4.1 Introduction:
The field of supramolecular chemistry [1] is certainly one of the most
interesting and promising areas of chemistry since the discovery of crown ethers in
1967, even though the term supramolecule was introduced in 1978. The 1987 Nobel
Prize to Cram, Lehn and Pederson motivated the researchers across the globe and is
evidenced by the growth of publications, books, conferences, international projects
etc., in this area of complex chemical systems. Supramolecular chemistry is a
relatively new field of chemistry and can be defined as in terms of Lehn words "the
chemistry beyond the molecule bearing the organized entities of higher complexity
that result from the association of two or more chemical species held together by
intermolecular forces." In a chemical molecule the atoms are held together by
covalent bonds by the sharing of electrons. Similarly, different molecules can be
held or joined together by means of weak intermolecular interactions such as
hydrogen bonding, n-n stacking, charge transfer interactions van der Waals and
electrostatic forces to give supramolecular species. Unfortunately, a so simple
definition based on the nature and strength of the different intermolecular
interactions which link together the molecular units into the supramolecular system is
not enough to define the supermolecule or supramolecular system. However, the
molecules linked by covalent bonds such as dendrimers or polynuclear complexes [2,
3] can be considered as supermolecules because these systems exhibit different
functional properties that the singular molecular components cannot exhibit, like
electron or energy-transfer processes. Therefore, it is necessary to distinguish
between a supermolecule and a large molecule. The supramolecular species consists
of a small and definite number of molecular components well organized in the space
which can also exist outside the supramolecular context and does not strongly
modify the original chemical and physical properties when joined in a superstructure.
Thus, the supermolecule is a system in which the properties are not just the sum of
the properties of individual molecular components but exhibits new properties as a
result of the cooperation between the molecular units. Hence, the design of new
objects resembling macroscopic shapes in nature by the arrangement of two or more
different molecular species which are different in shape, structure and dimensions
can be realized exhibiting varying functional properties. Thus, supramolecular
74
chemistry is today considered a powerful tool towards the realization of devices at
the molecular level with the abilities of performing specific functions to obtain new
materials with novel and useful properties and to understand the natural phenomena
underlying them.
The design of molecular components is crucial and critical for the
spontaneous generation of supramolecular architecture under the given experimental
conditions to achieve the organization at the supramolecular level. The molecular
self-assembly or self-organization process to exhibit different liquid crystalline
phases (either with the variation of temperature or concentration) is dependent on the
preorganization of the individual molecular components in a covalent molecule
possessing a prerequisite structure, shape and functions to promote the association of
noncovalent interactions.
The growing importance of hydrogen bonding in chemistry and in nature is
beyond the imagination of scientific community. Recent reports by several
researchers have demonstrated the importance of hydrogen bonding in achieving the
target compounds. In the new scientific field of research viz., Supramolecular
chemistry and Material science in recent years following the phenomena of
intermolecular hydrogen bonding several important breakthrough discoveries are
made to motivate several scientists across the globe. One such discovery in
condensed matter or soft matter research is replacement of covalent bonding by
strong intermolecular hydrogen bonding in the formation of new liquid crystalline
phases and functional materials. The ideal combination of the shape of the
molecules, magnitude and interactions between the molecules through hydrogen
bonding leads to new interactions, new molecular ordering, new phase structures and
molecular self assembly and self organization. The molecular self assembly and self
organization aided by segregation of molecular sub units leads to several interesting
physical properties. Calamitic and columnar liquid crystalline phases of low or high
molecular weight materials have been generated by this phenomenon from the non
mesogenic components.
After the discovery of hydrogen bonded liquid crystals by Kato and
Frechet in 1989 [4], another discovery of novel interesting phenomena in the area of
liquid crystals, is banana or bent core molecules exhibiting liquid crystalline
75
behaviour. Niori et al [5] discovered new liquid crystalline phases in bent shaped
molecules which are reported earlier by Matsunaga et al [6]. These compounds
which are achiral exhibited ferro, antiferroelectric phases, large spontaneous
polarization, non linear optical properties, chirality and novel smectic phases which
don't have analogues in calamitic liquid crystals. We are aware of two reports on
nonlinear molecules formed through hydrogen bonding which exhibit liquid
crystalline phases. The first one reported by Kato et al [7] on the hydrogen bonded
complexes of trans-4-n-decyloxy-4/-stilbazole and also two of its lower homologues
trans^-n-heptyloxy-^-stilbazole and trans-4-n-octyloxy-4/-stilbazole with
isophthalic acid (Figure 4.1a). When the report was published, the concept of
banana liquid crystal was unknown and they only reported that the complexes exhibit
smectic and unidentified mesophases. The compound trans-4-n-decyloxy-4/-
stilbazole exhibits smectic phase while isophthalic acid is non mesomorphic
compound. However, the complex exhibited unidentified mesomorphic and smectic
phases before decomposing at 250°C. In liquid crystals, the common belief of
nonlinear structural units such as 1,2- or 1,3-phenylene units is that they don't form
liquid crystalline phases since they are not compatible to form rod like molecules to
exhibit such behaviour. However, the mesomorphic behaviour of the complexes
exhibited by nonlinear structural units such as 1, 2- or 1, 3-substituted phenylene
units built through intermolecular hydrogen bonding with a stilbazole moiety
demonstrated that even nonlinear molecular structures can exhibit liquid crystal
behaviour. Subsequent reports of covalently bonded molecules by Matsunaga et al
[8] revealed the importance of nonlinear or bent molecules.
K 119°C M 150°C Sm 250°C decomposes
Figure 4.1a 26.1 20.7 kJ/mol —
76
Kato et al also reported [9] twin liquid crystalline complex (Figure 4.1b)
having two terminal mesogenic units and a central flexible spacer formed through
intermolecular hydrogen bonding between a nonmesogenic aliphatic diacid (chain
length n= 5-9) and mesogenic stilbazoles. They reported smectic and nematic phase
(Cr 146°C Sm 182°C N 230°C) in the hydrogen bonded complexes for the compound
with chain length n = 5'. The stilbazole exhibited nematic phase between 165 C-
213°C.
^ c X J \ ° ° / L Jl r ^ o f v s ^ v K , y ^^c"c^i o y I H ^-H-baadin§/ H M
^? (CH2)n n = 5-9
Figure 4.1b
The second one reported by Gimeno et al [10] in the area of banana liquid
crystals is the complex formation between /ra«5-4-{3-[4-(4'-«-tetradecyloxybenzoyl-
oxy)-benzoyloxy]phenyl}-stilbazole, 1 and 4-n-octadecyloxybenzoicacid, 3 or 4-(4/-
n-octadecyloxybenzoyloxy)-benzoic acid, 4 and trans-?/-[411-{A,"-n-
tetradecyloxy)benzoyl-oxy)-benzoyloxy]-4/-biphenyl-4-(4-stilbazole)benzoate, 2,
and 4-n-octadecyloxybenzoic acid, 3 (Table 4.1.1) which form hydrogen bonded
molecules of bent shape and exhibit switching phenomena associated with polar
smectic banana phase exhibited by covalent achiral molecules. Compounds 1 and 2
are non mesogenic while compound 3 and 4 are mesogenic. The compounds 1-3,1-4
and 2-3 exhibited banana mesomorphism.
77
Table 4.1.1
1. trans A- {3 - [4-^4 -/7-tetradecyloxybenzoyl-oxy)-benzoyloxy] phenyl} -stilbazole 2. trans-3'-[4 -(4 -n-tetradecyloxy)benzoyloxy)-benzoyloxy]-4-biphenyl-4-(4-stilbazole)benzoate 3. 4-n-octadecyloxybenzoicacid-4.4-(4/-n-octadecyloxybenzoyloxy)-benzoicacid
1
2
3
4
1-3
1-4
2-3
Cr
Cr
Cr
Cr
Cr
Cr
Cr
108.2°C 56.2 kJ/mol 168.9 ' 37.0 104.6 53.5 101.6 30.7 98.2 58.6 82.9 59.3 117.9 19.0
I
I
SmC
SmC
SmCP
SmCP
SmCP
125.0 7.9 206.5 13.8 118.8 29.6 142.6 26.1 173.8 28.7
Even though our preliminary efforts to design and synthesize rod or calamitic
shaped molecules exhibiting liquid crystalline behaviour through H-bonding is
successful, the same is not true with the bent shaped molecules of five member ring
systems in the beginning with pyridyl derivative (14PyA) and resorcinol or substituted
resorcinol. However, when the changes in the functional groups, participating in
hydrogen bonding are incorporated, the results are found to be interesting. Further,
78
the number of rings in the hydrogen bonded system when increased to seven, even
the pyridyl derivatives yielded banana liquid crystalline phases. The above
developments motivated us to synthesize new hydrogen bonded molecular structures
and to examine them for their liquid crystalline behaviour and phase transition
characteristics. To synthesize H-bonded bent shaped functional materials utilizing
the aforementioned H-bond donors or acceptors and a suitable central moiety of H-
bond acceptor or donor with novel characteristics, the structural variation (Figure
4.1c) in the molecule can be carried out in many ways viz., a) swapping the linking
or bridging groups and H-bonding, b) end alkyl chains can be replaced by chiral
alkyl chains or alkyloxy group, siloxane or carbosilane groups, perfluoroalkyl groups
c) introducing a substituent either on the central core ring and/or end rings etc. The
linking groups can be photochromic azo groups, imine linkages, carboxylate groups
etc. The substituents like chloro, cyano, nitro and methyl groups either on the central
or end phenyl rings. The influence of substituent on the central core or outer rings,
structural variation in end alkyl chains and the position of intermolecular H-bonding
are the possible options which can lead to new dimensions in this proposed work.
C10H2iO
The bridging groups are N=N, CH=N, N=CH, :H=CH, COO, OOC
7T~
M
- H-bonding-^ Jing X = N 0 2 , CH3, CN, Y=
X=H, Y = N0 2 , CH3, CN, CI -SUBSTITUENTS LIKE N02 , CN, CI
END CHIRAL ALKYL, ALKOXY^ Figure 4.1c SILOXANE, PERFLUORO GROUPS
OCj0H2i
79
4.2 Results and Discussion:
As a part of our work, the synthesis of the following compounds, described in
Table 4.2.1 were carried out and the results shall be presented as follows. The data
of elemental analyses is presented in Table 4.2.2. All the results of the elemental
analyses of the hydrogen bonded complexes for individual elements (C, H, and N)
and total content are found to be with in 0.2 percent of the calculated values.
