Synthesis, mesomorphic and physical properties of two new analogs of Schiff's base with an alkenic terminal chains

Article abstract of DOI:10.1016/j.molstruc.2010.12.056

Characterization and investigation of the physical properties of two new analogs of salicylaldimine compounds, which were synthesised for the first time by our group, are reported in this work. 5-(10-undecenyloxy)-2-[[[4-hexylphenyl] imino]methyl]phenol a

Full text of DOI:10.1016/j.molstruc.2010.12.056

Journal of Molecular Structure 990 (2011) 79–85
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, mesomorphic and physical properties of two new analogs of Schiff’s base
with an alkenic terminal chains
Nimet Yilmaz-Canli a, Belkis Bilgin-Eran b, Arif Nesrullajev c,
⇑
a Yildiz Technical University, Faculty of Science and Letters, Department of Physics, 34210 Esenler Istanbul, Turkey
b Yildiz Technical University, Faculty of Science and Letters, Department of Chemistry, 34210 Esenler Istanbul, Turkey
c Mugla University, Faculty of Science and Letters, Department of Physics, 48000 Kötekli Mug˘la, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 October 2010
Received in revised form 30 December 2010
Accepted 30 December 2010
Available online 22 January 2011
Characterization and investigation of the physical properties of two new analogs of salicylaldimine
compounds, which were synthesised for the first time by our group, are reported in this work. 5-(10-
undecenyloxy)-2-[[[4-hexylphenyl]imino]methyl]phenol and 5-(10-undecenyloxy)-2-[[[4-hexyloxyphe-
nyl]imino]methyl]phenol have been studied. Different degree of mesomorphism has been found in these
analogs. Typical textures and temperatures of the direct and reverse phase transitions, taking place in
these analogs, are presented. Temperature dependences of the optical transmission for both heating
and cooling are given.
Keywords:
Liquid crystals
Salicylaldimine compounds
Textures
Ó 2011 Elsevier B.V. All rights reserved.
Phase transition
Optical transmission
1. Introduction
In thisworkweare interested oncomparativepeculiaritiesoftwo
new salicylaldimine compound analogs with anisometric rod-like
Liquid crystalline materials exhibit simultaneously properties of
liquids, i.e. the rheological properties, and properties of solid crys-
tals, i.e. the physical anisotropic properties. Structural units of these
materials are the disc-like (sheet-like) and the anisometric rod-like
molecules. The rod-like molecules have various structural and phys-
ical properties. Shape, sizes, structures and anisometricity of such
molecules, availability and value of the dipole moment etc. param-
eters have an effect on the mesomorphic and physical properties of
liquid crystals [1–5]. Therefore the investigation of the connection
between type of molecules and the mesomorphic and physical
properties of materials is significantly important for the synthesis,
selection and condition of application of liquid crystals [6–9].
On the other hand, the salicylaldimine compounds are the ob-
jects of intensive investigations during the last one-two decades.
Unlike other liquid crystalline materials, the salicylaldimine com-
pounds have both the sheet-like and prolate molecules [10–13].
These compounds exhibit various types of mono- and polymor-
phism, are sufficiently sensitive to different external effects and
boundary conditions and can display the photochromic properties
[5,10–13]. Therefore these mesogenic compounds are sufficiently
interesting objects for scientific investigations and very perspec-
tive materials for technical and technological applications.
molecules, which were synthesised for the first time by our group.
Synthesis, characterization and investigation of the mesomorphic,
thermo-morphologic, thermotropic and thermo-optical properties
of 5-(10-undecenyloxy)-2-[[[4-hexylphenyl]imino]methyl]phenol
without the oxygen fragment and 5-(10-undecenyloxy)-2-[[[4-hex-
yloxyphenyl]imino]methyl]phenol with the oxygen fragment are
presented.
2. Experimental
2.1. Materials and samples
5-(10-undecenyloxy)-2-[[[4-hexylphenyl]imino]methyl]phenol
(1a)
and
5-(10-undecenyloxy)-2-[[[4-hexyloxyphenyl]imino]
methyl]phenol (1b) were objects of our investigation. These com-
pounds are the analogs and differ from each by oxygen in a hexyl
chain at the N-substituted phenyl ring of salicylaldimine molecule.
