New arylhydrazones of β-diketones and their optical and thermal properties

Article abstract of DOI:10.1016/j.molstruc.2012.03.054

New arylhydrazones of β-diketones, 2-(2-(4,4-dimethyl-2,6- dioxocyclohexylidene)hydrazinyl) benzoic acid (1) and (Z)-ethyl-2-(2-(2- nitrophenyl)hydrazono)-3-oxobutanoate (2), have been synthesized by reaction of activated β-diketones with the corresponding aryldiazonium salts, and characterized by IR, ¹H and ¹³C NMR spectroscopies and elemental analysis. In DMSO solution, 1 is stable exclusively in the hydrazone form, while 2 exists in DMSO and H₂O solutions as a mixture of enol-azo and hydrazone tautomeric forms. In the latter case, an increase in the solvent polarity shifts the tautomeric balance to the enol-azo form. Solvatochromic, thermal and photoluminescent properties of 1, 2 and the known related 2-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)benzoic acid (3), (2-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)phenyl)arsonic acid (4), (Z)-2-(2-(1,3-dioxo-1-phenylbutan-2-ylidene)hydrazinyl)benzoic acid (5) and 5-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)-2,3-dihydrophthalazine-1,4-dione (6) were studied. The obtained UV-vis absorption spectra confirm that _m depends on the solvent and on the nature of AHBD, but no clear correlation was found. Upon heating, 1-3, 5 and 6 are stable up to 474 K and decompose in two steps whereas 4 decomposes in three steps starting from 343 K. The kinetic parameters of the thermal decomposition were estimated suggesting a low rate of the thermal decomposition. Compounds 2 and 3 exhibit luminescence with intense emission bands with maxima at λ_em of 466.0 (λ_ex = 318 nm) and 532.5 nm (λ_ex = 315 nm), respectively, while compounds 4 and 6 show low-intensity bands at λ_em of 501 (λ_ex = 396 nm) and 503 nm (λ_ex = 389 nm). Compounds 1 and 5 display no photoluminescence.

Full text of DOI:10.1016/j.molstruc.2012.03.054

Journal of Molecular Structure 1019 (2012) 16–20
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
New arylhydrazones of b-diketones and their optical and thermal properties
Zhen Ma a,b, Abel M. Maharramov c, Ismayil A. Aliyev c, Irada N. Aliyeva c, Maximilian N. Kopylovich b,
b,
Gunel I. Amanullayeva d, Kamran T. Mahmudov b,c, , Armando J.L. Pombeiro
⇑
⇑
a School of Chemistry and Chemical Engineering, Guangxi University, Guangxi 530004, PR China
b Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
c Baku State University, Department of Chemistry, Z. Xalilov Str. 23, Az 1148 Baku, Azerbaijan
d Institute of Petrochemical Processes, National Academy of Sciences of Azerbaijan, Hojaly Ave. 30, 1025 Baku, Azerbaijan
a r t i c l e i n f o
a b s t r a c t
Article history:
New arylhydrazones of b-diketones, 2-(2-(4,4-dimethyl-2,6-dioxocyclohexylidene)hydrazinyl) benzoic
acid (1) and (Z)-ethyl-2-(2-(2-nitrophenyl)hydrazono)-3-oxobutanoate (2), have been synthesized by
reaction of activated b-diketones with the corresponding aryldiazonium salts, and characterized by IR,
1H and 13C NMR spectroscopies and elemental analysis. In DMSO solution, 1 is stable exclusively in the
hydrazone form, while 2 exists in DMSO and H2O solutions as a mixture of enol–azo and hydrazone tau-
tomeric forms. In the latter case, an increase in the solvent polarity shifts the tautomeric balance to the
enol–azo form. Solvatochromic, thermal and photoluminescent properties of 1, 2 and the known related
2-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)benzoic acid (3), (2-(2-(2,4-dioxopentan-3-ylidene)hydrazi-
nyl)phenyl)arsonic acid (4), (Z)-2-(2-(1,3-dioxo-1-phenylbutan-2-ylidene)hydrazinyl)benzoic acid (5)
and 5-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)-2,3-dihydrophthalazine-1,4-dione (6) were studied.