Elemental analyses of the complexes indicated the molecular composition as the 1:2
complex.
The IR spectra were recorded on a Perkin-Elmer L 120-000A spectrometer
(vmax in cm"1) on KBr disks. The 'H NMR (300 MHz, 500 MHz) spectra were
recorded on a JEOL-AL300 FTNMR spectrometer in CDCI3 (chemical shift in 8)
with TMS as internal standard. The elemental analysis was carried out using PE2400
elemental analyzer. The phase transition temperatures and liquid crystalline behaviour
of different phases were observed using polarizing microscope (Nikon optiphot-2-pol)
attached with a regulated hot stage (INSTEC, HCS302, with STC200) and the phase
transitions and associated enthalpy values are detected by differential scanning
calorimetry (Perkin-Elmer DSC Pyrisl system).
The compounds resorcinol, 2-nitroresorcinol, 2-methylresorcinol and 4-
chlororesorcinol are hydrogen bond donors and used as central moiety. None of
these compounds are liquid crystalline and exhibit solid to isotropic transition. The
compounds 4-n-Tetradecyl-N-(4/-pyridylmethylene)aniline (14PyA), N(4-n-
decyloxysalicylidene)^- cyanoaniline (10OSALCA), 4-(4/-n-dodecyloxybenzoyl-
oxy-N-(4'-pyridylmethylene)aniline) (120BPyA) are hydrogen bond acceptors. The
molecular structures are presented in Table 4.2.1. The details of the results on the
hydrogen bonded complexes are discussed below. The compound 4-n-Tetradecyl-N-
(4/-pyridylmethylene)aniline (14PyA) does not exhibit liquid crystalline behaviour.
The compounds N(4-n-decyloxysalicylidene)-4/-cyanoaniline (10OSALCA) and 4-(4y-n-
dodecyloxybenzoyloxy-N-(4/-pyridylmethylene)aniline) (HOBPyA) exhibit liquid
crystalline behaviour.
80
No Hydrogen bond donor
1. Resorcinol Res
2-nitroresorcinol
2NRes
4-chlororesorcinol
4CIRes
2.
3.
4. Resorcinol Res
2-nitroresorcinol 5.
2NRes
2-methylresorcinol 6.
2MeRes
4-chlororesorcinol 7.
4ClRes
8. Resorcinol Res
9.
10.
2-nitroresorcinol
2NRes
4-chlororesorcinol
4CiRes
Table 4.2.1
Hydrogen bond Acceptor
4-n-Tetradecyl-N-(4/-pyridylmethylene)aniline 14PyA
4-n-Tetradecyl-N-(4/-pyridylmethylene)aniline 14PyA
4-n-Tetradecyl-N-(4/-pyridylmethylene)aniline 14PyA
N(4-n-decyloxysalicylidene)-4/-cyanoaniline,
10OSALCA
N(4-n-decyloxysalicylidene)-4/-cyanoaniline,
10OSALCA
N(4-n-decyloxysalicylidene)-4/-cyanoaniline,
10OSALCA
N(4-n-decyloxysalicylidene)-4/-cyanoaniline,
10OSALCA
4-(4/-n-dodecyloxybenzoyloxyl-N-(4/-
pyridylmethylene)aniline)
120BPyA
4-(4/-n-dodecyloxybenzoyloxyl-N-(4/-
pyridylmethylene)aniline)
120BPyA
4-(4/-n-dodecyloxybenzoyloxyl-N-(4/-
pyridylmethylene)aniline)
120BPyA
81
No Hydrogen bond donor Hydrogen bond Acceptor
4-n-Tetradecyl-N-(4-pyridylmethylene)aniline Resorcinol (Res)
m.p.=lll°C l- _ , , , < > „ ( 1 4 p y A >
m.p.=65.1°C
ResorcinoI-4-n-Tetradecyl-N-(4/-pyridylmethylene)aniline: Res-[14PyA]2
N ^ H \ 0 / ^ v - ^ ^ - ^ "*>/.
Synthesis:
The synthesis of the compound 14PyA is described in chapter 2. The hydrogen
bonded assembly Res-[14PyA]2 was synthesized by thoroughly mixing the
hydrogen bond acceptor 4-n-tetradecy]-N-(4/-pyridylmethylene)aniline) (0.74 g,
2mmol) in freshly distilled dry pyridine (2 ml) and hydrogen bond donor
resorcinol (0.11 g, lmmol) in freshly prepared dry pyridine (2 ml) in the ratio 2:1.
The mixture was then allowed for few days in a vacuum desiccator for the solvent
to evaporate slowly to yield the required product. The formation of hydrogen
bonded complex was confirmed by thin layer chromatography, elemental analysis,
FTIR spectra, and NMR experiments. TLC showed that the materials gave a
single spot with acetone-hexane as eluent.
FTIR studies:
The FTIR spectra recorded for the hydrogen bonded complex of Resorcinol-4-n-
tetradecyl-N-(4/-pyridylmethylene)aniline) is shown in Figure 4.2a. The details of
the data of various bands observed for resorcinol (Res), 14PyA and Res-[14PyA]2
are presented in Table 4.2.3. Strong hydrogen bonding is present between
Resorcinol and 4-n-tetradecyl-N-(4/-pyridylmethylene)aniline) as evident from the
broad well defined v-OH bands of medium intensity around 3446 cm"1 which has
replaced the broad v-OH band in the region of 3400-3600 cm"1 in the parent
resorcinol. The FTIR data in the region 4000-800 cm"1 for all the complexes is
82
presented in Table 4.2.3 to confirm the formation of hydrogen bonded complexes
in all the cases. For a complex of phenol (pKa ~ 10) and pyridine the O-H
stretching band appears at 3010 cm"1 which indicates a type I weak hydrogen bond
[11]
DSC and Thermal Microscopy:
The compound resorcinol melts at 111 °C, which is a hydrogen bond donor, did not
exhibit liquid crystalline behaviour. Similarly the compound 4-n-tetrdecyl-N-(4/-
pyridylmethylene)aniline) (14PyA), which is a hydrogen bond acceptor is also
non-mesogenic and did not show any liquid crystal behaviour. It melts at 65.1°C
in the heating cycle and becomes solid at 53.6°C in the cooling cycle. The
hydrogen bonded compound resorcinol-4-n-Tetradecyl-N-(4/-
pyridylmethylene)aniline, Res-[14PyA]2 melted and did not exhibit liquid
crystalline behaviour. The compound Res-[14PyA]2 melts directly into isotropic
phase at 63.8°C (AH = 49.6 kJ/mol, AS = 147.2 J/K/mol) and in cooling solidifies
at 51.1°C (AH= 36.6 kJ/mol, AS = 113.0 J/K/mol).
2-nitroresorcinol 4-n-Tetradecyl-N-(4/-pyridylmethylene)aniline
2. (2NRes) (14PyA)
m.p. = 83°C m.p. = 65.1°C
2-nitroresorcinol-4-n-Tetradecyl-N-(4/-pyridylmethylene)aniline: 2NRes-
[14PyA]2
Cu^29 Ci4H29
Synthesis:
The synthesis of the compound 14PyA is described in chapter 2. The hydrogen
bonded assembly 2NRes-[14PyA]2 was synthesized by thoroughly mixing the
hydrogen bond acceptor 4-n-tetradecyl-N-(4/-pyridylmethylene)aniline) (0.74 g,
2mmol) in freshly distilled dry pyridine (2 ml) and hydrogen bond donor 2-
nitroresorcinol (0.15 g, 1 mmol) in freshly prepared dry pyridine (2 ml) in the ratio
83
2:1. The mixture was then allowed for few days in a vacuum desiccator for the
solvent to evaporate slowly to yield the required product. The formation of
hydrogen bonded complex was confirmed by thin layer chromatography,
elemental analysis, FTIR spectra, and NMR studies. TLC showed that the
materials gave a single spot with acetone-hexane as eluent.
FTIR studies:
The FTIR spectrum recorded for the hydrogen bonded complex of 2-
nitroresorcinol-4-n-tetradecyl-N-(4/-pyridylmethylene)aniline) is shown in Figure
4.2b. The details of the data of various bands observed for 2-nitroresorcinol
(2NRes), 14PyA and 2NRes-[14PyA]2 are presented in Table 4.2.3. Strong
hydrogen bonding is present between 2-nitroresorcinol and 4-n-tetradecyl-N-(4/-
pyridylmethylene)aniline) as evident from the broad well defined v-OH bands of
medium intensity around 3386 cm"1 which has replaced the broad v-OH band in
the region of 3400-3600 cm"1 in the parent resorcinol. The FTIR data in the
region 4000-800 cm"1 for all the complexes is presented below in Table 4.2.3 to
confirm the formation of hydrogen bonded complexes in all the cases. For a
complex of phenol (pKa ~ 10) and pyridine the O-H stretching band appears at
3010 cm"1 which indicates a type I weak hydrogen bond [11]
DSC and Thermal Microscopy:
2NRes-[14PyA]2, did not exhibit liquid crystal behaviour and directly melts into
isotropic phase at 88.6°C.
84
4-chlororesorcinol 4-n-Tetradecyl-N-(4 -pyridylmethylene)aniline
(4CIRes) (14PyA)
4-chlororesorcinol4-n-Tetradecyl-N-(4-pyridylmethylene)aniline: 4ClRes-
Synthesis:
The synthesis of the compound 14PyA is described in chapter 2. The hydrogen
bonded assembly 4ClRes-[14PyA]2 was synthesized by thoroughly mixing the
bond acceptor 4-n-tetradecyl-N-(4/-pyridylmethylene)aniline) (0.74 g, 2mmol) in
freshly distilled dry pyridine (2 ml) and hydrogen bond donor 4-chlororesorcinol
(0.14g, lmmol) in freshly prepared dry pyridine (2 ml) in the ratio 2:1. The
mixture was then allowed for few days in a vacuum desiccator for the solvent to
evaporate slowly to yield the required product. The formation of hydrogen bonded
complex was confirmed by thin layer chromatography, elemental analysis, FTIR
spectra, and NMR experiments. TLC showed that the materials gave a single spot
with acetone-hexane as eluent.
