Quantum chemical modeling of new derivatives of (E,E)-azomethines: Synthesis, spectroscopic (FT-IR, UV/Vis, polarization) and thermophysical investigations

Article abstract of DOI:10.1016/j.molstruc.2017.02.056

In the present work, the molecular structures of three new azomethine dyes: N-benzylidene-4-((E)-phenyldiazenyl)aniline (PAZB-1), 2-methoxy-4-(((4-((E)- phenyldiazenyl)phenyl)imino)methyl)phenol (PAZB-2) and 2-methoxy-5-((E)-((4-((E)- phenyldiazenyl)phenyl)imino)methyl)phenol (PAZB-8) have been predicted and investigated using Density Functional Theory (DFT) in dimethylformamide (DMF). The geometries of the azomethine dyes were optimized by PBE0/6-31?+?G* level of theory. The electronic spectra of these azomethine dyes in a DMF solution was carried out by TDPBE0/6-31?+?G* method. After quantum-chemical calculations three new azomethine dyes for optoelectronic applications were synthesized. FT-IR spectra of the title compounds are recorded and discussed. The computed absorption spectral data of the azomethine dyes are in good agreement with the experimental data, thus allowing an assignment of the UV/Vis spectra. On the basis of polyvinyl alcohol (PVA) and the new synthesized azomethine dyes polarizing films for Visible region of spectrum were developed. The main optical parameters of polarizing PVA-films (Transmittance, Polarization Efficiency and Dichroic Ratio) have been measured and discussed. Anisotropy of thermal conductivity of the PVA-films has been studied.

Full text of DOI:10.1016/j.molstruc.2017.02.056

Accepted Manuscript
Quantum Chemical Modeling of New Derivatives of (E,E)-Azomethines: Synthesis,
Spectroscopic (FT-IR, UV/Vis, Polarization) and Thermophysical Investigations
Siyamak Shahab, Masoome Sheikhi, Liudmila Filippovich, Dikusar Evgenij Anatol’
evich, Hooriye Yahyaei
PII:
S0022-2860(17)30200-4
10.1016/j.molstruc.2017.02.056
MOLSTR 23450
DOI:
Reference:
To appear in:
Journal of Molecular Structure
Received Date:
Revised Date:
Accepted Date:
21 November 2016
08 February 2017
13 February 2017
Please cite this article as: Siyamak Shahab, Masoome Sheikhi, Liudmila Filippovich, Dikusar
Evgenij Anatol’evich, Hooriye Yahyaei, Quantum Chemical Modeling of New Derivatives of (E,E)-
Azomethines: Synthesis, Spectroscopic (FT-IR, UV/Vis, Polarization) and Thermophysical
Investigations, Journal of Molecular Structure (2017), doi: 10.1016/j.molstruc.2017.02.056
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Highlights
 Modeling and Synthesis of new azomethine dyes.
 Investigation of electronic properties and NBO analysis.
 Preparation of polarizing PVA-films.
 Anisotropy of thermal conductivity of PVA-films contains new dyes.

Recording experimental and calculated UV–Vis spectra of new dyes.

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Sub: Submission of manuscript for full paper in Journal of Molecular Structure
Dear Sir,
Please find here with the enclosed manuscript:
Article title
Quantum Chemical Modeling of New Derivatives of (E,E)-Azomethines: Synthesis,
Spectroscopic (FT-IR, UV/Vis, Polarization) and Thermophysical Investigations
The name of journal:
Journal of Molecular Structure
The author’s affiliations with full postal address
Siyamak Shahab
Institute of Physical Organic Chemistry
National Academy of Sciences of Belarus, 13 Surganov Str., Minsk 220072
E-mail: siyamak.shahab@yahoo.com
Liudmila Filippovich
Institute of Physical Organic Chemistry
National Academy of Sciences of Belarus, 13 Surganov Str., Minsk 220072
E-mail: luda1977@list.ru
Masoome Sheikhi
Young Researchers and Elite Club, Gorgan Branch, Islamic Azad University, Gorgan, Iran
E-mail: m.sheikhi2@gmail.com
Dikusar Evgenij Anatol’evich
Institute of Physical Organic Chemistry
National Academy of Sciences of Belarus, 13 Surganov Str., Minsk 220072
E-mail: dikusar@ifoch.bas-net.by
Hooriye Yahyaei
Department of Chemistry, Zanjan Branch, Islamic Azad University, Zanjan, Iran
E-mail: Hooriye_yahyaei@yahoo.com
1

