Table 1 Temperature/uC and enthalpies/kJ mol21 (italic text) of phase transitions for compounds of series 4 and 6 from DSC
No
Cr1
Cr
SmC*
SmA
N*
Iso
4
–
–
*
–
*
*
–
*
*
*
*
*
*
*
*
*
443.8 27.7
418.8 26.3
437.5 16.7
361.3 24.6
529.6 20.6
488.2 26.2
489.1 36.7
324.9 19.5
*
*
*
*
(*
(*
(*
*
615.1 0.126
539.7 0.243
597.9 0.195
548.9 0.126
471.0) 0.021
463.5) 0.251
478.9) 0.795
412.8 0.795
*
*
*
*
*
*
*
*
750.3 6.69
645.6 4.77
730.0 3.72
616.7 1.25
570.6 2.34
517.9 4.48
505.8 2.84
419.1 1.51
–
–
–
*
–
–
–
–
*
*
*
*
*
*
*
*
4a
4b
4c
6
6a
6b
6c
402.8 5.32
627.6 2.17
446.3 7.53
233.6 2.22
236.5 14.4
6c. Yield 22%; FT -IR (cm2l) 1738 (CLOester), 1261 (CLS);
1H NMR (ppm) 0.83–2.54 (m, 29H), 4.02 (t, 2H, OCH2), 5.57
(m, 1H, NCH), 6.97–7.01 (m, 2H), 7.28 (m, 2H), 7.55–7.65 (m,
4H), 7.94 (m, 1Himide), 8.53–8.66 (m, 2Himide). 13C NMR (ppm)
11.7, 14.0, 16.3, 18.3, 22.7, 26.0, 28.5, 28.6, 29.0, 29.2, 29.4,
29.8, 31.9, 34.4, 60.6, 65.0, 121.7, 123.4, 124.6, 126.9, 127.8,
128.4, 128.6, 132.5, 134.7, 135.9, 139.9, 148.9, 160.1, 164.7,
195.7, 195.8. Visible l/nm (e/dm3 mol2l cm2l) 559 (60).
Elemental analysis: calc. C 71.78; H 7.15; N 2.33; S 10.63;
found C 71.72; H 7.12; N 2.36; S 10.55%.
[n A p*] of modest e values (22–225 e/dm3 mol2l cm21) in
the range of 505–560 nm.
Using DSC analysis and polarised optical microscopy we
found that all ester imides and their sulfur analogues have
liquid crystalline properties. The transitional data for the
compounds: 4, 4a, 4b, 4c and 6, 6a, 6b, 6c are presented in
Table 1.
All the investigated compounds have smectic C* and A
phases. They possess very typical microscopic texture and their
miscibility with smectic C* and A phases of well-known (S)-4-
(2-methylbutyl)phenyl 4-octylbiphenyl-4’-carboxylate makes it
possible to identify them correctly.8
Results and discussion
N-Substituted compounds with the 2-methylbutyl group (4,
4a, 4b, 4c) have enantiotropic smectic C* phases, while
compounds with the 1-methylpropyl group (6, 6a, 6b) have
monotropic smectic C* phases excluding (6c) dithioimides. The
phase difference results from reduction of the length of the
substituent as well as shortening of the distance between the
chiral centre and the imide ring. For both N-substituents,
introduction of one or two sulfur atoms into an imide ring
results in reduction of phase transition temperature values.
This is a consequence of the considerable change of compound
polarity and in the increase of the molecular breadth. In the
case of 4c dithioimides with a 2-methylbutyl constituent, a
chiral nematic phase is observed in a short temperature range.
Values of SmC*–SmA phase transition enthalpy are consider-
ably smaller than clearing or SmA–N* phase transition (see
Fig. 2). The only exception are compounds 6b and 6c where
the enthalpy of SmC*–SmA transition is comparable with
clearing enthalpy. Phase transition temperatures are the same
for heating and cooling cycles; hysteresis is observed only
for values of melting point (smectic C* phases over-cools
substantially).
The synthesis of ester imide 4 was performed via Mitsunobu
condensation.6 It led to introduction of a chiral N-substituent
using easily accessible optical active substrate (S)-2-methyl-
butan-1-ol. On the other hand, ester imide 6 was obtained by
the conventional method from (S)-2-aminobutane and trimel-
litic anhydride followed by esterification of 1 using DCC. Then,
the ester imides 4 and 6 were treated with Lawesson’s reagent
which led to the three main products. These compounds
formed three colour spots on TLC and could be easily
separated by column chromatography. In the same way, as
comprehensively described previously, we found that com-
pounds with the highest Rf values have two thiocarbonyl
groups.1 On the other hand, we assigned compounds of
intermediate mobility spots to the structures ‘‘b’’ and mono-
thioimides of low mobility spots to ‘‘a’’. A substitution of the
carbonyl oxygen atoms in the imide rings for sulfur atoms
resulted in coloured thioimides, whereas their parent imides
were colourless. The spectroscopic studies in the visible region
for thioimides studied revealed broad absorption bands
Conclusion
The compounds we have made are thermochemically stable.
Heating them for several hours over the clearing temperature
does not cause their decomposition and the temperatures of
phase transitions do not alter. Occurrence of the smectic C*
phases in all of the investigated compounds makes them good
components for liquid crystalline mixtures with ferro- and
antiferroelectric properties, however, high melting points limit
their application as basic compounds of the mixtures. The
distinct colour of mono and dithioimides is noteworthy.
Hitherto known coloured liquid crystalline azo-compounds
are less stable than the thioimides. Their presence in liquid
crystalline mixtures makes control of spectral characteristics
possible by cutting out the visible wavelength (red wavelength
spectrum). This property can be employed in non-linear optics.
References
´
E. Białecka-Florjanczyk and A. Orzeszko, J. Mater. Chem., 2000,
10, 1527.
E. Białecka-Florjanczyk, A. Orzeszko, I. Sledzinska and
1
´
´
E. Go´recka, J. Mater. Chem., 1999, 9, 371.
´
2
Fig. 2 Phase transitions for 4b and 6b as measured by DSC.
1314
J. Mater. Chem., 2002, 12, 1311–1315
Melon-Ksyta, Dorota
