Connector type-controlled mesophase structures in poly(propyl ether imine) dendritic liquid crystals of identical dendrimer generations

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Connector Type-Controlled Mesophase Structures in Poly(propyl ether

imine) Dendritic Liquid Crystals of Identical Dendrimer Generations

1

Prabhat Kumar,¹D. S. Shankar Rao,²S. K. Prasad,²N. Jayaraman

¹Department of Organic Chemistry, Indian Institute of Science, Bangalore 560012, Karnataka, India

²Centre for Nano and Soft Matter Sciences, Jalahalli, Bangalore 560013, Karnataka, India

Correspondence to: N. Jayaraman (E-mail: jayaraman@orgchem.iisc.ernet.in) or S. K. Prasad (E-mail: skpras@gmail.com)

Received 28 February 2017; accepted 21 June 2017; published online 00 Month 2017

DOI: 10.1002/pola.28709

ABSTRACT: Poly(propyl ether imine) (PETIM) dendrimers of one

to three generations are used as dendritic cores to identify the

influence of varying connector types that connect the dendritic

core with peripheral mesogens on the emerging liquid crystal-

line (LC) properties. The LC properties vary in these dendritic

liquid crystals, even when the dendrimer generations and thus

the number of peripheral mesogenic moieties remain identical.

PETIM dendrimer generations one to three, ester and amide

connectors varying with succinates, phthalates, and succina-

mides, are studied herein. Cholesteryl moieties are installed at

the peripheries through the above connectors to induce meso-

genic properties. These modified dendritic liquid crystals reveal

structure. A transition from layered to a rectangular columnar

structure results by a mere change in the connector varying

between a succinate or succinamide or phthalate, within one

particular dendrimer generation and without altering the

underlying dendrimer core or the number of mesogenic moie-

ties. The study demonstrates that in dendritic liquid crystals

with essentially identical chemical constitutions, a change in

the connector type connecting the mesogen with the den-

drimer core is sufficient to change the mesophase structures.

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layered mesophase structure in most ester and amide

connector-derivatives, whereas third-generation phthalate

ester dendrimer favors rectangular columnar mesophase

KEYWORDS: dendrimers; differential scanning calorimetry

a

(DSC); glass transition; liquid crystals; X-ray

a

functionalized carbosilane dendrimers of first to fourth genera-

tions that prefers a smectic layer arrangement, whereas the fifth

generation dendrimer of the same series prefers a rectangular

columnar arrangement.¹⁶

INTRODUCTION Fine structural features of a monomer build-

ing block govern the order and complexity of nanostructures.¹

Early pioneering work of Kunitake and Percec demonstrates that

order and complexity, such as, one dimensional lamellae, two

dimensional columns and three dimensional cubes can be mod-

eled by appropriate designs of the basic structural blocks and

attendant noncovalent interactions.^2,3In this context, nanophase

segregation of distinct segments within the molecules⁴having

dendritic structural features hold a promise.^5–11Studies of the

order and complexity, leading to distinct mesophase structures,

were studied systematically using preformed dendrimers by

modifying the peripheries with chosen mesogenic moieties.^12–23

Elegant examples are (i) amphiphilic ionic second generation

poly(amido amine) (PAMAM) dendrimer functionalized with

differing amounts of myristic acid that exhibit a smectic A meso-

phase¹²; (ii) second-generation poly(propyleneimine) den-

drimers peripherally functionalized with 4-methoxybiphenyl,

4-methoxyphenyl benzoate, trans-4-(4-pentylcyclohexyl)phenyl,

4-fluorobiphenyl, and 3,4,5-trifluorobiphenyl that exhibit a spon-

taneous homeotropic arrangement¹⁵and (iii) azobenzene-

In dendritic liquid crystals, dendritic cores are isotropic in

nature. However, functionalization of the peripheries with

anisotropic mesogenic moieties results in the formation of a

mesophase. In all instances so far, it is seen that the meso-

phase structural arrangement changes as dendrimer genera-

tions and consequently the underlying dendritic molecular

structures change drastically. For example, carbosilane den-

drimers functionalized fully with alkyloxyazo derivative or

butoxyphenylbenzoate exhibit a smectic A phase at zero to

four generations, having 8, 16, 32, and 64 mesogenic moie-

ties at their peripheries, respectively. However, the fifth gen-

eration dendrimer having 128 mesogenic moieties at the

periphery shows a rectangular columnar mesophase.²²This

change in the mesophase arrangement was accounted for by

a dense packing of peripheral mesogenic moieties at the fifth

generation. On the other hand, a lamellar arrangement is

Additional Supporting Information may be found in the online version of this article.

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FIGURE 1 PETIM dendrimer cores having cholesteryl moieties at their peripheries through succinate, succinamide, and phthalate

connectors connecting the peripheries with the core moiety. [Color figure can be viewed at wileyonlinelibrary.com]

preferred by decanoic, tetradecanoic, and octadecanoic acids-

functionalized PAMAM dendrimer based mesogens, even for

a higher generation dendrimer appended with 128 periph-

eral mesogenic units. Whereas when an altered dendrimer,

namely, poly(propylene imine) (PPI) that possess shorter

linker lengths between the branch points within the den-

dritic structure was used, a columnar arrangement in the

mesophase was observed when periphery is functionalized

with 64 mesogenic units only.²³

mesophase formation, specifically, without changing the

chemical structure of the dendritic core. A systematic change

in the rigidity and the nature of the connectors connecting

the dendritic core with the mesogenic moieties is of central

importance, to correlate the role of the nonmesogenic den-

dritic core and the attendant mesophase structures. In this

effort, we report herein a study of the first, second and third

generation PETIM dendrimers, functionalized with choles-

teryl moieties through three different types of connectors,

namely, succinate, phthalate, and succinamide (Fig. 1). As

many as nine derivatives are synthesized within these three

generations of dendrimers, having changes only in the con-

nector type connecting the mesogenic peripheral segment

with the dendritic core. A profound change in the mesophase

structures occurs as a result of a change in the connector,

even when the dendrimer core and peripheral mesogenic

constituents are identical within each generation.

Important studies in dendritic liquid crystals to understand

various aspects of mesophase evolution include: (i) changes

in the dendrimer types, such as, carbosilane,²⁴PAMAM,¹²

PPI,^13,15and siloxane,¹⁶and a homologous series of poly

(propyl ether imine) (PETIM)¹⁹dendrimers and changes in

the dendrimer generations;²⁵(ii) varying linker lengths con-

necting the dendrimer backbone and the mesogenic moi-

ety;²⁶(iii) varying alkyl chain length at the peripheries;²⁷

(iv) the mode of attachment of the mesogenic moiety to the

dendrimer, such as, side on or end on;²⁸(v) changing the

shape of mesogenic moieties, such as, linear, radial and

banana shaped²⁹and the degree of branching in the core.³⁰

In the studies of dendritic LCs, to the best of our knowledge,

no work has been reported so far which deals with the study

of change in the mesophase by varying the flexibility and

shape of the linkers within one particular dendrimer

generation.

RESULTS AND DISCUSSION

Synthesis

Amine and hydroxyl groups terminated PETIM dendrimers

up to three generations were used in the present study.

These dendrimers were synthesized by a divergent growth

method as established previously.³¹To covalently attach the

peripheries of these dendrimers, hydroxyl groups-terminated

dendrimers were reacted with cholesterylhemisuccinoyl chlo-

ride or cholesterylhemiphthaloyl chloride, in the presence of

Et₃N in chloroform at 0 8C for ꢀ10 h, to afford the corre-

sponding cholesteryl ester derivatives with succinate or

phthalate connectors in good yields (Scheme 1). Similarly,

amine-terminated PETIM dendrimers were reacted with cho-

lesterylhemisuccinoyl chloride to secure dendrimers having

succinamide connectors at their peripheries. The crude reac-

tion mixtures were subjected to differential solubility in a

solvent, so as to obtain the pure products. Thus, the crude

reaction mixture was made suspension in n-hexane, stirred

for ꢀ15 min., centrifuged, hexane-solubilized portion col-

lected, and solvent evaporated in vacuo. The resulting resi-

due was subjected to treatment with n-hexane iteratively for

few times, by which the products were isolated pure. The

dendritic liquid crystals are glassy solids and soluble in hex-

ane, toluene, dichloromethane, and chloroform and sparingly

soluble in methanol, dioxane, and THF. Molecular structures

Changes in dendrimer generations and changes in the under-

lying dendrimer core structures lead to differing mesophase

structures. Recently, we undertook an effort to verify as to

how the mesophase structures would differ when a particu-

lar dendrimer generation is changed only with respect to the

alkyl chains constituting the dendrimer core structure alone,

without changing the branching pattern and the number of

mesogenic moieties.¹⁹Thus, when the n-propyl moieties con-

necting the branch points at the interior dendrimer structure

was replaced with ethyl moieties, a distinct transition of the

mesophase structure from one-dimensional smectic (SmA) to

~

a columnar in-plane modulated smectic (modulated SmA)

structure emerged.

