Role of tautomerism and solvatochromism in UV-VIS spectra of arylhydrazones of β-diketones

Article abstract of DOI:10.1016/j.molliq.2012.03.023

New arylhydrazones of β-diketones, 5-chloro-3-(2-(1-ethoxy-1,3- dioxobutan-2-ylidene)hydrazinyl)-2-hydroxybenzenesulfonic acid (1), 3-(2-(1-ethoxy-1,3-dioxobutan-2-ylidene)hydrazinyl)-2-hydroxy-5- nitrobenzenesulfonic acid (2), and 3-(2-(4,4-dimethyl-2,6-dioxocyclohexylidene) hydrazinyl)-2-hydroxy-5-nitrobenzenesulfonic acid (3), have been synthesized and characterized by IR, ¹H and ¹³C NMR spectroscopies and elemental analysis. 3 and known 5-(2-(4,4-dimethyl-2,6-dioxocyclohexylidene) hydrazinyl)-4-hydroxybenzene-1,3-disulfonic acid (4) exist in DMSO solution exclusively in the hydrazone form, while 1 and 2 exist in DMSO and H ₂O solutions as a mixture of enol-azo and hydrazone tautomeric forms, in ratios dependent on the solvent polarity and inductive effect of the substituents. DFT and TDDFT approaches were applied for simulations of experimental UV-VIS absorption spectra of the studied compounds, taking into account solvatochromic as well as tautomeric effect. The performed simulations have established a correlation of substantial experimental 120 nm red shift of the enol-azo form with respect to hydrazone with HOMO and LUMO orbitals' delocalization.

Full text of DOI:10.1016/j.molliq.2012.03.023

Journal of Molecular Liquids 171 (2012) 11–15
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Role of tautomerism and solvatochromism in UV–VIS spectra of arylhydrazones
of β-diketones
Wojciech Kuznik a, Maximilian N. Kopylovich b, Gunel I. Amanullayeva c, Armando J.L. Pombeiro b,
,
⁎
Ali H. Reshak d,e, Kamran T. Mahmudov b, I.V. Kityk a,f,⁎⁎
a
Department of Physical Chemistry and Polymer Technology, Silesian University of Technology, Gliwice, Poland
Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, TU Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
Institute of Petrochemical Processes, National Academy of Sciences of Azerbaijan, Hojaly Ave. 30, 1025 Baku, Azerbaijan
School of Complex Systems, FFWP, University of South Bohemia, Nove Hrady 37333, Czech Republic
b
c
d
e
School of Material Engineering, Malaysia University of Perlis, P.O. Box 77, d/a Pejabat Pos Besar, 01007 Kangar, Perlis, Malaysia
f
Electrical Engineering Department, Czestochowa University of Technology, Av. Armii Krajowej 17/19, PL-42200 Czestochowa, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
New arylhydrazones of β-diketones, 5-chloro-3-(2-(1-ethoxy-1,3-dioxobutan-2-ylidene)hydrazinyl)-
2-hydroxybenzenesulfonic acid (1), 3-(2-(1-ethoxy-1,3-dioxobutan-2-ylidene)hydrazinyl)-2-hydroxy-
5-nitrobenzenesulfonic acid (2), and 3-(2-(4,4-dimethyl-2,6-dioxocyclohexylidene) hydrazinyl)-2-
hydroxy-5-nitrobenzenesulfonic acid (3), have been synthesized and characterized by IR, 1H and 13C NMR
spectroscopies and elemental analysis. 3 and known 5-(2-(4,4-dimethyl-2,6-dioxocyclohexylidene)hydrazinyl)-
4-hydroxybenzene-1,3-disulfonic acid (4) exist in DMSO solution exclusively in the hydrazone form, while 1
and 2 exist in DMSO and H2O solutions as a mixture of enol-azo and hydrazone tautomeric forms, in ratios
dependent on the solvent polarity and inductive effect of the substituents. DFT and TDDFT approaches were
applied for simulations of experimental UV–VIS absorption spectra of the studied compounds, taking into
account solvatochromic as well as tautomeric effect. The performed simulations have established a correlation of
substantial experimental 120 nm red shift of the enol-azo form with respect to hydrazone with HOMO and
LUMO orbitals' delocalization.
Received 8 September 2011
Received in revised form 21 March 2012
Accepted 23 March 2012
Available online 9 April 2012
Keywords:
Arylhydrazones of β-diketones
Tautomeric equilibrium
Solvatochromism
Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.