The chemicals used for the synthesis and purification of the
compounds 1a and 1b were from Aldrich Chemical Co.
The samples used in this study were the microslides as the
sandwich-cells. The samples were constructed by two optical glass
surfaces, Mylar spacer and glue. The spacer was placed between
glass surfaces and determines the thickness of the liquid crystalline
layer. The thickness of the compounds 1a and 1b in the microslides
⇑
Corresponding author.
E-mail address: arifnesr@gmail.com (A. Nesrullajev).
was fixed as 20 lm. The reference surfaces of the microslides were
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.12.056

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N. Yilmaz-Canli et al. / Journal of Molecular Structure 990 (2011) 79–85
preliminarily carefully cleaned by acetone and ethyl alcohol,
washed in an ultrasonic bath, rinsed by bidistilled and deionized
water and dried in a dry-oven at 320 K. Then the microslides were
constructed. The compounds 1a and 1b have been filled into the
microslides by capillary forces at the isotropic liquid state.
The determination of the temperature dependences of the opti-
cal transmission of the compounds 1a and 1b has been carried out
using the TOS. Our set-up consists of the light source as He–Ne la-
ser, special heater-thermostat, the digital temperature control sys-
tem, differential Cu–Co thermocouples, polarizer, analyzer, the
relative transmission object, power supply, multimeters, photodi-
ode and video-camera. The heating and cooling rate during the
2.2. Synthesis
optical measurements was 0.7 K minÀ1
.
The salicylaldimine compounds 1a and 1b were prepared as
previously described [14,15] by the p-toluensulfonic acid catalysed
condensation of 2-Hydroxy-4-(10-undecenyloxy)benzaldehyde
[16] with corresponding aniline in toluene. 2-Hydroxy-4-(10-
undecenyloxy)benzaldehyde (5 mmol), 6 mmol of 4-hexylaniline
and 4-hexyloxyaniline, respectively, and p-toluensulfonic acid
(80 mg) were dissolved in 50 ml toluene. A Dean–Stark trap was
adapted to the flask and the solution was boiled for 5 h under reflux.
After cooling, a yellow precipitate was obtained. The precipitate
was extracted with diethylether (3 Â 100 ml). The combined organ-
ic layers were washed with NaHCO3 and NaCl and dried with anhy-
drous Na2SO4 before the diethyl ether was removed under reduced
pressure. The crude product was purified by recrystallization from
acetone/methanol. The chemical structure of the compounds 1a
and 1b is similar, as it is presented in [6,14–18]. The structure of
the compounds 1a and 1b were confirmed by various spectroscopic
methods. These results are presented in Tables 1–4.
3. Results and discussion
3.1. Mesomorphic and thermo-morphologic properties of the
compound 1a and 1b
Investigations showed that the compound 1a exhibits two types
of liquid crystalline mesophases. These mesophases are enantio-
tropic and arise in this compound in strictly definite temperature
interval by both heating and cooling of the compound. These mes-
ophases are displayed by typical textures. Polarizing microscopic,
morphologic and conoscopic investigations showed that in the
compound 1a smectic C (SmC) and smectic A (SmA) mesophases
take place.
The low temperature mesophase of the compound 1a exhibits
texture, which is presented in Fig. 1a. This texture is complicated
and consists of two texture types, i.e. typical schlieren texture
and texture with destroyed confocal and polygonal formations.
As it is seen in Fig. 1a, the schlieren texture consists of the inver-
sion walls and the singular points. Investigations by the OM tech-
nique showed that here both the optically positive and negative
singular points with the disclination of strength as S = ½ and
S = 1 take place. Existence of the fan-like, confocal and polygonal
formations is typical for liquid crystalline mesophases with layer-
ing arrangement of molecules, i.e. for SmC and SmA mesophases.
