1,3-Dimethyl-5-(3,4,5-tris(alkoxy)benzoyl) barbituric acid derivatives and their liquid crystalline difluoroboron complexes: Synthesis, characterization and comparative investigations of mesomorphic, thermotropic and thermo-morphologic properties

Article abstract of DOI:10.1016/j.molstruc.2013.10.038

A series of 1,3-dimethyl-5-(3,4,5-tris(alkoxy)benzoyl) barbituric acid derivatives 1a-4a with various chain length were synthesized by our group for the first time through the addition of 1,3-dimethyl barbituric acid to 3,4,5-tris(alkoxy)benzoyl chloride at room temperature in presence of pyridine. For preparation of their difluoroboron complexes, the derivatives 1a-4a reacts with borontrifluoride in the presence of triethylamine affording 1b-4b in moderate yields. All derivatives and complexes have been fully characterized by MS, FT-IR and multinuclear NMR spectroscopy. We also explored their liquid crystal properties by using POM, OM, CTW and DSC techniques. The results show that 3b and 4b with longer alkyl chain are monomorphic mesogens and exhibited enantiotropic thermotropic liquid crystalline mesophases. Investigation of their mesomorphic, thermo-morphologic and thermotropic properties is presented in this work.

Full text of DOI:10.1016/j.molstruc.2013.10.038

Journal of Molecular Structure 1056–1057 (2014) 246–253
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
1,3-Dimethyl-5-(3,4,5-tris(alkoxy)benzoyl) barbituric acid derivatives
and their liquid crystalline difluoroboron complexes: Synthesis,
characterization and comparative investigations of mesomorphic,
thermotropic and thermo-morphologic properties
b
a
Emrah Giziroglu a, , Arif Nesrullajev , Nil Orhan
⇑
a Department of Chemistry, Faculty of Arts and Sciences, Adnan Menderes University, 09100 Aydın, Turkey
b Department of Physics, Faculty of Sciences, Mug˘la Sıtkı Koçman University, 48000 Kötekli, Mug˘la, Turkey
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
A series of 1,3-dimethyl-5-(3,4,5-tris(alkoxy)benzoyl) barbituric acid derivatives and their difluoroboron
complexes are synthesized. The mesomorphic, thermotropic and thermo-morphologic properties of these
compounds were studied by POM, CTW and DSC techniques.
ꢀ
ꢀ
ꢀ
ꢀ
Mesogenic barbituric acid
difluoroboron complexes were
synthesized for the first time.
Effect of the chain length on
mesomorphic properties has been
found.
Mesomorphic, thermotropic and
thermo-morphologic properties have
been investigated.
F
F
H
B
O
O
O
N
O
OCnH2n+1
OCnH2n+1
OCnH2n+1
OCnH2n+1
H3C
O
H3C
O
BF3.Et2O, NEt3
CHCl3
N
N
Typical textures and
microphotographs of the heterophase
regions are presented.
O
N
O
OCnH2n+1
CH3
OCnH2n+1
CH3
n: 8, 10, 12, 14
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 May 2013
Received in revised form 12 October 2013
Accepted 14 October 2013
Available online 23 October 2013
A series of 1,3-dimethyl-5-(3,4,5-tris(alkoxy)benzoyl) barbituric acid derivatives 1a–4a with various
chain length were synthesized by our group for the first time through the addition of 1,3-dimethyl bar-
bituric acid to 3,4,5-tris(alkoxy)benzoyl chloride at room temperature in presence of pyridine. For prep-
aration of their difluoroboron complexes, the derivatives 1a–4a reacts with borontrifluoride in the
presence of triethylamine affording 1b–4b in moderate yields. All derivatives and complexes have been
fully characterized by MS, FT-IR and multinuclear NMR spectroscopy. We also explored their liquid crys-
tal properties by using POM, OM, CTW and DSC techniques. The results show that 3b and 4b with longer
alkyl chain are monomorphic mesogens and exhibited enantiotropic thermotropic liquid crystalline mes-
ophases. Investigation of their mesomorphic, thermo-morphologic and thermotropic properties is pre-
sented in this work.