FTIR studies:
The FTIR spectrum recorded for the hydrogen bonded complex of 4-
chlororesorcinol-4-n-tetradecyl-N-(4/-pyridylmethylene)aniline) is shown in
Figure 4.2c. The details of the data of various bands observed for 4-
chlororesorcinol (4CIRes), 14PyA and 4ClRes-[14PyA]2 are presented in Table
4.2.3. Strong hydrogen bonding is present between 4-chlororesorcinol and 4-n-
tetradecyl-N-(4/-pyridylmethylene)aniline) as evident from the broad well defined
v-OH bands of medium intensity around 3363 cm'1 which has replaced the broad
v-OH band in the region of 3400-3600 cm"1 in the parent 4-chlororesorcinol. The
FTIR data in the region 4000-800 cm"1 for all the complexes is presented below in
Table 4.2.3 to confirm the formation of hydrogen bonded complexes in all the
cases. For a complex of phenol (pKa ~ 10) and pyridine the O-H stretching band
85
appears at 3010 cm"1 which indicates a type I weak hydrogen bond [11]
DSC and Thermal Microscopy:
4ClRes-(14PyA]2, did not exhibit liquid crystal behaviour and directly melts into
isotropic phase at 92.1°C.
In fact, the first report by Kato et al on the hydrogen bonded complexes of trans-4-
n-decyloxy^-stilbazole and also two of its lower homologues trans-4-n-
heptyloxy-4/-stilbazole and trans-4-n-octyloxy-4/-stilbazole with isophthalic acid
exhibited liquid crystalline phases. Even though the molecular structures of the
present compounds resemble the molecular structure of hydrogen bonded complex
of isophthalicacid-trans-4-n-octyloxy-4/-stilbazole, they did not exhibit liquid
crystalline behaviour. The reason may be the influence of linking groups in the
formation of hydrogen bonding leading to molecular association and self
assembling of molecules that influence the exhibition of liquid crystalline
behaviour. The linking groups forming the hydrogen bond in the present case is
phenolic hydroxyl and pyridyl nitrogen atom while it is carboxylic group and
pyridyl nitrogen in the reported compound.
K 119°C M 150°C Sm 250°C decomposes
26.1 20.7kJ/mol —
Isophthalic acid -[trans-4-n- decyloxy-V-stilbazole isophthalic acid]2
4. Resorcmol Res N(4-n-decyloxysalicylidene)-4-cyanoaniline,
(10OSALCA)
Resorcinol- N(4-n-decyIoxysalicyIidene)-4 -cyanoaniline, Res-[10OSALCA]2
86
Synthesis:
The synthesis of the compound 10OSALCA is described in chapter 2. The
hydrogen bonded assembly Res-[10OSALCA]2 was synthesized by thoroughly
mixing the hydrogen bond acceptor N(4-n-decyloxysalicylidene)-4/-cyanoaniline
(0.75 g, 2mmol) in freshly distilled dry pyridine (2 ml) and hydrogen bond donor
resorcinol (0.11 g, lmmol) in freshly prepared dry pyridine (2 ml) in the ratio 2:1.
The mixture was then allowed for few days in a vacuum desiccator for the solvent
to evaporate slowly to yield the required product. The formation of hydrogen
bonded complex was confirmed by thin layer chromatography, elemental analysis,
FTIR spectra, and NMR experiments. TLC showed that the materials gave a
single spot with acetone-hexane as eluent.
FTIR studies:
The FTIR spectrum recorded for the hydrogen bonded complex of Resorcinol-
N(4-n-decyloxysalicylidene)-4/-cyanoaniline, Res-[10OSALCA]2 is shown in
Figure 4.2d. The details of the data of various bands observed for resorcinol
(Res), 10OSALCA and Res-[10OSALCA]2 are presented in Table 4.2.3. Strong
hydrogen bonding is present between resorcinol and N(4-n-decyloxysalicylidene)-
4/-cyanoaniline as evident from the broad well defined v-OH bands of medium
intensity around 3357 cm"1 which has replaced the broad v-OH band in the region
of 3400-3600 cm"1 in the parent resorcinol. The FTIR data in the region 4000-800
cm"1 for all the complexes are presented in Table 4.2.3 to confirm the formation of
hydrogen bonded complexes in all the cases. The choice of nitriles was made to
develop a fundamental understanding of the trend in interaction between the -CN
group present in the liquid crystals and the -OH functional group. The trend
studied in the H-bonding behavior was from acetonitrile, having just a -CH3 end
group; to benzonitrile, which has a benzene ring; to the liquid crystal, having a
biphenyl structure with an alkyl bisubstituted amine at the other end of the ring
chain. Bertie and Lan studied the H-bonding behavior between liquid water and
acetonitrile using absolute integrated infrared absorption intensities. They
observed a shift in the -CN stretching vibration from 2275 to 2210 cm-1 and
concluded that the interaction is a result of H-bonding between the lone pair
electrons on the -CN group and the proton of the -OH group.
87
N(4-n-decyloxysalicylidene)-4/-cyanoaniline, 10OSALCA:
The compound N(4-n-decyloxysalicylidene)-4/:cyanoaniline, 10OSALCA
exhibited two transitions in the heating cycle at (69.7°C, AH = 35.3 kJ/mol, AS =
102.9 J/K/mol) and (126.7°C, AH = 2.76 kJ/mol, AS = 6.91 J/K/mol). The DSC
spectrum is shown in Figure I. In the cooling cycle also it exhibited enantiotropic
phase transitions at (125.2°C, AH = 2.67 kJ/mol, AS = 6.72 J/K/mol) and (62.3°C,
AH = 0.96 kJ/mol, AS = 2.87 J/K/mol). The low enthalpy and entropy in the
cooling at 62.3 C is due to super cooling and absence of crystallization. It is also
evident from the observation of paramorphotic texture on polarizing microscope in
the cooling cycle. The compound melts at 68.9°C and exhibits smectic A phase
with the characteristic focal conic fan texture or large homeotropic areas before
becoming isotropic at 126.7°C. In cooling also it exhibited only smectic A phase
and the paramorphotic texture remained till room temperature in the absence of
crystallization.
41.33 -i
40 •
30
1 2S
15.07
10OSALCA
50.69
Peak = 69.768 °C Area = 317.199 mJ Delta H = 93.294 J/g
Peak = 62.383 °C Area = -8.665 mJ Delta H = -2.548 J/g
70 80
Peak = 126.706 °C Area = 24.836 mJ Delta H = 7.305 J/g
Peak = 125.246 "C Area = -24.040 mJ Delta H = -7.071 J/g
90 100 Temperature ("C)
110 130 140 146
Figure I
DSC and Thermal microscopy:
The observed transition temperatures from thermal microscopy and differential
scanning calorimetry are presented in Table 4.2.4. We can see from the table that
the phase transition temperatures of resorcinol (Res), and mesophases of N(4-n-
88
decyloxysalicylidene)-4/-cyanoaniline (10OSALCA) and hydrogen bonded
complex are different. The hydrogen bonded complex Res-[10OSALCA]2
exhibits liquid crystalline phase between 65.1°C and 89.7°C in the heating cycle
and 30.3°C and 89.3°C in the cooling cycle. The DSC spectrum is shown in
Figure II. The liquid crystalline phase was identified as smectic phase resembling
the banana liquid crystalline phases, using a hot stage and polarized light. The
sample was placed between two untreated cover glasses. On cooling the isotropic
melt, batonnets formed in the mesophase, which coalesced to form a focal-conic
fan structure. In the same sample, extinct regions were also observed, indicating
homeotropic alignment of the molecules. The characteristic focal conic texture
with homeotropic regions of the liquid crystalline phase shown in plate 4.1, 4.2
and fully developed texture in plate 4.3. This supports the tentative identification
as the smectic phase of banana type or B6 phase. In a B6 mesophase, the
hydrogen bonded compounds form layers, and the long molecular axis of the
compounds is, on average, perpendicular to the layer planes. The observed texture
for banana smectic phase resemble the texture of B6 (1-4, where 4 is the number of
carbons in the alkyl chain length) observed for analogous bent shaped liquid
crystalline compounds (I-10, 11-10) [12] without hydrogen bonding. The
hydrogen bonded compound Res-[10OSALCA]2 possesses a hydrogen bond
between the cyano group and a phenolic hydrogen and differs from the bent
shaped compound 1-10 which possesses a covalent bond through ester linkage.
However, the confirmed identification is to be carried out by X-ray studies, which
is in progress as a part of future studies. When cooling the mesophase, no
crystallization was observed under the microscope and the texture of the
mesophase was frozen into the solid state. A glassy mesophase was formed.
Glass formation was noticed from the fact that it was no longer possible to shear
the cover glasses between which the sample was sandwiched. Moreover, when
cooling further, conchoidal fractures were observed in the texture. These
conchoidal fractures also indicate the presence of a glassy state. The DSC traces
showed crystallization at a cooling rate of 10°C/min, although a strong super
cooling was observed. These differences in behaviour between the microscopic
and DSC observations do not contradict each other, because we were studying a
thin film under the microscope at a very slow cooling rate, whereas a bulk sample
was used for the DSC measurements at a 10°C/min.
The ester group is replaced by a hydrogen bonded moiety between cyano and phenolic hydroxyl groups ,n the present work
C10H21O'
C 10 H 21° '
OC10H21
OC1 0H21
The melting
point for the complex is lower than the melting point of the relative proton
acceptor (89.5°C) and of the proton donor. On the other hand, the clearing point
for the complex is lower than the clearing point of the proton acceptor. The
thermal range of the liquid crystalline phase of the complex is higher than the
proton acceptor (75°C) in the cooling cycle. These results of differential
scanning calorimetry and thermal microscopy support the formation of bent
shaped hydrogen bonded complex which is stable over a large temperature range.
Further work is necessary to find out the electrical characteristics of the
compound and to confirm the phase assignment.