Availability of destroyed confocal and polygonal formations is
characteristic for SmC mesophase in liquid crystalline material,
which exhibits both SmC and SmA mesophases [29,30]. Such type
of texture was presented in [29–33] and corresponds to SmC meso-
phase. Optical investigations showed that the above mentioned
mesophase is optically biaxial. Taking into consideration optical
peculiarities of observed smectic mesophase and morphologic
and structural properties of the texture, we identify the above
mentioned mesophase as SmC. We would like to note that the
schlieren texture exhibit also nematic mesophases. But nematic
mesophase is optically biaxial and takes place in temperature re-
gions higher than SmA mesophase.
The high temperature mesophase of the compound 1a exhibits
the texture which is presented in Fig. 1b. This texture consists of
the fan-like and confocal formations. Such type of texture is well
known, is typical for SmA mesophase and has been observed for
this mesophase in [30,33–35]. As it is seen from comparison of
Figs. 1a and 1b, unlike texture of SmC mesophase with fan-like,
polygonal and confocal formations, in texture of SmA mesophase
these formations are characterized by greater clearness of the
boundaries between the formations, greater regularity of the for-
mations and fewer disclinations. This peculiarity is typical for tex-
tures of SmC and SmA textures with fan-like, polygonal and
confocal formations.
2.3. Methods
For characterization and investigations of the mesomorphic,
thermo-morphologic, thermotropic and thermo-optical properties
of the compounds 1a and 1b the differential scanning calorimeter
(DSC), the polarizing optical microscopy (POM), the capillary tem-
perature wedge (CTW) device and special thermo-optical set-up
(TOS) have been used.
The temperatures of the direct and reverse phase transitions in
the compounds 1a and 1b were determined by DSC and were con-
trolled by the temperature transformations of typical textures. The
DSC-thermograms were recorded on a Mettler TA 3000/DSC-30S
with TA 72.5 software of Perkin–Elmer DSC-7.
The mesomorphic and thermo-morphologic properties of the
above mentioned compounds have been studied by the POM tech-
nique using the trinoculer polarizing conoscopic/orthoscopic
microscope and microphotographic system from Olympus Optical
Co., Ltd. and also special heater-thermostat with digital tempera-
ture control system. Peculiarities of specific and non-specific tex-
tures have been studied using the crystal-optics methods and
also by means of the optical mapping (OM) technique. The OM
technique was presented in [19,20] and was widely used in [21–
24] for detailed investigations of liquid crystalline textures.
The study of thermo-morphologic and thermotropic peculiari-
ties of the biphasic regions of the phase transitions have been car-
ried out using the CTW device. The CTW device was presented in
[25–27] and provides the observations of all of the thermic states
of liquid crystalline materials in the real scale of time and in a wide
temperature range and also the calculate of the phase transition
temperatures and the temperature widths of the heterophase re-
gions with an accuracy not less than 10À3 K [26–28].
Table 1
Analytical data of the compounds 1a and 1b.
Compound
Molecular formula
Yield (%)
Molecular weight (g molÀ1
)
Elemental analysis
C
H
N
C
H
N
1a
1b
C
C
30H43NO2
30H43NO3
76
78
449.7
465.7
80.06
77.38
9.64
9.31
3.11
3.01
79.88
77.27
9.68
9.38
3.02
2.92

N. Yilmaz-Canli et al. / Journal of Molecular Structure 990 (2011) 79–85
81
Table 2
1H NMR data of the compounds 1a and 1b. Chemical shifts (d in ppm) and coupling constants (J in Hz).
Compound
OH
HC@N
Arom. H
CH2@CH
CH2@CH
OCH2
CH2
CH3
1a
13.86
8.50
7.24–7.17
(m, 5H)
6.47–6.44
(m, 2H)
5.83–5.76
(m, 1H)
4.99–4.91
(m, 2H)
3.98
(t, 2H)
J ꢀ 6.5
2.60
0.87
(t, 3H)
J ꢀ 6.8
(t,
a
-CH2)
J ꢀ 7.6
2.05–2.01
(m, 2H)
1.80–1.24
(m, 22H)
1b
13.85
8.49
7.25–7.22
(m, 3H)
6.92
5.84–5.77
(m, 1H)
5.01–4.92
(m, 2H)
3.99, 3.97
(2t, 4H)
J ꢀ 6.5
2.06–2.02
(m, 2H)
1.81–1.25
(m, 22H)
0.90
(t, 3H)
J ꢀ 7.0
(d, 2H)
J ꢀ 8.8
6.49–6.45
(m, 2H)
Table 3
13C NMR data of the compounds 1a and 1b. Chemical shifts (d in ppm) and coupling constants (J in Hz).
