S.-H. Han et al. / Journal of Molecular Structure 735–736 (2005) 375–382
377
12.7 mmol) were added to 2-butanone (50 ml) in 100 ml
two-necked round-bottom flask equipped with a reflux
condenser. The reaction mixture was stirred in oil bath at
150 8C. The reaction was monitored by TLC (CHCl3:
hexane, 9:1). After stirring for 5 h, the resultant yellow
solution was filtered, and the solvent was removed under
reduced pressure. The crude product was purified by
recrystallization from ethanol. The light yellow solid of D
was obtained (1.1 g, 3.3 mmol, yield: 78%). 1H NMR
(500 MHz, DMSO-d6) d: 8.52 (s, 1H, –CHaN–), 7.80
(d, 2H, H–Ar), 7.20 (d, 2H, H–Ar), 7.01 (d, 2H, H–Ar), 6.74
(d, 2H, H–Ar), 4.01 (t, 2H, –O–CH2–), 2.90 (s, 6H,
N–(CH3)2), 1.72 (m, 2H, –O–CH2–CH2–), 1.29–1.43
(m, 6H, –(CH2)3–) and 0.87 (t, 3H, –CH3). Anal. calcd for
C21H28N2O: C 77.74, H 8.70, N 8.63; found: C 77.75,
H 8.71, N 8.74.
peak top, and the enthalpy change was determined from the
peak area. In order to check the reproducibility, the
measurements were done in quadruplicate for the same
sample. The reproducibility of the phase transition tem-
perature and the enthalpy was G0.3 8C and G7%,
respectively. The entropy change was calculated by
assuming that the transition is sufficiently reversible.
The XRD measurements were performed on a MXP-18
(MAC Science Co., Ltd) diffractometer using Cu Ka1
radiation (lZ0.15405 nm). Infrared spectra were measured
using a FT-IR spectrometer (Shimadzu FTIR-8400S)
operating at 2 cmK1 resolution with an unpolarized beam
striking the sample at normal incidence. The transparent
KBr disks obtained (10 mm in diameter and 2 mm in
thickness) were used for the VT-IR measurements.
2.5. N-(4-n-hexyloxybenzylidene)-4-nitroaniline (A)
3. Results and discussion
A mixture of compound 2 (0.8 g, 3.3 mmol), 1-bromo-
hexane (1.6 g, 9.9 mmol) and K2CO3 (1.4 g, 9.9 mmol)
were added to 50 ml of 2-butanone in 100 ml two-necked
round-bottom flask equipped with a reflux condenser. The
reaction mixture was stirred in oil bath at 150 8C. The
reaction was monitored by TLC (CHCl3:hexane, 9:1). After
stirring for 5 h, the resultant yellow solution was filtered,
and the solvent was removed under reduced pressure. The
crude product was purified by recrystallization from
ethanol. The light yellow crystalline solids of A was
obtained (0.8 g, 2.5 mmol, yield: 76%). 1H NMR
(500 MHz, DMSO-d6) d: 8.56 (s, 1H, –CHaN–), 8.25
(d, 2H, H–Ar), 7.91 (d, 2H, H–Ar), 7.39 (d, 2H, H–Ar), 7.08
(d, 2H, H–Ar), 4.05 (t, 2H, –O–CH2–), 1.73 (m, 2H,
–O–CH2–CH2–), 1.29–1.43 (m, 6H, –(CH2)3–) and 0.87 (t,
3H, –CH3). Anal. calcd for C19H22N2O3: C 69.92, H 6.79, N
8.58; found: C 69.85, H 6.82, N 8.65.
Fig. 1 shows typical DSC thermograms observed for the
compounds D, A and the mixtures DA in the second heating
and cooling scanning. The measured enthalpy (DHSI) and
entropy (DSSI) changes on the second heating and cooling
for the compounds are summarized in Table 1. On the
second cooling scanning, the compounds D and A exhibit
only monotropic nematic phases (N) over relatively narrow
temperature range from 81.3 to 93.1 8C and from 75.6 to
79.5 8C, respectively. However, all of the mixtures DA on
the heating and cooling scanning display the smectic phase
(S) as identified by POM and XRD measurements. It should
be assumed that intermolecular interaction between the
electron donor and acceptor mesogens is responsible for the
formation of smectic phase. This is not surprising in view of
the previous studies with other similar compounds [14], but
it is significant to understand the nature and degree of
interactions between two different components. Addition-
ally, the mixture DA55 shows the two-phase region with
coexisting the crystalline phase and smectic phase from 74.1
to 95.9 8C on heating and from 59.3 to 72.6 8C on cooling.
Also, as shown in Table 1, the measured enthalpy and
entropy changes at the smectic to isotropic phase transition
on heating of the mixture DA55 were 10.6 and 27.1 J KK1
molK1, respectively. These results clearly indicate that the
mixtures DA28 and DA55 show a stable liquid-crystalline
phase and a simple phase transition behavior. In particular,
the mixture DA55 on cooling exhibits the most stable
liquid-crystalline phases as evidenced by the highest
TSI (119 8C), the widest temperature range of the smectic
phase (46.4 8C) and the highest values of DSSI (26.1 J KK1
molK1) among the mixtures DA examined.
2.6. Physical measurements
Molecular alignment and thermal stability on the phase
transition behavior of the compounds D, A and the mixtures
DA were evaluated by differential scanning calorimeter
(DSC: Seiko I&E DSC-6200), polarizing optical
microscopy (POM; Olympus Model BX-51), FT-IR spec-
trometer and X-ray diffractometer. During the VT (variable
temperature)-IR, melting-, and clearing-point measure-
ments on polarized microscopy analyses, temperature was
controlled using a hot stage (Imoto) with an accuracy of G
0.1 8C. The heating rate for all variable temperature
measurements was 5 8C minK1
.
The thermodynamic properties for phase transition of the
compounds D, A, and the mixtures DA were explored by
means of DSC. About 5 mg of the sample completely dried
was placed in aluminum sample pan and sealed. Measure-
ments were carried out in the temperature range from 30 to
130 8C. The phase transition temperature was taken as a
Fig. 2 displays the corresponding phase diagrams of the
mixtures DA for the content of the compound D on heating
and cooling cycle. The mixtures DA exhibit the smectic
phase when the content of the compound D was in the range
between 20 and 80 mol%, while the smectic phase was not
appeared in the individual compounds D and A. The mixture