Peak = 83 867 °C Area = 3.965 mJ Delta H = 1.724 J/g
Delta H = -1 376 J/g
70 75 80 Temperature ("C)
Figurell
90
< W ~ A ,oco<V>. —< N - i >-CHM 2-nitroresorcinol K.62.3°CSmA 125.2UCISO X
Q_H
2NRes N(4-n-decyloxysalicylidene)-4/-cyanoaniline,
10OSALCA
2-nitroresorcinol- N(4-n-decyloxysalicylidene)-4/-cyanoaniline, 2NRes-
[10OSALCA]2
^ C Cf VtL-bondi / iQL C ^
Synthesis:
The synthesis of the compound 10OSALCA is described in chapter 2. The
hydrogen bonded assembly 2NRes-[10OSALCA]2 was synthesized by thoroughly
mixing the hydrogen bond acceptor N(4-n-decyloxysalicylidene)-4/-cyanoaniline
(0.75g, 2mmol) in freshly distilled dry pyridine (2 ml) and hydrogen bond donor
2-nitroresorcinol (0.15g, lmmol) in freshly prepared dry pyridine (2 ml) in the
ratio 2:1. The mixture was then allowed for few days in a vacuum desiccator for
the solvent to evaporate slowly to yield the required product. The formation of
hydrogen bonded complex was confirmed by thin layer chromatography,
elemental analysis, FTIR spectra, and NMR experiments. TLC showed that the
materials gave a single spot with acetone-hexane as eluent.
FTIR studies:
The FTIR spectra recorded for the hydrogen bonded complex of Resorcinol-N(4-
n-decyloxysalicylidene)-4/-cyanoaniline, 2NRes-[10OSALCA]2 is shown in
Figure 4.2e. The details of the data of various bands observed for 2-
nitroresorcinol (2NRes), 10OSALCA and 2NRes-[10OSALCA]2 are presented in
Table 4.2.3. Strong hydrogen bonding is present between 2-nitroresorcinol and
N(4-n-decyloxysalicylidene)-4/-cyanoaniline as evident from the broad well
defined v-OH bands of medium intensity around 3387 cm'1 which has replaced the
broad v-OH band in the region of 3400-3600 cm'1 in the parent resorcinol. The
FTIR data in the region 4000-800 cm"1 for all the complexes is presented in Table
4.2.3 to confirm the formation of hydrogen bonded complexes in all the cases.
91
DSC and Thermal Microscopy:
The compound 2-nitroresorcinol melts at 83°C and does not exhibit liquid
crystalline behaviour. The compound N-(4-n-decyloxysalicylidene)-4/-
cyanoaniline exhibits liquid crystalline behaviour as described earlier and melts at
69.7°C exhibiting smectic A phase with the characteristic focal conic texture or
large homeotropic areas before becoming isotropic at 126.7°C. In the cooling
cycle also the compound exhibits mesomorphic behaviour between 125.2°C and
62.3°C. The hydrogen bonded compound 2-nitroresorcinol- [N-(4-n-
decyloxysalicylidene)-4/-cyanoaniline]2 exhibited two transitions in the heating
cycle at (61.8°C, AH = 70.7 kJ/mol, AS = 211.3 J/K/mol, melting point) and
(102.1°C, AH = 12.03 kJ/mol, AS = 32.07 J/K/mol, clearing point). In the cooling
cycle also it exhibited enantiotropic phase transitions at (97.5°C, AH = 1.30
kJ/mol, AS = 3.50 J/K/mol) and (62.5°C, AH = 2.78 kJ/mol, AS = 8.28 J/K/mol).
The DSC spectra (Figure HI) illustrates that the melting point of 2NRes-
[10OSALCA]2 is lower than that of individual components 2NRes as well as
[10OSALCA] and the clearing point of 2NRes-[10OSALCA]2is 24°C lower than
that of hydrogen bond acceptor [10OSALCA]. As a result the liquid crystalline
range for 2NRes-[10OSALCA]2 is 16°C smaller than one of the individual
component exhibiting liquid crystalline phase. This difference must be caused by
the difference in molecular structures. The decrease in electrostatic interactions in
the hydrogen bonded molecules due to the formation of hydrogen bond between
the cyano group and the hydroxyl group, when compared to the individual cyano
group's dipolar interactions, leads to a decrease in melting temperature. The
decrease in the clearing point presumably reflects the increase of steric interactions
between the bent shaped hydrogen bonded molecules of 2NRes-[10OSALCA]2,
when compared to the linear shaped molecules of 10OSALCA. These steric
interactions thereby promoting larger structural distortions lead to a decreased
overall structural anisotropy and in turn results in decreased stability of
mesophase. Further the rigidity of mesogenic complex of 2NRes-[10OSALCA]2
is weaker than that of [10OSALCA], as is evident by the bent shape of the
molecules. Hence, the phase transition temperatures of 2NRes-[10OSALCA]2 are
lower than those of [10OSALCA]2 because of their analogous structures. The
92
observed transition temperatures from thermal microscopy and differential
scanning calorimetry are presented in Table 4.2.4. We can see from the table that
the phase transition temperatures of 2-nitroresorcinol (2NRes) and mesophases of
N(4-n-decyloxysalicylidene)-4/-cyanoaniline (10OSALCA) and hydrogen bonded
complex are different.
The hydrogen bonded complex of 2NRes-[10OSALCA]2 exhibits liquid
crystalline phase between 65.1°C andi02.7°C in the heating cycle and in between
30.3°C and 102.3°C in the cooling cycle when observed by thermal microscopy.
The liquid crystalline phase was identified as smectic phase resembling the banana
liquid crystalline phases, using a hot stage and polarized light. The sample was
placed between two untreated cover glasses. On cooling the isotropic melt,
batonnets formed in the mesophase, which coalesced to form a focal-conic fan
structure. In the same sample, extinct regions were also observed, indicating
homeotropic alignment of the molecules. The characteristic focal conic texture
with homeotropic regions of the liquid crystalline phase shown in plate 4.4 and
fully developed texture in plate 4.5. This supports the tentative identification as
the smectic phase of banana type phase. Further cooling to room temperature also
yielded a texture of smectic phase shown in plate 4.6. In a banana mesophase, the
hydrogen bonded compounds form layers, and the long molecular axis of the
compounds is, on average, perpendicular to the layer planes. The observed texture
for banana smectic phase resemble the texture of B6 (1-4, where 4 is the number of
carbons in the alkyl chain length) observed for analogous bent shaped liquid
crystalline compounds (1-10, 11-10) [12] without hydrogen bonding. The
hydrogen bonded compound 2NRes-[10OSALCA]2 possesses a hydrogen bond
between the cyano group and a phenolic hydrogen and differs from the bent
shaped compound 1-10 which possesses a covalent bond through ester linkage.
However, the confirmed identification is to be carried out by X-ray studies, which
is in progress as a part of future studies. When cooling the mesophase, no
crystallization was observed under the microscope and the texture of the
mesophase was frozen into the solid state. A glassy mesophase was formed.
Glass formation was noticed from the fact that it was no longer possible to shear
the cover glasses between which the sample was sandwiched, indicating the
93
presence of a glassy state. The DSC traces showed crystallization at a cooling rate
of 10 C/min, although a strong super-cooling was observed. These differences in
behaviour between the microscopic and DSC observations do not contradict each
other, because we were studying a thin film under the microscope at a very slow
cooling rate, whereas a bulk sample was used for the DSC measurements at a
10°C/min.
40
!
20
2NRes-[10OSALCA12
Peak = 61.821 °C Area = 519.861 mJ Delta H = 77.591 J/g
Peak = 102.180 °C
Area = 88.391 mJ Delta H= 13.193 J/g
-+-f-Peak = 62.574 *C Area = -20 428 mJ Delta H = -3 049 J/g
Peak = 97.583 "C Area = -9.553 mJ Delta H =-1426 J/g
60 80 90 100 Temperature CO
2-methylresorcinol
6. 2MeRes
m.p.=114°C
K62.3uCSmA125.2°CIso V . . ~ \ f
Figure III /r~\
-QH / = \ O-H
N(4-n-decyloxysalicylidene)-4/-cyanoaniline,
10OSALCA
2-methylresorcinol-N(4-n-decyloxysalicylidene)-4/-cyanoaniline,
2MeRes-[10OSALCA]2
Synthesis:
The hydrogen bonded assembly 2MeRes-[10OSALCA]2 was synthesized by
thoroughly mixing the hydrogen bond acceptor N(4-n-decyloxysalicylidene)-4 -
cyanoaniline (0.75g, 2mmol) in freshly distilled dry pyridine (2 ml) and hydrogen
bond donor 2-methylresorcinol (0.12g, lmmol) in freshly prepared dry pyridine (2
ml) in the ratio 2:1. The mixture was then allowed for few days in a vacuum
desiccator for the solvent to evaporate slowly to yield the required product. The
formation of hydrogen bonded complex was confirmed by thin layer
chromatography, elemental analysis, FTIR spectra, and NMR experiments. TLC
showed that the materials gave a single spot with acetone-hexane as eluent.
FTIR studies:
The FTIR spectrum recorded for the hydrogen bonded complex of 2-
methylresorcinol-N(4-n-decyloxysalicylidene)-4/-cyanoaniline, 2MeRes-
[10OSALCAJ2 is shown in Figure 4.2f The details of the data of various bands
observed for resorcinol (2MeRes), 10OSALCA and 2MeRes-[10OSALCA]2 are
presented in Table 4.2.3. Strong hydrogen bonding is present between 2-
methylresorcinol and N(4-n-decyloxysalicylidene)-4/-cyanoaniline as evident from
the broad well defined v-OH bands of medium intensity around 3388 cm"1 which
has replaced the broad v-OH band in the region of 3400-3600 cm"1 in the parent
resorcinol. The FTIR data in the region 4000-800 cm"1 for all the complexes is
presented in Table 4.2.3 to confirm the formation of hydrogen bonded complexes
in all the cases.
NMR studies: The lH NMR data for the complex 2MeRes-[10OSALCA]2 has
been analyzed and confirms the formation of hydrogen bonded complex. The
details of the proton NMR are presented in Table 4.2.5. The NMR spectrum is
presented in Figure 4.2k.
DSC and Thermal Microscopy:
The compound 2-methylresorcinol melts at 114°C and does not exhibit liquid
crystalline behaviour. The compound N-(4-n-decyloxysalicylidene)-4-
cyanoaniline exhibits liquid crystalline behaviour as described earlier and melts at
69.7°C exhibiting smectic A phase with the characteristic focal conic texture or
large homeotropic areas before becoming isotropic at 126.7°C. In the cooling
cycle also the compound exhibits mesomorphic behaviour between 125.2°C and
62.3°C. The hydrogen bonded compound 2-methylresorcinol-[N-(4-n-
decyloxysalicylidene)-4/-cyanoaniline]2 exhibited one transition in the heating
cycle at (97.0°C, AH = 85.48 kJ/mol, AS = 234.6 J/K/mol, melting point). In the
95
cooling cycle also it exhibited two phase transitions at (66.5°C, AH = 24.50
kJ/mol, AS = 72.10 J/K/mol) and (66.1°C, AH = 18.52 kJ/mol, AS = 54.59
J/K/mol). In the DSC spectra (Figure IV&V) we are not able to obtain any
information except that the transition temperatures are different from the parent
compounds participating in hydrogen bonding. However, the thermal microscopy
indicated different phase transitions exhibiting liquid crystalline behaviour.