Compound
HC@N
Arom. C
CH2@CH
Arom. CH
CH@CH2
OCH2
68.21
CH2
35.50
-CH2)
33.79, 31.71
31.47, 29.48
29.40, 29.32
29.10, 29.07
28.94, 28.92
25.97, 22,60
CH3
1a
160.58
164.08
163.49
145.86
141.39
112.99
139.21
133.31
129.30
120.75
107.51
101.59
114.11
14.07
(a
1b
159.29
163.76
163.26
157.99
141.09
113.03
139.18
133.31
121.91
115.15
107.40
101.58
114.09
68.33
68.13
33.76, 31.56
29.45, 29.37
29.30, 29.21
29.07, 29.05
28.89, 25.95
25.68, 22.59
13.99
Investigations showed that the compound 1b exhibits only one
type of liquid crystalline mesophases. This mesophase is also enan-
tiotropic and arise in this compound in sufficiently large tempera-
ture interval by both heating and cooling of the compound. This
mesophase display classic fan-shaped confocal texture of SmA
mesophase (Fig. 2). The fan-shaped confocal texture took place
within temperature interval of the mesophase. Such type of texture
is well known, is typical for SmA mesophase and was presented in
[29,30,33–35]. In this texture the director basically lies in the plane
of the liquid crystalline layer and smectic layers are curved across
the confocals. By temperature increasing, smooth texture transfor-
mations have been observed. During these transformations a
change of shape, sizes and dispositions of the confocal formations
took place.
Table 4
UV–Vis, IR and MS data of the compounds 1a and 1b.
Compound UV–Vis k
IR cC@N
MS m/z (%)
(nm)
(cmÀ1
1617
)
1a
1b
243.0, 342.0
449 (100) [M+]
297 (82) [M+–C11H21
]
242.0, 349.0
1617
465 (59) [M+]
313 (54) [M+ À C11H21
]
229 (59)
[M+ À C11H21 À C6H13
]
Fig. 1. Textures of SmC mesophase at 321.0 K (a) and SmA mesophase at 352.0 K (b) in compound 1a. Crossed polarizers.

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N. Yilmaz-Canli et al. / Journal of Molecular Structure 990 (2011) 79–85
Thus, as investigation results show, an addition of oxygen frag-
(i.e. SmA mesophase) is stable. TÃCA; TAÃ C; TÃÃ and TÃÃ are connected
CA AC
ment in molecule of the compound 1a lead to a change of the
mesomorphic properties in the compound 1b. Namely, this addi-
tion leads to a disappearance of SmC mesophase in the compound
1b, i.e. a decrease of the mesomorphic degree of the compound 1b
takes place.
with temperatures TCA and TAC of the SmÃC–SmA and SmA–SmC
phase transitions as TÃCA < TCA < TÃÃ and TAC < TAC < TAÃÃC. TCA and
CA
TAC temperatures are determined by the DSC method. At TCA and
TAC the free energy of SmC and SmA mesophases have minima at
SC – 0 and SA – 0.
The phase transition between SmC and SmA mesophases has
been theoretically considered in [36–45]. Almost in most of the
works this transition appears to be of the second order. On the
other hand in [40] this transition is considered as the first order
and in [42–45] as both the first and the second order. Additionally,
in [42] it is indicated that for the first order transition between
SmC and SmA mesophases the region of SmC + SmA coexistence,
i.e. the biphasic region, must takes place.
As it is noted above, our results show that for the compounds 1a
and 1b the biphasic regions of the direct and reverse phase transi-
tions between SmC and SmA mesophases take place. This peculiar-
ity is typical for the first order phase transitions [1,46,47].
However, the temperature width of the biphasic region for the
SmC M SmA phase transition in the compounds 1a and 1b is signif-
icantly narrower than that for the first order SmC⁄ M I [48],
SmC M I [49], SmC M N [6] and N M I [5] transitions. Additionally,
investigations by the DSC method show that the enthalpy values of
the SmC–SmA and SmA–SmC transitions are very low for the first
order transitions (Table 5). Therefore can be concluded that the
phase transition between SmC and SmA mesophases in the com-
pound 1a is obviously the weak first order transition.