1. Introduction
in solution the investigated unsymmetrical AHBD exist as a mixture of
enol-azo and hydrazone tautomers (Scheme 1) [1].
Arylhydrazones of β-diketones (AHBD, Scheme 1) are compounds
extensively studied due to their prototropic tautomerism and strong
intramolecular resonance-assisted hydrogen bonds (RAHB) [1–5],
which are similar to those formed within the widely used β-diketones
[6,7]. The mentioned RAHB system can play a principal role for the
application of AHBD e.g. as bistate molecular switches [8–11]. The
equilibrium between enol-azo⇌hydrazone tautomeric forms is depen-
dent on several factors determined by the molecular structure of AHBD
and external factors (e.g. solvent, temperature) [1]. It was established
that in AHBD formed by asymmetric β-diketones a six-membered
H-bonded ring is generated at the more sterically favorable side of the
molecule [1,12,13]. Moreover, usually in solid phase all the structurally
studied AHBD are stabilized in the hydazone form [1,3,10,14–16], while
On the other hand, study of the solvatochromic properties of
AHBD demonstrated that they can be applied for qualitative analysis
of aprotic solvents in protic ones [16]. Upon dissolution the
intermolecular hydrogen and van-der-Waals interactions with the
solvent molecules change the partial distribution of the tautomers.
Sometimes the presence of both tautomeric forms can hamper the
interpretation of the spectroscopic data due to the bands overlapping
[1], while theoretical calculations allow one to overcome these
difficulties by rationalizing the relation between the tautomeric
ratio and properties [1,3,17].
The principal goals of this work are as follows: i) to synthesize new
AHBD, namely 5-chloro-3-(2-(1-ethoxy-1,3-dioxobutan-2-ylidene)
hydrazinyl)-2-hydroxybenzenesulfonic acid (1), 3-(2-(1-ethoxy-1,3-
dioxobutan-2-ylidene)hydrazinyl)-2-hydroxy-5-nitrobenzenesulfonic
acid (2), and 3-(2-(4,4-dimethyl-2,6-dioxocyclohexylidene)hydrazinyl)-
2-hydroxy-5-nitrobenzenesulfonic acid (3) (Scheme 1); ii) to trace the
influence of the introduced substituents on the tautomeric balance
and the physico-chemical properties of AHBD as well as their known
⁎
Corresponding author. Fax: +351 218464455.
⁎⁎ Correspondence to: I.V. Kityk, Electrical Engineering Department, Czestochowa
University of Technology, Av. Armii Krajowej 17/19, PL-42200 Czestochowa, Poland.
Fax: +48 34 3250 821.
E-mail addresses: pombeiro@ist.utl.pt (A.J.L. Pombeiro), iwank74@gmail.com
(I.V. Kityk).
analog
5-(2-(4,4-dimethyl-2,6-dioxocyclohexylidene)hydrazinyl)-4-
hydroxybenzene-1,3-disulfonic acid (4) [5]; iii) to present a detailed
0167-7322/$ – see front matter. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.molliq.2012.03.023

12
W. Kuznik et al. / Journal of Molecular Liquids 171 (2012) 11–15
Scheme 1. Arylhydrazones of β-diketones considered in this work (both the enol-azo and hydrazone forms are presented).
procedure to simulate UV–VIS spectra of these compounds performing
theoretical simulation at the DFT level, taking into account both
solvatochromic and tautomeric effects. The tautomeric equilibrium of
azo chromophores can lead to significant changes in absorption spectra.
We attempt to explain this observed shift by delocalization of LUMO
orbital and hence change in the excitation energy of the first excited
state.