The hydrogen bonded complex 2MeRes-[10OSALCA]2 exhibits liquid
crystalline phase between 65.1°C and 91.7°C in the heating cycle and in between
30.3 C and 90.3°C in the cooling cycle when observed by thermal microscopy.
The liquid crystalline phase was identified as smectic phase resembling the banana
liquid crystalline phases, using a hot stage and polarized light. The sample was
placed between two untreated cover glasses. On cooling the isotropic melt,
batonnets formed in the mesophase, which coalesced to form a focal-conic fan
structure. In the same sample, extinct regions were also observed, indicating
homeotropic alignment of the molecules. The characteristic focal conic texture
with homeotropic regions of the liquid crystalline phase shown in plate 4.7 and
fully developed texture in plate 4.8. This supports the tentative identification as
the smectic phase of banana type. Further, cooling to room temperature also
yielded a texture of smectic phase shown in plate 4.9. In a banana mesophase, the
hydrogen bonded compounds form layers, and the long molecular axis of the
compounds is, on average, perpendicular to the layer planes. The observed texture
for banana smectic phase resemble the texture of B6 (1-4, where 4 is the number of
carbons in the alkyl chain length) observed for analogous bent shaped liquid
crystalline compounds (1-10, 11-10) [12] without hydrogen bonding. The
hydrogen bonded compound 2MeRes-[10OSALCA]2 possesses a hydrogen bond
between the cyano group and a phenolic hydrogen and differs from the bent
shaped compound 1-10 which possesses a covalent bond through ester linkage.
However, further work is in progress as a part of future studies, to reason out the
discrepancy between thermal microscopy and DSC and also to confirm the exact
phase. The texture of the mesophase was observed as a glassy mesophase till the
room temperature. The observed transition temperatures from DSC and thermal
microscopy are presented in Table 4.2.4.
55.61 60 65 70 75 80 85 30 95 100 105 107 Temper ahxe ("C)
Figure IV 23.79 1
Figure V
7. 4ClRes
m.p.= 107 C N(4-n-decyloxysalicylidene)-4/-cyanoaniline,
10OSALCA
4-chlororesorcinol- N(4-n-decyloxysalicylidene)-4/-cyanoaniline, 4ClRes-
10OSALCA
97
Synthesis:
The hydrogen bonded assembly 4ClRes-[10OSALCA]2 was synthesized by
thoroughly mixing the hydrogen bond acceptor N(4-n-decyloxysalicylidene)-4/-
cyanoaniline (0.75g, 2mmol) in freshly distilled dry pyridine (2 ml) and hydrogen
bond donor 4-chlororesorcinol (0.14g, lmmol) in freshly prepared dry pyridine (2
ml) in the ratio 2:1. The mixture was then allowed for few days in a vacuum
desiccator for the solvent to evaporate slowly to yield the required product. The
formation of hydrogen bonded complex was confirmed by thin layer
chromatography, elemental analysis, FTIR spectra, and NMR experiments. TLC
showed that the materials gave a single spot with acetone-hexane as eluent.
FTIR studies:
The FTIR spectra recorded for the hydrogen bonded complex of Resorcinol-N(4-
n-decyloxysalicylidene)-4/-cyanoaniline, 4CIRes-[10OSALCA]2 is shown in
Figure 4.2g. The details of the data of various bands observed for 4-
chlororesorcinol (4ClRes), 10OSALCA and 4ClRes-[10OSALCA]2 are presented
in Table 4.2.3. Strong hydrogen bonding is present between 4-chlororesorcinol
and N(4-n-decyloxysalicylidene)-4/-cyanoaniline as evident from the broad well
defined v-OH bands of medium intensity around 3318 cm"1 which has replaced the
broad v-OH band in the region of 3400-3600 cm"1 in the parent 4-chlororesorcinol.
The FTIR data in the region 4000-800 cm"1 for all the complexes is presented
below in Table 4.2.3 to confirm the formation of hydrogen bonded complexes in
all the cases.
NMR studies: The lH NMR data for the complex 4CIRes-[10OSALCA]2 has
been analyzed and confirms the formation of hydrogen bonded complex. The
details of the proton NMR are presented in Table 4.2.5. The NMR spectra is
presented in Figure 4.21
98
DSC and Thermal Microscopy:
The compound 4-chlororesorcinol melts at 107.1°C and does not exhibit liquid
crystalline behaviour. The compound N-(4-n-decyloxysalicylidene)-4/-
cyanoaniline exhibits liquid crystalline behaviour as described earlier and melts at
69.7 C exhibiting smectic A phase with the characteristic focal conic texture or
large homeotropic areas before becoming isotropic at 126.7°C. In the cooling
cycle also the compound exhibits mesomorphic behaviour between 125.2°C and
62.3°C. The hydrogen bonded compound 4-chlororesorcinol-[N-(4-n-
decyloxysalicylidene)-4/-cyanoaniline]2 exhibited four transitions in the heating
cycle at (52.4°C, AH = 7.85 kJ/mol, AS = 24.1 J/K/mol, Cr-Crl transition point),
(56.8°C, AH - 1.56 kJ/mol, AS = 4.74 J/K/mol, Crl-Cr2 transition point), (72.2°C,
AH = 5.74 kJ/mol, AS = 16.64 J/K/mol, Cr2-mesophase transition point),and
(95.3°C, AH = 1.20 kJ/mol, AS = 3.27 J/K/mol, clearing point). In the cooling
cycle also it exhibited enantiotropic phase transitions at (87.2°C, AH = 0.19
kJ/mol, AS = 0.53 J/K/mol) and (63.4°C, AH = 1.66 kJ/mol, AS = 4.96 J/K/mol).
The DSC spectra (Figure VI) illustrates that the melting point of 4CIRes-
[10OSALCA]2 is lower than that of individual components 4ClRes as well as
110OSALCA] and the clearing point of 4ClRes-[10OSALCA]2 is 31°C lower
than that of hydrogen bond acceptor [lOOSALCAfc. As a result the liquid
crystalline range for 4ClRes-[10OSALCA]2 is smaller than one of the individual
component exhibiting liquid crystalline phase. This difference must be caused by
the difference in molecular structures. The decrease in electrostatic interactions in
the hydrogen bonded molecules due to the formation of hydrogen bond between
the cyano group and the hydroxyl group, when compared to the individual cyano
groups dipolar interactions leads to a decrease in melting temperature. The
decrease in the clearing point presumably reflects the increase of steric interactions
between the bent shaped hydrogen bonded molecules of 4ClRes-[10OSALCA]2
aided by lateral chloro substituent, when compared to the linear shaped molecules
of 10OSALCA. These steric interactions thereby promoting larger structural
distortions lead to a decreased overall structural anisotropy and in turn results in
decreased stability of mesophase. Further, the rigidity of mesogenic complex of
4ClRes-[10OSALCA]2 is weaker than that of [10OSALCA]2, as is evident by the
99
bent shape of the molecules. Hence the phase transition temperatures for 4ClRes-
[10OSALCA]2 are lower than those of [lOOSALCAk because of their analogous
structures. The observed transition temperatures from thermal microscopy and
differential scanning calorimetry are presented in Table 4.2.4. We can see from
the table that the phase transition temperatures of the mesophases of N(4-n-
decyloxysalicylidene^-cyanoaniline (10OSALCA) and hydrogen bonded
complex 4CIRes-[10OSALCA]2 are different.
The hydrogen bonded complex 4ClRes-[10OSALCA]2 exhibits liquid
crystalline phase between 65.1°C and 87.9°C in the heating cycle and in between
30.3°C and 87.3°C in the cooling cycle when observed by thermal microscopy.
The liquid crystalline phase was identified as smectic phase resembling the banana
liquid crystalline phases, using a hot stage and polarized light. The sample was
placed between two untreated cover glasses. On cooling the isotropic melt,
batonnets formed in the mesophase, which coalesced to form a focal-conic fan
structure with uniform birefringence. In the same sample, very few extinct regions
were also observed, indicating homeotropic alignment of the molecules. The
characteristic focal conic texture with very few homeotropic regions of the liquid
crystalline phase shown in plate 4.10. This supports the tentative identification as
the smectic phase of banana type phase. Further cooling to room temperature also
yielded a similar texture of smectic phase shown in plate 4.11. In a banana
mesophase, the hydrogen bonded compounds form layers, and the long molecular
axis of the compounds is, on average, perpendicular to the layer planes. The
observed texture for banana smectic phase resembles the texture of B2 observed
for conventional bent shaped liquid crystalline compounds [13] without hydrogen
bonding. The hydrogen bonded compound 4ClRes-[10OSALCA]2 possesses a
hydrogen bond between the cyano group and a phenolic hydrogen and differs from
the bent shaped compounds which possesses a covalent bond through ester or
imine linkage. However, the confirmed identification is to be carried out by X-ray
studies, which is in progress as a part of future studies. When cooling the
mesophase, change in texture was observed under the microscope and the texture
of the mesophase was shown in plate 4.12. No glass formation was noticed from
the fact that it was possible to shear the cover glasses between which the sample
100
was sandwiched and indicating the absence of a glassy state. The differences in
behaviour between the microscopic and DSC observations do not contradict each
other, because we were studying a thin film under the microscope at a very slow
cooling rate, whereas a bulk sample was used for the DSC measurements at a
10°C/min.
320 n
Temper ature ("C)
Figure VI
[4-(4/-n-dodecyloxybenzoyloxyl-N-(4/-8. Resorcinol: Res
pyridylmethylene)aniline)] 120BPyA
Resorcinol: Res
The compound resorcinol is not a liquid crystal and melts at 111°C to form
isotropic phase.
(4-(4/-n-dodecyloxybenzoyloxyl-N-(4/-pyridylmethylene)aniline)] 120BPyA:
The synthesis of 120BPyA is discussed in chapter 2.