3.2. Thermotropic and thermo-optical properties of the compounds 1a
and 1b
Investigations showed that the addition of the oxygen fragment
in a hexyl chain at the N-substituted phenyl ring of salicylaldimine
compound has an effect on their thermotropic properties. Namely,
the enlargement of temperature interval of SmA mesophase in the
compound 1b from 25.0 K (in compound 1a) to 57.6 (in compound
1b) by heating and from 26.5 K (in compound 1a) to 95 K (in com-
pound 1b) by cooling has been found. Additionally, change of the
general temperature interval of liquid crystalline state from
52.2 K (in compound 1a) to 57.6 K (in compound 1b) by heating
and from 88.9 K in compound 1a) to 95.0 K (in compound 1b) by
cooling has been observed.
Results of the calorimetric investigations, i.e. temperatures and
enthalpies of the direct and reverse phase transitions in the com-
pounds 1a and 1b, which have been obtained by the thermograms,
are presented in Table 5. As it is seen in this table, temperatures of
the direct and reverse phase transitions in these compounds do not
coincide. Namely, temperatures of the direct SmC–SmA and re-
verse SmA–SmC phase transitions in the compound 1a are differ-
ent. This fact indicates on the thermic hysteresis for the phase
transition between SmC and SmA mesophases.
Calorimetric investigations also showed that temperatures of
the direct SmA–I and reverse I–SmA phase transitions in both the
compounds 1a and 1b are different. Namely, for the reverse I–
SmA phase transition in both the compounds 1a and 1b the shift
Investigations using the CTW method showed that in the com-
pound 1a in the SmC–SmA and SmA–SmC phase transition regions
in strongly definite temperature interval simultaneous coexistence
of SmC and SmA mesophases is observed, i.e. the biphasic regions
of above mentioned phase transitions take place (Fig. 3). Investiga-
tions also showed that the temperature width of the biphasic re-
gions for the direct and reverse phase transitions between SmC
and SmA mesophases are different, i.e. a thermic hysteresis takes
place also for the biphasic regions of the above mentioned phase
transition (Table 5).
Table 5
Features of the compounds 1a and 1b. Solid crystal – Cr; smectic C – SmC; smectic A –
SmA; isotropic liquid – I.
Types of phase
transitions
Temperatures (T, K), temperature widths (
D
T, K) and
enthalpies (
D
H, kJ molÀ1 of phase transitions)
1a
1b
Cr–SmC
Cr–SmA
T = 310.3 K;
D
H = 24.83
–
–
T = 333.9 K;
The biphasic regions of the SmC–SmA and SmA–SmC phase
D
–
D
H = 35.34
transitions can be characterized by the
D
D
TCA = TÃCÃA À TÃCA and
SmC–SmA
SmA–I
T = 337.5 K;
T = 362.5 K;
D
D
H = 1.19
T = 1.97 K; T = 391.5 K;
TAC = TÃAÃC À TÃAC. TCÃA and TAÃ C are the low limits of the biphasic re-
H = 5.68
D
T = 1.58 K;
T = 357.3 K;
T = 4.93 K;
D
H = 5.48
gions of the SmC–SmA and SmA–SmC phase transitions, respec-
tively. At these temperatures the low temperature phase (i.e.
SmC mesophase) is stable but high-temperature phase (i.e. SmA
I–SmA
D
T = 5.52 K; T = 387.1 K;
D
H = À12.20
D
D
H = À11.62
SmA–SmC
SmC–Cr
SmA–Cr
T = 331.3 K;
T = 268.4 K;
–
D
D
H = À3.82
–
–
ÃÃ
ÃÃ
H = À33.35
mesophase) is metastable. T and T are the high limits of the bi-
CA
AC
T = 292.1 K;
H = À62.06
phasic regions of the SmC–SmA and SmA–SmC phase transitions,
respectively. At these temperatures the low temperature phase
(i.e. SmC mesophase) is metastable but high-temperature phase
D
Fig. 2. Textures of SmA mesophase in the compound 1b at 369.0 K (a) and 372.5 K (b). Crossed polarizers.