Keywords:
Barbituric acid
Liquid crystals
Difluoroboron
b-Diketonate ligands
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
not the full translational symmetry as solid crystals. Liquid crystals
are attracting considerable experimental, theoretical and applied
Liquid crystalline materials are the specific fluids which possess
partial molecular orientational and positional ordering but have
interest for their fascinating physical and physico-chemical prop-
erties. These materials exhibit anisotropies in optical, electrical,
magnetic, and viscous-elastic properties and display various types
of structures, which are sufficiently sensitive to different external
effects (temperatures, electric and magnetic fields, deformations,
⇑
Corresponding author. Tel.: +90 5535520171.
E-mail address: giziroglu@hotmail.com (E. Giziroglu).
0022-2860/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2013.10.038

E. Giziroglu et al. / Journal of Molecular Structure 1056–1057 (2014) 246–253
247
surfaces etc.) [1–5]. Therefore liquid crystals are important materi-
als in scientific and engineering areas [3,6–9]. For example, these
materials have been widely used in many practical applications
such as photovoltaic solar cells [10], electroluminescent displays
[11], electron transport systems [12], addressing systems [13],
and thermography [14]. Because of the importance of molecular
shape and size in the mesogenic structure, several studies deal
with synthesis of new type mesogenic compounds [15–19].
b-diketonate complexes of boron compounds have been widely
investigated in many different fields of material science because
they show high stability in ambient air conditions. Especially their
high luminescence quantum efficiency has led to useful applica-
tions for light emitting materials [20,21]. Recently the b-diketonate
complexes of difluoroboron have been using for liquid crystals
system. These species may solve some problematic issues in
mesogenic optic nanomaterials because they combine lumines-
cence properties and liquid crystallinity in the same compounds
[22–26]. Other newly designed and synthesized liquid crystal
systems have been reported to contain barbituric acid derivatives.
Interestingly, although over many years a large number of liquid–
crystalline compounds including heterocyclic moiety has been
synthesized, there are very few examples of mesogenic barbituric
acid derivatives [27–29].
lary temperature wedge (CTW) device. [38–41] The CTW provides,
in a real scale of time and in a wide temperature range, an obser-
vation and study of all of the thermal states of liquid crystalline
materials. The CTW also provides the calculation of the tempera-
ture widths of the biphasic regions with an accuracy of 10À2
and determination of the linear widths of these regions with an
accuracy of 0.2 Â 10À3 mm [39,40]. The DSC-thermograms for
phase transitions in materials under investigations were recorded
on a Mettler TA 3000/DSC-30S with TA 72.5 software of Perkin–El-
mer DSC-7.
2.2. Materials
2.2.1. General procedure for the synthesis of 1a–4a derivatives
A solution of 1,3-dimethyl barbituric acid (12.8 g, 0.1 mol) in
30 mL toluene/pyridine mixture (1:1) was added dropwise to a
suspension of 3,4,5-tris(alkoxy)benzoyl chloride (0.1 mol) in pyri-
dine (5 mL) at 0 °C. The reaction mixture was stirred at room tem-
perature for 24 h. Then the mixture was poured into 8 M aqueous
hydrochloric acid solution (250 mL). Resulting suspension was
heated about 2 h at 70 °C and allowed to cool down to room tem-
perature. The resultant precipitates were filtered, thoroughly
washed with distilled water, dried and crystallized from
2-propanol.
While searching for novel mesogenic compounds for new appli-
cations in material sciences, we chose to target compounds featur-
ing barbituric acid and difluoroboron groups. In this work we
report our preliminary results, which are connected with the syn-
thesis, characterization and liquid crystalline investigation of 1,3-
dimethyl-5-(3,4,5-tris(alkoxy)benzoyl) barbituric acid derivatives
and their difluoroboron complexes.