The obtained UV–vis absorption spectra confirm that ema[ depends on the solvent and on the nature of
AHBD, but no clear correlation was found. Upon heating, 1–3, 5 and 6 are stable up to 474 K and decom-
pose in two steps whereas 4 decomposes in three steps starting from 343 K. The kinetic parameters of the
thermal decomposition were estimated suggesting a low rate of the thermal decomposition. Compounds
2 and 3 exhibit luminescence with intense emission bands with maxima at kem of 466.0 (kex = 318 nm)
and 532.5 nm (kex = 315 nm), respectively, while compounds 4 and 6 show low-intensity bands at kem
of 501 (kex = 396 nm) and 503 nm (kex = 389 nm). Compounds 1 and 5 display no photoluminescence.
Crown Copyright Ó 2012 Published by Elsevier B.V. All rights reserved.
Received 17 February 2012
Received in revised form 22 March 2012
Accepted 23 March 2012
Available online 2 April 2012
Keywords:
Arylhydrazones of b-diketones
Tautomeric balance
Photoluminescence properties
1. Introduction
E/Z-hydrazone), while the hydrazone ꢀ enol–azo tautomeric
transitions are related to the
p-electron delocalization within
Arylhydrazones of b-diketones (AHBDs) have lately attracted a
great attention due to their wide range of applications, e.g. as semi-
conductors [1], ionophores [2], analytical reagents for spectropho-
tometric determination of some metal ions [3–5], high-density
recordable optical storage [6], spin-coating films [7], liquid crystals
[8], self-assembled layers [9], syntons in organic synthesis [10], etc.
A significant part of these applications is related to the spectral
properties of AHBD and their structural transformations. For exam-
ple, structural modifications within the heterodienic systems
forming a strong intramolecular resonance assisted hydrogen bond
(RAHB) can be used to create bistate molecular switches [11–13].
AHBDs possessing such intramolecular RAHB can exist in several
tautomeric and isomeric forms (E/Z-enol–azo, keto–azo and
RAHB [13]. It was demonstrated that all the studied symmetrical
AHBDs are stabilized in the hydrazone form in solution and in
the solid phase [10–14], while unsymmetrical AHBDs exist in solu-
tion as a mixture of enol–azo and hydrazone tautomers [14]. One
can notice that formally AHBDs have structural features to possess
interesting photochromic properties [15–18] and in particular pho-
toluminescent ones, which, however, have not yet been studied.
On the other hand, thermal properties of the compounds are also
important for some of the above mentioned applications (e.g. opti-
cal data storage or production of spin-coating films).
Thus, we decided to prepare the new AHBDs 2-(2-(4,4-dimethyl-
2,6-dioxocyclohexylidene)hydrazinyl) benzoic acid (1) and (Z)-
ethyl-2-(2-(2-nitrophenyl)hydrazono)-3-oxobutanoate (2), and study
their thermal and photoluminescence properties together with
those of the known related 2-(2-(2,4-dioxopentan-3-ylidene)
hydrazinyl)benzoic acid (3) [19], (2-(2-(2,4-dioxopentan-3-yli-
dene)hydrazinyl)phenyl)arsonic acid (4) [19], (E)-2-(2-(1,3-dioxo-
1-phenylbutan-2-ylidene)hydrazinyl)benzoic acid (5) [20] and
⇑
Corresponding authors. Address: Centro de Química Estrutural, Complexo I,
Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-
001 Lisbon, Portugal (K.T. Mahmudov).
E-mail addresses: kamran_chem@yahoo.com (K.T. Mahmudov), pombeiro@
ist.utl.pt (A.J.L. Pombeiro).
0022-2860/$ - see front matter Crown Copyright Ó 2012 Published by Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.03.054

Z. Ma et al. / Journal of Molecular Structure 1019 (2012) 16–20
17
5-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)-2,3-dihydrophthal-
azine-1,4-dione (6) (Scheme 1) [21].
stirring for 1 h. The formed precipitate of 1 (or 2) was recrystallized
from ethanol and dried in air.
