CHAPTER 4shodhganga.inflibnet.ac.in/bitstream/10603/90425/11... · condensed matter or soft matter...

CHAPTER 4

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"cî 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



N(4-n-decyloxysalicylidene)-4/-cyanoaniline,

10OSALCA


10OSALCA


10OSALCA


10OSALCA

4-(4/-n-dodecyloxybenzoyloxyl-N-(4/-

pyridylmethylene)aniline)

120BPyA



120BPyA



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:


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]


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:


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:


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]


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 = 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


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


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


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





crystalline compounds (1-10, 11-10) [12] without hydrogen bonding. The

hydrogen bonded compound 2NRes-[10OSALCA]2 possesses a hydrogen bond



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 = 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


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:


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.


The compound 2-methylresorcinol melts at 114°C and does not exhibit liquid

crystalline behaviour. The compound N-(4-n-decyloxysalicylidene)-4-


69.7°C exhibiting smectic A phase with the characteristic focal conic texture or



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.





structure. In the same sample, extinct regions were also observed, indicating


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





crystalline compounds (1-10, 11-10) [12] without hydrogen bonding. The

hydrogen bonded compound 2MeRes-[10OSALCA]2 possesses a hydrogen bond



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



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


The compound 4-chlororesorcinol melts at 107.1°C and does not exhibit liquid

crystalline behaviour. The compound N-(4-n-decyloxysalicylidene)-4/-


69.7 C exhibiting smectic A phase with the characteristic focal conic texture or



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.





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



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.


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


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



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



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^VÔC1 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


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


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

FIGURES AND TABLES

OF

CHAPTER 4

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

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3363

3357

3387

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3318

3382

3444

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3030

2952

2953

3072

3072

3072

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2953

2919

2925

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2954

2954

2954

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(as)

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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)

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2226

2226

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1252

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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

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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

Plate 4.17: 2NR-120BPyA 131°C

Plate 4.21: 2NR-120BPyA 61 8°C

Plate 4.25: 4ClR-120BPyA 107 2°C

Plate 4.18: 2NR-120BPyA 130.0°C

Plate 4.26: 4ClR-120BPyA 53.9°C

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