2.2.1.1. 1,3-Dimethyl-5-(3,4,5-tris(octyl)benzoyl) barbituric acid 1a
derivative. Yield: 70%. 1H NMR (400 MHz, CDCl3): d 17.65 (br, 1H,
OÁ Á ÁHAO); 6.81 (s, 2H, ACHAr); 4.03 (t, JHH = 6.4 Hz, 2H, AOCH2A);
3.95 (t, JHH = 6.4 Hz, 4H, ACH2A); 3.42 (s, 3H, NACH3); 3.31 (s, 3H,
NACH3); 1.73 (m, 6H, ACH2A); 1.25–1.18 (m, 30H, A(CH2)9A);
0.84 (t, JHH = 7.3 Hz, 9H, ACH3) ppm. 13C NMR (100 MHz, CDCl3):
d = 191.1, 171.3, 160.3, 152.6, 151.0, 142.7, 129.1, 108.7, 95.1,
73.8, 69.3, 66.1, 32.3, 32.2, 30.1, 30.0–29.5 (m, ACH2A), 28.4,
2. Experimental
28.2, 26.3, 26.2, 22.9, 14.6 ppm. FT-IR (KBr) t: 2953, 2919, 2846,
2.1. Methods and samples
1725, 1695, 1557, 1247, 1119 cmÀ1. MS (m/z): 644 (M+1).
All procedures were performed under argon using standard
Schlenk techniques. Commercially available reagents were used
without further purification. 3,4,5-trialkoxy benzoyl chlorides
(1–4) were prepared according to the reported procedures
[30,31]. All reagents were purchased from Sigma Aldrich and used
without further purification. Toluene was distilled over sodium
and chloroform was distilled over calcium hydride before use.
Melting points were measured with an Electro thermal 9200
melting point apparatus. 1H, 13C NMR spectra were recorded on a
Bruker Ultrashield 400 Plus NMR spectrometer. Chemical shifts
are reported in ppm downfield from Me4Si and were referenced
to solvent peaks. Mass Spectra results were recorded on a Shimadzu
LC-MS-8030 Triple Quadupole Mass Spectrometer. IR spectra were
obtained on a Varian 900 FTIR spectrometer using KBr pellets.
The mesomorphic and thermo-morphologic properties have
been studied by the polarizing optical microscopy (POM) tech-
nique using the trinoculer polarizing conoscopic/orthoscopic
microscope, optical filters, compensators, k-plates and micropho-
tographic system from Olympus Optical Co., Ltd. and also special
heater-thermostat with digital temperature control system. The
POM is a sufficiently convenient and informative method for inves-
tigation of mesomorphic and morphologic properties of liquid
crystals and also for identification of liquid crystalline mesophases.
Morphologic and optical peculiarities of textures have been stud-
ied using the optical mapping (OM) technique [32,33]. This tech-
nique was applied for investigations of morphologic properties,
peculiarities of specific and defective textures of liquid crystalline
materials and identification of mesophases [34–37]. Studies of
the thermotropic and thermo-optical properties of the heterophase
regions of phase transitions have been carried out using the capil-
2.2.1.2. 1,3-Dimethyl-5-(3,4,5-tris(decyloxy)benzoyl) barbituric acid
2a derivative. Yield: 86%. 1H NMR (400 MHz, CDCl3): d 17.63 (br,
1H, OÁ Á ÁHAO); 6.80 (s, 2H, ACHAr); 4.10 (t, JHH = 6.4 Hz, 2H, AOCH2-
A); 3.97 (t, JHH = 6.4 Hz, 4H, ACH2A); 3.43 (s, 3H, NACH3); 3.29 (s,
3H, NACH3); 1.78 (m, 6H, ACH2A); 1.23–1.16 (m, 42H, A(CH2)9A);
0.88 (t, JHH = 7.3 Hz, 9H, ACH3) ppm. 13C NMR (100 MHz, CDCl3):
d = 191.5, 170.9, 160.3, 152.7, 151.0, 142.3, 129.0, 108.5, 95.8,
73.7, 69.6, 66.1, 32.4, 32.2, 30.8, 30.3–29.8 (m, ACH2A), 28.5,
28.2, 26.1, 26.0, 22.7, 14.1 ppm. FT-IR (KBr) t: 2949, 2916, 2843,
1723, 1693, 1555, 1243, 1115 cmÀ1. MS (m/z): 729 (M+1).