The studies warrant identifying the role of the functional

group that act as connecters to connect the isotropic den-

drimer core with the peripheral mesogenic segment in the

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SCHEME 1 Synthesis of succinate, succinamide and phthalate ester connector type dendritic liquid crystals of generations 1 - 3.

[Color figure can be viewed at wileyonlinelibrary.com]

of only the third generation dendritic liquid crystals are shown

in Figure 2. The constitutions and structural homogeneities of

all derivatives were characterized by spectroscopies and ele-

mental analyses. In the FTIR spectrum, carbonyl stretching fre-

quency was observed at ꢀ1732 cm²¹, corresponding to the

ester functionality. In ¹H NMR spectrum, methylene protons

attached to peripheral hydroxyl group of dendrimers shifted

from d 5 3.6 to 4.1 ppm and appeared as a triplet, with a cou-

pling constant of ꢀ5.8 Hz, corresponding to CH₂OCO function-

alities in succinate connected dendrimers. In ¹³C NMR

spectrum, appearance of resonance at ꢀ170 ppm confirmed

the ester functionality. Elemental composition analyses con-

firmed the homogeneity of the products. In the case of the

amide series, IR spectrum showed disappearance of peak at

1704 cm²¹(ACO₂H) and appearance of peaks at ꢀ1650 and

ꢀ1550 cm²¹, corresponding to the amide bond stretching fre-

quencies. The amide bond formation led to a downfield shift of

ACH₂NH₂moieties of un-functionalized dendrimers from 2.7

to 3.35 ppm, corresponding to the formation of CH₂NHCS link-

1

age. Resonance at ꢀ5.38 and ꢀ3.35 ppm in H NMR spectra

corresponded to olefinic protons of cholesteryl moiety and

NHACH₂A protons of the dendrimer scaffold, respectively. In

¹³C NMR spectrum, resonance at ꢀ170 ppm corresponded to

carbonyl-moiety of the ester and amide functionalized den-

drimers. Elemental analyses confirmed further the structural

homogeneities of all the derivatives.

Mesophase Studies of Dendritic Liquid Crystals

Molecular masses of the dendritic liquid crystals range

between 1070 and 11712 g mol²¹, representing molecular

FIGURE 2 Molecular structures of G3OCS₁₆, G3NHCS₁₆, and G3OCP₁₆dendritic liquid crystals.

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FIGURE 3 POM textures of (a) G3OCS₁₆at 82 8C; (b) G3OCP₁₆at 98 8C, and (c) G3NHCS₁₆at 90 8C in the cooling cycle. [Color fig-

ure can be viewed at wileyonlinelibrary.com]

masses of low molecular weight compounds to macromole-

cules. Even with such large gradations in the molecular

masses, facile characterization of mesomorphic properties

was possible on all the derivatives, through polarizing optical

microscope (POM), differential scanning calorimeter (DSC),

and powder X-ray diffraction (XRD) analyses.

(iii) the glass transition temperatures of the phthalate con-

nector series are observed to be higher than remaining two

series (Fig. 4). Within each connector series, both glass tran-

sition and clearing temperatures are not significantly differ-

ent. Higher glass transition temperature in the case of

phthalate connector series implies that aromatic linker short-

ens the mesophase temperature at the expense of the glass

transition temperature, as opposed to the connectors being

aliphatic in nature. The amide connector series exhibited

higher clearing temperatures, implying a more rigid molecu-

lar structure.

Thermal characterization by POM reveals that functionaliza-

tion of the dendrimer peripheries with cholesteryl moieties

induces a mesomorphic behavior on all derivatives. An enan-

tiotropic mesophase texture is observed with all derivatives

in POM between room temperature and isotropic transition.

The mesophase to isotropic transition temperature varied

with each cholesteryl-phthalate dendritic mesogens, between

111 and 117 8C. The transition temperatures were: G1OCP₄,

with 4 phthalates, melted at 110 8C and birefringence

regained at 99 8C on cooling; G2OCP₈, with 8 phthalates,

Phase transitions were analyzed subsequently through DSC

technique, with heating-cooling rate maintained at 10

8C min²¹, using hermetically sealed pans. Thermal data of all

dendritic LCs are given in Table 1. Enantiotropic nature of

the mesophase transitions was observed in the DSC analysis

of the ester series dendrimers. The broad step transition

near room temperature in the heating and cooling cycles and

a shift in the base line prior-to and after the transition in all

derivatives suggested a glass transition, rather than a crystal-

lization transition. The succinic ester connector series

showed glass transition temperature range between 18 and

24 8C, and isotropization temperature range between 100

melted at 107 8C, retrieved birefringence at 96 8C; G3OCP₁₆

,

with 16 phthalates, showed clearing transition at 117 8C and

mesophase reappeared at 108 8C in the cooling cycle. Subse-

quent heating-cooling cycles showed similar transitions and

the phase transition temperatures were traced nearly the

same. In the case of the amide connectors, first generation

G1NHCS₄exhibited isotropic phase at 157 8C and upon cool-

ing, a leaflet structure began to appear from 148 8C. Second

generation G2NHCS₈exhibited an enantiotropic mesophase,

^

which was recognised by characteristic battonets, arising

from the dark isotropic phase at 134 8C in the cooling cycle,

which were fully grown to a fan-like texture. The homeo-

tropic regions of the texture retained till room temperature.

The transitions from isotropic to mesophase for G3NHCS₁₆

at 150 8C were accompanied by the formation of focal conic,

which was retained till room temperature. G3OCS₁₆

,

G3OCP₁₆, and G3NHCS₁₆showed a mesophase to isotropic

transition occurred at 104, 117, and 161 8C, respectively,

which upon cooling regained the texture (Fig. 3).

A complete extinction of the texture was observed when the

analysis was performed on a substrate coated with a surfac-

tant, which is a hallmark of the phase being non-tilted

type.³²Important observations are that (i) the succinate con-

nector series have lower glass transition and clearing tem-

peratures than other two connectors series; (ii) the clearing

temperatures of the amide connector series are higher and

FIGURE 4 Phase transitions of dendritic liquid crystals.

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TABLE 1 Thermal and Thermodynamic Data for the Phase Transitions Observed in Second Heating-Cooling Scan (10 8C min²¹

)

Compound [Mass (kDa)]

Transitions^a(8C), DH (kJ mol²¹

)

G1OCS₄(2.239)

G1NHCS₄(2.468)

G1OCP₄(2.432)

G2OCS₈(4.807)

G2NHCS₈(5.264)

G2OCP₈(5.192)

G3OCS₁₆(9.943)

G3NHCS₁₆(10.856)

G3OCP₁₆(11.712)

g 19 SmA 100 (5.0) I 100 (5.4) SmA 18 g

g 31 SmA 157 (10.4) I 148 (9.2) SmA 26 g

g 63 SmA 110 (4.96) I 99 (6.13) SmA 54 g

g 24 SmA 128 (7.7) I 121 (8.5) SmA 12 g

g 31 SmA 148 (17.9) I 134 (16.8) SmA 23.5 g

g 51 SmA 107 (8.40) I 96 (8.26) SmA 44 g

g 18 SmA 104 (30.40) I 98 (28.8) SmA 17 g

g 35 SmA 161 (25.2) I 150 (25.4) SmA 27 g

g 54 Col_r114 (16.60) I 102 (16.71) Col_r48 g

a

g, glass; Sm, smectic; I, isotropic.

and 128 8C. When comparing the role of connector moiety,

the isotropization temperature for phthalate ester connector

series were between 107 and 117 8C, whereas the glass tran-

sition temperature was observed between 51 and 63 8C (Fig.

5). The glass and isotropization transition temperatures for

the first generation derivative G1OCP₄were 63 at 110 8C,

respectively, in the heating scan. Whereas, on cooling, these

transitions were observed at 99 and 54 8C. Second genera-

tion G2OCP₈showed glass transition and mesophase to iso-

tropic transition at 51 and 107 8C in the heating scan,

whereas the cooling scan showed these transitions at 96 and

44 8C. For third generation dendrimer G3OCP₁₆, glass transi-

tion and isotropization temperatures were 54 and 117 8C in

the heating scan, and cooling scan showed transitions at 108

and 48 8C, respectively. Phase transitions of succinate ester

series G1OCS₄and G2OCS₈were observed between 19 and

128 8C. G3OCS₁₆showed glass transition and isotropization

temperatures at 18 and 104 8C in the heating cycle, respec-

tively, whereas in the cooling scan, these transitions were

found to be 99 and 17 8C, with a change in molar enthalpy

generation G2NHCS₈showed a narrower mesophase range,

during heating scan, the glass transition and clearing transi-

tion temperatures were observed at 31 and 148 8C, whereas

these transitions were observed at 134 and 24 8C during

cooling scan. The third generation G3NHCS₁₆showed transi-

tions at 35 and 161 8C during heating scan, whereas these

were observed at 150 and 27 8C during cooling scan. Fur-

ther, change in molar enthalpy was found to be increasing

across the generations and the change in molar enthalpy per

mesogenic unit was found to be between 1.5 and 2.5

kJ mol²¹. DH values were seen to be progressively higher as

the generations advance, indicating an increased molecular

packing in the higher generations. Among the third genera-

tion dendrimers, a higher DH value of SmA to isotropic tran-

sition was observed for G3OCS₁₆, which might result from

an altered molecular packing of this third generation, succi-

nate connector derivative, when compared with amide and

phthalate connected dendrimers. A general trend of den-

drimer generations is that the prolate-shaped structures of

lower generation become spheroidal in nature in higher gen-

eration dendrimers.³³It is likely that this topological change

among dendrimer generations causes the molecular packing

different among the generations and the resulting molar

enthalpy changes of phase transitions. The work of Serrano

and coworkers shows a similar change in isotropization

entropies and temperatures wherein the columnar mesophase

(DH) per mesogenic unit of 1.9 kJ mol²¹

.