The identity of 1 and 2 was demonstrated by element analysis,
IR and 1H and 13C NMR spectroscopies.
1: Yield: 76% (based on 5,5-dimethylcyclohexane-1,3-dione),
yellow powder soluble in methanol, ethanol, water and insoluble
2. Experimental
2.1. Materials and instrumentation
in benzene and chloroform. Anal. Calcd for
(M = 288.30): C, 62.49; H, 5.59; N, 9.72. Found: C, 62.45; H, 5.45;
N, 9.57. IR (KBr, selected bands, cmꢀ1): 3427
(OH), 2958 (NH),
1672 (C@O), 1618
(C@Oꢂ ꢂ ꢂH), 1591
(C@N). 1H NMR
C15H16N2O4
All the chemicals were obtained from commercial sources (Al-
drich) and used as received. Infrared spectra (4000–400 cmꢀ1) were
recorded on BIO-RAD FTS 3000MX instrument in KBr pellets. 1H and
13C NMR spectra were recorded on Bruker Avance II+ 300 and
400 MHz (UltraShield™ Magnet) spectrometers at ambient temper-
ature. Chemical shifts (d) are relative to internal TMS. Thermal
properties were analyzed with a Perkin–Elmer Instruction system
(STA6000) at a heating rate of 10 K minꢀ1 under a dinitrogen atmo-
sphere. Solvents of spectrophotometric grade were purchased from
Sigma–Aldrich and used without extra purification. The UV–vis
absorption spectra in the 200–700 nm regions were recorded with
a scan rate of 240 nm minꢀ1 by using a Lambda 35 UV–vis spectro-
photometer (Perkin–Elmer) in 1.00 cm quartz cells at room temper-
ature, with a concentration of 1–6 of 4.00 ꢁ 10ꢀ5 mol Lꢀ1. The
excitation and emission spectra were recorded at room tempera-
ture on a Perkin–Elmer LS55 fluorescence spectrometer.
m
m
m
m
m
(300.13 MHz, DMSO-d6), d: 1.02 (3H, CH3), 1.63 (3H, CH3), 3.41
(4H, 2CH2), 7.14–7.99 (4H, ArAH), 15.61 (1H, NH). 13C{1H} NMR
(75.468 MHz, DMSO-d6), d: 25.3 (CH3), 28.1 (CH3), 30.1 (Cipso),
52.2 (2CH2), 115.0, 124.7, 126.8 and 130.2 (4ArAH), 130.5
(ArACOOH), 131.6 (C@N), 143.2 (ArANHAN), 168.7 (COOH),
175.2 and 193.3 (C@O).
2: Yield: 64% (based on 1-ethoxybutane-1,3-dione), yellow
powder soluble in methanol, ethanol, water and insoluble in ben-
zene and chloroform. Anal. Calcd for C12H13N3O5 (M = 279.25): C,
51.61; H, 4.69; N, 15.05. Found: C, 51.77; H, 4.63; N, 15.02. IR
(KBr, selected bands, cmꢀ1): 3433
(C@O), 1640
(C@Oꢂ ꢂ ꢂH), 1560
m
(OH), 2983
m(NH), 1682
m
m
m
(C@N). 1H NMR of a mixture of
tautomeric enol–azo and hydrazone forms (300.13 MHz, DMSO-
d6). Enol–azo, d: 1.26–1.29 (3H, CH3), 2.40 (3H, CH3), 3.64–3.69
(2H, CH2), 7.10–7.70 (4H, ArAH), 12.67 (1H, HO-enol). Hydrazone,
d: 1.70 (3H, CH3), CH3 signals were overlapped with the solvent
peak, 4.27–4.29 (2H, CH2), 7.10–7.70 (24H, ArAH), 14.76 (1H,
NH). 13C{1H} NMR (75.468 MHz, DMSO-d6). Enol–azo, d: 14.1
(CH3), 24.4 (CH3), 60.7 (CH2), 103.7 (CAN), 108.3, 115.3, 124.3
and 130.5 (ArAH), 138.4 (ArAN@N), 149.2 (ArANO2), 164.5
(C@O), 175.6 (CAO). Hydrazone, d: 14.4 (CH3), 26.2 CH3), 61.4
(CH2), 115.0, 123.2, 126.7 and 130.8 (4ArAH), 133.9 (C@N), 138.7
(ArANO2), 140.3 (ArANHAN), 161.4 and 194.3 (C@O). 1H NMR of
2.2. Synthesis of 1 and 2
The compounds were prepared via the Japp–Klingemann reac-
tion [22] involving diazotization of aromatic amines with following
azocoupling of the thus formed diazonium salts and b-diketones, in
water solution containing sodium hydroxide [23].