2.2.1.3. 1,3-Dimethyl-5-(3,4,5-tris(dodecyloxy)benzoyl) barbituric acid
3a derivative. Yield: 84%. 1H NMR (400 MHz, CDCl3): d 17.67 (br, 1H,
OÁ Á ÁHAO); 6.84 (s, 2H, ACHAr); 4.04 (t, JHH = 6.4 Hz, 2H, AOCH2A);
3.96 (t, JHH = 6.4 Hz, 4H, ACH2A); 3.43 (s, 3H, NACH3); 3.30 (s, 3H,
NACH3); 1.77 (m, 6H, ACH2A); 1.26–1.18 (m, 54H, A(CH2)9A);
0.88 (t, JHH = 7.3 Hz, 9H, ACH3) ppm. 13C NMR (100 MHz, CDCl3):
d = 191.4, 170.6, 160.0, 152.6, 150.8, 142.5, 129.0, 108.3, 95.0, 73.9,
69.6, 66.1, 32.3, 32.2, 30.7, 30.5–29.5 (m, ACH2A), 28.5, 28.4, 26.4,
26.2, 22.9, 14.4 ppm. FT-IR (KBr) t: 2954, 2917, 2848, 1726, 1693,
1558, 1247, 1119 cmÀ1. MS (m/z): 813 (M+1).
2.2.1.4. 1,3-Dimethyl-5-(3,4,5-tris(tetradecyloxy)benzoyl) barbituric
acid 4a derivative. Yield: 88%. 1H NMR (400 MHz, CDCl3): d 17.62
(br, 1H, OÁ Á ÁHAO); 6.81 (s, 2H, ACHAr); 4.08 (t, JHH = 6.4 Hz, 2H,
AOCH2A); 3.93 (t, JHH = 6.4 Hz, 4H, ACH2A); 3.41 (s, 3H, NACH3);
3.32 (s, 3H, NACH3); 1.76 (m, 6H, ACH2A); 1.25–1.17 (m, 66H,
A(CH2)9A); 0.87 (t, JHH = 7.3 Hz, 9H, ACH3) ppm. 13C NMR
(100 MHz, CDCl3): d = 191.3, 170.5, 159.9, 152.5, 150.7, 142.6,
129.0, 108.1, 95.2, 73.7, 69.5, 66.2, 32.1, 32.0, 30.6, 29.9–29.0 (m,

248
E. Giziroglu et al. / Journal of Molecular Structure 1056–1057 (2014) 246–253
ACH2A), 28.5, 28.2, 26.3, 26.1, 22.9, 14.3 ppm. FT-IR (KBr)
t
: 2951,
70 mL at room temperature. After stirring for 5 h at the same tem-
perature the reaction mixture was refluxed for 4 h. After quenching
with water, the organic phase was separated and the aqueous
phase was extracted with CHCl3. The combined organic phases
were washed with water, dried over anhydrous MgSO4 and evapo-
rated. The crude product was crystallized form toluene at À30 °C
and give pure yellow solid.
2914, 2847, 1726, 1691, 1557, 1247, 1115 cmÀ1. MS (m/z): 897
(M+1).
2.2.2. General procedure for the synthesis of 1b–4b complexes
BF3ÁEt2O (2 mL, 8 mmol) was added dropwise to a solution of
triethylamine (2 mL, 15 mmol) and 1a–4a (0.8 mmol) in dry CHCl3
O
O
O
OCnH2n+1
H3C
O
OCnH2n+1
OCnH2n+1
H3C
O
O
Pyridine/Toluene
N
N
OCnH2n+1
+
Cl
N
O
N
O
OCnH2n+1
CH3
OCnH2n+1
CH3
1 - 4
H
O
O
N
1, 1a 2, 2a
3, 3a
12
4, 4a
14
OCnH2n+1
OCnH2n+1
H3C
N
n
8
10
O
O
OCnH2n+1
CH3
1a - 4a
Fig. 1. 1,3-Dimethyl-5-(3,4,5-tris(alkoxy)benzoyl) barbituric acid derivatives 1a–4a.