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Quantum Chemical Modeling of New Derivatives of (E,E)-Azomethines: Synthesis,
Spectroscopic (FT-IR, UV/Vis, Polarization) and Thermophysical Investigations
Siyamak Shahaba,b, Masoome Sheikhic, Liudmila Filippovicha,b, Dikusar Evgenij Anatol’evicha, Hooriye Yahyaeid
aInstitute of Physical Organic Chemistry, National Academy of Sciences of Belarus,13 Surganov Str, Minsk 220072
bInstitute of chemistry of new materials, National Academy of Sciences of Belarus, 36 Skarina Str., Minsk 220141
cYoung Researchers and Elite Club, Gorgan Branch, Islamic Azad University, Gorgan, Iran
dDepartment of Chemistry, Zanjan Branch, Islamic Azad University, Zanjan, Iran
Abstract
In the present work, the molecular structures of three new azomethine dyes:
N-benzylidene-4-((E)-phenyldiazenyl)aniline
phenyldiazenyl)phenyl)imino)methyl)phenol
(PAZB-1),
(PAZB-2) and
2-methoxy-4-(((4-((E)-
2-methoxy-5-((E)-((4-((E)-
phenyldiazenyl)phenyl)imino)methyl)phenol (PAZB-8) have been predicted and investigated
using Density Functional Theory (DFT) in dimethylformamide (DMF). The geometries of the
azomethine dyes were optimized by PBE0/6-31+G* level of theory. The electronic spectra of
these azomethine dyes in a DMF solution was carried out by TDPBE0/6-31+G* method. After
quantum-chemical calculations three new azomethine dyes for optoelectronic applications were
synthesized. FT-IR spectra of the title compounds are recorded and discussed. The computed
absorption spectral data of the azomethine dyes are in good agreement with the experimental
data, thus allowing an assignment of the UV/Vis spectra. On the basis of polyvinyl alcohol
(PVA) and the new senthesized azomethine dyes polarizing films for Visible region of spectrum
were developed. The main optical parameters of polarizing PVA-films (Transmittance,
Polarization Efficiency and Dichroic Ratio) have been measured and discussed. Anisotropy of
thermal conductivity of the PVA-films has been studied.
Keywords
Azomethine dye; DFT calculation; UV/Vis spectrum; Polarizing film; Anisotropy of thermal
conductivity
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Corresponding authors: Corresponding authors: m.sheikhi2@gmail.com (M. Sheikhi); siyamak.shahab@yahoo.com
(S. Shahab)
1. Introduction
Azomethines with phenyl rings isolated by an azo (–N=N–) bond, serves as the guardian
molecule for a wide class of aromatic compounds. These chromophores are adaptable atoms, and
have obtained much consideration in both fundamental and applied research. Azo groups are
moderately strong and chemically stable, has provoked broad investigation of azomethines based
structures as dyes and colorants [1,2]. Azomethines have flexible relevance in different areas
running from complexes [3], photoluminescence materials [4] to advanced applications such as
optical materials and devices [5,6], organic light-emitting diodes [7], photovoltaic cells [8] and
polarizing films [1,2,5]. Azomethines also possess interesting properties like cis-trans
photoisomerization about the azo p-bond when heated or irradiated in UV [9]. They are the most
widely used classes of dyes for photonic applications like lasers, spectroscopic analysis, liquid
crystal devices and optoelectronic systems [1-6]. Conventionally, polarizing films are
manufactured from uniaxially oriented polymer sheet containing dichroic material such as
azomethines. These structures are beneficial for achieving higher dichroism due to their linear
structure and anisotropic transition moment. Theoretical quantum chemistry methods based on
HF and DFT are widely used for the calculation of optimized geometry, absorption spectrum,
UV, IR and NMR spectra of organic molecules [4-5,7-15]. According to the authors [9,10] DFT
method fully describes the geometry of molecules, vibration spectra and excited states of
platinum-Olefin complexes and benznidazole. Electronic transitions of benznidazole were also
obtained after DFT calculations. Molecular geometry optimizations and absorption peaks were
also obtained within the DFT and TD-DFT methods and it has been found that there is excellent
agreement between theory and experiment [11,12]. It has been claimed that the ab initio method
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provides more accurate results than thesemi-empirical calculation of the intensity in the IR
spectra of compounds. Researchers have also presented the results of TD-DFT calculations of the
oxazine dyes [13,14]. The gas-phase optimized geometries of the dyes were used as the basis for
the single point excited state calculations. From the literature survey it has been observed that the
ab initio Hartree-Fock-Roothaan with different choices of basis sets compared to other ab initio
quantum chemistry methods fully describes the features of the electronic structure of molecules
containing the biphenyl fragment [4-5]. In this study we predicted and modeled geometrical
parameters, UV/Vis and IR spectra of new synthesized azomethines by PBE0 method with 6-
31+G* basis set. On the basis of PVA, the new synthesized dichroic structures polarizing films
absorbing in Visible region of spectrum with high anisotropy of thermal conductivity were
developed.
2. Experimental details
2.1 Reagent and apparatus
All chemicals used were of analytical reagent grade. PVA used in this work «Mowiol 28-99»
was purchased from Hoёchst Akiengesllschaft Co. (Germany). The experimental UV absorption
spectra of the title molecules were recorded on UV-Visible Spectrophotometer Cary300 (Varian,
USA). The optical transmission spectra were measured in polarized light with UV-NIR
Spectrophotometer HR4000 (Ocean optics, USA). Experimental IR-spectra of films was
recorded in the frequency region 400-4000 cm-1 on a Spectrophotometer of Protégé 460 (Nicolet,
US). Thermal conductivity of films was measured on the complex equipment LC–201 (Alfa
Laval Group, Sweden) using indicator method of determining the thermal conductivity of
polymer materials and thin films.
2.2 Preparation of polarizing PVA-films
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The PVA-films were prepared from (wt. %) 10 PVA solution containing 0.01-0.03 PAZB-1,
PAZB-2, PAZB-8 (0.10-0.30 in film), 0.01 boric acid (H3BO3), 6.0 ethyl alcohol (C2H5OH) and
water. An initial composition was prepared by dissolving PVA indistilled water and ethyl
alcohol. The composition was mixed at temperature 85-90 °C. The compounds PAZB-1, PAZB-
2, PAZB-8 and additives were added after 3 hours after starting of heating PVA solution at
intervals 20 min. The mixture was heated for 3 h. The hot solution was filtered through two
layers of technical nylon. Deaeration was occurred during 12-15 h. The composition was cast on
the polished glasses and dried in the closed box at temperature 20-22 °C. Uniaxial orientation
was done in the 4 % boric acid solution at temperature 42-45 °C. The washed film was dried for
30 min. at temperature 60-63 °C. The value of Stretching Degree (Rs) was determined as the
ratio between length of the films after and before (laft / lbef) uniaxial orientation. The thickness of
the resulting films was between 50 to 55 µm [1,2]. The film thickness was measured with
amicrometer with an accuracy of 5 µm (GS SSSR6507-90).
Accuracy of measurements in this research limits the accuracy of the results:
- Sample of the starting composition for preparation of solutions and films for casting taken on
an analytical balance accurate to 0.0005 g;
- Temperature measurement error was:
2.0 C in the preparation of polymer solutions with additives,
1.0 C in the chemical treatment of the films,
3.0 C at thermal fixation and drying films;
- Relative error of spectrophotometric analysis did not exceed 1.0 % and thermal conductivity
0.1 %.
The standard deviation of parallel measurements determined by the formula [12-15]:
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(d  d)2 / n 1
S(d) =
(1)