N. Yilmaz-Canli et al. / Journal of Molecular Structure 990 (2011) 79–85
83
of the phase transition temperatures to the lower temperatures
takes place (Table 5). This fact indicates on the thermic hysteresis
for the phase transition between SmA mesophase and isotropic li-
quid. Investigations using the CTW method showed that in both
the compounds 1a and 1b in the SmA–I and I–SmA phase transi-
tion regions in strongly definite temperature interval simultaneous
coexistence of SmA mesophase and isotropic liquid observes. I.e.
the biphasic regions of above mentioned phase transitions take
place (Figs. 4 and 5). Investigations also showed that the tempera-
ture widths of the biphasic regions for the I–SmA phase transition
are larger than that for the SmA–I phase transitions (Table 5). We
would like to note that in the compound 1a the I–SmA phase tran-
sition has been observed at 357.3 K, but in the compound 1b this
transition has been observed at 387.1 K. Thus it is clear that the
addition of the oxygen in molecule of the compound 1a leads to
an increase of the I–SmA phase transition in the compound 1b of
29.8 K.
The biphasic regions of the SmA–I and I–SmA phase ÃtÃransitions
can be characterized by the
D
TAI = TÃÃ À TÃAI and
D
TIA = TIA À TÃIA. TÃIA
AI
and TÃAI are the low limits of the biphasic regions of the SmA–I and
I–SmA phase transitions, respectively. At these temperatures the
low temperature phase (i.e. SmA mesophase) is stable but high-
ÃÃ
ÃÃ
temperature phase (i.e. isotropic liquid) is metastable. T and T
AI
IA
are the high limits of the biphasic regions of the SmA–I and I–
SmA phase transitions, respectively. At these temperatures the
low temperature phase (i.e. SmA mesophase) is metastable but
high-temperature phase (i.e. isotropic liquid) is stable. TÃAI; TIÃA; TÃÃ
AI
ÃÃ
and T are connected with temperatures TAI and TIA of the SmA–I
IA
and I–SmA phase transitions as TÃAI < TAI < TÃÃ and TÃIA < TIA < TÃÃ
.
AI
IA
TAI and TIA temperatures are determined by the DSC method. At
Fig. 3. Biphasic regions of the SmC–SmA (a) and SmA–SmC (b) phase transitions in the compound 1a. Crossed polarizers.
Fig. 4. Biphasic regions of the SmA–I (a) and I–SmA (b) transition in the compound 1a. Crossed polarizers.
Fig. 5. Biphasic regions of the SmA–I (a) and I–SmA (b) transition in the compound 1b. Crossed polarizers.

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N. Yilmaz-Canli et al. / Journal of Molecular Structure 990 (2011) 79–85
TAI and TIA the free energy of SmA mesophase and isotropic liquid
have minima at SA – 0 and SI = 0.
(a)
0,40
0,38
0,36
0,34
0,32
0,30
Investigations of the phase transition between SmA mesophase
and isotropic liquid, also as other liquid crystalline mesophase – iso-
tropic liquid (e.g. SmC–I, SmC⁄–I, N–I, Ch–I etc.) transitions, are
important topics from both fundamental and application points
of view. Peculiarities of the SmA–I phase transition have been
experimentally studied by various scientists in [50–56]. In [50–
56] were found that the SmA–I phase transition is the first order
transition. Additionally, this transition is more strongly first order
than the N–I transition, which is known to be very weakly first or-
der transition. The SmA–I transition has been theoretically investi-
gated within a phenomenological Ginzburg–Landau approach [57–
60]. In these works the transition is found to be of the strong first
order. Character of the thermotropic properties of the compounds
1a and 1b, availability of the thermic hysteresis for the phase tran-
sitions between SmA mesophase and isotropic liquid and existence
of the biphasic regions for these transitions indicate on the first or-
der of these transitions in these compounds.