In the amide connector series, first generation G1NHCS₄

showed glass transition and isotropization temperatures at

31 and 157 8C in the heating scan, whereas these transitions

were observed at 148 and 26 8C during cooling scan. Second

FIGURE 5 DSC thermograms of (a) ester-linked and (b) amide-linked PETIM dendritic liquid crystals (heating-cooling rate

10 8C min²¹, second cycle).

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FIGURE 6 (a) XRD profile of amide-linked dendritic liquid crystals (Inset: Lorentzean fit for wide angle region) and (b) change in

layer thickness with temperature. [Color figure can be viewed at wileyonlinelibrary.com]

has smaller isotropization entropy than that of lamellar meso-

phase. This effect was attributed to conformational changes

within the molecules, originating from different segments of

the codendrimer molecules.³⁴

halo suggested a short range, liquid-like order. A generation-

dependent trend in the layer thickness was found in den-

dritic liquid crystals. Concerning the influence of generation

and the type of linkage on the magnitude of the spacing, the

layer thickness of the compounds were found to be increas-

ing across the generations (Figs. 6 and 7). The layer thick-

ness in both succinate and phthalate series decreased

linearly with increasing temperature at principal and higher

order reflections. Increasing temperatures thus shortened

the molecular length marginally, possibly as a result of

altered segmental balance between the relatively hydrophilic

dendritic core region and lyophilic cholesteryl peripheral

region. A weak but perceptible increase in one of the inter-

molecular distances also occurred with increasing tempera-

ture (Table 2). In addition to the trend of the larger spacing

inferred from small angle diffraction pattern, the observed

XRD Study

Variable temperature XRD studies were conducted to enable

the identification of the mesophase structures of all deriva-

tives. For all the dendritic LCs, variable temperature XRD

patterns, within the mesomorphic range, consisted of at least

two sharp equidistant peaks in the low-angle region and a

broad, diffuse maximum in the wide angle region (Figs. 6–8,

Table 2). The ratio of the reciprocal of the spacings of low

angle reflections, being integral numbers, indicated the pres-

ence of a lamellar arrangement in the mesophase for all the

dendritic liquid crystals, except G3OCP₁₆. The broad, diffuse

FIGURE 7 Left: XRD profile of G3OCS₁₆at 23 8C bringing out the lamellar nature of the structure. Inset: Diffuse maximum in the

wide angle region described by a sum (black line) of two Lorentzian functions with the resolved individual peaks depicted by blue

and red lines. Right: Change in layer thickness with temperature. [Color figure can be viewed at wileyonlinelibrary.com]

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FIGURE 8 Small angle XRD profiles of G1OCP₄and G2OCP₈(left). The inset shows the wide angle maximum of G2OCP₈(black

line) being described by two Lorentzians (blue and red lines). Variable temperature XRD profiles of G3OCP₁₆, presenting the

increase of the lamellar spacing (lowering of Bragg angle) with decreasing temperature (right). (Inset: Diffraction in the wide angle

region for G3OCP₁₆). [Color figure can be viewed at wileyonlinelibrary.com]

diffuse halo in the wide angle region corresponded to short

range order. The wide angle profiles were fit into a sum of

two Lorentzeans, suggesting to the possibility of two types

of packing within the layer. Two partially overlapping broad

peaks centered at about 5.5 and 4.5 Å (D_w1and D_w2in Table

2), with the former corresponding to the average distance

between the cholesterol moieties and the latter arising from

the flexible dendritic core.

TABLE 2 XRD Spacings Corresponding to the Layer Periodicity, Its Harmonics, and Intermolecular Distance (D) Within the Layer of

Dendritic LCs

˚

Compound

T (8C)

d₁₀₀(A)

d₂₀₀(A)

d₃₀₀(A)

D_w1(A)

D_w2(A)

D_W3(A)

G1OCS₄

23

50.46

49.87

48.79

48.08

48.34

46.51

46.61

45.91

49.33

49.18

48.27

50.23

48.77

51.09

51.12

50.63

58.39

57.66

55.32

55.35

54.32

25.19

24.90

24.35

23.95

23.94

23.28

23.32

23.00

24.65

24.72

24.28

24.39

24.25

25.65

25.67

25.32

29.15

28.78

27.61

27.51

27.06

16.79

16.6

5.4

4.5

60

5.5

4.6

90

5.5

4.5

G1NHCS₄

G1OCP₄

26

15.93

15.90

15.49

15.53

15.32

5.59

5.70

5.64

5.66

5.70

5.5

4.58

4.47

4.46

4.44

4.30

4.4

150

25

2.85

2.86

60

100

24

G2OCS₈

100

130

27

5.6

4.5

G2NHCS₈

G2OCP₈

16.26

5.59

5.66

5.62

5.66

5.68

5.41

4.57

4.27

4.40

4.41

4.31

4.46

140

26

17.12

17.10

16.88

19.44

19.14

2.85

2.86

60

100

23

G3OCS₁₆

50

90

5.48

5.51

5.65

4.56

4.50

4.62

G3NHCS₁₆

28

18.29

17.93

120

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TABLE 3 XRD Spacings Corresponding to the Layer Periodicity, Its Harmonics, and Intermolecular Distance Within the Layer of

G3OCP₁₆

25 8C

70 8C

100 8C

Lattice

parameter

˚

d_obs(A)

d_calc(A)

hkl

(A): Col_r

d_obs(A)

d_calc(A)

hkl

(A): Col_r

d_obs(A)

d_calc(A)

hkl

(A): Col_r

52.13

34.62

26.16

17.31

13.81

52.13

34.62

26.06

17.31

13.90

010

110

020

030

040

a 5 46.3

b 5 52.1

52.22

34.69

26.18

17.38

13.90

52.22

34.69

26.11

17.41

13.92

010

110

020

030

230

a 5 46.4

b 5 52.2

52.66

34.81

26.36

17.53

5.80

52.66

34.87

26.33

17.55

5.81

010

110

020

030

190

a 5 46.6

b 5 52.7

Presence of the second diffuse peak is more pronounced,

which is assumed to be due to the increased number of cho-

lesterol moieties present in higher generation dendritic LCs.

A comparison between the two series of connectors shows

interesting difference due to the linkers. Between G1OCS₄

and G1OCP₄, the layer thickness reduced considerably in

G1OCP₄. The phthalate connector thus rigidified the mole-

cule more than the flexible succinate, even when in both the

cases the diester moieties are separated by two carbons

only. The intermolecular distance of 5.4 Å in G1OCS₄to 5.64

Å in G1OCP₄would correspond to the average distance

between the cholesterol moieties. Whereas, the observed sec-

ond intermolecular distance of 4.5 and 4.46 Å would corre-

spond distance arising from the disordered dendritic

backbone. These intermolecular distances did not change

with linker variation. A third distance (D_w3) was observed in

the phthalate series only, the origin of which is likely to be

the inter-phthalate moiety distance within the molecule.

Such a distance, measured from wide angle region, however,

could not be identified in the case of the succinate connector

series. A further point that may be noted from the tempera-

ture dependence of the lamellar spacing is that the succinate

connector dendritic liquid crystals possessed a larger varia-

tion than the phthalate ester connector dendritic liquid crys-

tals, possibly as a result of succinate connector being more

flexible than phthalate ester system.

primary layer spacing owing to a layer formation constituted

by each molecule without much interdigitation and the

molecular compaction and/or (ii) tilting of the individual

cholesterol units with respect to the dendrimer core seg-

ment, with a randomness in the tilting direction.