2.2.1. Diazotization
2-Carboxyaniline or 2-nitroaniline (0.025 mol) was dissolved in
50 mL of water and then 1.00 g 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; 5.00 mL (33%) HCl were then
added in portions for 1 h. The temperature of the mixture should
not exceed 278 K. The resulting diazonium solution was used di-
rectly in the following coupling procedure.
a
mixture of tautomeric enol–azo and hydrazone forms
(300.13 MHz, D2O). Enol–azo, d: 1.29–1.33 (3H, CH3), 2.40 (3H,
CH3), 3.25 (2H, CH2), 7.14–7.74 (4H, ArAH). Hydrazone, d: 1.85
(3H, CH3), 2.46 (3H, CH3), 4.33–4.35 (2H, CH2), 7.14–7.74 (4H,
ArAH).
2.3. Thermal decomposition of 1–6
2.2.2. Azocoupling
The thermal properties of 1–6 were investigated by thermo-
gravimetric analysis (TG), derivative thermogravimetry (DTG)
and differential thermal analysis (DTA). The thermodynamic
parameters of decomposition of the compounds, namely the acti-
NaOH (1.00 g, 0.025 mol) was added to a mixture of 0.025 mol
of 5,5-dimethylcyclohexane-1,3-dione or 1-ethoxybutane-1,3-
dione with 50 mL of water. The solution was cooled in an ice bath
to ca. 273 K, and a suspension of 2-substituted phenyldiazonium
chloride (see above) was added in three portions under vigorous
vation energy (Ea), enthalpy (
àG) and the pre-exponential factor (A) were evaluated graphi-
cally using the Coats–Redfern relationship [24,25]:
D D
àH), entropy ( àS), free energy
(D
OH
HN NH
Þꢃ=T2g ¼ ꢀEa=RT þ ln½AR=
Eaꢃ;
u
.
. . O
.
C
. . O
H
C
C
O
lnf½ꢀ lnð1 ꢀ
a
...
...
O
C
H
O
C
where
a
is the fraction of the sample decomposed at temperature T,
the heating rate, Ea the activation
)]/T2} against
N
H3C
O
C
C
N
H2C
C
C
A is the pre-exponential factor,
energy and R the gas constant. A plot of ln{[ꢀln(1 ꢀ
1/T gives a slope from which Ea was calculated, and A was deter-
mined from the intercept. The activation entropy (
àS), enthalpy
àH) and free energy change ( àG) were calculated using the fol-
lowing equations:
u
H3C
H3C
N
N
C
a
6
1
H2C
CH3
O
D
(D
D
D
D
D
zS ¼ 2:303R logðAh=kTsÞ;
zH ¼ Ea ꢀ RTs;
zG ¼
D
zH ꢀ TsDzS;
where k, h and Ts are the Boltzman constant, the Planck constant
Scheme 1. AHBDs studied in this work.
and a peak temperature of the thermal effect, respectively.

18
Z. Ma et al. / Journal of Molecular Structure 1019 (2012) 16–20
Scheme 2. Tautomeric equilibria in 2.
polarities of the ground and excited states of a chromophore are
3. Results and discussion
different, a solvent change results in differential stabilization of
the ground and excited states, thereby altering the energy gap be-
tween the electronic states. Therefore, a study of the solvent effect
is quite useful in evaluating the excited state behavior of organic
compounds. On the other hand, electronic absorption spectra of
AHBDs are of great analytical interest [5]. Taking all the above
mentioned in mind, we studied the AHBD compounds by UV–vis
absorption spectroscopy at room temperature (298 K) in various
solvents of different polarity; the concentration of AHBD dyes in
all cases was 4 ꢁ 10ꢀ5 mol Lꢀ1; the selected spectral data are sum-
marized in Table 1 and for compound 1 in Fig. 1.