F
F
H
B
O
O
O
N
O
OCnH2n+1
OCnH2n+1
H3C
H3C
BF3 Et2O, NEt3
N
N
CHCl3
OCnH2n+1
OCnH2n+1
O
O
OCnH2n+1
OCnH2n+1
O
N
O
CH3
CH3
1b- 4b
1a- 4a
Fig. 2. Difluoroboron complexes of 1,3-dimethyl-5-(3,4,5-tris(alkoxy)benzoyl) barbituric acid derivatives 1b–4b.
(a)
(b)
Fig. 3. 1H NMR spectra of 1,3-dimethyl-5-(3,4,5-tris(dodecyloxy)benzoyl) barbituric acid (a) and its difluoroboron complex (b).

E. Giziroglu et al. / Journal of Molecular Structure 1056–1057 (2014) 246–253
249
Fig. 4. Microphotographs, connected with 1b and 2b derivatives. Crossed polarizers; magnification Â200. (a) typical texture of crystalline phase at 299.7 K; (b) heterophase
region of the Cr – I phase transition; (c) heterophase region of the I – Cr phase transition.
2.2.2.1. Difluoroboron complex of 1,3-dimethyl-5-(3,4,5-tris(octyl-
Table 1
oxy)benzoyl) barbituric acid 1b complex. Yield: 35%. 1H NMR
Temperatures and corresponding enthalpies of the phase transitions for 3b and 4b.
(400 MHz, CDCl3): d 6.93 (s, 2H, ACHAr); 4.12 (t, JHH = 6.6 Hz, 2H,
Compounds
3b
Transitionsa
Tb (K)
DH (J/g)
AOCH2A); 3.87 (t, JHH = 6.6 Hz, 4H, ACH2A); 3.50 (s, 3H, NACH3);
3.32 (s, 3H, NACH3); 1.74 (m, 6H, ACH2A); 1.37–1.18 (m, 30H,
A(CH2)9A); 0.80 (t, JHH = 6.9 Hz, 9H, ACH3) ppm. 13C NMR
(100 MHz, CDCl3): d = 188.5, 168.1, 158.2, 152.2, 150.7, 146.3,
126.4, 110.2, 93.6, 74.1, 69.5, 66.1, 32.1, 32.0, 30.6, 30.0–29.0 (m,
ACH2A), 28.4, 28.2, 26.2, 26.1, 22.9, 15.0 ppm. 11B NMR (96 MHz,
CDCl3): d = À0.82 ppm.
CrAN
NAI
327.1
344.2
51.82
17.76
4b
CrAN
NAI
335.8
342.0
58.68
14.32
a
Abbreviations: Cr = crystalline phase; N = nematic phase; I = isotropic liquid.
Onset temperatures obtained by DSC at heating rates of 10 °C minÀ1 (He
b
atmosphere). Values were taken from second heating run.
FT-IR (KBr) t: 2950, 2915, 2850, 1723, 1692, 1560, 1380, 1245,
1118 cmÀ1. MS (m/z): 692 (M+1).
ACH2A), 28.4, 28.3, 26.3, 26.2, 22.9, 15.2 ppm. 11B NMR (96 MHz,
CDCl3): d = À0.81 ppm.
FT-IR (KBr) t: 2955, 2918, 2849, 1726, 1693, 1560, 1382, 1247,
2.2.2.2. Difluoroboron complex of 1,3-dimethyl-5-(3,4,5-tris(decyl-
oxy)benzoyl) barbituric acid 2b complex. Yield: 45%. 1H NMR
(400 MHz, CDCl3): d 6.91 (s, 2H, ACHAr); 4.10 (t, JHH = 6.6 Hz, 2H,
AOCH2A); 3.87 (t, JHH = 6.6 Hz, 4H, ACH2A); 3.49 (s, 3H, NACH3);
3.30 (s, 3H, NACH3); 1.74 (m, 6H, ACH2A); 1.37–1.19 (m, 42H,
A(CH2)9A); 0.80 (t, JHH = 6.9 Hz, 9H, ACH3) ppm. 13C NMR
(100 MHz, CDCl3): d = 188.5, 168.0, 158.2, 152.1, 150.3, 146.2,
126.4, 110.1, 93.6, 74.0, 69.5, 66.0, 32.4, 32.1, 30.5, 30.2–29.3 (m,
ACH2A), 28.2, 28.1, 26.3, 26.0, 22.8, 15.1 ppm. 11B NMR (96 MHz,
CDCl3): d = À0.88 ppm.