Variable temperature powder XRD pattern of G3OCP₁₆dif-

fered significantly from those of remaining dendritic liquid

crystals studied herein. At 100 8C, five peaks were observed

in small angle region, the qualitative pattern remaining the

same at different temperatures (Fig. 8). Presence of multiple

sharp peaks, with a nonintegral ratio between them, together

with a diffuse maximum in the wide angle region and the

plane group P2mg, suggests the formation of two-

dimensional self-assembled noncentered rectangular col-

umns. The multiple sharp peaks also suggest a two dimen-

sional lattice. These features are also observed at other

temperatures for which the scans are obtained. The relevant

spacing and lattice parameters are listed in Table 3. A sche-

matic representation of the molecular arrangements in the

columnar mesophase is given in Figure 9.

The non-centered rectangular columnar mesophase³⁶can be

referred equivalently to the modulated smectic A phase, with

the lattice directions one in the layer plane and another

along the layer normal.³⁷However, we find that the observed

reflections consistent a rectangular columnar structure with

a P2mg symmetry. Comparing the layer thickness of the den-

dritic LCs, the lattice parameter of G3OCP₁₆along one of the

axes is comparable to the layer thickness of the remaining

third generation dendritic liquid crystals studied herein. The

volume fractions of dendritic core versus the peripheral moi-

eties is ꢀ 3% larger with succinate and amide connector

derivatives, in comparison with phthalate connector deriva-

tives, by which the accessible region for individual peripheral

cholesteryl moieties is marginally larger for G1OCS₄,

The layer thickness was compared with the length of a den-

dritic LCs, assuming that the dendrimer is prolate in shape,

with the cholesterol units stretching out on both sides of the

central dendrimer core. For this purpose, the diameter of

dendrimers cores of 8, 15, and 22 Å were used, as evaluated

by molecular dynamics simulations, for the G1, G2, and G3

dendrimers, respectively.³³The length of one cholesterol unit

is about 18 Å.³⁵Combining with the connector lengths, the

length of G1, G2, and G3 generation dendrimers are esti-

mated to be ꢀ 56, 63, and 70 Å, respectively. The observed

d₁₀₀values for all these dendritic LCs at room temperature

are lower than the estimated molecular lengths. We premise

that the difference between the observed spacings and the

estimated molecular lengths is due to: (i) a shortening of

G2OCS₈, G3OCS₁₆

, G1NHCS₄, G2NHCS₈, and G3NHCS₁₆

derivatives than for G1OCP₄, G2OCP₈, and G3OCP₁₆deriva-

tives. The more pronounced effect for the third generation

G3OCP₁₆to adopt a rectangular columnar mesophase struc-

ture, in comparison to third generation G3OCS₁₆and

G3NHCS₁₆that adopt

a lamellar structure, could be

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moieties, presence of mono- to multiple mesogen-inducing

segments at the peripheries, multiplicities of branching at

the dendritic core and branch junctures were studied in

detail for a long time. Frey and coworkers demonstrated in

an early work that carbosilane dendrimers installed with 12,

36, and 108 perflouroalkyl moieties of one to three genera-

tions exhibited generation dependent mesophase properties.

Whereas the first generation dendrimer showed a layered

phase, second and third generation dendrimers adopted a

hexagonal columnar phase, due to high density of surface

moieties and the lack of sufficient spacer length to decouple

the perfluoroalkyl groups and the dendrimer core.⁴⁵

Meijer and coworkers demonstrated in a very early work

that PPI dendrimers derivatized with 4, 16, and 64 pentylox-

ycyanobiphenyl and decyloxycyano-biphenyl moieties at the

peripheries of first, second, and generation dendrimers,

respectively, all exhibited a layered smectic phase only. A

phase separation of dendiritic core with distorted conforma-

tion and the peripheral cyanobiphenyl moiety oriented in an

antiparallel arrangement, leading to an interdigitated bilayer

structure, was suggested to rationalize the observations.⁴⁶

Similar smectic phase was observed in another series of PPI

that were tethered with x-(4⁰-cyanobiphenyloxy)alkyl

substituted first and second generation dendritic liquid crys-

tals by Yonetake and Ueda.⁴⁷

FIGURE 9 A representation of the molecular arrangement of

the noncentered rectangular columnar structure with plane

symmetry P2mg exhibited by G3OCP₁₆dendritic liquid crystal.

[Color figure can be viewed at wileyonlinelibrary.com]

attributed to the presence of ortho-disubstituted phthalic moi-

ety. We premise that changes in the globular structures among

the three third generation dendrimers, varying only with

respect to the nature of succinate, phthalate, and amide con-

nectors, alter the mesophase structure, between a lamellar

structure and a noncentered rectangular columnar structure.

A fine balance of the linker length and densities of the

peripheral moieties on the evolution of mesogenic properties

was observed on dendrimers possessing triphenylene core

and sugar-coated peripheries, that are connected through the

alkylene linkers. A decyl-linker connecting the core with

mono-sugar moiety at the periphery exhibited a rectangular

columnar arrangement. Whereas, the same linker connecting

the core with a tris-sugar moiety at the periphery led to hex-

agonal columnar mesophase structure.⁴⁸

The appearance of rectangular columnar phase has been

observed commonly in many instances earlier. Few examples

are (i) ionic liquid crystals derived from 3,4,5-trialkoxyben-

zyl trimethyl - benzenammonium cation with BF₄and PF₆

counteranions;³⁸(ii) dodecyl chains attached at the periph-

ery of the aryl moiety at one imide position of a perylenedii-

mide or naphthalenediimide core and triethyleneglycol

chains at the periphery of the aryl moiety on the other side

of the molecules;^39,40(iii) viologens possessing tri-alkoxy

phenyl moiety at each terminal having dodecyl and hexa-

decyl chain;⁴¹and (iv) liquid crystals derived from N,N⁰-

bis(3,4,5-trialkoxylphenyl)ureas with octyl, dodecyl, and hex-

adecyl chains.⁴²

Serrano and coworkers systematically studied functionalizing

the peripheries of PAMAM and PPI dendrimers with salicy-

laldimine moieties bearing one, two and three terminal ali-

phatic chains. From the studies, the authors identified that

whereas the one terminal alkyl chain functionalized den-

drimer generation exhibited varied lamellar smectic phases,

two and three terminal aliphatic chain bearing dendrimers

showed a hexagonal columnar mesophase. There were no

differences in the mesophase structures of dendritic LCs aris-

ing from these two different types of dendrimer cores.

Higher densities of aliphatic chains at the peripheries

induced a curved and radial arrangement of the mesogenic

moieties, leading to stacking of the molecules and formation

of a columnar mesomorphism.⁴⁹In another study, a hexago-

nal columnar mesomorphism was observed with third and

fourth generation PPI and PAMAM dendrimers, peripherally

functionalized with mesogenic groups. The functionalization

of dendrimer with bulkier mesogenic group was performed

with an aim to achieve cubic mesomorphism, however due

to congestion of peripheral moieties, complete functionaliza-

tion of dendrimer could not be achieved and a Colh

Rectangular columnar mesophase are shown by dendritic liq-

uid crystals previously. For example, (a) a fourth generation

amine-terminated PAMAM complexed with linear tetradeca-

noic acid;²³(b) a third generation PAMAM dendrimer, func-

tionalized with varying proportions of two types of

promesogen moieties;^34,43(c) triazine-based dendrimers con-

taining central linkers with odd numbers of carbon atoms

and C3-symmetrical dendrimers with rigid core;⁴⁴and (d) a

carbosilane fifth generation dendrimer fully functionalized

with alkyloxyazo derivative or butoxyphenylbenzoate deriva-

tive at its periphery.²²The effect was attributed to varying

dendrimer generations, namely, lower-to-higher dendrimer

generations and thus, a drastic structural change of the

underlying dendritic core itself.

The effect of the dendrimer generations, the role of linkers

or spacers connecting the dendritic core with the peripheral

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arrangement was observed for all the dendrimers, irrespec-

tive of the nature and generation of dendrimers and the

promesogenic groups.⁵⁰

or different anisotropic segments form the branching cells

with double multiplicity, respectively, was studied for their

mesogenic properties by Donnio and coworkers.⁵⁶Both the

series showed either a lamellar or a columnar mesophase

structures. Eight-armed dendrimers possessing one terminal

alkyloxy chains at the peripheral aromatic moieties exhibited

a lamellar phase, whereas incorporation of second alkyloxy

chains at the same peripheral aromatic moieties led to the

formation of a columnar phase. Incorporation of additional

alkyl chain appeared to prevent parallel orientation of the

mesogen moieties rather a radial arrangement around the

dendritic core occurred, leading to column formation.⁵⁶

Importance of the spacer moiety connecting the peripheral

mesogen with the dendritic core is studied in detail. Carbosi-

lane dendrimers tethered directly with 36 and 108 choles-

teryl groups, without a spacer moiety, do not show a

mesogenic behavior,⁵¹whereas similar carbosilane den-

drimers possessing cyanobiphenyl moieties connected with

the aid of undecyl chain exhibit generation-dependent meso-

phase behavior. Thus, dendrimer generations 1–4 remain to

be smectic A and C mesogens, that of the fifth generation

turns out to be not only lamellar, but also columnar meso-

phase structure, due to crowding of the mesogenic groups

and the attendant spherical shape of the molecule.⁵²

From a series of above studies and developments in den-

dritic liquid crystals, it becomes apparent that steric crowd-

ing is an important feature in those derivatives that show

columnar mesophases. A steric crowding results frequently

in a higher generation dendrimer, wherein the space and vol-

ume available to each peripheral mesogen-inducing moieties

become progressively less, when compared to lower genera-

tion dendrimers. Second type of steric crowding at the

peripheries are those derivatives in which more than one

substituents, such as, long alkyl chains are installed at the

outer-most moieties, primarily aromatic moieties. In these

instances, locating one versus two or three long chain sub-

stituents leads to lamellar or columnar mesophase struc-

tures. Separation of peripheral mesogen-inducing moieties

from the dendritic core with the of spacers is critical,

absence of spacers renders the derivatives nonmesogenic.