δ: 1.33–1.37 (3H, CH3), 2.34 (3H, CH3), 4.32–4.35 (2H, CH2), 7.36–7.53
(2H, Ar\H). 1H NMR of a mixture of tautomeric enol-azo and
hydrazone forms (300.13 MHz, DMSO-d6). Enol-azo, δ: 1.25–1.28
(3H, CH3), 2.42 (3H, CH3), 4.26–4.29 (2H, CH2), 7.18–7.48 (2H, Ar\H),
11.19 (1H, Ar\OH), 12.35 (1H, HO-enol). Hydrazone, δ: 1.30–1.33
(3H, CH3), CH3 signals were overlapped with the solvent peak,
4.31–4.33 (2H, CH2), 7.18–7.48 (2H, Ar\H), 11.19 (1H, Ar\OH),
14.41 (1H, NH). 13C{1H} NMR (75.468 MHz, DMSO-d6). Enol-azo,
δ: 14.0 (CH3), 26.8 (CH3), 61.2 (CH2), 114.4 (C\N), 114.7 (Ar\N_N),
122.8 (Ar\Cl), 127.3 and 132.7 (Ar\H), 133.5 (Ar\SO3H), 141.9
(Ar\OH), 162.4 (C\O), 193.5 (C_O). Hydrazone, δ: 14.2 (CH3), 30.6
(CH3), 60.7 (CH2), 117.6 and 121.1 (Ar\H), 122.0 (C_N), 129.0
(Ar\Cl), 131.3 (Ar\NH\N), 132.4 (Ar\SO3H), 141.3 (Ar\OH), 164.1
and 196.4 (C_O).
2: yield: 62% (based on 1-ethoxybutane-1,3-dione), yellow powder
soluble in methanol, ethanol, and water and insoluble in benzene and
chloroform. Anal. Calcd for C12H14N2O10S2 (M=410.38): C, 35.12; H,
3.44; N, 6.83. Found: C, 35.06; H, 3.37; N, 6.76. IR (KBr, selected bands,
cm−1): 3516 ν(OH), 3043 ν(NH), 1737 ν(C_O), 1629 ν(C_O⋯H), 1548
ν(C_N). 1H NMR of a mixture of tautomeric enol-azo and hydrazone
forms (300.13 MHz, D2O). Enol-azo, δ: 0.43–0.49 (3H, CH3), 2.56
(3H, CH3), 4.38–4.40 (2H, CH2), 7.84–8.12 (2H, Ar\H). Hydrazone,
δ: 1.33–1.38 (3H, CH3), 2.39 (3H, CH3), 4.38–4.40 (2H, CH2),
7.84–8.12 (2H, Ar\H). 1H NMR of a mixture of tautomeric enol-azo
and hydrazone forms (300.13 MHz, DMSO-d6). Enol-azo, δ: 1.27–1.30
(3H, CH3), 2.41 (3H, CH3), 4.27–4.29 (2H, CH2), 7.58–7.84 (2H, Ar\H),
11.35 (1H, Ar\OH), 12.52 (1H, HO-enol). Hydrazone, δ: 1.27–1.30
(3H, CH3), CH3 signals were overlapped with the solvent peak,
4.31–4.33 (2H, CH2), 7.58–7.84 (2H, Ar\H), 11.39 (1H, Ar\OH), 14.66
(1H, NH). 13C{1H} NMR (75.468 MHz, DMSO-d6). Enol-azo, δ: 14.0
(CH3), 26.6 (CH3), 61.0 (CH2), 112.5 (C\N), 113.2 (Ar\N_N), 126.7
(Ar\H), 128.7 (Ar\SO3H), 130.0 (Ar\H), 139.6 (Ar\SO3H), 142.5
(Ar\OH), 162.7 (C\O), 193.2 (C_O). Hydrazone, δ: 14.3 (CH3), 30.6
(CH3), 60.5 (CH2), 120.1 and 121.0 (Ar\H), 128.1 (C_N), 128.6
(Ar\NH\N), 130.0 and 139.7 (Ar\SO3H), 142.1 (Ar\OH), 164.3 and
196.2 (C_O).
2. Experimental section
2.1. Materials and methods
The 1H and 13C NMR spectra were recorded at an ambient
temperature on a Bruker Avance II+300 (UltraShield™ Magnet)
spectrometer operating at 300.130 and 75.468 MHz for proton and
carbon-13, respectively. The chemical shifts are reported in ppm
using tetramethylsilane (TMS) as an internal reference. The infrared
spectra (4000–400 cm−1) were recorded on a BIO-RAD FTS 3000MX
instrument in KBr pellets. All the UV–VIS spectra were recorded with
HP 8453 spectrophotometer in distilled water with
a spectral
resolution of 1 nm. Quartz cells with a light path of 1 cm were used.
2.2. Synthesis of the arylhydrazones of β-diketones
The studied compounds were prepared via the Japp–Klingemann
reaction [18] involving diazotization of aromatic amines following
azocoupling of thus formed diazonium salt and β-diketones in water
solution containing sodium acetate [12,13].