1118 cmÀ1. MS (m/z): 861 (M+1).
2.2.2.4. Difluoroboron complex of 1,3-dimethyl-5-(3,4,5-tris(tetrade-
cyloxy)benzoyl) barbituric acid 4b complex. Yield: 60%. 1H NMR
(400 MHz, CDCl3): d 6.92 (s, 2H, ACHAr); 4.11 (t, JHH = 6.6 Hz, 2H,
AOCH2A); 3.87 (t, JHH = 6.6 Hz, 4H, ACH2A); 3.53 (s, 3H, NACH3);
3.32 (s, 3H, NACH3); 1.75 (m, 6H, ACH2A); 1.37–1.19 (m, 66H,
A(CH2)9A); 0.82 (t, JHH = 6.9 Hz, 9H, ACH3) ppm. 13C NMR
(100 MHz, CDCl3): d = 188.7, 168.2, 158.3, 152.2, 150.8, 146.3,
126.5, 110.2, 93.6, 74.0, 69.6, 65.9, 32.1, 32.0, 30.6, 29.9–29.3 (m,
ACH2A), 28.3, 28.2, 26.3, 26.1, 22.9, 15.0 ppm. 11B NMR (96 MHz,
CDCl3): d = À0.82 ppm.
FT-IR (KBr) t: 2950, 2919, 2850, 1725, 1695, 1561, 1381, 1246,
1117 cmÀ1. MS (m/z): 776 (M+1).
FT-IR (KBr) t: 2956, 2920, 2849, 1725, 1695, 1560, 1380, 1245,
1113 cmÀ1. MS (m/z): 945 (M+1).
2.2.2.3. Difluoroboron complex of 1,3-dimethyl-5-(3,4,5-tris(dodecyl-
oxy)benzoyl) barbituric acid 3b complex. Yield: 51%. 1H NMR
(400 MHz, CDCl3): d 6.94 (s, 2H, ACHAr); 4.14 (t, JHH = 6.6 Hz, 2H,
AOCH2A); 3.89 (t, JHH = 6.6 Hz, 4H, ACH2A); 3.50 (s, 3H, NACH3);
3.33 (s, 3H, NACH3); 1.75 (m, 6H, ACH2A); 1.39–1.19 (m, 54H,
A(CH2)9A); 0.81 (t, JHH = 6.9 Hz, 9H, ACH3) ppm. 13C NMR
(100 MHz, CDCl3): d = 188.6, 168.1, 158.4, 152.3, 150.8, 146.3,
126.5, 110.3, 93.7, 74.1, 69.6, 66.1, 32.2, 32.1, 30.6, 30.0–29.5 (m,
3. Results and discussion
3.1. Synthesis
1,3-dimethyl-5-(3,4,5-tris(alkoxy)benzoyl)
derivatives 1a–4a were formed through the reactions of
barbituric
acid

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E. Giziroglu et al. / Journal of Molecular Structure 1056–1057 (2014) 246–253
Fig. 5. Typical textures of 3b and 4b, (a) texture of 3b at 329.7 K (b) texture of 3b at 338.7 K (c) texture of 4b at 336.7 K and (d) texture of 4b at 340.5 K. Crossed polarizers;
magnification Â100.
compounds in good yields. Indeed, according to FT-IR and 1H
NMR spectra: all of benzoyl barbiturates 1a–4a can exist in
enol–keto tautomers because of acidic hydrogen atom attached
C-5 position [42] (Fig. 1).