3.1. Synthesis of 1–6 and their characterization
The new AHBD compounds 1 and 2, and the known [19–21]
analogs 3–6 were prepared by reactions of b-diketones with aryldi-
azonium chlorides in the presence of sodium hydroxide.
Compound 1, prepared from a symmetric b-diketone (5,5-dimeth-
ylcyclohexane-1,3-dione), is stabilized in DMSO-d6 solution in the
hydrazone form, as reported for the symmetric analogs 3–6
[19–21]. However, compound 2, prepared from an unsymmetrical
b-diketone (1-ethoxybutane-1,3-dione) exists in DMSO-d6 and D2O
solutions as a mixture of enol–azo and hydrazone tautomers
(Scheme 2). The mole fraction of each tautomeric form has been
determined by the relative integration of the methyl (or methy-
lene) group of each tautomer [14]. Thus it was found that with in-
crease in the polarity of solvents (DMSO < D2O) the tautomeric
balance shifts to the enol–azo form (36% hydrazone, 64% enol–
azo in DMSO and 25% hydrazone, 75% enol–azo in D2O). Although
2 exists in solution as a mixture of two tautomeric forms, its IR
Three electronic transitions, viz.,
p–
pꢄ, n–pꢄ and hydrazo to
enol–azo are expected to occur within the AHBD due to the pres-
ence of the C@N and C@O moieties [28]. The observed maxima in
absorption spectra of AHBDs are shifted depending on the polarity
of the solvent. Thus, in many cases, kmax in a polar solvent, e.g.
DMSO and water, are shifted to lower wavelengths as compared
to less polar solvents. These kmax shifts indicate that there is no
strong solute–solvent interaction between the AHBD molecules
and the polar environment. The polar protic (methanol) and apro-
tic (DMSO) solvents with rich H-bond donor–acceptor properties
perform a significant effect on the absorption band shifts. Hence,
the solvent polarity and hydrogen bonding between solvent mole-
cules and AHBDs may effectively contribute to the dye ground and
excited state stabilization. However, values of kmax do not defi-
nitely correlate with a particular property of the solvent, such as
spectrum in KBr pellet [3433
m(OH), 2983 m(NH), 1682 m(C@O),
1640
m
(C@Oꢂ ꢂ ꢂH), 1560
m
(C@N) cmꢀ1] demonstrates that, in the so-
lid state, it is stabilized in the hydrazone form (Scheme 2) similarly
to the reported analogs [14,19–21].
3.2. UV–vis spectra
polarity, H-bond donor or acceptor ability (
a or b) or electric per-
As it is well known, the solvent sensitivity of UV–vis absorption
spectra is closely related to the solvent–solute interactions: since
mittivity ( ). Thus, neither the electrostatic solvation nor specific
e
Table 1
Selected data from UV–vis spectra of 1–6 in different solvents at 298 K.
Compound
Solvent
ea
ab [26]
bc [27]
Peak 1
kmax (nm)
260
Peak 2
kmax (nm)
381
Peak 3
kmax (nm)
393
d
d
d
ema[
ema[
ema[
1
2–6
Acetone
21
33
0.08
0.93
0.48
0.62
11,080
3450
–
2650
e
e
e
e
e
e
–
–
–
–
–
1
2
3
4
5
6
Methanol
264
246
247
255
295
10,650
11,000
10,900
12,500
13,460
380
373
367
382
375
4970
10,670
10,650
10,760
11,240
442
394
416
405
423
3010
2680
2282
2770
2930
e
e
e
e
e
e
–
–
–
–
–
–
1
2
3
4
5
6
DMSO
Water
47
80
0.00
1.17
0.76
0.18
270
256
257
245
236
264
12,800
11,190
10,760
11,350
11,100
10,780
354
313
345
348
325
358
11,348
10,000
10,730
10,720
10,300
10,700
435
376
373
381
377
377
10,490
10,650
10,650
10,000
10,680
10,030
1
2
3
4
5
6
261
248
252
264
1120
10,650
10,660
9800
283
317
356
318
1860
4500
4230
8460
404
381
414
407
1980
4520
2820
2770
e
e
e
e
e
e
–
–
–
–
–
–
–
e
e
e
e
e
e
–
–
–
–
–
a
b
c
Electric permittivity of solvent.