2.2.1. Diazotization
A
0.025 mol portion of 3-amino-2-hydroxy-5-(substituted)
benzenesulfonic acid was dissolved in 50 mL of water and then
1.00 g (0.025 mol) of crystalline NaOH was added. The solution was
cooled in an ice bath to 273 K and then 1.725 g (0.025 mol) of
NaNO2 was added; after that 5.00 mL (33%) HCl was added in
portions for 1 h. The temperature of the mixture should not exceed
278 K. The resulting diazonium solution was used directly in the
following coupling procedure.
3: yield: 87% (based on 5,5-dimethylcyclohexane-1,3-dione),
yellow powder soluble in methanol, ethanol, water and insoluble in
benzene and chloroform. Anal. Calcd for C14H15N3O8S (M=385.35):
C, 43.64; H, 3.92; N, 10.90. Found: C, 43.45; H, 4.79; N, 10.74. IR (KBr,
selected bands, cm−1): 3620 ν(OH), 2960 ν(NH), 1688 ν(C_O),
1632 ν(C_O⋯H), 1592 ν(C_N). 1H NMR (300.13 MHz, DMSO-d6), δ:
1.03 (6H, 2CH3), 2.39 (3H, CH3), 2.60 (2H, CH2), 2.69 (2H, CH2),
8.12–8.35 (2H, Ar\H), 10.49 (1H, Ar\OH), 14.91 (1H, NH). 13C{1H}
NMR (75.468 MHz, DMSO-d6), δ: 28.0 (CH3), 30.4 (CH3), 38.7 (Cipso),
51.9 (CH2), 52.0 (CH2), 110.9 and 118.9 (Ar\H), 130.6 (Ar\NH\N),
131.4 (Ar\SO3H), 131.8 (C_N), 140.0 (Ar\NO2), 148.1 (Ar\OH),
193.0 and 198.2 (C_O).
2.2.2. Azocoupling
8.20 g (0.100 mol) of CH3COONa was added to a mixture of
0.025 mol of β-diketone with 100 mL of ethanol. The solution was
cooled in an ice bath to ca. 273 K, and a suspension of 2-hydroxy-3-
sulfo-5-(substituted)aryldiazonium chloride (see above) was added
in three portions under vigorous stirring for 1 h.
The identity of 1–3 was demonstrated by element analysis, IR and
1H and 13C NMR spectrometry.
1: yield: 65% (based on 1-ethoxybutane-1,3-dione), yellow powder
soluble in methanol, ethanol, water and insoluble in benzene and
chloroform. Anal. Calcd for C12H13ClN2O7S (M=364.76): C, 39.51;
H, 3.59; N, 7.68. Found: C, 39.37; H, 3.34; N, 7.52. IR (KBr, selected bands,
cm−1): 3678 ν(OH), 3065 ν(NH), 1745 ν(C_O), 1627 ν(C_O⋯H),
1541 ν(C_N). 1H NMR of a mixture of tautomeric enol-azo and
hydrazone forms (300.13 MHz, D2O). Enol-azo, δ: 0.38–0.44 (3H, CH3),
2.45 (3H, CH3), 4.32–4.35 (2H, CH2), 7.36–7.53 (2H, Ar\H). Hydrazone,
2.3. Computational procedure
All the DFT calculations were performed using GAUSSIAN09
package [19]. GABEDIT 2.3.6 Graphical User Interface [20] was used
to generate input files and to depict graphs from output files. The
calculations were performed at 6-31G (d,p) DFT B3LYP level with

W. Kuznik et al. / Journal of Molecular Liquids 171 (2012) 11–15
13
1.0
PCM (Polarizable Continuum Model) [21,22] taking into account
1TDDFT
the external environment and simulated solvatochromism. Time-
dependent density functional theory (TD-DFT) was used to simulate
UV–VIS absorption spectra. Default geometry optimization algo-
rithms converge to hydrazone form; to enforce enol-azo geometry
Modredundant option was used and the OH bond was frozen during
the calculation at length optimized in Molecular Mechanics run.