Formation of smectic phase is seen prominently in PPI den-

drimers attached with 4, 8, and 16 cholesteryl carbamate moi-

ety at the peripheries of first, second and third generations, as

a result of nanophase segregation of incompatible dendritic

core and peripheral segments in these dendritic LCs.⁵³

Nanophase segregation of the dendritic core from the periph-

eral mesogenic groups is suggested as rationale for the obser-

vation of columnar mesophases in PPI dendrimers

functionalized with 4, 8, 16, 32, and 64 peripheral triphenylene

moieties, having a decylene spacer, in the first to fifth genera-

tions, respectively. Whereas the first generation dendritic LC

showed a rectangular columnar arrangement, the remaining

dendritic LCs possessed a hexagonal columnar arrangement.⁵⁴

This work illustrates the role of connectors, between ali-

phatic versus aromatic or ester versus amide connecting the

dendrimer peripheries with the mesogenic units in identical

dendrimer generations. Presence of succinate, succinamide,

and phthalate ester connectors connecting the dendrimers

with cholesterols provided a lesser volume fraction of den-

drimers for phthalate ester connector in comparison to suc-

cinate ester and amide connectors within each generation,

without changing the number of mesogenic moieties and the

dendrimer generations. In addition to reduced volume frac-

tions, extended rigidity and ortho-disubstitution in the struc-

ture of the mesogenic group facilitated the formation of two-

dimensional rectangular columnar mesophase in the case of

phthalate ester-connected third generation dendritic liquid

crystal. It is thus inferred that the connectors connecting the

dendritic core with peripheral mesogenic moieties play an

important role in the molecular packing in the mesophase

structures, even when the underlying dendritic core struc-

tures do not change. We premise that this observation is

similar to that reported by Belaissaoui et al. wherein varia-

tions of mesophase structures were related to branching

sugar moieties at the outer shell and very little or none of

the effect arising due to the dendritic core sugar moiety.⁵⁷

Synthesis and phase behavior studies of carbosilane den-

drimers functionalized with butoxyphenylbenzoate groups at

the peripheries of first to five generations were studied by

Agina and coworkers. Whereas first to fourth generation den-

drimers possessing 8, 16, 32, and 64 mesogen moieties at the

peripheries exhibited a lamellar phase (smectic C phase) that

of the fifth generation dendrimer installed with 124 peripheral

mesogen moiety showed supramolecular columnar structures.

A microphase segregation of alternating dendritic core and the

mesogenic moieties constituted the layer in the lamellar phase,

whereas the whole molecule served as a structural unit in the

case of the columnar phase. Further, the lamellar spacing

increased with increasing temperature in all four generations,

due to dendritic core assuming an isotropic conformation at

higher temperature and overcome the interaction of meso-

genic segments. Small angle neutron scattering studies further

reiterated the observations from XRD studies^22bSimilar LC

behavior was also observed to the series of carbosilane den-

drimers functionalized with azobenzene mesogens linked

through decylene chains.^22a

A long spacer is critical in order to make the peripheral

mesogenic moieties independent of the influence of the den-

dritic core, to derive a stable mesophase structure.^22a,55

CONCLUSIONS

In summary, the first, second and third generation amine and

hydroxyl groups terminated PETIM dendrimers functionalized

with cholesteryl moieties having succinate, succinamide, and

A series of homolithic and heterolithic eight-armed dendritic

liquid crystals, in which either identical anisotropic segments

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phthalate connectors were synthesized and their liquid crys-

talline (LC) properties were investigated through POM, DSC,

and powder XRD analyses. The series of experiments demon-

strated that LC dendrimers showed enantiotropic mesophase

property. All the dendritic liquid crystals showed lamellar

arrangement, except phthalate ester-linked G3OCP₁₆, which

showed a two-dimensional rectangular columnar arrangement.

The observed smectic phase of the dendritic LCs results from

the dendritic core adopting topological changes as enforced

by peripheral structurally rigid mesogenic segments and the

flexible dendritic core. An introduction of the rigidity in the

connectors, structure without changing its length from suc-

cinic to phthalic moieties showed a switch from smectic to

two-dimensional non-centered rectangular columnar meso-

phase at the third generation, whereas first and second gener-

ation dendrimers showed smectic mesophase irrespective of

their ester or amide connectors in their molecular structures.

This study demonstrates a correlation between the connectors

that connect the dendritic core with the peripheral mesogenic

moieties and the resulting mesophase structures in dendritic

liquid crystals, within a particular dendrimer generation, hav-

ing identical underlying dendrimer core structures.

chloroform (50 mL) was added to it. The organic layer was

subsequently washed with aq. HCl (1 N) (2 x 50 mL), satu-

rated NaHCO₃(2 3 50 mL), brine solution (50 mL) and

dried over anhydrous Na₂SO₄, followed by solvent evapora-

tion in vacuo. The crude product was purified by column

chromatography (SiO₂, 20% EtOAc-hexane) to afford 2, as a

white amorphous powder. Yield 5 6.7 g (97%); R_f0.5 (1:9

MeOH/CHCl₃); mp: 178.85 8C from DSC trace, second cycle;

[a]_D²⁰5 236.02 (c 1.00, CHCl₃); FTIR (neat): m 2943, 1722,

1

1714, 1469, 1298, 1131, 1076, 946, 41 cm²¹; H NMR (400

MHz, CDCl₃): d 0.6–2.1 (m, 41 H, cholesteryl), 2. 49 (m, 2 H,

CH₂), 4.89 (m, 1 H, OCH), 5.43 (m, 1 H, CH), 7.58 (m, 2 H,

CH), 7.71 (dd, J₁5 7.6 Hz, J₂5 1.2 Hz, 1 H, CH), 7.91 (dd,

J₁5 7.6 Hz, J₂5 1.6 Hz, 1 H, CH); ¹³C NMR (100 MHz,

CDCl₃): d 171.8, 167.5, 139.4, 133.6, 132.0, 130.7, 129.9,

128.8, 122.9, 121.8, 75.8, 56.7, 56.1, 50.0, 42.2, 42.1, 39.7,

39.5, 37.8, 36.9, 36.6, 36.4, 36.1, 35.8, 31.8, 31.5, 28.2, 28.0,

27.7, 27.4 24.2, 23.8, 22.8, 22.7, 22.5, 21.0, 19.3, 18.7, 11.8;

HRMS: m/z C₃₅H₅₀O₄Na calcd. 557.3607, found 557.3608.

G3OCS₁₆

Oxalyl chloride (62 lL, 0.74 mmol) was added to a solution

of cholesteryl hemisuccinate (0.3 g, 0.62 mmol) in CH₂Cl₂

(5 mL), stirred for 10 min at 0 8C and then for 2 h at room

temperature. Solvents were removed in vacuo and dried to

afford cholesteryl hemisuccinate acid chloride. A solution of

the acid chloride in CH₂Cl₂(10 mL) was added to a solution

of third generation hydroxyl group terminated PETIM den-

drimer (0.063 g, 0.025 mmol), Et₃N (0.12 mL, 0.86 mmol),

and DMAP (cat.) in CH₂Cl₂(15 mL). The reaction mixture

stirred at room temperature for ꢀ10 h, diluted with CH₂Cl₂

(20 mL), washed with water (2 3 25 mL), the organic por-

tion dried (Na₂SO₄), filtered, filtrate concentrated in vacuo

and dried to afford a crude product. The crude product was

triturated with n-hexane (25 mL), centrifuged, filtrate col-

lected, evaporated in vacuo. The resulting residue was tritu-

rated again with n-hexane, centrifuged, filtrate collected and

solvents evaporated in vacuo. The procedure was repeated 4

times, by which absence of insoluble cholesteryl hemisuc-

cinic acid was ensured. The solvent was evaporated in vacuo

and dried thoroughly to afford G3OCS₁₆, as a gummy solid.