i
i
Wheredi -the result of a single measurement,
d- Arithmetic mean
n- Number of measurements.
2.3 Computational methods
In this work, we have carried out quantum theoretical calculations and have optimized structures
of the title compounds using the Density Functional Theory (DFT) method with 6-31+G* basis
set by the Gaussian 09W program package [16] in a solvent DMF. The optimized molecular
structures, HOMO and LUMO surfaces were visualized using GaussView 05 program. The
obtained structures were fully optimized by functional PBE0 (One-parameter hybrid PBE
functional incorporating 25% HF exchange) at 6-31+G* basis set. Inaddition to optimization, the
Time Dependent Density Functional Theory (TD-DFT) was also used for computing the
electronic transitions. To account solvent effect Polarized Continuum Model (PCM) was used
[15]. Theoretical absorption spectrum of all the molecules in a solvent DMF was calculated
using TDPBE0/6-31+G* method. Also the theoretical IR spectra of optimized structures was
calculated using PBE0/6-31+G* method. The electronic properties such as EHOMO, ELUMO
,
HOMO-LUMO energy gap (Eg) and natural charges were calculated [6]. Also the electronic
structure of the title compound were studied using Natural Bond Orbital (NBO) analysis [17] at
the PBE0/6-31+G* level of energy in order to understand hyperconjugative interactions and
charge delocalization.
2.3.1 Optimized structure of the compounds PAZB-1, PAZB-2, PAZB-8
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DFT calculations were performed for the three new compounds PAZB-1, PAZB-2, PAZB-8 and
their optimized molecular structures are shown in Fig. 1. The entire quantum chemical
calculations were performed using the Gaussian 09 software package and Gauss view 05
visualization programs [16] on a Pentium IV/4.02 GHz personal computer. The theoretical
molecular structure of the title compounds in the ground state was optimized by DFT/PBE0/6-
31+G* level of theory. To account solvent (DMF) effect the IEFPCM (Integral Equation
Formalism PCM) method coupled to UAKS radii was used. The Integral Equation Formalism
PCM, by Cances, Mennucci and Tomasi is the most popular PCM version. It employs a molecule
shaped cavity composed of spheres centered on the nuclei, while the reaction field is modeled by
placing charges on the cavity surface.
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Fig. 1. Optimized molecular structures of compounds PAZB-1, PAZB-2, PAZB-8 calculated by PBE0/6-31+G*
method.
2.3.2 Electronic Structure and Excited States of the compounds PAZB-1, PAZB-2, PAZB-8
Theoretical absorption spectra of the title compounds optimized in DMF were calculated using
TDPBE0/6-31+G* method. The equations were solved for 20 excited states, where the
computational studies were performed using the IEFPCM (Integral Equation Formalism PCM)
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method coupled to UAKS radii. The TDDFT method is able to detect accurate absorption
wavelength at a relatively small computing time, which corresponds to electronic transitions
computed on the ground state geometry.
PAZB-1) The broad absorption band at λmax = 369 nm and the oscillator strength f = 1.45 refers
to the transition of the molecule to excited singlet state S3 (Table 1). The strong peak at 369 nm is
due to the Charge-Transfer (CT) excited singlet state. Excitation of one electron at 369 nm
belonged to the transition into the excited singlet state S3 and describes by a wave function
corresponding to configuration for one-electron excitation from (HOMO)→(LUMO). According
to Fig. 2, the electron density of HOMO is mainly focused on azo group (-N=N-) and LUMO is
mainly focused on double bonds (-C=C-) of three aryl rings and azo group (-N=N-). Therefore
the electronic transitions from the HOMO to LUMO are due to the contribution of pi (π) bonds.
The other excited states have very small intensity (f ≈ 0): these transitions are nearly forbidden
by orbital symmetry considerations (Table 1).
Table 1
Electronic absorption spectrum of the compound PAZB-1 calculated by TDPBE0/6-31+G* method.
Excited Wavelength
Excitation
Energy (eV)
2.28
Configurations Composition
(corresponding transition orbitals)
-0.12(H-2→L) + 0.67(H-1→L) + 0.16(H-1→L+1)
0.12(H-2→L) - 0.20(H-2→L+1) + 0.12(H-1→L)
0.71(H→L)
0.54(H-4→L) +0.40(H-3→L)- 0.12(H→L+1)
0.49(H-6→L) - 0.17(H-5→L) + 0.33(H-4→L)
-0.30(H-3→L) + 0.12(H→L+2)
Oscillator
Strength (f)
0.00
State
S1
S2
S3
(nm)
545
440
369
324
2.82
3.36
3.82
0.00
1.45
0.00
S4
S5
S6
320
319
3.88
3.89
0.11
0.00
0.36(H-6→L) - 0.17(H-5→L) - 0.25(H-4→L)
+ 0.37(H-3→L) - 0.36(H→L+1)
S7
S8
S9
S10
S11
317
311
308
292
264
3.91
3.99
4.02
4.25
4.68
0.26(H-6→L) + 0.64(H-5→L)
0.03
0.00
0.00
0.18
0.01
0.21(H-2→L) + 0.59(H-2→L+1) + 0.32(H-1→L+1)
- 0.33(H-2→L+1) - 0.16(H-1→L) + 0.60(H-1→L+1)
0.18(H-6→L) + 0.33(H-3→L) + 0.59(H→L+1)
0.68(H-7→L) + 0.14(H→L+5)
0.12(H-5→L) + 0.56(H-5→L+1) - 0.10(H-4→L+1)
+ 0.12(H-3→L+1) - 0.10(H-3→L+2) + 0.30(H→L+2)
- 0.12(H→L+4)
0.48(H-6→L+1) + 0.13 (H-5→L+1) - 0.44(H-3→L+1)
- 0.19(H→L+4)
S12
S13
252
249
4.91
4.98
0.00
0.09
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- 0.12(H-4→L) + 0.56(H-4→L+1) + 0.21(H-3→L+1)
- 0.29(H→L+3)
0.45(H-6→L+1) - 0.17(H-4→L+1) + 0.45(H-3→L+1)
- 0.17(H→L+5)
S14
S15
243
241
5.10
5.13
0.00
0.08
S16
S17
240
239
5.15
5.16
0.55(H-1→L+2) - 0.10(H-→L+3) + 0.42(H-1→L+4)
- 0.13(H-2→L+3) + 0.67(H-1→L+3) + 0.16(H-1→L+4)
- 0.13(H-6→L) + 0.13(H-6→L+1) - 0.12(H-6→L+5) -
0.18(H-5→L+1) + 0.55(H→L+2) + 0.29(H→L+4)
0.62(H-2→L+2) + 0.31(H-2→L+4)
0.00
0.08
S18
238
5.21
0.00
S19
S20
231
229
5.36
5.42
0.12
0.06
0.33(H-4→L+1) + 0.59(H→L+3)
*H-HOMO, L-LUMO
Fig. 2. Form of the MO involved in formation of absorption spectrum of the compound PAZB-1 at λmax = 369 nm.
Experimental UV/Vis spectrum of the compound PAZB-1 in DMF at concentration 4.0·10–4M
and calculated spectrum in DMF is presented in Fig. 3a,b. The experimental absorption spectrum
of the title compound (Fig. 3b) has a wide absorption at 367 nm with D = 1.282.
(a)
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(b)