H-bond donating ability of solvent.
H-bonding acceptor ability of solvent.
d
e
L molꢀ1 cmꢀ1
No soluble.
.

Z. Ma et al. / Journal of Molecular Structure 1019 (2012) 16–20
19
Fig. 1. Absorption spectra of 1.
Fig. 2. Emission spectra of 2–4 and 6 in the solid state. The excitation wavelengths
solute–solvent interactions can solely explain the observed
solvatochromism.
are those of Table 3.
Table 3
3.3. Thermal behavior
Photoluminescent data for compounds 2–4 and 6.
Compound
kem (nm)
kex (nm)
Stoke shift (nm)
The thermal properties of 1–6 were investigated by thermo-
gravimetric analysis (TGA) and differential thermogravimetry
(DTG) within the temperature range of 298–1073 K and at the
heating rate of 10 K minꢀ1 (Table 2). The thermal behavior of 1–6
is related to their structures, for example, compound 4 starts to
decompose at 343 K due to the presence of hydrate water, while
all the other AHBDs are stable up to 474 K. Under heating, most
of AHBDs decompose in two consecutive steps, the thermal stabil-
ity being dependent on the substituents of b-diketone and aro-
matic parts.
2
3
4
6
466
533
501
503
385
398
396
389
81
135
105
114
(298 K), and the corresponding emission spectra are shown in
Fig. 2. Compounds 2 and 3 exhibit luminescence with intense
emission bands with maxima at kem of 466.0 and 532.5 nm, respec-
tively, if excited at kex of 318 and 315 nm (Table 3). In contrast,
compounds 4 and 6 show only low-intensity bands at kem of
501 nm (kex = 396 nm) and 503 nm (kex = 389 nm). No photolumi-
nescent properties of compound 1 and 5 were observed. From
the emission spectra, it is reasonable to ascribe the luminescence
of the compounds to be of an intra-ligand transition nature.
As can be seen, not only the emission wavelengths but also the
Stokes shifts are different, possibly due to the structure variation of
the compounds. Except for the two compounds with no photolu-
minescent properties, the sequence of the observed emission
bands is as follows:
The evaluated Ea and
D
àH differ by a small value of 4.24–
4.39 kJ molꢀ1 meaning that within the experimental error they
are equivalent. On the other hand, all the steps proceed with a neg-
ative
D
àS suggesting a low rate of the thermal decomposition [29].
The values of the pre-exponential factor in the Arrhenius equation
(A) are within 10ꢀ2–1010 sꢀ1, not allowing to establish the reaction
molecularity [29–31]. The found parameters with a sharp thermal
decomposition threshold and high mass loss are favorable for opti-
cal storage materials with a small and sharp recording mark edge
[7,32].
k3emð533Þ > ke6mð503Þ > k4emð501Þ > k2emð466Þ:
3.4. Photoluminescent properties
The photoluminescent properties of the compounds have been
studied in the solid state (powder samples) at room temperature
What concerns the Stokes shift, it is largest for compound 3
(135 nm) and smallest for compound 2 (81 nm).
Table 2
Thermal behaviors and kinetic parameters of 1–6.