1 TDDFT Water
1 Experiment
0.5
0.0
1.0
200
250
300
350
400
450
500
Wavelength [nm]
3. Results and discussion
1' TDDFT
1' TDDFT Water
1' Experiment
3.1. Synthesis of 1–3 and spectroscopic study
0.5
0.0
New hydrazone compounds 1–3 and known [5] analog 4 were
prepared by reaction of the β-diketones with the corresponding
aryldiazonium chloride in the presence of sodium acetate. Compounds
1 and 2, prepared from asymmetric β-diketone (1-ethoxybutane-1,3-
dione), exist in D2O and DMSO-d6 solutions as mixtures of enol-azo and
hydrazone tautomers (Scheme 1). The mole fraction of each tautomeric
form has been determined by relative integration of the methyl (or
methylene) group (Fig. 1) of each tautomer as reported [1]. With
increase in the polarity of solvents (DMSObD2O) and the inductive
effect of substituents (\Clb\SO3H, compare 1 and 2) the tautomeric
balance shifts to the enol-azo form (38% hydrazone, 62% enol-azo in
DMSO and 14% hydrazone, 86% enol-azo in D2O for 1, and 13%
hydrazone, 87% enol-azo in DMSO and 5% hydrazone, 95% enol-azo in
D2O for 2). Nevertheless 1 and 2 were proved to exist in solution as a
mixture of two tautomeric forms, IR spectrum (ν(NH) and ν(C_N)
vibrations at 3065 and 3043, and 1541 and 1548 cm−1, respectively)
shows that in the solid state they are stabilized in the hydrazone form
(Scheme 1) similarly to the reported analog [1]. In contrast, prepared
from symmetrical 5,5-dimethylcyclohexane-1,3-dione compounds 3
and 4 are stabilized in both the mentioned solvents exclusively in the
hydrazone form. It should be noted that the obtained data may be useful
for some analytical applications [5,16] which require the knowledge of
the distribution of the tautomers in a particular solvent.
200
250
300
350
400
450
500
Wavelength [nm]
Fig. 2. Comparison of theoretically simulated and experimental UV–VIS spectra of 1
(top panel) and 1′ (bottom).
simulations of both tautomers demonstrate similar absorption
spectra (Figs. 4 and 5). According to NMR data these compounds
exist in hydrazone form, however our simulations show that for 4
both forms have virtually identical absorption spectra, meaning that
the results for 1 and 2 show significant difference for hydrazone and
enol-azo forms. The TDDFT simulation for hydrazone tautomers
indicates the first absorption peak in the spectral range of
250–280 nm. This is in evident contradiction with experimental
data
— the first absorption peak has a spectral maximum at
approximately 370 nm. The enol-azo tautomers, on the other hand,
were predicted to absorb light in the vicinity of 400 nm (no solvation
model used) or 430 nm (PCM-simulated water influence). The reason
for this considerable (up to 150 nm) red spectral shift between the
hydrazone and enol-azo forms is the longer conjugated and orbital
delocalized state of the latter both for HOMO and LUMO orbitals
(Fig. 6), whereas for 3 and 4 tautomeric reaction does not result in
significant change in orbital shape (Fig. 6). For the first chromophore
these orbitals are localized in the carbonyl group, while for the latter
they are both spread throughout the aromatic ring, including the
hydroxyl substituent which is lying in one plane with the ring and the
azo group. However, these tautomers do not differ significantly in
atomic positions, different bond conjugations shift orbital energies
significantly (Table 1). The NMR spectra confirm that the enol-azo
3.2. Comparison of experimental and theoretical UV–VIS spectra
The experimental and theoretically simulated UV–VIS absorption
spectra are presented in Figs. 2–5. In all the graphs experimental data
are indicated by rectangles and theoretical predictions are indicated
by solid (TDDFT without PCM) or dashed (TDDFT with PCM model
compensating for water influence) lines. Spectra obtained for
hydrazone forms of the studied compounds are given in top panels,
while enol-azo forms are in bottom panels. In the case of 3 and 4 DFT
2 TDDFT
1.0
2 TDDFT Water
2 Experiment
0.5
0.0
200
250
300
350
400
450
500
2' TDDFT
Wavelength [nm]
1.0
0.5
0.0
2' TDDFT Water
2 Experiment
200
250
300
350
400
450
500
Wavelength [nm]
Fig. 3. Comparison of theoretically simulated and experimental UV–VIS spectra of 2
(top panel) and 2′ (bottom).
Fig. 1. Determination of the tautomeric ratio for 1 in D2O 1H NMR (see text).

