K. Gak Simi ´c , I. Ðordevi ´c , G. Janji ´c et al.
Journal of Molecular Liquids xxx (xxxx) xxx
2
. Material and methods
29.4, 29.5, 68.1, 114.9, 123.9, 124.2, 126.5, 128.4, 128.8, 133.0,
1
44 2 6
44.3, 146.4, 159.9; elemental analysis calcd [ꢀ] for C40H N O :
All starting materials, reagents and solvents were obtained from
C 74.05, H 6.84, N 4.32; found: C 74.08, H 6.80 N, 4.38.
commercial suppliers and used without further purification. The
synthetic route to the investigated LC dimer is presented in
Scheme 1. 4-Hydroxy-4 -nitrostilbene was prepared according to
2.2. Quantum chemical calculations
0
a procedure from the literature [15]. Because the characterization
data of this compound are in agreement with those previously
reported, experimental details are not included here.
The calculations were performed using the Gaussian09 program
package [16]. Three compound isomers were optimized by using
the B3LYP functional, 6-31G(d,p) basis set and SMD solvation
model for DMF solvent. Molecular Electrostatic Potential Surface
(MEPS) calculations were performed at same level of theory. Time
dependent density functional theory (TD-DFT) was employed to
compute the UV–Vis spectra. For these calculations, a benchmark
study was performed using BMK and CAM-B3LYP functionals, 6-
31G(d,p) and def2-TZVP basis sets, and PCM and SMD solvation
models for DMF solvent.
The prediction of the conversion mechanism between three iso-
mer forms were performed at B3LYP/6-31G(d,p) level of theory.
The general protocol used for investigation of mechanisms was
as follows: obtaining the structure of the transition state (using
TS calculations), and verifying the truthfulness of the TS by IRC (in-
trinsic reaction coordinate) calculations. IRC calculations also pro-
vided the reaction path, followed in two directions from the
transition structure to the equilibrium geometries of reactants
and products.
The FTIR spectrum of the synthesized compound was recorded
with a Bomem MB series 100 spectrophotometer in the ATR mode.
The NMR spectral measurements were performed on a Bruker 300
1
13
spectrometer at 400 MHz for the H NMR and 100 MHz for the
NMR spectra. The spectra were recorded at room temperature in
CDCl using TMS as the internal standard. The elemental analysis
C
3
of the synthesized compound was carried out by standard analyt-
ical micromethods using an Elemental Vario EL III microanalyzer.
Its results were found to be in good agreement (±0.3ꢀ) with the
calculated values.
The UV–Vis spectrum was recorded using spectroscopy grade
–
6
–3
ꢀ3
DMF at 5∙10 and 1∙10 mol dm concentrations, with an Ocean
Optics QE65 Pro spectrometer with tungsten and halogen lamps.
Photoluminescence emission spectra were recorded by a Horiba
Nanolog spectrofluorimeter, with 384 nm excitation and
05 nm longpass filter.
The POM textures of the compound were investigated using
a
4
Zeiss Axio Imager A1 polarizing microscope by placing LC sand-
wich cells with weak planar anchoring (achieved by unidirection-
ally rubbed glass plates) in an Instec heat stage. The POM
textures were studied in an extremely slow heating–cooling cycle
at ~ ±0.1 °C /min rate. DSC was performed using a TA Q20. The sam-
ples were obtained directly from recrystallization and measured at
3
. Results and discussion
A symmetric LC dimer where two 4-nitrostilbene units are con-
nected with a dodecamethylene spacer via ether linkages, 1,12-
bis(4-(2-(4-nitrophenyl)ethenyl)phenoxy)dodecane, was synthe-
sized and characterized here. The synthetic route for the prepara-
tion of this compound involved a condensation reaction between
5
°C/min heating and cooling rates.
4
-nitrophenylacetic acid and 4-hydroxybenzaldehzyde giving 4-
0
2.1. Synthesis of 1,12-bis(4-(2-(4-nitrophenyl)ethenyl)
hydroxy-4 -nitrostilbene
and
its
reaction
with
1,12-
phenoxy)dodecane
dibromododecane in the presence of K
2
CO (Scheme 1).
3
The investigated compound is an enantiotropic LC (Fig. 1a–1e),
which exhibits a conventional nematic phase in a temperature
range of 20 and 30 °C on heating and cooling, respectively
(Fig. 1). Attard and co-workers reported a structurally-related LC
dimer consisting of two 4-nitroazobenzene units and the same
spacer (Fig. S4, Supplementary data, [17]). This compound also
enantiotropically exhibited a nematic phase, but its clearing point
was lower for 20 °C. A LC dimer having the 4-(4-nitrobenzoyloxy)
phenoxy group as two identical mesogenic terminal units con-
nected via dodecamethylene spacer, however, formed a monotro-
pic smectic phase in a narrow temperature range, as reported by
Jin et al. (Fig. S4, Supplementary data, [18]). Evidently, such a trend
implies that the charge transfer interaction between two 4-
nitrostilbene units is greater than between two 4-
nitroazobenzene or 4-(4-nitrobenzoyloxy)phenyl units [3]. Fig. 1f
presents the potential surface in the molecule affecting the meso-
0
4
-Hydroxy-4 -nitrostilbene (0.48 g, 2.0 mmol) was dissolved in
DMF (30 mL) and potassium carbonate (1.38 g, 10 mmol) was
added. After 30 min of stirring, 1,12-dibromododecane (0.32 mg,
.98 mmol) was added and after 18 h of stirring at room tempera-
ture, the reaction mixture is poured into water (150 mL). The pre-
cipitate formed was filtered and recrystallized from DMF to give
yellow solid. Yield: 38ꢀ. FTIR (ATR) ʋ 2920, 2850, 1587, 1572,
0
1
9
505, 1473, 1334, 1323, 1269, 1246, 1173, 1108, 1033, 1004,
ꢀ1
1
75, 952, 875, 841, 749, 716, 686, 630, 582, 530, 452 cm
) d [ppm]: 1.26–1.39 (m, 12H, –CH –), 1.44–1.51 (m,
–), 1.81 (quin, 4H, J = 7.1 Hz, –CH –), 3.99 (t, 4H,
J = 6.6 Hz, –CH O–), 6.92 (d, 4H, J = 8.8 Hz, –C –), 7.0 (d, 2H,
J = 16.4 Hz, –CH = CH–), 7.23 (d, 2H, J = 16.4 Hz, –CH = CH–) 7.49
; H
NMR (CDCl
H, –CH
3
2
4
2
2
2
6 4
H
(
(
d, 4H, J = 8.8 Hz, –C
d, 4H, J = 8.8 Hz, –C
6
H
4
–), 7.60 (d, 4H, J = 8.8 Hz, –C
6
H
4
–), 8.21
13
6
4 3
H –). C NMR (CDCl ) d [ppm]: 26.0, 29.2,
Scheme 1. Synthesis of 1,12-bis(4-(2-(4-nitrophenyl)ethenyl)phenoxy)dodecane. Reagents and conditions: i) piperidine, 110 °C, 6 h; ii) 1,12-dibromododecane, K
rt, 18 h.
2 3
CO , DMF,
2
Gak Simi?, Kristina