Compound Temperature range
(K)
% Weight loss
found
DTG peak temperature
(K)
A (sꢀ1
)
Ea
D
àH
D
àS
D
àG
(kJ molꢀ1
)
(kJ molꢀ1
)
(J Kꢀ1 molꢀ1
)
(kJ molꢀ1
)
1
509–587
751–972
30.1
45.7
549
820
3.6 ꢁ 1010 141
137
229
ꢀ47.9
ꢀ294
ꢀ117
ꢀ261
ꢀ115
ꢀ260
ꢀ267
ꢀ262
ꢀ216
163
264
7.4 ꢁ 10ꢀ2 29.7
2
490–575
575–619
31.8
5.8
550
586
1.2 ꢁ 107
104
27.8
100
23.0
164
177
0.34
3 [19]
4 [19]
491–574
574–620
31.8
5.8
551
585
1.1 ꢁ 107
105
28.9
100
24.0
163
176
0.31
343–388
466–504
520–593
1.98
1.78
17.8
368
484
575
9.2 ꢁ 10ꢀ2 22.5
19.4
27.5
51.0
118
154
175
0.21
62.6
31.5
55.8
5
6
474–574
888–988
43.3
18.9
535
909
1.1 ꢁ 10ꢀ2 111
106
27.3
ꢀ77
148
257
1.1 ꢁ 10ꢀ2 34.9
ꢀ253
476–625
688–739
25.3
20.4
581
716
4.53
0.25
43.4
34.0
38.6
28.0
ꢀ238
ꢀ264
177
217

20
Z. Ma et al. / Journal of Molecular Structure 1019 (2012) 16–20
[6] Z. Chen, Y. Wu, D. Gu, F. Gan, Dyes Pigm. 76 (2008) 624–631.
4. Conclusions
[7] F. Huang, Y. Wu, D. Gu, F. Gan, Thin Solid Films 483 (2005) 251–256.
[8] M.J. Jeong, J.H. Park, C. Lee, J.Y. Chang, Org. Lett. 8 (2006) 2221–2224.
[9] J. Marten, A. Erbe, K. Critchley, J.P. Bramble, E. Weber, S.D. Evans, Langmuir 24
(2008) 2479–2486.
[10] E.V. Shchegol’kov, Y.V. Burgart, O.G. Khudina, V.I. Saloutin, O.N. Chupakhin,
Russ. Chem. Rev. 79 (2010) 31–61.
Two new AHBDs (1 and 2) were synthesized and characterized
by IR, multi-nuclear NMR spectroscopies and elemental analysis. 2
exists in D2O and DMSO-d6 solutions as a mixture of enol–azo and
hydrazone tautomers with predominance of the enol–azo form,
while its amount depends on the solvent polarity. The electronic
absorption spectra of 1, 2 and known analogs 3–6 disclose a
blue-violet light absorption at about 236–442 nm, while the solva-
tochromic behavior is dependent on the nature of solvents and
substituents in the b-diketone fragment and aromatic moiety.
The solvent–solute interactions are controlled by the H-bond do-
nor or acceptor ability or the electric permittivity of the solvents.
In the solid state, compounds 2–4 and 6 display a strong photolu-
minescence at room temperature; the photoluminescent proper-
[11] P. Gilli, V. Bertolasi, L. Pretto, A. Lycka, G. Gilli, J. Am. Chem. Soc. 124 (2002)
13554–13567.
[12] P. Gilli, V. Bertolasi, L. Pretto, G. Gilli, J. Mol. Struct. 790 (2006) 40–49.
[13] P. Gilli, L. Pretto, V. Bertolasi, G. Gilli, Acc. Chem. Res. 42 (2009) 33–44.
[14] M.N. Kopylovich, K.T. Mahmudov, M.F.C. Guedes da Silva, M.L. Kuznetsov, P.J.
Figiel, Y.Y. Karabach, K.V. Luzyanin, A.J.L. Pombeiro, Inorg. Chem. 50 (2011)
918–931.
[15] J.C. Crano, R.J. Guglielmetti, Topics in Applied Chemistry, Organic
Photochromic and Thermochromic Compounds, Plenum Press, New York,
1999.
[16] Y. Ito, K. Amimoto, T. Kawato, Dyes Pigm. 100 (2011) 319–323.
[17] S. Kawata, Y. Kawata, Chem. Rev. 100 (2000) 1777–1788.