Yield: 0.23 g (90%); [a]_D²⁰5 225.4 (c 1.00, CHCl₃). FTIR

(neat) m 2947, 1732, 1467, 1376, 1166, 760; ¹H NMR (400

EXPERIMENTAL

Materials

Chemicals were purchased from commercial sources and

were used without further purification. Solvents were dried

and distilled using literature procedures. Triethylamine was

stored over KOH. Analytical TLC was performed on commer-

cial Merck plates, coated with silica gel 60 F₂₅₄(0.25 mm)

and aluminum oxide 60 F₂₅₄(0.25 mm). Compounds were

visualized by exposure to a UV lamp or incubation in a glass

chamber containing iodine. Compounds were purified by col-

umn chromatography using neutral aluminum oxide and sil-

ica gel (100–200 mesh, SRL, India). G1OCS₄and G2OCS₈

were prepared as described previously.¹⁹FTIR spectra were

recorded on a Perkin-Elmer spectrometer, as neat samples.

¹H and ¹³C NMR spectral analyses were performed on a

Bruker-ARX400 operating at 400 and 100 MHz, respectively.

Chemical shifts are reported with respect to tetramethylsi-

lane (TMS) for ¹H NMR and the central line (77.0 ppm) of

CDCl₃for ¹³C NMR. Chemical shift values are reported in

ppm relative to TMS and the following abbreviations are

used to explain the multiplicities: s, singlet; d, doublet; t,

triplet; q, quartet; m, multiplet; br, broad; dd, double doublet.

Coupling constant (J) are reported in Hertz (Hz). Microanaly-

sis was performed on an automated Carlo-Erba C, H, and N

analyzer. High resolution mass spectra were obtained from a

Micromass Q-TOF instrument by an electrospray ionization

technique.

MHz, CDCl₃):

d

0.5–2.10 (band, 772 H; cholesteryl,

CH₂ACH₂ACH₂), 2.15–2.70 (br, 148 H, NACH₂, ACH₂OCOA,

AOCOCH₂), 3.32 (t, J 5 5.8 Hz, 52 H, ACH₂AOACH₂), 4.09 (t,

J 5 5.8 Hz, 32 H, CH₂COOCHA), 4.58 (br, 16 H, OACH), 5.28

(br, 16 H, @CH); ¹³C NMR (100 MHz, CDCl₃): d 172.3, 171.6,

139.5, 122.6, 74.2, 68.8, 62.9, 56.6, 56.0, 50.5, 50.2, 49.9,

42.2, 39.6, 39.4, 38.0, 36.9, 36.5, 36.1, 35.7, 31.8, 31.87, 29.4,

29.0, 28.2, 27.9, 27.7, 24.2, 23.8, 22.8, 22.5, 21.00, 19.3, 18.7,

11.8. Elemental analyses: calcd. for

75.14, H 10.50, N 1.97; found: C 75.15, H 10.31, N 2.44.

C₆₂₂H₁₀₃₆O₇₇N₁₄: C

Synthesis of Cholesteryl Hydrogenphthalate

Triethyl amine (1.3 g, 12.9 mmol) and phthalic anhydride

(1.92 g, 12.9 mmol) were added to a solution of cholesterol

(5 g, 12.9 mmol) in CHCl₃(50 mL). The solution was stirred

at room temperature for 15 h. Progress of the reaction was

monitored by TLC (SiO₂, I₂). After completion of the reaction,

G1OCP₄

Oxalyl chloride (0.38 lL, 0.45 mmol), a solution of choles-

teryl hemiphthalate (0.22 g, 0.41 mmol) in CH₂Cl₂(5 mL),

first generation hydroxyl group terminated PETIM dendrimer

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(0.03 g, 0.082 mmol), and Et₃N (0.075 mL, 0.54 mmol) in

CHCl₃(15 mL) and the reaction was proceeded further as

given in the general method. Yield 5 187 mg (97%);

[a]_D²⁰5 234.80 (c 1.00, CHCl₃); ¹H NMR (400 MHz, CDCl₃):

d 0.5–2.20 (br, 184 H, cholesteryl, CH₂ACH₂ACH₂), 2.43 (m,

12 H, CH₂NCH₂), 3.41 (m, 4 H, OACH₂), 4.34 (br, 8 H,

OACH₂), 4.81 (br, 4 H, OCH), 5.39 (br, 4 H, @CH), 7.47 (br,

8 H, ArH), 7.64–7.71 (m, 8 H, ArH); ¹³C NMR (100 MHz,

CDCl₃): d 171.4, 167.5, 139.7, 139.4, 132.3, 132.1, 131.0,

130.9, 130.7, 130.2, 129.2, 128.9, 128.8, 128.5, 122.9, 122.7,

75.4, 75.2, 63.2, 56.7, 56.2, 50.0, 42.3, 39.7, 39.5, 38.0, 37.9,

37.0, 36.9, 36.5, 36.1, 35.8, 31.9, 31.8, 30.9, 29.9, 29.6, 29.3,

28.2, 27.9, 27.7, 24.2, 23.8, 22.8, 22.5, 21.00, 19.3, 18.7, 11.8;

Elemental analysis. calcd for C₁₅₈H₂₃₂O₁₇N₂: C 78.04, H 9.62,

N 1.15; found: C 77.92, H 9.35, N 1.35.

G1NHCS₄

Oxalyl chloride (46 lL, 0.54 mmol), a solution of cholesteryl

hemisuccinate (0.22 g, 0.45 mmol) in CH₂Cl₂(5 mL), first

generation amine terminated PETIM dendrimer (0.053 g,

0.089 mmol), and Et₃N (0.090 mL, 0.65 mmol) in CHCl₃

(15 mL) and the reaction was proceeded further as

described in the synthesis of G3OCS₁₆. Yield 5 0.22 g (98%);

[a]_D²⁰5 228.40 (c 1.00, CHCl₃); FTIR (neat): m 3310, 2933,

2868, 1729, 1650, 1552, 1469, 1374, 1170, 1111; ¹H NMR

(400 MHz, CDCl₃):

d 0.5–2.1 (br, 184 H, cholesteryl,

CH₂ACH₂ACH₂), 2.30 (m, 8 H, CH₂), 2.45 (m, 12 H, CH₂),

2.62 (m, 16 H, CH₂), 3.32 (m, 8 H, NHACH₂), 3.45 (m, 20 H,

OACH₂), 4.60 (br, 4 H, OACH), 5.35 (br, 4 H, @CH), 6.6 (br,

4 H, NH); ¹³C NMR (100 MHz, CDCl₃): d 172.4, 171.7, 139.6,

122.5, 74.2, 69.0, 68.7, 56.7, 56.1, 50.0, 42.3, 39.7, 39.5, 38.0,

37.1, 36.9, 36.5, 36.1, 35.8, 31.9, 31.8, 30.9, 29.9, 29.6, 29.3,

28.2, 27.9, 27.7, 24.2, 23.8, 22.8, 22.5, 21.00, 19.3, 18.7, 11.8;

Elemental analysis. calcd for C₁₅₄H₂₆₀O₁₇N₆: C 74.95, H

10.62, N 3.41; found: C 74.94, H 10.51, N 3.26.

G2OCP₈

Oxalyl chloride (49 lL, 0.58 mmol), a solution of cholesteryl

hemiphthalate (0.31 g, 0.58 mmol) in CH₂Cl₂(5 mL), second

generation hydroxyl group terminated PETIM dendrimer

(0.061 g, 0.058 mmol), and Et₃N (0.096 mL, 0.69 mmol) in

CHCl₃(15 mL) and the reaction was proceeded further as

given in the general method. Yield 5 267 mg (94%);

[a]_D²⁰5 230.60 (c 1.00, CHCl₃); FTIR (neat): m 3311, 2938,

G2NHCS₈

Oxalyl chloride (40 lL, 0.46 mmol), a solution of cholesteryl

hemisuccinate (0.185 g, 0.38 mmol) in CH₂Cl₂(5 mL), sec-

ond generation amine terminated PETIM dendrimer

(0.057 g, 0.038 mmol) and Et₃N (0.070 mL, 0.50 mmol) in

CHCl₃(15 mL) and the reaction was proceeded further as

described in the synthesis of G3OCS₁₆. Yield 5 0.19 g (95%);

[a]_D²⁰5 229.80 (c 1.00, CHCl₃); FTIR (neat): m 3311, 2938,

2867, 1730, 1656, 1550, 1469, 1374, 1167, 1108 cm^{21 1}H

;

NMR (400 MHz, CDCl₃): d 0.4–2.60 (br, 380 H, cholesteryl,

ACH₂A), 2.79 (br, 20 H, CH₂), 3.32 (m, 20 H, CH₂OCH₂), 3.77

(br, 16 H, CH₂), 4.70 (br, 16 H, COOCH₂), 5.37 (br, 8 H,

OACH), 5.76 (br, 8 H, @CH), 7.73–8.08 (br, 32 H, ArH); ¹³C

NMR (100 MHz, CDCl₃): d 167.7, 140.7, 139.5, 139.4, 131.5,

130.9, 128.9, 122.5, 121.7, 75.6, 71.8, 60.3, 56.7, 56.2, 50.1,

50.0, 42.3, 42.2, 39.7, 39.5, 39.0, 37.8, 37.3, 36.9, 36.6, 36.5,

36.2, 35.8, 33.4, 31.9, 31.8, 31.7, 31.5, 29.7, 28.2, 28.0, 27.5,

24.3, 23.9, 22.8, 22.5, 21.0, 19.3, 18.7, 11.8; Elemental analy-

sis. calcd for C₃₃₄H₅₀₀O₃₇N₆: C 77.27, H 9.71, N 1.62; found:

C 77.05, H 9.61, N 1.41.