14
W. Kuznik et al. / Journal of Molecular Liquids 171 (2012) 11–15
1.0
0.5
tautomer is dominant in both 1 and 2 following the conclusion from
3 TDDFT
3 TDDFT Water
3 Experiment
the TDDFT predicted absorption spectra. It is reasonable to assume
that the tautomeric ratio is similar in D2O used in the NMR
experiment and H2O used in the UV–VIS absorption measurement.
0.0
1.0
4. Conclusions
200
250
300
350
400
450
500
Wavelength [nm]
New AHBD (1–3) chromophores are synthesized and characterized.
1 and 2 exist in D2O and DMSO-d6 solutions as mixtures of enol-azo and
hydrazone tautomers with predominance of the enol-azo form. The
amount of enol-azo form depends on the substituent in the aromatic
part of AHBD and solvent polarity, especially when this tautomer has
longer conjugation length than the hydrazone one. TDDFT analysis of
absorption spectra was validated with experimental data measured in
water. DFT simulations of UV–VIS spectra of the studied compounds are
confirmed by the NMR results, indicating a substantial red spectral shift
of the enol-azo tautomer in the case for two of the studied compounds.
Analysis of the theoretical simulations allows concluding that the
significant (150 nm) spectral red shift between hydrazone and enol-azo
tautomers originated from HOMO and LUMO orbital delocalization in
the latter, which is obviously more important for compounds 1 and 2
with respect to 3 and 4. It is principal that following the performed
simulations at this level of theory hydrazone tautomers are the most
stable in all the cases, regardless whether or not PCM solvation model
was implemented for the calculations. Setting the enol group to freeze
during the optimization algorithm was used in this study to enforce
convergence to enol-azo geometry. Taking into account that presented
AHBD compounds can exist in a number of tautomeric forms and their
different conformations the results presented hereby are in satisfactory
agreement with the UV–VIS experimental data.
3' TDDFT
3' TDDFT Water
3 Experiment
0.5
0.0
200
250
300
350
400
450
500
Wavelength [nm]
Fig. 4. Comparison of theoretically simulated and experimental UV–VIS spectra of 3
(top panel) and 3′ (bottom).
1.0
4 TDDFT
4 TDDFT Water
4 Experiment
0.5
0.0
200
250
300
350
400
450
500
Wavelength [nm]
1.0
0.5
0.0
4' TDDFT
Acknowledgments
4' TDDFT Water
4 Experiment
This work has been partially supported by the Foundation for
Science and Technology (FCT), Portugal, and its PPCDT (FEDER
funded) and “Science 2007” programs. M.N.K. and K.T.M. express
gratitude to the FCT for a working contract and a post-doc fellowship.
The authors gratefully acknowledge the Portuguese NMR Network
(IST-UTL Center) for the NMR facility.
200
250
300
350
Wavelength [nm]
400
450
500
Calculations have been carried out in Wroclaw Centre for Network-
ing and Supercomputing (http://www.wcss.wroc.pl), grant no. 135.
Fig. 5. Comparison of theoretically simulated and experimental UV–VIS spectra of 4
(top panel) and 4′ (bottom).
Fig. 6. 1 hydrazone form optimized in water (PCM) — HOMO (a)–LUMO (b) orbital; 1′ enol-azo form optimized in water (PCM) — HOMO (c)–LUMO (d) orbital; 4 hydrazone (e) and
4′ enol-azo (f) form optimized in water (PCM) — LUMO orbital.

W. Kuznik et al. / Journal of Molecular Liquids 171 (2012) 11–15
15
Table 1
HOMO and LUMO orbital energies of the studied compounds, tautomeric forms and solvent influence simulated by PCM are presented (1′–4′ represent the enol-azo form of
compounds 1–4).
eV
1
1′
2
2′
3
3′
4
4′
HOMO
LUMO
HOMO (water)
LUMO (water)
−5.91
−3.16
−5.63
−2.72
−5.36
−3.33
−5.24
−3.14
−5.80
−3.14
−5.47
−2.75
−5.85
−3.69
−5.52
−3.32
−5.19
−3.38
−5.65
−3.40
−5.14
−3.42
−5.23
−3.33
−5.49
−3.56
−5.46
−3.38
−5.41
−3.53
−5.43
−3.38
[11] P. Gilli, V. Bertolasi, L. Pretto, A. Lycka, G. Gilli, Journal of the American Chemical
Society 124 (2002) 13554.