[18] A. Hagfeldt, G. Boschloo, L. Sun, L. Kloo, H. Pettersson, Chem. Rev. 110 (2010)
6595–6663.
[19] 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 Trans. 40 (2011)
2822–2836.
ties, e.g. kex
, kem and Stoke’s shift, are dependent on the
structures. All the compounds 1–6 show a high thermal stability
and sharp thermal decomposition threshold, important character-
istics for optical recording media [6,7,32,33].
[20] W. Kuznik, I.V. Kityk, M.N. Kopylovich, K.T. Mahmudov, K. Ozga, G.
Lakshminarayana, A.J.L. Pombeiro, Spectrochim. Acta, Part A: Mol. Biomol.
Spectrosc. 78 (2011) 1287–1294.
[21] K. Krishnankutty, N. Thankarajan, Proc. Indian Acad. Sci. (Chem. Sci.) 98 (1987)
193–197.
Acknowledgements
[22] F.R. Japp, F. Klingemann, Liebigs Ann. Chem. 247 (1888) 190–225.
[23] M.N. Kopylovich, K.T. Mahmudov, M.F.C.G. Silva, L.M.D.R.S. Martins, M.L.
Kuznetsov, T.F.S. Silva, J.J.R.F. Silva, A.J.L. Pombeiro, J. Phys. Org. Chem. 24
(2011) 764–773.
[24] A.W. Coats, J.P. Redfern, Nature 20 (1964) 68–69.
[25] E. Urbanovici, C. Popescu, E. Segal, J. Therm. Anal. Calorim. 58 (1999) 683–700.
[26] A. Airinei, E. Rusu, D. Dorohoi, Spectrosc. Lett. 34 (2001) 65–74.
[27] M.J. Kamlet, J.L.M. Abboud, M.H. Abraham, R.W. Taft, J. Org. Chem. 48 (1983)
2877–2887.
[28] K.T. Mahmudov, A.M. Maharramov, R.A. Aliyeva, I.A. Aliyev, R.K. Askerov, R.
Batmaz, M.N. Kopylovich, A.J.L. Pombeiro, J. Photochem. Photobiol., A: Chem.
219 (2011) 159–165.
[29] H.M. Cordes, J. Phys. Chem. 72 (1968) 2185–2189.
[30] J. Sestak, Thermodynamical Properties of Solids, Academia, Prague, 1984.
[31] J.M. Criado, L.A. Perez-Maqueda, P.E. Sanchez-Jimenez, J. Therm. Anal. Calorim.
82 (2005) 671–675.
This work has been partially supported by the Foundation for
Science and Technology (FCT) (Projects PTDC/QUI-QUI/102150/
2008 and PEst-OE/QUI/UI0100/2011), Portugal, and ‘‘Science’’ Pro-
grams. The authors acknowledge the Portuguese NMR Network for
providing access to the NMR facility.
References
[1] H.B. Hassib, Y.M. Issa, W.S. Mohamed, J. Therm. Anal. Calorim. 92 (2008) 775–
782.
[2] M.N. Kopylovich, K.T. Mahmudov, A.J.L. Pombeiro, J. Hazard. Mater. 186 (2011)
1154–1162.
[3] S.R. Gadjieva, T.M. Mursalov, K.T. Mahmudov, F.G. Pashaev, F.M. Chyragov, J.
Anal. Chem. 61 (2006) 550–555.
[4] K.T. Mahmudov, R.A. Aliyeva, S.R. Gadjieva, F.M. Chyragov, J. Anal. Chem. 63
(2008) 435–438.
[32] F.X. Huang, Y.Q. Wu, D.H. Gu, F.X. Gan, Spectrochim. Acta, Part A: Mol. Biomol.
Spectrosc. 61 (2005) 2856–2860.
[33] X. Li, Y. Wu, D. Gu, F. Gan, J. Therm. Anal. Calorim. 98 (2009) 387–394.
[5] K.T. Mahmudov, A.M. Maharramov, R.A. Aliyeva, I.A. Aliyev, M.N. Kopylovich,
A.J.L. Pombeiro, Anal. Lett. 43 (2010) 2923–2938.