Fig. 3. UV/Vis spectrum of the PAZB-1 in DMF: a) calculated by TDPBE0/6-31+G* method and b) experimental at
concentration of dye: 4.0·10–4M.
PAZB-2) According to Table 2, the highest oscillationis observed in λmax = 380 nm at f = 1.08.
Calculations show excitation of one electron from (HOMO)→(LUMO) gives the main
contribution to the formation of the absorption band at 380 nm that belonged to the transition
into the excited singlet state S2. According to Fig. 4, the electron density of HOMO is mainly
focused on azo group (-N=N-) and LUMO is mainly focused on double bonds (-C=C-) of three
aryl rings and azo group (-N=N-). Therefore the electronic transitions from the HOMO to
LUMO are due to the contribution of pi (π) bonds. The other excited states have very small
intensity (f ≈ 0): these transitions are nearly forbidden by orbital symmetry considerations (Table
2).
Table 2
Electronic absorption spectrum of the compound PAZB-2 calculated by TDPBE0/6-31+G*.
Excited Wavelength
Excitation
Energy (eV)
2.41
Configurations Composition
(corresponding transition orbitals)
0.68(H-1→L) + 0.14(H-1→L+1)
0.70(H→L)
Oscillator
Strength (f)
0.00
State
S1
S2
S3
(nm)
515
380
371
3.26
3.34
1.08
0.08
0.65(H-2→L) - 0.22(H→L+1)
- 0.36(H-3→L) + 0.21(H-2→L) + 0.11(H-2→L+1)
+ 0.51(H→ L+1)
S4
352
3.52
0.02
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S5
S6
305
301
4.06
4.11
0.65(H-4→L) + 0.19(H-3→L)
0.01
0.00
- 0.33(H-6→L) + 0.58(H-5→L) + 0.16(H→L+2)
- 0.16(H-4→L) + 0.56(H-3→L) + 0.12(H-2→L) +
0.16(H-2→L+1) + 0.32(H→L+1)
S7
299
4.14
0.00
- 0.14(H-8→L) + 0.57(H-6→L) + 0.31(H-5→L)
- 0.15(H→ L+1)
S8
S9
294
289
4.21
4.29
0.00
0.03
- 0.14(H-1→L) + 0.68(H-1→L+1)
- 0.11(H-8→L) - 0.10(H-5→L+1) - 0.11(H-3→L)
- 0.14(H-3→L+1) + 0.59(H-2→L+1) - 0.19(H→L+1)
+ 0.12(H→L+3)
- 0.13(H-7→L) - 0.12(H-6→L+1) - 0.15(H-5→L+1) +
0.11(H-3→L) + 0.50(H-3→L+1) + 0.13(H-2→L+3)
- 0.32(H→L+3)
S10
S11
283
263
4.37
4.71
0.07
0.06
0.55(H-8→L) + 0.26(H-7→L) - 0.12(H-6→L) +
0.19(H-2→L+1) - 0.15(H→L+5)
- 0.29(H-8→L) + 0.61 (H-7→L) - 0.14(H-7→L+1)
+ 0.12(H-3→L+1)
0.19(H-6→L+1) - 0.11(H-5→L) - 0.41(H-5→L+1) +
0.47(H→L+2)
S12
S13
S14
259
255
250
4.78
4.86
4.95
0.10
0.00
0.01
- 0.19(H-8→L) - 0.18(H-8→L+1) + 0.35(H-6→L+1) +
0.35(H-5→L+1) + 0.17(H-4→L+1) + 0.13(H-3→L+1)
+ 0.18(H-2→L+1) + 0.24(H→L+2)
S15
249
4.96
0.00
0.15(H-6→L+1) + 0.13(H-4→L) - 0.31(H-4→L+1) +
0.11(H-2→L+4) - 0.20(H→L+2) + 0.15(H→L+3) +
0.51(H→L+4)
0.44(H-6→L+1) - 0.29(H-5→L+1) + 0.19(H-1→L+2)
- 0.31(H→L+2) - 0.18(H→L+4)
S16
S17
246
244
5.04
5.08
0.06
0.00
S18
S19
S20
241
241
237
5.14
5.15
5.22
- 0.13(H-6→L+1) + 0.67(H-1→L+2) + 0.12(H→L+2)
0.36(H-3→L+1) + 0.54(H→L+3) - 0.17(H→L+4)
0.18(H-1→L+3) + 0.67(H-1→L+4)
0.06
0.00
0.01
*H-HOMO, L-LUMO
Fig. 4. Form of the MO involved in formation of absorption spectrum of the compound PAZB-2 at λmax = 380 nm.
The experimental absorption spectrum of the compound PAZB-2 (Fig. 5b) has a wide absorption
at 383 nm with D = 2.575. Comparison of calculated and experimental absorption spectra of the
compound PAZB-2 shows high accuracy of the constructed model calculations (Fig. 5a,b).
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(a)
(b)
Fig. 5. UV/Vis spectrum of the PAZB-2 in DMF: a) calculated by TDPBE0/6-31+G* method and b) experimental at
concentration of dye: 3.6·10–4M.
PAZB-8) As seen in Table 3, intense absorption band with the highest oscillation are observed in
λmax = 378 nm at f = 1.12. Calculations show that the excited state at 378 nm described by a
wave function corresponding to the imposition of the three configurations for single-electron
excitations [(H-2→L+1), (H-1→L) and (H→L+1)]. Excitation of an electron from (H-1→L)
gives the main contribution to the formation of the absorption band at 378 nm (Table 3).
According to Fig. 6, the electron density of HOMO-1 is mainly focused on imin group (-C=N-)
and aryl ring with substituents hydroxyl and methoxy, whereas LUMO is mainly focused on
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double bonds (-C=C-) of two aryl rings and azo group (-N=N). Therefore the electronic
transitions from the HOMO-1 to LUMO are due to the contribution of pi (π) bonds. Molecular
orbitals involved in formation of absorption spectrum of the PAZB-8 are demonstrated in Fig. 6.
Table 3
Electronic absorption spectrum of the compound PAZB-8 calculated by TDPBE0/6-31+G* method.
Excited Wavelength
Excitation
Energy (eV)
2.35
Configurations Composition
(corresponding transition orbitals)
- 0.10(H-5→L) + 0.24(H-2→L) + 0.64(H→L)
0.26(H-2→L) - 0.15(H-2→L+1) - 0.31(H-1→L)
- 0.16(H→ L) + 0.52(H→ L+1)
- 0.11(H-2→L+1) + 0.58(H-1→L) + 0.37(H→L+1)
0.11(H-4→L) +0.55(H-2→L) + 0.24(H-1→L)
- 0.20(H→L) - 0.20(H→L+1)
Oscillator
Strength (f)
0.00
State
(nm)
S1
528
S2
376
378
361
3.24
3.37
3.43
0.04
1.12
0.07
S3
S4
- 0.14(H-5→L) + 0.52(H-4→L) - 0.38(H-3→L)
- 0.13(H-2→L) - 0.15(H→L+2)
0.10(H-6→L) - 0.30(H-5→L) + 0.15(H-3→L)
- 0.12(H-3→L+1) - 0.13(H-2→L) + 0.55(H-1→L+1)
0.53(H-5→L) + 0.26(H-4→L) + 0.17(H-3→L) +
0.24(H-1→L+1) - 0.13(H→L+2)
0.24(H-6→L) - 0.11(H-5→L) + 0.30(H-4→L) +
0.47(H-3→L)- 0.27(H-1→L+1) + 0.11(H→L+2)
- 0.12(H-6→L) + 0.62(H-2→L+) + 0.20(H→L+1)
- 0.15(H→L+2)
0.17(H-6→L) + 0.24(H-5→L) - 0.32 (H-3→L) +
0.32(H-2→L+1) + 0.42(H→L+2) + 0.11(H→L+3)
- 0.35(H-5→L) + 0.16(H-4→L) - 0.12(H-2→L+1)
+ 0.52(H→L+2) - 0.18(H→L+3)
- 0.10(H-6→L) + 0.59(H-3→L+1) + 0.17(H-1→L+1)
- 0.22(H-1→L+2) - 0.15(H-1→L+4)
- 0.22(H-6→L) + 0.61(H→L+3) + 0.10(H→L+4)
+ 0.13(H→L+5)
- 0.24(H-6→L+1) - 0.15(H-5→L+1) + 0.56(H-4→L+1)
- 0.12(H-3→L+1)- 0.23(H-1→L+2) - 0.15(H→L+4)
0.16(H-4→L+1) + 0.13(H-3→L+1) + 0.60(H-1→L+2)
- 0.10(H-1→L+4) - 0.24(H→L+4)
0.18(H-4→L+1) - 0.18(H-2→L+2) + 0.13(H-1→L+2)
+ 0.58(H→L+4) - 0.15(H→L+5)
S5
S6
311
303
299
298
296
288
274
264
256
253
249
245
3.98
4.09
4.14
4.16
4.19
4.30
4.51
4.69
4.83
4.90
4.97
5.06
0.01
0.07
0.01
0.01
0.05
0.01
0.09
0.09
0.03
0.00
0.00
0.05
S7
S8
S9
S10
S11
S12
S13
S14
S15
S16
S17
S18
S19
S20
241
237
236
233
5.14
5.23
5.26
5.32
0.10(H-5→L+1) - 0.16(H→L+3) + 0.62(H→L+5)
0.19(H-6→L+1) + 0.61(H-5→L+1) + 0.23(H-4→L+1)
0.65(H-2→L+2) + 0.15(H→L+4)
0.00
0.04
0.01
0.01
- 0.40(H-7→L) + 0.53(H-1→L+3) - 0.14(H-1→L+4)
*H-HOMO, L-LUMO
14