Heating
cooling
290
300
310
320
330
T,K
340
350
360
370
(b)
0,40
0,35
0,30
0,25
0,20
Investigations show that the addition of oxygen in a hexyl chain
at the N-substituted phenyl ring of the compound 1a lead to signif-
icant changes of the thermotropic and thermo-morphologic prop-
erties in the compound 1b. Namely, this addition leads to an
increase of the melting point of 23.6 K and the clearing point of
29.0 K in the compound 1b. Additionally, as it is seen in Table 5,
the enthalpy of the SmA–I and I–SmA phase transitions in the com-
pound 1b is somewhat higher than that in the compound 1a. This
difference is obviously connected with an increase of the polarity
anisotropy and change of sizes and shapes of molecule in the com-
pound 1b as effect of the oxygen.
In this work temperature behaviour of the optical transmission
for both the heating and cooling processes in the compounds 1a
and 1b has been studied. Temperature dependences of the optical
transmission are presented in Fig. 6. As it is seen in this figure, by
an increase and decrease of temperature the nonlinear behaviour
of the optical transmission takes place. Namely, in sufficiently large
temperature interval unremitting and fluent changes of the optical
transmission and jump-like behaviour of this transmission for both
the compounds 1a and 1b have been observed. Then, as it is also
seen in Fig. 6, the linear dependences of the optical transmission
vs. temperature took place for these compounds. Comparison of
the temperature dependences of the optical transmission with
character of temperature transformations of typical textures
showed that the unremitting and fluent changes of the optical
transmission are connected with transformations in textures; the
jump-like changes of the optical transmission took place in the bi-
phasic regions of phase transitions; linear behaviour of the optical
transmission took place in isotropic liquid. Thus, investigations
showed that the character of temperature behaviour of the optical
transmission, i.e. the character of the thermo-optical properties,
corresponds to the character of temperature transformations of
typical textures, i.e. the character of thermo-morphologic
properties.
Heating
Cooling
300
320
340
360
380
400
T,K
Fig. 6. Temperature dependences of the optical transmission for the compounds 1a
(a) and 1b (b).
scientists for number physical parameters of liquid crystals in
[18,60–68].
4. Summary
In this work synthesis of new Schiff bases 1a and 1b with an
alkenic terminal chains, which have been obtained for the first
time by our group, and comparative investigations of the meso-
morphic, thermo-morphologic, thermotropic and thermo-optical
properties of these compounds have been carried out. These com-
pounds differ only by the oxygen fragment in a hexyl chain at the
N-substituted phenyl ring of salicylaldimine compound molecule.
The compound 1a exhibits SmC and SmA mesophases and has solid
crystal ? SmC ? SmA ? isotropic liquid ? SmA ? SmC ? solid crys-
tal sequence of the direct and reverse phase transitions. The com-
pound 1b exhibits only SmA mesophase and has solid
crystal ? SmA ? isotropic liquid ? SmA ? solid crystal sequence of
the direct and reverse phase transitions.
In the compounds 1a and 1b interesting texture transforma-
tions vs. temperature have been observed. Character of these trans-
formations is in good conformity with temperature behaviour of
temperature dependences of the optical transmission of typical
textures of the compounds 1a and 1b. Jump of the optical trans-
mission in the compounds 1a and 1b took place at the phase tran-
sition temperatures.
Comparison of the temperature behaviour of the optical trans-
mission with the DSC thermograms showed that temperatures of
the jumps in Fig. 6 correspond to temperatures of the phase tran-
sitions (Table 5). Additionally, as it is seen in Fig. 6, the jumps of
the optical transmission, which are connected with phase transi-
tions in both the compounds 1a and 1b, are shifted to the lower
temperatures by a cooling of the compounds. These results are in
full conformity with the thermotropic properties of the compounds
1a and 1b (Table 5). Such behaviour of the optical transmission
indicates that the thermic hysteresis take place also for the ther-
mo-optical properties of the compounds 1a and 1b. In conclusion
we would like to note that the thermic hysteresis for the first order
phase transitions have been experimentally observed by various
Peculiarities of the thermotropic behaviour, availability of the
thermic hysteresis for the phase transitions between SmA meso-
phase and isotropic liquid and existence of the biphasic regions
for these transitions indicate on the first order of these transitions

N. Yilmaz-Canli et al. / Journal of Molecular Structure 990 (2011) 79–85
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