for 8 h to give the solid title compound which was filtered off
and dried in air. The hydrolyzing solution was added to 1 litre
of water. The organic layer was separated and after filtration
evaporated to dryness to give an additional amount of the
mesogenic phenol.
1H-NMR (in ppm, 200 MHz, CDCl3): 10.5 (s, 1H, ArOH),
7.7 (dd, J1 ~ 8.5, J2~ 2.2, 1H, para to CH3O), 7.55 (d, J ~ 2.2,
1H, ortho to CH3O), 7.65 and 7.58 (m, 4H, ortho to Ar), 7.26
(d, J ~ 8.8, 2H, ortho to -OCO), 6.99 (d, J ~ 8.8, 2H, ortho
to OR), 6.93 (d, J ~ 8.3, 1H, ortho to -OH), 3.98 (t, J ~ 6.5,
2H, CH2O), 3.92 (s, 3H, CH3O), 1.71 (quintet, J ~ 6.5, 2H,
OCH2CH2), 1.15–1.5 (m, 14H, CH2), 0.9 (m, 3H, CH3).
Final product 3
A solution of 5 mmol of isophthalic dichloride in 50 ml of
dichloromethane was added to a stirred solution of 10 mmol of
mesogenic phenol 2 in 50 ml of dry dichloromethane and 20 ml
of pyridine and the mixture was stirred under reflux for 20 h.
The cold reaction mixture was after 3 days poured into dilute
HCl and extracted with dichloromethane. The organic extract
was washed twice with dilute HCl, twice with water and then
dried over anhydrous sodium sulfate. The solvent was removed
and the residue was purified by column chromatography on
silica gel (Kieselgel 60, Merck, particle size 0.063–0.2 mm)
using a mixture of dichloromethane and acetone (98 : 2) as
eluent. The collected product was crystallized from acetone.
The results of elemental analysis for the final compound:
found C 75.49% and H 6.81%, calc. C 75.42% and H 6.84%.
1H-NMR (in ppm, 200 MHz, CDCl3): 9.1 (s, 1H, ortho to
-COO), 8.5 (dd, J1 ~ 8.0, J2 ~ 1.5, 2H, ortho to -COO), 7.95
(dd, J1 ~ 8.5, J2 ~ 2.0, 2H, para to CH3O-), 7.88 (d, J ~ 2.2, 2H,
ortho to CH3O-), 7.75 (t, J ~ 7.8, 1H, meta to -COO), 7.6 (m, 8H,
ortho to -Ar), 7.3 (m, 2H, meta to CH3O 1 4H, ortho to OCOAr),
6.98 (d, J ~ 8.7, 4H, ortho to RO-), 4.0 (t, J ~ 6.5, 4H, CH2OAr),
3.95 (s, 6H, CH3O), 1.8 (quintet, J ~ 6.5, 4H, CH2CH2OAr),
1.2–1.6 (m, 28 H, CH2), 0.9 (t, J ~ 6.4, 6H, CH3).
Fig. 2 Texture of the BH phase (identified with the B2 phase) observed
at T ~ 187 uC under crossed polarizers with horizontal and vertical
polarization directions. The width of the picture is 400 mm.
Iso–BH: 213 uC (DH ~ 222.2 J g21
BH–BL: 173 uC (DH ~ 20.7 J g21
BL–Cryst: 112 uC (DH ~ 211.9 J g21
)
)
)
Microscopic observation and dielectric measurements were
carried out on planar cells prepared from indium–tin-oxide
(ITO) coated glass plates separated by mylar spacers 6 and
25 mm thick. The cells were filled in the isotropic phase. The
temperature was changed and stabilized with an accuracy of
¡0.1 uC on a hot stage apparatus (Linkam). In the BH phase
a schlieren texture usually appeared, which was converted to
a fan-shaped texture under an ac electric field. In thin samples
both schlieren and fan-shaped textures may appear sponta-
neously.
A typical texture of the BH phase, observed in a planar 6 mm
thick sample after the application of the electric field, is shown
in Fig. 2. The occurrence of the fan-shaped texture suggests a
layered (smectic) structure. The stripes are parallel to the
smectic layers. The parts of the sample with stripes parallel to
the directions of the light polarization (horizontal or vertical)
are areas of optical extinction (see dark areas in Fig. 2). Under
a dc electric field of 0.5–1 V mm21 the majority of the stripes
disappear. In such a structure the extinction remains the same
as in the case of zero field, the optical axis being parallel to the
smectic layer normal. This finding indicates the anticlinic
orientation of the director in the adjacent layers.3 Under a
sufficiently high field the extinction position may deviate from
the previous optical axis, symmetrically for the opposite fields.
This deviation corresponds to removal of the anticlinic
structure. The value of inclination represents an apparent tilt
angle Hs of y10–12u. In another observation the optical
extinction does not change even under high electric fields.
In the low temperature phase BL the texture is finer but fans
confirming a smectic structure are still seen. The stripes
represent either defects or narrow domains with different
orientations of the structure (see Fig. 3).
Experimental results
The phase transition temperatures were determined by differ-
ential scanning calorimetry (DSC7, Perkin Elmer) and by
observation under a polarizing microscope (Nicon Eclipse
E600). During calorimetric measurements cooling and heating
rates of 5 K min21 were applied. The mass of the samples was
about 8 mg. The samples were placed in a nitrogen atmosphere
and hermetically closed in aluminium pans.
The DSC graph is shown in Fig. 1. Two mesophases, the
high temperature one, BH, and the low temperature one, BL,
have been found between the isotropic phase and the crystalline
phase. The phase transition peak between BH and BL has a
very low enthalpy and is shown in detail in the inset. Phase
transition temperatures and values of enthalpy have been
evaluated on cooling:
A free standing film is easily formed in the BH phase by
spreading the material across a circular hole 3 mm in diameter
made in a thin metallic plate. The film persists even on cooling
below the phase transition to the BL phase. The textures in both
phases are shown in Figs. 4 and 5. In the BH phase a schlieren
texture is observed indicating a full degeneracy of the director
in-plane orientation. The texture in the BL phase suggests an in-
plane ordering.
Fig. 1 DSC plots recorded on subsequent heating and cooling. The
inset shows the BH–BL phase transition in a magnified scale.
Dielectric measurements were performed during cooling in
2222
J. Mater. Chem., 2002, 12, 2221–2224