In the next step when the 1,3-dimethyl-5-(3,4,5-tris(alk-
oxy)benzoyl) barbituric acid derivatives 1a–4a were treated with
boron trifluoride diethyl etherate in presence of triethylamine,
boron difluoride complex of 1,3-dimethyl-5-(3,4,5-tris(alkoxy)
benzoyl) barbituric acid 1b–4b were obtained in moderate yields.
(Fig. 2).
All the compounds are air stable, nonhydroscopic and have
been characterized by MS, FT-IR, 1H, 13C and 11B NMR spectros-
copy. Spectroscopic data of the synthesized compounds are given
in Section 2. An example of 1H NMR spectra for 3a and 3b are
shown in Fig. 3. The other 1H NMR spectra of 1,3-dimethyl-5-
(3,4,5-tris(alkoxy)benzoyl) barbituric acid derivatives and their
difluoroboron complexes were similar to that of 3a and 3b with
the exception of the chemical shifts from the alkoxy groups.
The 1H NMR spectra of compounds 1a–4a revealed a broad peak
at ca. 17.6 ppm which was readily assigned to OH protons. There-
fore we infer that the enol forms are more preferable than keto
Fig. 6. Sketch of the marble-like texture in uniaxial nematic mesophase.
1,3-dimethyl barbituric acid with 3,4,5-tris(alkoxy)benzoyl
chloride (1–4) at room temperature in presence of pyridine. The
reaction proceeded smoothly producing the corresponding
Fig. 7. N – I phase transition region in 3b (a) and 4b (b). Crossed polarizers; magnification Â200.

E. Giziroglu et al. / Journal of Molecular Structure 1056–1057 (2014) 246–253
251
Fig. 8. Microphotographs of the heterophase regions of the I – N phase transition. 3b (a) and 4b (b). Crossed polarizers; magnification Â100.
of them are overlapped. The very strong bands in the range
2910–2840 cmÀ1 can be attributed to CAH stretching associated
with longer aliphatic chain.
In the case of 1a–4a, we do not observed a broad peak in the ca.
3300–2600 cmÀ1 region which possesses intramolecular H–bond-
ing vibration. Therefore we can conclude that there is a shift of
equilibrium to keto form in the solid state for 1a–4a [46,47]. The
most significant differences between the FT-IR spectra of the 1,3-
dimethyl-5-(3,4,5-tris(alkoxy)benzoyl) barbituric acid derivatives
and their boron complexes are BAO vibration at ca. 1380 cmÀ1 [25].
3.2. Mesomorphic, thermotropic and thermo-morphologic properties
Fig. 9. Texture of crystalline state of 3b at 299.7 K. Crossed polarizers; magnifica-
tion Â200.
Investigations showed that, 1a, 2a, 3a, 4a, 1b and 2b com-
pounds have not mesomorphic properties. We did not observe
clear crystalline state and phase transition for 1a–4a. However
1b and 2b compounds exhibit crystalline phase and display crystal-
line state – isotropic liquid (Cr – I) and isotropic liquid – crystalline
state (I – Cr) phase transitions. Textures of crystalline phase for
1b and 2b compounds were very similiar. As an example, such tex-
ture for 2b is presented in Fig. 4a. This texture consists of so-called
spherulite formations. Spherulites represent three dimensional fig-
ures, which consist in radially arranged elongated color formations
with sharp grain boundaries. By heating of the samples, these for-
mations melted to isotropic liquid (Fig. 4b); by cooling of the sam-
ples, these formations arose again in isotropic liquid (Fig. 4c).
3b and 4b complexes exhibit monomorphic mesomorphism
and display enantiotropic nematic liquid crystalline mesophase.
In these complexes the direct crystal – nematic mesophase – isotro-
pic liquid and the reverse isotropic liquid – nematic mesophase –
crystal phase transitions have been observed. Temperatures of
these phase transitions are presented in Table 1.
