mol)
q
=M
l
(D)
AD1
d(1)
AD2
AD3
ln
q
p1
p1
p1
d(1)
d(1)
Methanol (M) 1.3314 31.0
n-Hexane (H) 1.375 1.89 0.6548
0.7918
32.04
86.18
24.713 1.69
7.598
ln 1ꢁp
ln 1ꢁp
ln 1ꢁp
1
1
1
0
–
0
–
0
–
0
–
ꢁ1.774
ꢁ1.025
0.072
1.169
2.266
–
ꢁ0.091
ꢁ0.193
ꢁ0.375
ꢁ0.442
ꢁ0.335
0
ꢁ2.863
ꢁ2.571
ꢁ1.791
ꢁ0.749
0.286
–
ꢁ0.122
ꢁ0.219
ꢁ0.427
ꢁ0.627
ꢁ0.406
0
ꢁ3.749
ꢁ3.055
ꢁ2.254
ꢁ1.849
0.000
–
ꢁ0.074
ꢁ0.121
ꢁ0.161
ꢁ0.640
ꢁ0.049
0
ꢁ2.566
ꢁ1.791
ꢁ0.588
0.588
1.791
–
Table 6
Supply of each type of intermolecular interactions in n-Hexane and Methanol.
ADi
cmꢁ1
C1f(
%
e
)
C2f(n)
C3b
C4
a
C1f(
e
)
C2f(n)
C3b
C4
a
n-Hexane
ꢁ180
ꢁ73
AD1
AD2
AD3
ꢁ1172
ꢁ1621
ꢁ1406
0
0
0
0
0
0
13
4
4
87
96
96
0
0
0
0
0
0
+65
Methanol
ꢁ706
AD1
AD2
AD3
ꢁ1041
ꢁ1441
ꢁ1249
ꢁ51
ꢁ226
ꢁ56
148
166
160
36
14
15
53
68
72
3
10
72
8
8
9
ꢁ294
+261
Table 7
Volumetric ratio C1 (%) of active solvent (1), electric permittivity
e
of binary solvent,
wavenumbers vðcm Þ in the maximum of
p ?
p * band of azobenzenes, molar
ꢁ1
ꢀ
fraction x1 of active solvent and average statistic weight p1 of the solvent (1) in the
first solvation shell of azo-benzenes for ternary solution ADi + M + H (i = 1, 2, 3).
ꢁ1
C1 (%)
e
ꢀ
v
x1
p1
ðcm
Þ
AD1
AD2
AD3
AD1
AD2
AD3
0
5
2.00 30,490 30,210 30,490 0.000 0.000 0.000 0.000
6.00 30,475 30,205 30,500 0.145 0.054 0.023 0.071
10
25
50
75
100
10.00 30,470 30,200 30,510 0.264 0.071 0.045 0.143
17.8
23.0
25.2
31.0
30,450 30,190 30,540 0.518 0.143 0.091 0.357
30,400 30,180 30,580 0.763 0.321 0.136 0.643
30,330 30,100 30,610 0.906 0.571 0.500 0.857
30,210 29,990 30,630 1.000 1.000 1.000 1.000
Fig. 3. p1 vs. x1 for AD1 in binary solvent Methanol + n-Hexane.
In these conditions, one can suppose that the dispersive–induc-
tive interactions are of the same strength in ternary solutions when
the active solvent concentration is varied. Only orientation-induc-
tion or possible specific interactions will contribute to the spectral
shifts measured in ternary solutions with the active solvent in var-
iable volumetric ratios.
The data regarding the ternary solution Azo-benzene deriva-
tive + Methanol + n-Hexane are listed in Tables 5 and 7. From these
tables it results an exponential increase of the average statistic
weight of Methanol in the first solvation shell of azo-benzene
p1
x1
Fig. 4. (a–c) ln 1ꢁp vs. ln 1ꢁx for ADi, i = 1, 2, 3.
1
1
Please cite this article in press as: L.M. Ivan et al., About intermolecular interactions in binary and ternary solutions of some azo-benzene derivatives, Spec-
trochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.07.083

L.M. Ivan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx
7
Table 9
Regression coefficients in equation ln 1ꢁp ¼ m ln 1ꢁx þ n for ADi, i = 1, 2, 3.
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1
1
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Solvent
Molecule m
D
m
n
D
n
R
SD w2 ꢁ w1
(10ꢁ20 J)
Methanol + n-
Hexane
AD1
AD2
AD3
0.80 0.06 ꢁ1.65 0.09 0.97 0.19 ꢁ 0.67 0.03
0.85 0.12 ꢁ2.31 0.18 0.92 0.39 ꢁ 0.94 0.07
1.08 0.01 ꢁ0.67 0.01 0.99 0.01 ꢁ0.27 0.00
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derivatives (see Fig. 3) when its molar fraction in the binary solvent
increases (see Table 8)
In binary solvent M + H, the excess function d(1) is negative,
showing a prevalence of non-polar solvent n-Hexane in the first
solvation shell of the studied azo-benzene derivatives. This result
is in accordance with the positive value of the computed by Hyper-
Chem parameter logP which is positive, showing the hydrophobic
nature of ADi, i = 1, 2, 3.
p1
x1
The linear dependencies of the quantities ln 1ꢁp and ln 1ꢁx
,
shown in Fig. 4a–c, demonstrate the applicability of the ternar1y
solutions model to the spectral data obtained for ADi + M + H
(i = 1, 2, 3).
1
In Table 9 are listed the regression coefficients of the lines
p1
x1
ln 1ꢁp ¼ m ln 1ꢁx þ n illustrated in Fig. 4a–c.
1
1
As it results from Table 9, the slope m is near the unity for AD3
and smaller the unity for AD1 and AD2 in ternary solutions ADi
(i = 1, 2, 3) + M + H.
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Conclusions
The
p ?
p* band of azo-benzene derivatives generally shifts
bathochromically under the influence of the universal interactions,
while the specific interactions with the solvents having H-bonding
acceptor ability contribute to its hypsochromic shift.
By using a semi-empirical formula of the type (9), the contribu-
tion of the universal and of the specific interactions can be sepa-
rated from the total spectral shift measured in the electronic
absorption spectra of azobenzene.
The difference between the interaction energies in solute–sol-
vent molecular pairs of the types u ꢁ v1 and u ꢁ v2 azo-benzene
derivative-active solvent and azo-benzene derivative-inactive sol-
vent was estimated on the basis of the cell theory of ternary solu-
tions. The negative values of the difference w2 ꢁ w1 show that
|w2| > |w1| and are in accordance with hydrophobic nature of the
studied compounds.
The slope of Eq. (10) linearly depends on the correlation coeffi-
cient C1(cmꢁ1).
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Please cite this article in press as: L.M. Ivan et al., About intermolecular interactions in binary and ternary solutions of some azo-benzene derivatives, Spec-
trochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.07.083