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Fig. 6. Form of the MO involved in formation of absorption spectrum of the compound PAZB-8 at λmax = 378 nm.
15

ACCEPTED MANUSCRIPT
The experimental UV/Vis spectrum of the PAZB-8 in DMF (Fig. 7b) has a wide absorption at
about 310-430 nm which characterized by maximum at 373 nm with D = 0.946 and calculated
spectrum in DMF (Fig. 7a) shows the highest oscillation in 378 nm at f = 1.12.
(a)
(b)
Fig. 7. UV/Vis spectrum of the PAZB-8 in DMF: a) calculated by TDPBE0/6-31+G* method and b) experimental at
concentration of dye: 3.6·10–4M.
2.3.3 Frontier molecular orbital analysis of compounds PAZB-1, PAZB-2, PAZB-8
Quantum chemical methods are important for obtaining information about molecular structure
and electrochemical behavior. The frontier molecular orbitals (FMO) analysis plays an important
role in the electronic and optical properties, as well as in UV/Vis spectrum and chemical
16

ACCEPTED MANUSCRIPT
reactions. The values of energy of the highest occupied molecular orbital (EHOMO) can act as an
electron donor and the lowest unoccupied molecular orbital (ELUMO) can act as the electron
acceptor. Also the HOMO-LUMO energy gap is a important parameter in determining molecular
electrical transport properties. For the compound PAZB-1, LUMO energy is -5.85 eV and
HOMO -2.44 eV. The energy gap of HOMO-LUMO (3.41 eV) explains the ultimate charge
transfer interaction within the molecule (Table 4). The energy of HOMO is directly related to the
ionization potential (I = - EHOMO), while the energy of LUMO is related to the electron affinity (A
= - ELUMO). The global hardness (η=I -A/2), electronegativity (χ=I + A/2), electronic chemical
potential (µ=-(I + A)/2) and electrophilicity (ω=µ2/2η) [6], chemical softness (S=1/η) [10] are
calculated. The global hardness (η) corresponds to the HOMO-LUMO energy gap. A molecule
with a small energy gap has high chemical reactivity, low kinetic stability and is a soft molecule,
while a hard molecule has a large energy gap [10]. Electronegativity (χ) is a measure of the
power of an atom or a group of atoms to attract electrons and the chemical softness (S) describes
the capacity of an atom or a group of atoms to receive electrons. These values for structures
PAZB-1, PAZB-2, PAZB-8 are summarized inTable 4.
Table 4
The calculated electronic properties of the compounds PAZB-1, PAZB-2, PAZB-8.
Property
PAZB-1
PAZB-2
PAZB-8
EHOMO (eV)
ELUMO (eV)
Energy gap (eV)
-5.85
-2.44
3.41
5.85
2.44
4.14
1.70
-4.14
5.04
-5.59
-2.17
3.42
5.59
2.17
3.88
1.71
-3.88
4.40
-5.24
-1.66
3.58
5.24
1.66
3.45
1.79
-3.45
3.32
Ionisation potential, I (eV)
Electron affinity, A (eV)
Electronegativity, χ(eV)
Global hardness, η(eV)
Chemical potential, μ(eV)
Global electrophilicity, ω (eV)
Chemical softness, S (eV-1)
Dipole moment (Debye)
0.59
2.1967
0.58
4.4138
0.56
8.7451
17

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Total electronic densities of states (DOSs) [10] of the compounds PAZB-1, PAZB-2, PAZB-8
were computed (Fig. 8). The DOS analysis indicates that the HOMO–LUMO energy gaps (Eg)
of the compounds PAZB-1, PAZB-2, PAZB-8 are about 3.41 eV, 3.42 eV and 3.58 eV at the
PBE0/6-31+G*method, respectively. The energy gap of the compound PAZB-8 has the highest
value (3.58 eV) therefore it is less reactive compared with structures PAZB-1 and PAZB-2. It
implies that the electronic transfer in the molecules PAZB-1 and PAZB-2 is easier.
Fig. 8. Calculated DOS plots of the compounds PAZB-1, PAZB-2, PAZB-8 by PBE0/6-31+G* method.
2.3.4 Natural charge analysis of the compounds PAZB-1, PAZB-2, PAZB-8
18

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The atomic charges play an important role on molecular polarizability, dipole moment, electronic
structure and lot of related properties of molecular systems. The charge distributions over the
atoms suggest the formation of donor and acceptor pairs involving the charge transferring the
molecule. We calculated the charge distributions for equilibrium geometry of the compound
PAZB-1, PAZB-2, PAZB-8 by the NBO (natural charge) charges [6] using the PBE0/6-31+G*
level of energy. The Fig. 9 shows results of natural charges in graphical form (Atoms labeling is
according to Fig. 1).
19

ACCEPTED MANUSCRIPT
Fig. 9. Natural charges distribution of the compounds PAZB-1, PAZB-2, PAZB-8 calculated by PBE0/6-31+G*
method.
The total charge of the investigated compounds is equal to zero. The natural charge (NBO)
analysis of the title compounds show that carbon atoms have both positive and negative charges
magnitudes. According to results, all carbon atoms of the compound PAZB-1 have negative
charge excepting C6, C11, C14 and C16 atoms due to attachment to nitrogen atoms. Also in the
compounds PAZB-2 and PAZB-8, the positive carbons are observed for the carbons atoms
attachment to the electron-withdrawing nitrogen and oxygen atoms (C6, C9, C12, C16, C20, C21
atoms for PAZB-2 and C6, C11, C14, C16, C21, C22 atoms for PAZB-8). The highest negative
charge in the compounds PAZB-1, PAZB-2 and PAZB-8 is observed for N15 (-0.475e), O23 (-
0.679e) and O23 (-0.693e) atoms, respectively. According to Natural charge’s plot (Fig. 9) all
hydrogen atoms have the positive charge. In PAZB-2 and PAZB-8, the H39 atom of O-H group
has the highest positive charge (0.491e for PAZB-8 and 0.504e for PAZB-8) compared with
other hydrogen atoms due to the electron-withdrawing nature of the O23, therefore it is more
acidic.
2.3.5 NBO analysis of the compounds PAZB-1, PAZB-2, PAZB-8
20