Fig. 10. Heterophase region of the nematic mesophase M crystalline state phase
transition for 3b. Crossed polarizers; magnification Â100.
forms in the solution due to an internal hydrogen bond (referred to
as chelated enol) [42,43]. 3,4,5-tris(alkoxy)benzoyl- group shows a
well defined singlet at ca. 6.8 ppm from aromatic proton. The ali-
phatic protons on the 1,3-dimethyl barbituric acid moiety appear
at ca. 3.4 and 3.3 ppm. Examination of the 13C NMR spectra of
1a–4a in CDCl3 solution revealed that the chemical shift of the
three carbonyl carbons have characteristic values at ca. 191, 170,
160 ppm [42,44].
Nematic mesophase in 3b and 4b complexes exhibit textures,
which are presented in Fig. 5. As is seen Fig. 5, these textures are
the marble-like textures and are specific for nematic mesophase
[48–50]. Marble-like texture is mosaic texture and consists of sep-
~
arate regions with uniform alignment. In each region the director n
has strongly definite orientation, but different regions are charac-
~
terized by different orientation of the director n. As is seen in in
Figs. 4 and 5, the color of different regions is different. This is
due to a change of the birefringence from both in-plane and
The most significant changes between the 1H NMR spectrum of
the 1a–4a and their boron complexes were absence of the reso-
nance signal of hydroxyl protons at ca. 17.6 ppm. After complexa-
tion of 1,3-dimethyl-5-(3,4,5-tris(alkoxy)benzoyl) barbituric acid
derivatives with difluoroboron, 13C NMR signals shifted approxi-
mately 1–5 ppm to high field. 11B NMR resonance at ca. 0.8 ppm
is in agreement with the existence of a four coordinate boron atom
[45].
~
out-of-plane variation of the director n. In Fig. 6 a sketch of such
texture is presented. Optical investigations showed that the
boundaries between separate uniform regions are the disclinations
and the inversion walls. The disclinations and the inversion walls
represent the places of texture, where the breaks of optical conti-
nuity of mesophase take place. Optical and morphologic investiga-
tions showed that some of these disclinations and walls were
placed perpendicular to the reference surfaces of the sandwich-
cell, but others were placed tilted to these surfaces.
In the Infrared spectra of all compounds, carbonyl stretching
frequencies vary from ca. 1585 cmÀ1 to ca. 1705 cmÀ1 and some

252
E. Giziroglu et al. / Journal of Molecular Structure 1056–1057 (2014) 246–253
(Fig. 10). As is seen in Fig. 10, in the heterophase region of this
phase transition coexistence of low temperature phase (crystalline
state) and high temperature phase (nematic mesophase) takes
place.
DSC thermograms for phase transitions in 3b and 4b were
shown in Fig. 11. The corresponding phase transition, tempera-
tures and associated enthalpy changes (
summarized in Table 1.
DH) of the transition were
4. Conclusion
In this work the synthesis, characterization and investigation of
the mesomorphic, thermotropic and thermo-morphologic proper-
ties of four novel 1,3-dimethyl-5-(3,4,5-tris(alkoxy)benzoyl) barbi-
turic acid derivatives as well as their difluoroboron complexes are
presented. These materials were characterized by various spectro-
scopic techniques such as MS, FT-IR, 1H, and 13C, 11B NMR spectros-
copy. The mesomorphic, thermotropic and thermo-morphologic
properties of these compounds were studied by POM, CTW and
DSC techniques. Liquid crystalline properties have been found in
3b and 4b compounds with longer alkyl chains. These complexes
exhibit nematic mesophase in relatively large temperature interval
and have phase transition temperatures at sufficiently low
temperatures.
It is important to note that 3b and 4b complexes are one of rare
examples of liquid crystalline materials, which contain the barbitu-
ric acid and difluoroboron groups. On the other hand, thermotropic
properties of these complexes make such materials interesting ob-
jects from both fundamental and application points of view. There-
fore, modifications of the structures and photo-physical properties
of such materials, e.g. electronic absorption spectra and fluores-
cence spectra are under active investigation.
Acknowledgements
Authors are thankful to National Boron Research Institute
(Project Number: 2012.C0345) for financial assistance. This work
has been partially supported by the Research Foundation of Mug˘la
Sıtkı Koçman University, Grant No. 12/40.
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