[12] H.C. Yao, P. Resnick, Journal of the American Chemical Society 84 (1962) 3514.
[13] H.C. Yao, Journal of Organic Chemistry 29 (1964) 2959.
[14] J. Marten, W. Seichter, E. Weber, U. Bohme, CrystEngComm 10 (2008) 541.
[15] A.M. Maharramov, R.A. Aliyeva, I.A. Aliyev, F.G. Pashaev, A.G. Gasanov, S.I. Azimova,
R.K. Askerov, A.V. Kurbanov, K.T. Mahmudov, Dyes and Pigments 85 (2010) 1.
[16] K.T. Mahmudov, A.M. Maharramov, R.A. Aliyeva, I.A. Aliyev, R.K. Askerov, R.
Batmaz, M.N. Kopylovich, A.J.L. Pombeiro, Journal of Photochemistry and
Photobiology A: Chemistry 219 (2011) 159.
[17] W. Kuznik, I.V. Kityk, M.N. Kopylovich, K.T. Mahmudov, K. Ozga, G. Lakshminarayana,
A.J.L. Pombeiro, Spectrochimica Acta Part A: Molecular and Biomolecular Spectros-
copy 78 (2011) 1287.
[18] F.R. Japp, F. Klingemann, Liebigs Annalen der Chemie 247 (1888) 190.
[19] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G.
Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H.P.
Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T.
Vreven, J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers,
K.N. Kudin, V.N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell,
J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox,
J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev,
A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G.
Zakrzewski, G.A. Voth, P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O.
Farkas, J.B. Foresman, J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian 09, Revision A.02,
Gaussian, Inc., Wallingford CT, 2009.
For author Ali H. Reshak the work was supported by the program
RDI of the Czech Republic, the project CENAKVA (No. CZ.1.05/2.1.00/
01.0024), and grant no. 152/2010/Z from the Grant Agency of the
University of South Bohemia. Ali H. Reshak also acknowledges the
School of Material Engineering, Malaysia University of Perlis, P.O. Box
77, d/a Pejabat Pos Besar, 01007 Kangar, Perlis, Malaysia.
References
[1] M.N. Kopylovich, K.T. Mahmudov, M.F.C.G. da Silva, M.L. Kuznetsov, P.J. Figiel, Y.Y.
Karabach, K.V. Luzyanin, A.J.L. Pombeiro, Inorganic Chemistry 50 (2011) 918.
[2] K.T. Mahmudov, R.A. Rahimov, M.B. Babanly, P.Q. Hasanov, F.G. Pashaev, A.G.
Gasanov, M.N. Kopylovich, A.J.L. Pombeiro, Journal of Molecular Liquids 162
(2011) 84.
[3] J. Marten, W. Seichter, E. Weber, U. Bohme, Journal of Physical Organic Chemistry
20 (2007) 716.
[4] M.N. Kopylovich, A.C.C. Nunes, K.T. Mahmudov, M. Haukka, T.C.O. Mac Leod,
L.M.D.R.S. Martins, M.L. Kuznetsov, A.J.L. Pombeiro, Dalton Transactions 40
(2011) 2822.
[5] K.T. Mahmudov, A.M. Maharramov, R.A. Aliyeva, I.A. Aliyev, M.N. Kopylovich,
A.J.L. Pombeiro, Analytical Letters 43 (2010) 2923.
[6] G. Aromi, P. Gamez, J. Reedijk, Coordination Chemistry Reviews 252 (2008) 964.
[7] P.A. Vigato, V. Peruzzo, S. Tamburini, Coordination Chemistry Reviews 253
(2009) 1099.
[8] P. Gilli, L. Pretto, V. Bertolasi, G. Gilli, Accounts of Chemical Research 42 (2009) 33.
[9] V. Bertolasi, V. Ferretti, P. Gilli, G. Gilli, Y.M. Issa, O.E. Sherif, Journal of the
Chemical Society, Perkin Transactions 2 (1993) 2223.
[20] A.R. Allouche, Journal of Computational Chemistry 32 (2011) 174.
[21] S. Miertus, E. Scrocco, J. Tomasi, Chemical Physics 55 (1981) 117.
[22] S. Miertus, J. Tomasi, Chemical Physics 65 (1982) 239.
[10] V. Bertolasi, P. Gilli, V. Ferretti, G. Gilli, K. Vaughan, New Journal of Chemistry 23
(1999) 1261.