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Natural bond orbital (NBO) analysis is important method for studying intra- and inter-molecular
bonding and interaction between bonds [17]. Electron donor orbital, acceptor orbital and the
interacting stabilization energy resulting from the second-order micro disturbance theory are
reported in Table 5.
Table 5
Significant donor–acceptor interactions and second order perturbation energies of the compound PAZB-2 calculated
using the PBE0/6-31+G* level of energy.
Donor (i)
Occupancy
1.61401
Acceptor (j)
Occupancy
E(2)a
kcal/mol
E(j)-E(i)b
a.u.
F(i , j)c
a.u.
π(C1-C6)
π*(C2-C3)
π*(C4-C5)
π*(N7-N8)
π*(C1-C6)
π*(C4-C5)
π*(C1-C6)
π*(C2-C3)
π*(C1-C6)
π*(C9-C10)
π*(N7-N8)
π*(C11-C12)
π*(C13-C14)
π*(C9-C10)
π*(C13-C14)
π*(C1-C6)
π*(C9-C10)
π*(C13-C14)
π*(C17-C18)
π*(C21-C22)
σ*(C1-C6)
σ*(C2-C3)
σ*(C6-N7)
σ*(C3-C4)
σ*(C2-C3)
σ*(C4-C5)
σ*(C6-N7)
σ*(C4-C5)
σ*(C6-N7)
σ*(C1-C2)
σ*(N8-C9)
σ*(C12-C13)
σ*(C19-C20)
σ*(C21-C22)
σ*(O24-C25)
σ*(C17-C22)
σ*(C19-C20)
σ*(C1-C6)
σ*(C5-C6)
0.32682
0.29037
0.22149
0.37340
0.29037
0.37340
0.32682
0.37340
0.38560
0.22149
0.38468
0.26588
0.38500
0.26588
0.37340
0.38560
0.26588
0.39432
0.31198
0.02145
0.01557
0.02853
0.01600
0.01557
0.01430
0.02853
0.01430
0.02853
0.01391
0.02796
0.02500
0.02457
0.02315
0.00920
0.02032
0.02457
0.02145
0.03143
19.36
19.17
20.09
20.95
18.44
19.19
20.58
10.73
10.62
21.23
19.01
18.78
23.07
15.81
26.69
28.87
213.14
242.37
157.21
2.54
2.51
3.14
2.35
2.37
2.45
4.32
2.47
0.78
1.87
0.84
2.08
2.96
2.87
0.58
1.55
1.44
0.28
0.28
0.23
0.28
0.29
0.28
0.28
0.39
0.39
0.23
0.28
0.29
0.28
0.29
0.05
0.05
0.01
0.01
0.02
1.26
1.27
1.13
1.26
1.27
1.28
1.13
1.28
1.12
1.34
1.13
1.43
1.26
1.30
1.00
1.44
1.43
0.97
0.96
0.067
0.067
0.063
0.069
0.066
0.067
0.068
0.062
0.062
0.065
0.065
0.068
0.072
0.062
0.059
0.060
0.080
0.081
0.081
0.051
0.051
0.053
0.049
0.049
0.051
0.062
0.050
0.027
0.045
0.027
0.049
0.055
0.055
0.022
0.042
0.041
0.022
0.080
π(C2-C3)
π(C4-C5)
π(N7-N8)
π(C9-C10)
1.65964
1.67718
1.98696
1.60982
π(C11-C12)
π*(N7-N8)
1.62335
0.22149
π*(C11-C12)
π*(C19-C20)
0.38468
0.39118
σ(C1-C2)
1.97983
σ(C2-C3)
σ(C3-C4)
1.98124
1.98141
σ(C4-C5)
σ(C5-C6)
1.97886
1.97926
σ(C6-N7)
σ(C9-C14)
σ(N15-C16)
σ(C20-C21)
1.98020
1.97900
1.98712
1.97408
σ(C21-O24)
1.98983
1.95732
n1(N7)
0.60
8.21
21

ACCEPTED MANUSCRIPT
σ*(C9-C10)
σ*(C14-H34)
σ*(C1-C6)
0.02155
0.01536
0.02145
0.01554
0.02155
0.03189
0.02500
0.03141
0.04016
0.02457
0.02034
0.39118
0.04487
0.02315
0.31198
0.04487
0.02315
0.31198
0.82
0.66
0.82
0.69
0.65
8.40
0.71
2.83
13.09
6.08
0.67
29.22
6.87
0.51
2.26
2.44
5.09
9.16
0.97
0.88
0.97
0.88
0.97
0.96
0.89
0.83
0.76
1.16
1.06
0.35
1.02
1.08
0.53
0.87
0.94
0.38
0.025
0.022
0.025
0.022
0.22
n1(N8)
1.95649
σ*(C5-H30)
σ*(C9-C10)
σ*(C9-C14)
σ*(C12-C13)
σ*(C16-C17)
σ*(C16-H35)
σ*(C19-C20)
σ*(C25-H41)
π*(C19-C20)
σ*(C20-C21)
σ*(C21-C22)
π*(C21-C22)
σ*(C20-C21)
σ*(C21-C22)
π*(C21-C22)
0.080
0.023
0.044
0.091
0.075
0.024
0.097
0.075
0.021
0.033
0.042
0.063
0.056
n1(N15)
n1(O23)
1.87899
1.97856
n2(O23)
n1(O24)
1.86455
1.95038
n2(O24)
1.90766
aE(2) Energy of hyperconjucative interactions,
b Energy difference between donor and acceptor i and j NBO orbitals.
c F(i, j) is the Fock matrix element between i and j NBO orbitals.
The electron delocalization from filled NBOs (donors) to the empty NBOs (acceptors) describes
a conjugative electron transfer process between them. For each donor (i) and acceptor (j), the
stabilization energy E(2) associated with the delocalization i→j is estimated:
퐹(푖,푗)2
퐸(2) = ∆퐸푖푗 = 푞
(2)
푖 휀푗 ‒ 휀푖
where qi is the donor orbital occupancy, εj and εi are diagonal elements and F(i,j) is the off
diagonal NBO Fock matrix element. The resonance energy (E(2)) detected the quantity of
participation of electrons in the resonance between atoms. The larger E(2) value, the more
intensive is the interaction between electron donors and acceptor, i.e. the more donation tendency
from electron donors to electron acceptors and the greater the extent of conjugation of the whole
system [18]. Delocalization of electron density between occupied Lewis-type (bond or lone pair)
NBO orbitals and formally unoccupied (antibond or Rydgberg) non Lewis NBO orbitals
correspond to a stabilization donor–acceptor interaction. NBO analysis has been performed for
the title compound at the PBE0/6-31+G* level of energy in order to elucidate the intramolecular,
22

ACCEPTED MANUSCRIPT
rehybridization and delocalization of electron density within the compound PAZB-2. The strong,
moderate and weak intramolecular hyperconjugative interactions of the title compound such as
π→π*, π*→π*, σ→σ*, n→σ* and n→π* transitions are presented in Table 5. According to NBO
analysis, the σ(C4-C5)→σ*(C6-N7) transition has the highest resonance energy (4.32 kcal/mol)
compared with other σ→σ* transitions of the title compound. The σ(C1-C2) orbital in phenyl
ring participates as donor and the anti-bonding σ*(C1-C6), σ*(C2-C3) and σ*(C6-N7) orbitals
act as acceptor with resonance energies (E(2)) of is 2.54 kcal/mol, 2.51 kcal/mol and 3.14
kcal/mol, respectively. These values indicate σ(C1-C2)→σ*(C6-N7) transition has the highest
resonance energy (3.14 kcal/mol) compared with σ(C1-C2)→σ*(C1-C6) and σ(C1-C2)→σ*(C2-
C3).
The intramolecular hyperconjugative interactions of the π→π* transitions in phenyl ring that lead
to a strong delocalization are such as C9-C10→N7-N8 and C11-C12→C9-C10 with resonance
energies (E(2)) 21.23 kcal/mol and 23.07 kcal/mol, respectively. The important intramolecular
hyperconjugative interaction of the π→π* in phenyl ring is C20-C21→C18-C19 transition that
show the strong stabilization energy of 26.54 kcal/mol. The π*→π* transitions have the highest
resonance energies compared with other interactions of the title compound such as C11-
C12→C13-C14, C19-C20→C17-C18 and C19-C20→C21-C22 with resonance energies (E(2))
213.14, 242.37 and 157.21 kcal/mol respectively, that lead to stability of the title compound. The
strongest n→σ* interactions are due to n1(N15)→σ*(C16-H35), n2(O23)→π*(C19-C20) and
n2(O24)→π*(C21-C22) interactions with stabilization energies of 13.09 kcal/mol, 29.22
kcal/mol and 9.16 kcal/mol, respectively.
The results of NBO analysis such as the occupation numbers with their energies for the
interacting NBOs [interaction between natural bond orbital A and natural bond orbital B (A-B)]
23