The compound 4-(4/-n-dodecyloxybenzoyloxy-N-(4/-pyridylmethylene) aniline)
exhibited two transitions in the heating cycle at (89.5°C, AH = 36.5 kJ/mol, AS =
100.8 J/K/mol) and (141.3°C, AH = 2.99 kJ/mol, AS = 7.22 J/K/mol). In the
cooling cycle also it exhibited enantiotropic phase transitions at (140.6°C, AH =
2.99 kJ/mol, AS = 7.24 J/K/mol) and (65.5°C, AH = 34.9 kJ/mol, AS = 103.2
J/K/mol) as is evident from the DSC spectra shown in Figure VII. The compound
melts at 89.5°C and exhibits smectic A phase with the characteristic focal conic
101
texture or large homeotropic areas before becoming isotropic at 141.3 C. In
cooling also it exhibited only smectic A phase.
46.17
40
35 •
30
=> 25
20 •
x 15 •
120BPYA
Peak = 89.536 "C Area = 262.984 mJ Delta H = 75.138 J/g
Peak =140.611 X Area = -21.572 mJ Delta H = -6 163 J/g
Peak = 65.589 "C Area = -251.352 mJ Delia H =-71.815 J/g
60 80 100 120 Temperature ("C)
140 180 201
Figure VII
Resorcinol-[4-(4/-n-dodecyloxybenzoyloxyl-N-(4/-pyridylmethylene)aniline)]2,
Res-[120BPyA]2:
A
C 12 H 25°
Synthesis:
The hydrogen bonded assembly Res-[120BPyA]2 was synthesized by thoroughly
mixing equimolar quantities of hydrogen bond acceptor 4-(4/-n-
dodecyloxybenzoyloxyl-N-(4/-pyridylmethylene)aniline) (0.973g, 2mmol) in
freshly distilled dry pyridine (2 ml) and hydrogen bond donor resorcinol (0.1 lg,
lmmol) in freshly prepared dry pyridine (2 ml) in the ratio 2:1. The mixture was
then allowed for few days in a vacuum desiccator for the solvent to evaporate
slowly to yield the required product. The formation of hydrogen bonded complex
was confirmed by thin layer chromatography, elemental analysis, FTIR spectra,
and NMR experiments. TLC showed that the materials gave a single spot with
acetone-hexane as eluent.
FTIR studies:
The FTIR spectra recorded for the hydrogen bonded complex of Resorcinol-4-(4 -
n-dodecyloxybenzoyloxyl-N-(4/-pyridylmethylene)aniline), Res-[120BPyA]2 is
shown in Figure 4.2h. The details of the data of various bands observed for
resorcinol (Res), 120BPyA and Res-[120BPyA]2 are presented in Table 4.2.3.
Strong hydrogen bonding is present between resorcinol and (4-n-
dodecyloxybenzoyloxyl-N-(4/-pyridylmethylene)-aniline) as evident from the
broad well defined v-OH bands of medium intensity around 3382 cm"1 which has
replaced the broad v-OH band in the region of 3400-3600 cm"1 in the parent
resorcinol. The carbonyl band of the ester appeared as a shoulder at 1728cm"1.
The 1728 cm"1 is attributable to the free carbonyl group. The formation of the
equilibrium constant could not be estimated due to the complex nature of the
spectrum. The FTIR data in the region 4000-800 cm"1 for all the complexes is
presented below in Table 4.2.3 to confirm the formation of hydrogen bonded
complexes in all the cases.
DSC and Thermal Microscopy:
The compound Resorcinol-4-(4/-n-dodecyloxybenzoyloxy-N-(4 -
pyridylmethylene) aniline) Res-[120BPyA]2 exhibited two transitions in the
heating cycle at (87.2°C, AH = 58.4 kJ/mol, AS = 162.1 J/K/mol) and (129.1°C,
AH = 2.39 kJ/mol, AS = 5.95 J/K/mol). In the cooling cycle also it exhibited
enantiotropic phase transitions at (119.3°C, AH = 1.48 kJ/mol, AS = 3.78 J/K/mol)
and (50.2°C, AH = 16.54 kJ/mol, AS = 51.16 J/K/mol) as is evident from Figure
VIII.
= 129.195 °C = 5.752 mJ H = 2.212 J/g
Peak •= 119309 DehaH=2.802
45 50 60 70 80 90 100 110 120 130 14( Temperature ("C)
Figure VIII
The observed transition temperatures from thermal microscopy and differential
scanning calorimetry are presented in Table 4.2.4. We can see from the table that
the phase transition temperatures of 4-(4/-n-dodecyloxybenzoyloxy-N-(4/-
pyridylmethylene) aniline) (120BPyA) and the hydrogen bonded complex Res-
[120BPyA]2 are different. The hydrogen bonded complex Res-[120BPyA]2
exhibits liquid crystalline phase between 87.2°C and 129.1°C in the heating cycle
and in between 119.3°C and 50.2°C in the cooling cycle. The characteristic fringe
pattern or circular domain texture of the liquid crystalline phase shown in plates
4.13 and 4.14 resembles the normally observed for antiferroelectric smectic CP
phase. The solidification of the complex is shown in plates 4.15 and 4.16. The
melting point for the complex is lower than the melting point of the relative proton
acceptor (89.5°C) and of the proton donor. On the other hand, the clearing point
for the complex is lower than the clearing point of the proton acceptor. The
thermal range of the liquid crystalline phase of the complex is 69°C which is
smaller than the proton acceptor (75°C) in the cooling cycle. These results of
differential scanning calorimetry and thermal microscopy support the formation of
bent shaped hydrogen bonded complex which is stable over a large temperature
range. Further work is necessary to find out the electrical characteristics of the
compound and to confirm the phase assignment.
104
2-nitroresorcinol [4-(4 -n-dodecyloxybenzoyloxyl-N-(4 -
2NRes pyridylmethylene)aniline)] HOBPyA
2-nitroresorcinol-[4-(4/-n-dodecyIoxybenzoyloxyl-N-(4/-
pyridylmethylene)aniline)]2, 2NRes -[120BPyA]2
Synthesis:
The hydrogen bonded assembly 2NRes-[120BPyA]2 was synthesized by
thoroughly mixing the hydrogen bond acceptor 4-(4/-n-dodecyloxybenzoyloxyl-N-
(4/-pyridylmethylene)aniline) (0.973g, 2mmol) in freshly distilled dry pyridine (2
ml) and hydrogen bond donor 2-nitroresorcinol (0.15g, lmmol) in freshly prepared
dry pyridine (2 ml) in the ratio 2:1. The mixture was then allowed for few days in
a vacuum desiccator for the solvent to evaporate slowly to yield the required
product. The formation of hydrogen bonded complex was confirmed by thin layer
chromatography, elemental analysis, FTIR spectra, and NMR experiments. TLC
showed that the materials gave a single spot with acetone-hexane as eluent.
FTIR studies:
The FTIR spectra recorded for the hydrogen bonded complex of Resorcinol-4-(4/-
n-dodecyIoxybenzoyloxyl-N-(4/-pyridylmethylene)aniline), 2NRes-[120BPyAl2
is shown in Figure 4.2i. The details of the data of various bands observed for 2-
nitroresorcinol (Res), 120BPyA and 2NRes-[120BPyA]2 are presented in Table
4.2.3. Strong hydrogen bonding is present between resorcinol and (4-n-
dodecyloxybenzoyloxyl-N-(4/-pyridylmethylene)-aniline) as evident from the
broad well defined v-OH bands of medium intensity around 3382 cm"1 which has
replaced the broad v-OH band in the region of 3400-3600 cm"1 in the parent
resorcinol. The carbonyl band of the ester appeared as a shoulder at 1728cm" .
The 1728 cm"1 is attributable to the free carbonyl group. The formation of the
equilibrium constant could not be estimated due to the complex nature of the
spectrum. The FTIR data in the region 4000-800 cm"1 for all the complexes as
presented in Table 4.2.3 confirms the formation of hydrogen bonded complexes in
all the cases.
NMR studies:
The stoichiometry of the complexes was also determined by integration of NMR
signals from the proton strength of 2-nitroresorcinol and [4-(4;-n-
dodecyloxybenzoyloxy-N-(4/-pyridylmethylene)aniline)]2, moieties of the
complex. The NMR spectra are presented in Figure4.2m. The detailed NMR
analysis of the complex 2NRes-[120BPyA]2 is presented below in Figure IX and
was found to be in good agreement with the elemental analysis results.
H,,3= 6.96, (9.2Hz, 4H), H2,4= 8.13, (8.8Hz, 4H), H5;7= 7.25, (6.4Hz, 4H), H6,8=
7.30, (8.8Hz, 4H), H9,n = 7.75, (5.6Hz, 4H), H10,i2 = 8.74, (6.0Hz, 4H), H13 =
8.46, (s, 2H), H,4, H,6 = 6.97, (s, 2H), H15 = 8.46, (s, 1H), HA = 3.99, (t, 6.4Hz,
4H), HB = 1.79, (q,7.2Hz, 4H), Hc = 1.47-1.25, (m, 36H), HD = 0.86, (t, 6.4Hz,
6H)
M10 H l 4 P10
M6 H s y k ^ H - g ^ H s 1 . H ,
H3C(H2C)9H2CH2CO'^f"H4 Hj Ml H4^V^OC1 2H2 5
«3 H 3
H13= 6.96, 9.2Hz, 4H, H2,4= 8.13, 8.8Hz, 4H. H5,7= 7.25, 6.4Hz, 4H, H6,8= 7.30, 8.8Hz, 4H, H9l1i = 7.75, 5.6Hz, 4H, H10,12 = 8.74, 5.6Hz, 4H, H13 = 8.46, s, 2H, H14, H16 = 6.97, s, 2H, H15 = 8.46, s, 1H, HA = 3.99, t, 6.4Hz, 4H, HB = 1 79, q,7.2Hz, 4H, H c = 1.47-1.25, m,HD = 0.86, t, 6.4Hz
Figure IX
DSC and Thermal Microscopy:
The compound 2-nitroresorcinol melts at 83°C and does not exhibit liquid
crystalline behaviour. The compound 4-(4/-n-dodecyloxybenzoyloxyl-N-(4/-
pyridylmethylene)aniline) exhibit liquid crystalline behaviour as described earlier
and melts at 89.5 C exhibiting smectic A phase with the characteristic focal conic
texture or large homeotropic areas before becoming isotropic at 141.3°C. In the
cooling cycle also the compound exhibits mesomorphic behaviour between
140.6°C and 65.5°C. The hydrogen bonded compound 2-nitroresorcinol-[4-(4/-n-
dodecyloxybenzoyloxy-N-(4/-pyridylmethylene)aniline)]2 exhibited two
transitions in the heating cycle at (84.4°C, AH = 75.5 kJ/mol, AS = 211.3 J/K/mol,
melting point) and (129.8°C, AH = 4.04 kJ/mol, AS = 10.04 J/K/mol, clearing
106
point). In the cooling cycle also it exhibited enantiotropic phase transitions at
(128.7°C, AH = 3.25 kJ/mol, AS = 8.10 J/K/mol) and (60.5°C, AH = 66.5 kJ/mol,
AS = 199.4 J/K/mol). The DSC spectra (Figure X) illustrates that the melting
point of 2NRes-[120BPyA]2 is slightly higher than that of individual components
2NRes as well as [120BPyA] and the clearing point of 2NRes-[120BPyA]2 is
12 C lower than that of hydrogen bond acceptor [120BPyA]. As a result, the
liquid crystalline range for 2NRes-[120BPyA]2 is 7°C smaller than one of the
individual component exhibiting liquid crystalline phase. This difference must be
caused by the difference in molecular structures. The rigidity of mesogenic
complex of 2NRes-[120BPyA]2 is weaker than that of [120BPyA], as is evident
by the bent shape of the molecules. Hence the phase transition temperatures for
2NRes-[120BPyA]2 are lower than those of [120BPyA] because of their
analogous structures.