2867, 1730, 1656, 1550, 1469, 1374, 1167, 1108 cm²^{1 1}H

;

NMR (400 MHz, CDCl₃): d 0.5–2.0 (br, 380 H, cholesteryl,

CH₂ACH₂ACH₂), 2.10–2.80 (m, 84 H, CH₂), 3.32 (m, 16 H,

NHACH₂), 3.45 (m, 52 H, OACH₂), 4.60 (br, 8 H, OACH),

5.35 (br, 8 H, @CH), 6.6 (br, 8 H, NH); ¹³C NMR (100 MHz,

CDCl₃): d 172.4, 171.7, 139.7, 122.6, 74.2, 74.0, 68.7, 68.3,

56.7, 56.2, 50.0, 42.3, 39.7, 39.5, 38.0, 37.1, 36.9, 36.6, 36.2,

35.8, 31.9, 31.8, 30.9, 30.3, 29.9, 29.4, 28.2, 28.0, 27.7, 27.2,

26.2, 25.2, 24.3, 23.9, 22.8, 22.5, 21.0, 19.3, 18.7, 11.8; Ele-

mental analysis. calcd for C₃₂₆H₅₅₆O₃₇N₁₄: C 74.38, H 10.65,

N 3.73; found: C 74.28, H 10.55, N 3.56.

G3OCP₁₆

G3NHCS₁₆

Oxalyl chloride (37 lL, 0.44 mmol), a solution of cholesteryl

hemiphthalate (0.23 g, 0.43 mmol) in CH₂Cl₂(5 mL), a solu-

tion of third generation hydroxyl group terminated PETIM

dendrimer (0.053 g, 0.022 mmol), and Et₃N (0.067 mL, 0.48

mmol) in CH₂Cl₂(15 mL). and the reaction was proceeded

further as given in the general method. Yield 5 0.21 g

(92%); [a]_D²⁰5 227.6 (c 1.00, CHCl₃). ¹H NMR (400 MHz,

CDCl₃): d 0.5–2.0 (band, 784 H, cholesteryl, CH₂ACH₂ACH₂),

2.43 (m, 32 H, CH₂), 2.80–3.30 (br, 60 H, ACH₂A), 3.39 (m,

32 H, ACH₂AOACH₂), 3.60 (m, 16 H, NCH₂), 4.33 (br, 16 H,

OACH₂), 4.77 (br, 16 H, OACH), 5.36 (br, 16 H, @CH), 7.35–

7.70 (m, 64 H, ArH); ¹³C NMR (100 MHz, CDCl₃): d 167.9,

139.7, 139.3, 131.7, 130.5, 128.9, 128.5, 128.1, 122.9, 122.5

74.8, 56.6, 56.1,49.9, 42.2, 39.6, 39.4, 37.9, 36.6, 36.1, 35.7,

31.9, 31.7, 28.1, 27.9, 24.2, 23.8, 22.7, 22.5, 21.0, 19.3, 18.7,

11.9; Elemental analysis calcd. for C₆₈₆H₁₀₃₆O₇₇N₁₄: C 76.92,

H 9.75, N 1.83; found: C 77.02, H 9.54, N 1.61.

Oxalyl chloride (40 lL, 0.47 mmol), a solution of cholesteryl

hemisuccinate (0.19 g, 0.39 mmol) in CH₂Cl₂(5 mL), a solu-

tion of third generation amine terminated PETIM dendrimer

(0.065 g, 0.019 mmol), and Et₃N (0.070 mL, 0.5 mmol) in

CH₂Cl₂(15 mL) and the reaction was proceeded further as

described in the synthesis of G3OCS₁₆. Yield 0.21 g (95%);

[a]_D²⁰5 226.46 (c 1.00, CHCl₃). FTIR (neat): m 3317, 2938,

2856, 1732, 1653, 1563, 1464, 1375, 1256, 1174, 1120; ¹H

NMR (400 MHz, CDCl₃): d 0.5–2.1 (band, 772 H, cholesteryl,

CH₂ACH₂ACH₂), 2.20–2.70 (m, 180 H, CH₂ACH₂ACH₂NH,

NACH₂, COACH₂ACH₂ACO), 3.32 (m, 32 H, NHACH₂), 3.45

(m, 116 H, ACH₂AOACH₂), 4.60 (br, 16 H, OACH), 5.35 (br,

16 H, @CH), 6.4 (br, 16 H, NH); ¹³C NMR (100 MHz, CDCl₃):

d 172.4, 171.4, 139.7, 122.7, 74.3, 69.3, 56.7, 56.2, 50.9, 50.8,

50.0, 42.3, 39.8, 39.5, 38.1, 37.8, 37.0, 36.6, 36.2, 35.8, 31.9,

31.6, 31.4, 31.0, 30.5, 30.2, 29.9, 29.7, 29.5, 29.3, 29.1, 28.2,

28.0, 27.8, 27.6, 27.5, 26.2, 24.3, 23.9, 22.8, 22.6, 22.5, 21.0,

12

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17 J. Sun, Y. Lin, J. Polym. Sci. Part A: Polym. Chem. 2013, 51, 71.

19.3, 18.7, 14.1, 11.9. Elemental analysis calcd. for

C₆₇₀H₁₁₄₈O₇₇N₃₀: C 74.12, H 10.66, N 3.87; found: C 74.31, H

10.46, N 3.59.

18 L. L. Lai, J. W. Hsieh, K. L. Cheng, S. H. Liu, J. J. Lee, H,F.

Hsu, Chem. Eur. J. 2014, 20, 5160.

19 P. Kumar, D. S. S. Rao, S. K. Prasad, N. Jayaraman, Poly-

mer. 2016, 86, 98.

Instrumentation

The mesophase was characterized on untreated glass plate

using a POM fitted with a hot stage. The transition tempera-

tures and enthalpies were determined by DSC with nitrogen

purging at a heating- cooling rate of 10 8C min²¹for three

cycles. From the second cycle, the maxima of the peaks were

taken as transition temperatures and the mid-point of the

heat capacity change were taken as glass transition tempera-

ture. Variable-temperature powder XRD studies were carried

out with samples filled in Lindemann capillaries. The appara-

tus essentially involved a high-resolution X-ray powder dif-

fractometer (PANalytical X’Pert PRO) with a high-resolution

fast detector PIXCEL.⁵⁸

20 B. Donnio, D. Guillon, Adv. Polym. Sci. 2006, 201, 45–155.

ꢀ

21 S. Ferin, F. Cameral, R. Ziessel, J. Barbera, R. Deschenaux,

Chem. Mater. 2009, 21, 3950.

22 (a) B. I. Ostrovskii, S. N. Sulyanov, N. I. Boiko, V. P.

Shibaev, S. B. Astafev, L. G. Yanusova, W. H. de Jeu, Eur.

Phys. J. E. 2013, 36, 134; (b) E. V. Agina, N. I. Boiko, R. M.

Richardson, B. I. Ostrovskii, V. P. Shibaev, E. A. Rebrov, A. M.

Muzafarov, Polym. Sci. Ser. A 2007, 49, 412.

ꢀ

23 R. Martin-Rapun, M. Marcos, A. Omenat, J. Barbera, P.

Ramero, J. L. Serrano, J. Am. Chem. Soc. 2005, 127, 7397.

24 (a) S. A. Ponomarenko, E. A. Rebrov, A. Y. Bobrovsky, N. I.

Boiko, A. M. Muzafarov, V. P. Shibaev, Liq. Cryst. 2006, 33,

1497; (b) N. I. Boiko, I. D. Leshchiner, E. V. Agina, R.

Richardson, V. P. Shibaev, Polym. Sci. Ser. A 2011, 53, 645.

25 O. Haba, K.-I. Okuyama, H. Osawa, K. Yonetake, Liq. Cryst.

2005, 32, 633.

ACKNOWLEDGMENTS

€

26 M. W. P. L. Baars, S. H. M. Sontjens, H. M. Fischer, H. W. I.

Peerlings, E. W. Meijer, Chem. Eur. J. 1998, 4, 2256.

The authors are grateful to Department of Science and Technol-

ogy, New Delhi, for a financial support of the work. P. Kumar

acknowledges Council of Scientific and Industrial Research,

New Delhi, for a research fellowship.

27 L. Pastor, J. Barbera, M. McKenna, M. Marcos, R. Martin-

Rapun, J. L. Serrano, G. R. Luckhurst, A. Mainal, Macromole-

cules. 2004, 37, 9386.