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and the polarization coefficient amounts of atoms in title compound are presented using the
PBE0/6-31+G* method is summarized in Table 6 (Atoms labeling is according to Fig. 1).
Table 6
Calculated natural bond orbitals (NBO) and the polarization coefficient for each hybrid in selected bonds of the
compound PAZB-2 using the PBE0/6-31+G* level of energy.
Occupancy
(a.u.)
Bond (A-B)a
Energy
(a.u.)
EDA (%)
EDB (%)
NBO
S(%)
(A)
S(%)
(B)
P(%)
(A)
P(%)
(B)
1.97983
1.97671
1.61401
1.98124
1.97926
1.98020
1.98696
1.90724
σ(C1-C2)
σ(C1-C6)
π(C1-C6)
σ(C2-C3)
σ(C5-C6)
σ(C6-N7)
σ(N7-N8)
π(N7-N8)
-0.68703
-0.68300
-0.23932
-0.72102
-0.68418
-0.75387
-0.93713
-0.35162
50.12
49.37
48.25
50.05
49.37
41.44
49.92
50.26
49.88
50.63
51.75
49.95
50.63
58.56
50.08
49.74
0.7080 (sp1.81) + 0.7063 (sp1.85
0.7027 (sp1.89) + 0.7115 (sp1.85
0.6946 (sp1.00) + 0.7194 (sp1.00
0.7074 (sp1.84) + 0.7068 (sp1.84
0.7026 (sp1.95) + 0.7116 (sp1.72
)
)
)
)
)
35.57
34.59
0.00
35.10
35.06
0.00
64.39
65.36
99.96
64.81
66.13
71.84
69.64
99.73
64.85
64.90
99.98
64.71
63.22
68.03
69.58
99.72
35.15
33.83
28.06
30.24
0.00
35.25
36.75
31.89
30.31
0.00
0.64.37 (sp2.56) + 0.7653 (sp2.13
)
0.7065 (sp2.30) + 0.7077 (sp2.30
0.7090 (sp1.00) + 0.7052 (sp1.00
0.7657 (sp2.09) + 0.6432 (sp2.53
0.7105 (sp1.86) + 0.7037 (sp1.88
0.6405 (sp2.48) + 0.7680 (sp2.00
0.7716 (sp1.56) + 0.6361 (sp2.02
)
)
1.98035
1.97639
1.98123
1.98712
1.90455
1.97570
σ(N8-C9)
σ(C9-C10)
σ(C12-N15)
σ(N15-C16)
π(N15-C16)
σ(C17-C18)
-0.75993
-0.68343
-0.76729
-0.86850
-0.32318
-0.69320
58.63
50.48
41.02
38.95
59.35
50.86
41.37
49.52
58.98
33.14
40.65
49.14
)
)
)
)
32.30
34.93
28.73
38.95
0.43
28.33
34.67
33.25
33.14
0.41
67.62
65.03
71.21
60.86
99.33
66.01
71.57
65.29
66.60
66.80
99.50
99.98
0.7704 (sp99.99) + 0.6376 (sp99.99
)
0.7131 (sp1.94) + 0.7010 (sp1.83
)
33.96
35.28
1.99456
1.98983
1.98651
1.99739
1.98335
1.98854
1.95732
1.95649
1.87899
1.97856
1.86455
1.95038
1.90766
σ(C20-O23)
σ(C21-O24)
σ(C16-H35)
σ(C25-H40)
σ(C3-H28)
σ(O23-H39)
n1(N7)
-0.92292
-0.86920
-0.53595
-0.51755
-0.51779
-0.74729
-0.39311
-0.39247
-0.33363
-0.60742
-0.33102
-0.49408
-0.34871
33.00
67.00
0.5745 (sp3.04) + 0.8185 (sp1.88
)
)
24.72
25.59
31.29
26.26
29.64
20.61
38.10
37.62
27.31
44.69
0.00
34.66
75.07
74.22
68.65
73.67
70.30
79.29
61.84
62.33
72.55
55.25
99.88
66.86
90.84
65.27
33.62
66.38
0.5798 (sp2.90) + 0.8248 (sp2.17
31.56
68.36
60.36
39.64
0.7769 (sp2.19) + 0.6296 (s)
100
-
-
-
-
-
-
-
-
-
-
-
60.46
39.54
0.7776 (sp2.81) + 0.6288 (s)
100
61.94
38.06
0.7870 (sp2.37) + 0.6170 (s)
100
74.80
25.20
0.8649 (sp3.85) + 0.5020 (s)
100
-
-
-
-
-
-
-
-
-
-
-
-
-
-
sp1.62
sp1.66
sp2.66
sp1.24
sp1.00
sp2.02
sp10.00
-
-
-
-
-
-
-
n1(N8)
n1(N15)
n1(O23)
n2(O23)
n1(O24)
33.07
9.08
n2(O24)
a
A-B is the bond between atom A and atom B. (A: natural bond orbital and the polarization coefficient of atom; A-B: natural bond orbital and the
polarization coefficient of atom B).
The size of polarization coefficients shows the importance of the two hybrids in the formation of
the bond. The differences in electronegativity of the atoms involved in the bond formation are
24

ACCEPTED MANUSCRIPT
reflected in the larger differences in the polarization coefficients of the atoms (C-O, C-H C-N
bonds). The calculated bonding orbital for the σ(C20-O23) bond is the
σ=0.5745(sp3.04)+0.8185(sp1.88) with high occupancy 1.99456 a.u. and low energy -0.92292 a.u.
The polarization coefficients of C20=0.5745 and O23=0.8185 shows importance of O23 in
forming σ(C20-O23) bond compared with C20 atom. The calculated bonding orbital for the
σ(N7-N8) bond is σ=0.7065(sp2.30)+0.7077(sp2.30) with low energy -0.93713 a.u. and high
occupancy 1.98696 a.u. The polarization coefficients of N7=0.7065 and N8=0.7077 shows low
difference in polarization coefficients N7 and N8 atoms in N7-N8 bond and importance of two
atoms in forming bond. According to NBO analysis, the natural hybrid orbital n2(O23) with low
occupancy 1.86455 a.u. and high energy -0.33102 a.u. has p-character (99.88%), whereas
n1(O23) occupy a lower energy orbital (-0.60742 a.u) with p-character (55.25%) and high
occupation number (1.97856 a.u). The pure p-type lone pair orbital n2(O23) participates the
electron donation to π*(C19-c20) for n2(O23)→π*(C19-C20) interaction with high resonance
energies (E(2)) 29.22 kcal/mol in the title compound. Also the natural hybrid orbital n1(N15) with
occupancy 1.87899 a.u. has p-character (72.55%), whereas n1(N7) and n1(N8) have p-character
(61.84%) and (62.33%). From Table 5, it is found that the p-type lone pair orbital n1(N15)
participates the electron donation to σ*(C16-H35) forn1(N15)→σ*(C16-H35) interaction with
high resonance energies (E(2)) 13.09 kcal/mol.
2.4.1 Synthesis of the compounds PAZA-1, PAZB-2, PAZB-8
25