The hydrogen bonded complex 2NRes-[120BPyA]2 exhibits liquid crystalline
phase between 60.9°C and 13l.9°C. In cooling the sample, it exhibits
characteristic focal conic fan texture below 1 k.7°C (plates 4.17-4.20),
characterizing it as orthogonal smectic A phase. The growth of characteristic focal
conic domain texture of the layered smectic phase resembling smectic A phase
texture is shown in plate 4.17 and 4.18, which is normally observed for
antiferroelectric smectic CP or B2 phase. The uniform birefringent texture is the
distinct characteristic of banana phase shown in plates 4.19 and 4.20 which differs
from the conventional smectic A phase texture. However, the arcs across the fans
as shown in plate 4.21 suggests banana liquid crystalline phase of B2 type. On
further cooling, the sample transformed into solid phase at 60.5°C as indicated by
the texture in plate 4.22. The thermal microscopy and differential scanning
calorimetry results confirm the formation of hydrogen bonded complex 2NRes-
[120BPyA]2.
Peak = 128.705 *C Area = -9375 mj De»aH = -3.472 Jlfc;
2NRes-[120BPv-A]2
90 100 Temperature ("C)
14(
Figure X
From the molecular structure of H-bonded bent shaped compound formed between
4-(4 -n-dodecyloxybenzoyloxy-N-(4/-pyridylmethylene)-anilme) and resorcinol
Res-[120BPyA]2, and its 2-nitro analogue 2NRes-[120BPyA]2 the difference
being the introduction of nitro group in the 2-position of the central phenyl core of
the complex. The microphotographs of the hydrogen bonded complexes viz.,
circular domain texture exhibited by Res-[120BPyA]2 and focal conic domain
texture exhibited by 2NRes-[120BPyA]2 are also shown in plates 4.13 and 4.20
respectively reflecting the difference in the molecular ordering.
4-chlororesorcinol [4-(4/-n-dodecyloxybenzoyloxyl-N-(4/-
4ClRes pyridylmethylene)aniline)] 120BPyA
4-chlororesorcinol-[4-(4/-n-dodecyloxybenzoyloxy-N-(4/-
pyridylmethylene)aniline)]2, 4ClRes-[120BPyA]2
H X X C ' H
C1 2H2 50' OC12H25
Synthesis:
The hydrogen bonded assembly 4ClRes-[120BPyAJ2 was synthesized by
thoroughly mixing the hydrogen bond acceptor 4-(4/-n-dodecyloxybenzoyloxyl-N-
(4/-pyridylmethylene)aniline) (0.973g, 2mmol) in freshly distilled dry pyridine (2
ml) and hydrogen bond donor 4-chlororesorcinol (0.14g, lmmol) in freshly
prepared dry pyridine (2 ml) in the ratio 2:1. The mixture was then allowed for
few days in a vacuum desiccator for the solvent to evaporate slowly to yield the
required product. The formation of hydrogen bonded complex was confirmed by
thin layer chromatography, elemental analysis, FTER spectra, and NMR
experiments. TLC showed that the materials gave a single spot with acetone-
hexane as eluent.
FTIR studies:
The FTIR spectra recorded for the hydrogen bonded complex of 4-
chlororesorcinol-4-(4/-n-dodecyloxybenzoyloxyl-N-(4/-pyridylmethylene)aniline),
4ClRes-[120BPyA]2 is shown in Figure 4.2j. The details of the data of various
bands observed for 4-chlororesorcinol (4ClRes), 120BPyA and 4CIRes-
[120BPyA]2 are presented in Table 4.2.3. Strong hydrogen bonding is present
between 4-chlororesorcinol and (4/-n-dodecyloxybenzoyloxyl-N-(4-
pyridylmethylene)-aniline) as evident from the broad well defined v-OH bands of
medium intensity around 3382 cm"1 which has replaced the broad v-OH band in
the region of 3400-3600 cm"1 in the parent resorcinol. The carbonyl band of the
ester appeared as a shoulder at 1728cm"1. The 1728 cm"1 is attributable to the free
carbonyl group. The formation of the equilibrium constant could not be estimated
due to the complex nature of the spectrum. The FTIR data in the region 4000-800
cm"1 for all the complexes is presented below in Table 4.2.3 to confirm the
formation of hydrogen bonded complexes in all the cases.
NMR studies:
The stoichiometry of the complexes was also determined by integration of NMR
signals from the proton strength of 4-chlororesorcinol and [4-(47-n-
dodecyloxybenzoyloxy-N-(4/-pyridylmethylene)aniline)]2, moieties of the
complex. The NMR spectra are presented in Figure4.2n. The detailed NMR
analysis of the complex 40Res-[120BPyA]2 is presented below in Figure XI and
was found to be in good agreement with the elemental analysis results.
Hi,3= 6.96, (9.2Hz, 4H), H2,4 - 8.12, (8.8Hz, 4H), H5>7= 7.25, (6.4Hz, 4H), H6>8 =
7.30, (8.8Hz, 4H), H9,n = 7.75, (5.6Hz, 4H), H10,i2 = 8.74, (6.0Hz, 4H), H13 =
8.46, (s, 2H), H14, H,5 = 6.97, (s, 2H), Hi6 = 8.46, (s, 1H), HA = 3.99, (t, 6.4Hz,
4H), HB = 2.13, (s, 4H), Hc = 1.27-1.83, (m, 36H), HD = 0.88, (t, 6.4Hz, 6H)
109
Mm H i s > r V C I
H t* : 1 5 T T .. V10.
M2 ^ V Y M6
H 9 Y ^ ^ H x r ^ f ^ ^ t f V H 8 Me
WH, H14 H12-V^C"NYVH^ "13 K K H&KK<> D c B A "ivNVY^Ha"13 A" ^ V V ^ V Y " 1
H3C(H2C)9H2CH2CO'y^H4 H ? H? H<r*J OC12H25 H3 H3
H1i3=6.96, 9.2Hz, 4H, H2l4= 8.12, 8.8Hz, 4H, H5,7= 7.25, 6.4Hz, 4H, H6l8= 7.30, 8.8Hz, 4H, H9l11 = 7.75, 5.6Hz, 4H, H10,12 = 8.74, 6.0Hz, 4H, H13 = 8.46, s, 2H, H14, H15 = 6.97, s, 2H, H16 = 8.46, s, 1H, HA = 4.03, t, 6.4Hz, 4H, HB= 1.81,q, 6Hz,4H, Hc = 1.47-1.26, m,HD = 0.88, t 6.4Hz,6H.
Figure XI
DSC and Thermal Microscopy:
The compound 4-chlororesorcinol melts at 107.1°C and does not exhibit liquid
crystalline behaviour. The compound 4-(4/-n-dodecyloxybenzoyloxyl-N-(4/-
pyridylmethylene)aniline) exhibit liquid crystalline behaviour as described earlier
and melts at 89.5°C exhibiting smectic A phase with the characteristic focal conic
texture or large homeotropic areas before becoming isotropic at 141.3°C. In the
cooling cycle also the compound exhibits mesomorphic behaviour between
140.6°C and 65.5°C. The hydrogen bonded compound 4-chlororesorcinol-[4-(4/-n-
dodecyloxybenzoyloxyl-N-(4/-pyridylmethylene)aniline)]2 exhibit three transitions
in the heating cycle at (87.1°C, AH = 60.8 kJ/mol, AS = 168.9 J/K/mol, melting
point), (140.2°C, AH = 17.58 kJ/mol, AS = 42.66 J/K/mol), (144.8°C, AH = 0.66
kJ/mol, AS = 1.59 J/K/mol, clearing point). In the cooling cycle it exhibited only
one enantiotropic phase transitions at (107.0°C, AH = 1.82 kJ/mol, AS = 4.80
J/K/mol) and continued to exist in the super-cooled state. The DSC spectra
(Figure XII) illustrates that the melting point of 4ClRes-[120BPyA]2 is lower
than that of individual components 4ClRes as well as [120BPyA] and the clearing
point of 4CLRes-[120BPyA]2 is slightly lower than that of hydrogen bond
acceptor [120BPyA]. The liquid crystalline range for 4ClRes-[120BPyA]2 is
almost same as that of one of the individual component exhibiting liquid
crystalline phase in spite of the difference in molecular structures. The rigidity of
mesogenic complex of 4ClRes-[120BPyA]2 is weaker than that of [120BPyA] as
is evident by the bent shape of the molecules. Hence, the phase transition
temperatures for 4CLRes-[120BPyA]2 are slightly lower than those of
[120BPyA] because of their analogous structures.