€^

28 (a) R. Elsauer, G. H. Mehl, J. W. Goodby, M. Veith, Angew.

Chem. Int. Ed. 2001, 40, 2688–2690; (b) I. M. Saez, J. W.

Goodby, Chem. Eur. J. 2003, 9, 4869.

REFERENCES AND NOTES

ꢀ

29 B. Donnio, J. Barbera, R. Gimenez, D. Guillon, M. Marcos, J.

1 J.-M. Lehn, Supramolecular Chemistry: Concepts and Per-

spectives; Wiley-VCH: Weinheim, 1995.

L. Serrano, Macromolecules. 2002, 35, 370.

30 L. Gehringer, C. Bourgogne, D. Guillon, B. Donnio, J. Mater.

Chem. 2005, 15, 1696.

2 K. Ariga, T. Kunitake, Supramolecular Chemistry - Fundamen-

tals and Applications; Springer-Verlag: Berlin, 2006.

31 (a) T. R. Krishna, N. Jayaraman, J. Org. Chem. 2003, 68,

9694; (b) G. Jayamurugan, N. Jayaraman, Tetrahedron 2006,

62, 9582.

3 B. M. Rosen, C. J. Wilson, D. A. Wilson, M. Peterca, M. R.

Imam, V. Percec, Chem. Rev. 2009, 109, 6275.

4 C. Tschierske, J. Mater. Chem. 2001, 11, 2647.

32 I. Dierking, Textures of Liquid Crystals; Wiley-VCH: Wein-

heim, 2003.

5 G. R. Newkome, C. Shreiner, Chem. Rev. 2010, 110, 6338.

33 C. Jana, G. Jayamurugan, R. Ganapathy, P. K. Maiti, N.

Jayaraman, A. K. Sood, J. Chem. Phys. 2006, 124, 204719.

6 A.- M. Caminade, C. O. Turrin, R. Laurent, A. Quali, B. D.

Nicot, Dendrimer: Towards Catalytic, Material and Biomedical

Uses; Wiley-VCH: Weinheim, 2011.

ꢀ

34 J.-M. Rueff, J. Barbera, B. Donnio, D. Guillon, M. Marcos, J.

L. Serrano, Macromolecules. 2003, 36, 8368.

7 N. E. Domracheva, V. I. Morozov, M. S. Gruzdev, R. A.

Manapov, A. V. Pyataev, G. Lattermann, Macromol. Chem.

Phys. 2010, 211, 791.

35 B. M. Craven, G. T. DeTitta, J. Chem. Soc. Perkin Trans.

1976, 2, 814.

8 A. Yoshizawa, Polym. J. 2012, 44, 490.

36 A.-M. Levelut, J. Phys. Lett. 1984, 45, L-603.

ꢀ

9 M. Marcos, R. Martın-Rapun, A. Omenat, J. L. Serrano,

37 See for example: Liquid Crystals Materials Design and Self-

Assembly; C. Tschierske, Ed.; Springer-Verlag: Berlin, 2012; pp 41.

Chem. Soc. Rev. 2007, 36, 1889.

10 M. Yoshio, R. Konishi, T. Sakamoto, T. Kato, New J. Chem.

2013, 37, 143.

38 B. Soberats, M. Yoshio, T. Ichikawa, X. Zeng, H. Ohno, G.

Ungar, T. Kato, J. Am. Chem. Soc. 2015, 137, 13212.

11 B. Donnio, S. Buathong, I. Bury, D. Guillon, Chem. Soc. Rev.

2007, 36, 1495.

39 T. Sakurai, Y. Tsutsui, K. Kato, M. Takata, S. Seki, J. Mater.

Chem. C 2016, 4, 1490.

12 S. Hernandez-Ainsa, E. Fedeli, J. Barbera, M. Marcos, T.

Sierra, J. L. Serrano, Soft Matter. 2014, 10, 281.

40 K. Tanabe, T. Yasuda, M. Yoshio, T. Kato, Org. Lett. 2007, 9, 4271.

41 K. Kishikawa, S. Nakahara, Y. Nishikawa, S. Kohmoto, M.

Yamamoto, J. Am. Chem. Soc. 2005, 127, 2565.

ꢀ

13 J. D. Barrio, R. M. Tejedor, L. S. Chinelatto, C. Sanchez, M.

~

Pinol, L. Oriol, Chem. Mater. 2010, 22, 1714.

ꢀ

42 S. Hernandez-Ainsa, J. Barbera, M. Marcos, J. L. Serrano,

14 T. Felekis, D. Tsiourvas, L. Tziveleka, C. M. Paleos, Liq.

Cryst. 2005, 32, 39.

Soft Matter. 2011, 7, 2560.

~

43 A. van-Quynh, D. Filip, C. Cruz, P. J. Sebastiao, A. C.

15 O. Haba, D. Hiratsuke, T. Shiraiwa, T. Koda, K. Yonetake, Y.

Momoi, K. Furuta, Mol. Cryst. Liq. Cryst. 2013, 574, 84.

Ribeiro, J.-M. Rueff, M. Marcos, J. L. Serrano, Eur. Phys. J. E.

2005, 18, 149.

16 A. Bobrovsky, N. I. Boiko, V. Shibaev, Polymer. 2015, 56,

263.

44 L.-L. Lai, S.-J. Hsu, H.-C. Hsu, S.-W. Wang, K.-L. Cheng, C.-J.

Chen, T.-H. Wang, H.-F. Hsu, Chem. Eur. J. 2012, 18, 6542.

WWW.MATERIALSVIEWS.COM

JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2017, 00, 000–000

13

JOURNAL OF

POLYMER SCIENCE

ARTICLE

WWW.POLYMERCHEMISTRY.ORG

€

45 K. Lorenz, H. Frey, B. Stuhn, R. Mulhaupt, Macromoleules.

1997, 30, 6860.

52 S. A. Ponomarenko, N. I. Boiko, V. P. Shibaev, R. M.

Richardson, I. J. Whitehouse, E. A. Rebrov, A. M. Muzafarov,

Macromolecules. 2000, 33, 5549.

€

46 M. W. P. L. Baars, S. H. M. Sontjens, H. M. Fischer, H. W. I.

Peerlings, E. W. Meijer, Chem. Eur. J. 1998, 4, 2456.

53 D. Tsiourvas, T. Felekis, Z. Sideratou, C. M. Paleos, Macro-

molecules. 2002, 35, 6466.

47 K. Yonetake, T. Masuko, T. Morishita, K. Suzuki, M. Ueda, R.

Nagahata, Macromolecules. 1999, 32, 6578.

ꢀ

54 M. D. McKenna, J. Barbera, M. Marcos, J. L. Serrano, J. Am.

Chem. Soc. 2005, 127, 619.

ꢀ

48 (a) J. Barbera, A. C. Garces, N. Jayaraman, A. Omenat, J. L.

ꢀ

Serrano, J. F. Stoddart, Polym. Prep. Am. Chem. Soc. Div.

55 R. Martın-Rapun, M. Marcos, A. Omenat, J.-L. Serrano, G. R.

ꢀ

Polym. Chem. 1999, 40, 488; (b) J. Barbera, A. C. Garces, N.

Jayaraman, A. Omenat, J. L. Serrano, J. F. Stoddart, Adv.

Mater. 2001, 13, 175.

Luckhurst, A. Mainal, Chem. Mater. 2004, 16, 4969.

56 (a) L. Gehringer, C. Bourgogne, D. Guillon, B. Donnio, J.

Am. Chem. Soc. 2004, 126, 3856; (b) J. Wolska, J. Mieczkowski,

D. Pociecha, S. Buathong, B. Donnio, D. Guillon, E. Gorecka,

Macromolecules. 2009, 42, 6375.

ꢀ

49 M. Marcos, R. Gimenez, J. L. Serrano, B. Donnio, B.

Heinrich, D. Guillon, Chem. Eur. J. 2001, 7. 1006.

ꢀ

50 J.-M. Rueff, J. Barbera, M. Marcos, A. Omenat, R. Martin-

57 A. Belaissaoui, I. M. Saez, S. J. Cowling, J. W. Goodby,

Macromolecules. 2013, 46, 1268.

ꢀ

Rapun, B. Donnio, D. Guillon, J. L. Serrano, Chem. Mater.

2006, 18, 249.

58 D. S. Shankar Rao, M. Vijay Kumar, S. Krishna Prasad, U. S.

Hiremath, M. Sarvamangala, S. Basavaraja, J. Mater. Chem. C.

2013, 1, 7488.

€

51 K. Lorenz, D. Holter, H. Frey, B. Stuhn, Polym. Mater. Sci.

Eng. 1997, 77, 168.

14

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Connector type-controlled mesophase structures in poly(propyl ether imine) dendritic liquid crystals of identical dendrimer generations

DOI: 10.1002/pola.28709

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