ACCEPTED MANUSCRIPT
R
NH2
R1
H
CHO
N
R1
R
2
N
N
MeOH, AcOH
N
N
1
PAZB-1
PAZB-2
PAZB-8
Fig. 10. Scheme of synthesis of the compounds PAZB-1, PAZB-2 and PAZB-8.
PAZB-1: A mixture of 4-aminoazobenzne (1) (2 mmol) and aldehyde (2) (2 mmol) in 30 ml
methanol was prepared. Then 2 drops of glacial acetic acid was added to the mixture and was
refluxed for 1 h. The hot solution was filtered through a paper filter, cooled and left for 15 h. at
0-5°C. The solid was dissolved in cold methanol and washed with water and dried at 22-25 °C.
PAZB-2: A mixture of 4-aminoazobenzne (1) (2.4 mmol) and aldehyde (2.1) (2 mmol) in 33 ml
methanol was prepared. Then 3 drops of glacial acetic acid was added to the mixture and was
refluxed for 2 h. The hot solution was filtered through a paper filter, cooled and left for 10 h. at
0-5°C. The solid was dissolved in cold methanol and washed with water and dried at 22-25 °C.
PAZB-8: A mixture of 4-aminoazobenzne (1) (2.6 mmol) and aldehyde (2.3) (2 mmol) in 28 ml
methanol was prepared. Then 4 drops of glacial acetic acid was added to the mixture and was
refluxed for 4 h. The hot solution was filtered through a paper filter, cooled and left for 7 h. at 10
26

ACCEPTED MANUSCRIPT
°C. The solid was dissolved in cold methanol and washed with water and dried at 22-25 °C
(Fig.10).
2.4.2 Vibrational frequencies of the compounds PAZB-1, PAZB-2, PAZB-8
In order to confirm the accuracy of our findings, IR spectroscopy was used. The theoretical IR
spectra of optimized PAZB-1, PAZB-2, PAZB-8 was calculated using the PBE0/6-31+G*
method. The important calculated and experimental vibrational frequencies of PAZB-1, PAZB-2,
PAZB-8 are summarized in Table 7, Table 8 and Table 9, respectively. The experimental and
calculated spectra of the title compounds are found to be in good agreement with each other. The
title compounds have the main vibrational modes:
PAZB-1) 1622 cm-1 (C=N stretching vibration),1572 cm-1 (N=N stretching vibration), 1285 cm-1
(N stretching vibration), that indicates the presence of PAZB-1 (Table 7).
PAZB-2) 1620 cm-1 (C=N stretching vibration), 1599 cm-1 (N=N stretching vibrations), 1261
cm-1 (C-N stretching vibration), 1571 cm-1(C-O stretching vibration), 1302 cm-1(O-H bending
vibration), 3090 cm-1 (asymmetric C-H stretching vibrations of CH3) that indicates the presence
of PAZB-2 (Table 8).
PAZB-8) 1614 cm-1 (C=N stretching vibration), 1578 cm-1 (N=N stretching vibrations), 1221
cm-1 (C-N stretching vibration), 1560 cm-1(C-O stretching vibration), 1278 cm-1(O-H bending
vibration), 3075 cm-1 (asymmetric C-H stretching vibrations of CH3) that indicates the presence
of PAZB-8 (Table 9).
Table 7
Experimental and calculated vibrational frequencies and their assignment of PAZB-1 by using PBE0/6-31+G*
method.
νexp. (cm-1)
562
νcal. (cm-1)
580.99
673.48
Assignment
C-H aromatic bending vibrations, out of plane
C-H aromatic bending vibrations, out of plane
C-H aromatic bending vibrations, out of plane
687
760
769.95
27

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877
970
879.20
974.84
1006.21
1106.2
C-H aromatic bending vibrations, out of plane
C-H aromatic bending vibrations, out of plane
C-H aromatic bending vibrations, out of plane
C-H aromatic bending vibrations
1001
1103
1141
1155
1186
1220
1285
1310
1363
1448
1493
1572
1585
1622
3040
3059
3090
1136.16
1154.61
1172.79
1229.06
1273.31
1317.33
1351.55
1453.02
1492.67
1547.15
1561.24
1642.52
3044.32
3183.25
3185.25
C-H aromatic bending vibrations
C-N stretching vibrations, C-H aromatic bending vibrations
C-N stretching vibrations, C-H aromatic bending vibrations
C-N stretching vibrations, C-H aromatic bending vibrations
C-N stretching vibrations, C-H aromatic bending vibrations
C-H aromatic bending vibrations
C=C aromatic ring stretching vibrations, C-H aromatic bending vibrations
N=N stretching vibrations, C=C aromatic stretching vibrations
N=N stretching vibrations, C=C aromatic stretching vibrations
N=N stretching vibrations, C=C aromatic stretching vibrations
C-H bending vibrations of N=C-H
C=N stretching vibrations
C-H stretching vibrations of N=C-H
Asymmetric C-H aromatic stretching vibrations
Asymmetric C-H aromatic stretching vibrations
Table 8
Experimental and calculated vibrational frequencies and their assignment of PAZB-2 by using PBE0/6-31+G*
method.
νexp. (cm-1)
685
νcal. (cm-1)
702.67
791.43
885.57
915.16
Assignment
C-H aromatic bending vibrations, out of plane
C-H aromatic bending vibrations, out of plane
C-H aromatic bending vibrations, out of plane
C-H aromatic bending vibrations, out of plane
C-H aromatic bending vibrations, out of plane
C-H aromatic bending vibrations
766
870
920
970
983.74
1124
1160
1177
1210
1261
1284
1302
1385
1427
1463
1515
1571
1599
1620
3001
3040
3060
3085
3090
1133.30
1167.00
1181.35
1218.80
1270.20
1288.61
1302.28
1392.11
1426.57
1461.16
1519.31
1559.79
1610.83
1637.33
3027.39
3037.34
3113.84
3156.78
3167.82
C-N stretching vibrations, C-H aromatic bending vibrations
C-H aromatic bending vibrations
C-N stretching vibrations, C-H aromatic bending vibrations
C-N stretching vibrations, C-H aromatic bending vibrations
C-O stretching vibrations, O-H bending vibrations
C-H aromatic bending vibrations
C=C aromatic stretching vibrations, O-H bending vibrations
C-H bending vibrations of N=C-H
N=N stretching vibrations, C=C aromatic stretching vibrations
N=N stretching vibrations, C-H aromaticbending vibrations
C-O stretching vibrations, C=C aromatic stretching vibrations
N=N stretching vibrations, C=C aromatic stretching vibrations
C=N stretching vibrations
C-H stretching vibrations of N=C-H
Symmetric C-H stretching vibrations of CH3
Asymmetric C-H stretching vibrations of CH3
Asymmetric C-H stretching vibrations of CH3
Asymmetric C-H stretching vibrations of CH3
Table 9
28