110
Temper atire ("C)
Figure XII
The hydrogen bonded complex of 4ClRes-[120BPyA]2 exhibit liquid crystalline
phase between 87.1°C and 144.5°C. The growth of characteristic focal conic
domain texture of the layered smectic phase resembling smectic A phase texture
below 140 C, shown in plate 4.24, from the large homeotropic regions with small
patches of focal conic texture below 138.8°C (plate 4.23), is indicative of smectic
molecular structure. Such type of texture is normally observed for antiferroelectric
smectic CP or B2 phase. The uniform birefringent texture is the distinct
characteristic of banana phase shown in plates 4.23 and 4.24 which differs from
the conventional smectic A phase texture. The melting point and clearing
temperatures for the complex is almost same as the melting and clearing
temperatures of the proton acceptor. The mesophase-mesophase transformation
as observed in microscopic texture, shown in plate 4.25 atlO?.2°C is not detected
by differential scanning calorimetry. On further cooling, the sample transformed
into solid phase at 53.9°C with some regions of supercooled liquid crystalline
phase as indicated by the texture in plate 4.26 which is not detected by differential
scanning calorimetry. The thermal microscopy and differential scanning
calorimetry results confirm the formation of hydrogen bonded complex 4ClRes-
[120BPyA]2.
Lee et. al. [13] reported the hydrogen bonded complex of 3-
cholesteryloxycarbonylpentanoicacid-[4-(4/-n-dodecyloxybenzoyloxy-N-(4-pyri-
111
dylmethylene)aniline)] lOOBPyA. 3-cholesteryloxycarbonylpentanoicacid
exhibits liquid crystalline behaviour of cholesteric phase between 134°C and
148°C and acts as proton donor. The compound 4-(pyridin-4-
ylmethyleneimino)phenyl-4-n-alkoxybenzoate (SEOCH with n = 4 or n = 10) acts
as proton acceptor and exhibits nematic, smectic A and smectic C phases.
However on complexation the hydrogen bonded complex exhibits enhanced
cholesteric phase of 64°C.
O-H SEOC10
; CH6A Crl34N*148I ^—{
O-H-N^ -CH j_y= \_
Cr94 SmC 133 SmA 143 N 145 I
CH6A-SEOC10 Cr 126 SmA 135 N* 1921
The hydrogen bonded complex which consists of cholesteryl compound which is
rich in chiral centres and achiral 4-(pyridin-4-ylmethyleneimino)phenyl-4-n-
alkoxybenzoate did not exhibit even smectic C* phase, while the substituted
resorcinol based bent shaped hydrogen bonded molecules formed with achiral 4-
(pyridin-4-ylmethyleneimino)phenyl-4-n-dodecyloxyben2:oate did exhibit chiral
phases.
112
4.3 REFERENCES:
1. J. M. Lehn, Science 227,849, 1985, J. M. Lehn; Angew. Chem. Int. Ed. Engl.
27, 89,1988; J. M. Lehn; Angew. Chem. Int. Ed. Engl. 29,1304,1990
2. D. Gust, T. A. Mooore, A. L. Moore, L. R. Markings, G. R. Seely, X. C. Ma,
T. T. Trier, F. Gao J. Am. Chem. Soc. 110, 7565, 1999
3. V. Balzani, A. Juri, M. Venturi, S. Campagna, S. Serroni, Chem Rev., 96,
759,1996
4. T. Kato and J. M. J. Frchet, J. Am. Chem. Soc 111, 8533 (1989)
5. T.Niori, T.Sekine, J.Watanabe, T.Furukawa,, H.Takezoe J.Mat. Chem.
6,1231,1996
6. a) Y. Matsunaga and S. Miyamoto, Mol. Cryst. Liq. Cryst, 237, 1993; b) M.
Kuboshita, Y. Matsunaga and H. Matsuzaki, Mol. Cryst. Liq. Cryst., 199, 319,
1991.
7. T. Kato, A. Fujishima and J. M. J. Frchet, Chem. Lett., 265,1992.
8. a) H. Matsuzaki and Y. Matsunaga., Liq. Cryst., 14,105, 1993. b) T.
Akutagawa, Y. Matsunaga, and K. Yashahura, Liq. Cryst., 17, 659, 1994.
9. T. Kato, A. Fujishima and J. M. J. Frechet Chem. Lett. 919,1990
10. N. Gimeno, ,M. B. Ros, J. L. Serrano,and M. R. de la Fuente ACIE
43,523, 5,2004
11. S. E. Odinokov, V. P. Mashkovsky, V. P. Glazunov, A. V. Iogansen, B. V.;
Rassadin, Spectrochim. Acta 32A, 1355,1976
12. R. Achten, A. Koudijs, Z. Karczmarzyk, A. T. M. Marcelis, E. J. R. Sudholter,
Liq. Cryst. 31, 215, 2004
13. J. W. Lee, J.-I. Jin, M. F. Achard and F. Hardouin, Liq. Cryst., 28, 663, 2001
113
Table 4.2.2 C H N Analysis of bent shaped compounds
(Figure inside the bracket are theoretical value)
Compound
Res-[14PyA]2
2NRes-[14PyA]2
4ClRes-[14PyA]2
Res-[10OSALCA]2
2NRes-[lOOSALCAh
2MeRes-[lOOSALCAh
4ClRes-flOOSALCAlz
Res-[120BPyA]2
2NRes-[lOOSALCAh
4ClRes-[lOOSALCAlz
%C" Percentage of Carbon
80.36(80.37)
76.39(76.39)
77.31(77.33)
74.81(74.82)
71.12(71.13)
75.00(75.00)
71.99(72.00)
73.19(73.19)
70.29(70.28)
70.97(70.97)
%H' Percentage of Hydrogen
9.46(9.47)
8.89(8.89)
9.01(9.00)
7.62(7.62)
7.14(7.14)
7.71(7.72)
7.21(7.22)
7.56(7.58)
7.19(7.19)
7.24(7.26)
%N14
Percentage of Nitrogen 6.48(6.47)
7.67(7.68)
6.22(6.22)
6.48(6.47)
7.68(7.68)
6.36(6.36)
6.22(6.22)
5.17(5.18)
6.22(6.21)
5.02(5.02)
Table 4.2.3 IR Spectral analysis of bent shaped compounds
SI No
1. 2.
3.
4.
5.
6.
7.
8.
9.
10.
Compounds
Res-[14PyAl2
2NRes-[14PyAh 4ClRes-[14PyAl2
Res-[10OSALCA]2
2NRes-[10OSALCA]2
2MeRes-[lOOSALCAb
4ClRes-[lOOSALCAh
Res-[120BPyAl2
2NRes-[120BPyAl2
4ClRes-[120BPyAl2
VO-H
(intermol.
H-bond)
3446 3386
3363
3357
3387
3388
3318
3382
3444
3383
Vc-H
(ar)
3030
2952
2953
3072
3072
3072
VCH3
2953 2953
2953
2919
2925
2922
2919
2954
2954
2954
VCH2
(as)
2849 2849
2849
2849
2846
2852
2850
2849
2849
2849
Vc=0(cster)
1732
1733
1733
VC=N
(imine)
1626 1606
1606
1627
1618
1615
1629
1607
1608
1607
VC=C(ar)
1550 1516
1515
1598
1558
1557
1599
1551
1551
1551
Vc=N(cyano)
2222
2226
2226
2221
vco (ether)
1252
1250
1251
1254
1256
1258
1255
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Table 4.2.4 Transition temperatures(T), enthalpies (AH) and entropies (AS) of bent shaped compounds.
Compounds
120BPyA
Res-[120BPyA]2
2NRes-[120BPyA]2
4CIRes-[120BPyA]2
10OSALCA
2NRes-[lOOSALCAh
2MeRes-[lOOSALCAh
4ClRes-[10OSALCA)2
Res-[10OSALCA]2
Transitions
K->LC1 LC1->I I->LC1 LC1-»K
K->LC1 LC1->I I->LC1 LC1->K
K->LC1 LC1->I I->LC1 LC1-+K K-»LC1
LC1->LC2 LC2->I I->LC
K->LC1 LC1->I I->LC1 LC1-»K
K-»LC1 LC1->I I->LC1 LC1->K
K->I I-»LC1 LC1->K K->LC1
LC1->LC2 LC2-»LC3
LC3->I I->LC LC-»K K'->K2
K2->K3
K3->K4
K4-»LC1 LC1->I I->LC1
T/°C
89.5 141.3 140.6 65.6
87.3 129.2 119.3 50.2
84.95 129.8 128.7 60.6
87.2 140.2 144.9 106.8
69.8 126.7 125.2 62.4
61.8 102.2 97.6 62.6
91.28 66.6 66.1 52.4 56.9 72.3 95.4 87.2 63.4
49.8 52.5 56.5 66.3 83.8 55.0
AH / kJ mol '
36.51 2.99 2.99 34.90
62.98 2.39 3.03 15.88
75.45 4.04 4.04 66.99
60.77 17.56 0.665 1.82
35.27 2.76 2.67 0.96
70.68 12.02 1.29 2.78
85.37 24.74 13.06 7.85 1.56 5.74 1.20 0.19 1.67
0.38 0.37 0.65 9.62 1.49 1.15
AS/Jmol'K1
100.74 7.22 7.24
103.08
174.79 5.95 7.73
49.15
211.0 10.03 10.06
200.82
168.71 42.49 1.75 4.79
102.87 6.91 6.71 2.87
211.12 32.03 3.51 8.28
234.35 72.84 38.53 24.11 4.74 15.58 3.27 0.53 4.95
1.19 1.13 1.97
28.35 4.18 3.50
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Plate 4.1: R-10OSALCA82 9°C Plate 4.2: R-10OSALCA 80.9°C
Plate 4.3: R-IOOSALCA 78 5°C Plate 4.4: 2NR-10OSALCA 100.8°C
Plate 4.5: 2NR-10OSALCA 74.9°C Plate 4.6: 2NR-10OSALCA 54 1°C
Plate 4.7: 2MeR-10OSALCA 90 1°C Plate 4.8: 2MeR-10OSALCA 83 3°C
Plate 4.9: 2MeR-10OSALCA 43.4°C Plate 4.10: 4C1R-10OSALCA 91.8°C
Plate 4.11: 4C1R-10OSALCA 74.8°C Plate 4.12: 4C1R-10OSALCA 29.6T
Plate 4.13:R-120BPyA 129.9°C Plate 4.14: R-120BPyA 128.0%
Plate 4.15: R-120BPyA 54.0°C Plate 4.16: R-120BPyA 50.8°C