Preparation of mesogen-functionalized dendrimers for second-order nonlinear optics

Article abstract of DOI:10.1021/ma010290j

Liquid crystalline dendrimers with peripheral mesogen-containing units have been prepared. Multistep synthesis with several selective reactions was used in the preparation of the mesogen-containing molecules, 4″-[10-(hydroxycarbonyl)decyloxy]phenyl 4-[4′-

Full text of DOI:10.1021/ma010290j

Macromolecules 2002, 35, 1663-1671
1663
Preparation of Mesogen-Functionalized Dendrimers for Second-Order
Nonlinear Optics
P . Bu sson , J . O2 r tegr en , H. Ih r e, U. W. Ged d e, a n d A. Hu lt*
Department of Polymer Technology, Royal Institute of Technology, SE-100 44 Stockholm, Sweden
G. An d er sson
Department of Physics, Chalmers University of Technology, SE-412 96 Go¨teborg, Sweden
A. Er ik sson a n d M. Lin d gr en
IFM-Chemical Physics, Linko¨ping University, SE-581 83 Linko¨ping, Sweden
Received February 19, 2001; Revised Manuscript Received November 5, 2001
ABSTRACT: Liquid crystalline dendrimers with peripheral mesogen-containing units have been prepared.
Multistep synthesis with several selective reactions was used in the preparation of the mesogen-containing
molecules, 4′′-[10-(hydroxycarbonyl)decyloxy]phenyl 4-[4′-(2-(R)-octyloxy)-3′-nitrophenyl]benzoate and 4′′-
[10-(hydroxycarbonyl)decyloxy]biphenyl 4-[4′-(2-(R)-octyloxy)-3′-nitrophenyl]benzoate. Both molecules
possessed an electron-accepting nitro group placed perpendicular to the long axis of the molecules in
order to enhance the nonlinear optical activity. A second generation hydroxyl functional aliphatic
dendrimer based on the dihydroxy acid, 2,2-bis(hydroxymethyl)propionic acid, was used as dendritic
scaffold and was subsequently functionalized with the aforementioned groups. The purity and structure
of the two liquid crystalline dendrimers were determined by 1H NMR spectroscopy, size exclusion
chromatography, and elemental analysis. The synthesis of both the mesogen-containing units and the
liquid crystalline dendrimers is described in detail. Investigation of the liquid crystalline properties of
the materials by differential scanning calorimetry and optical microscopy showed that they exhibited
different mesophases, including the chiral smectic C phase. Ferroelectric switching was observed in this
tilted phase, and electrooptical properties, including tilt angle and spontaneous polarization measurements,
were investigated. Finally, the nonlinear optical properties of one of the materials were preliminary
characterized.
In tr od u ction
During the past decade, there has been a growing
effort in developing organic and polymeric materials for
second-order nonlinear optics (NLO).1 However, a com-
mon problem with organic and polymeric materials is
their low degree of polar order. Liquid crystalline (LC)
materials have shown to be promising candidates for
the preparation of NLO materials. Unfortunately, al-
though they can form highly ordered phases, they
possess an intrinsic quadrupolar order but in general
not a dipolar one.2 In chiral smectic C (SmC*) liquid
crystals or ferroelectric liquid crystals (FLCs), however,
the molecular symmetry allows a local dipolar order
perpendicular to the tilt plane3 which can be extended
to the whole sample either by orienting all the molecular
dipoles in an external electric field or by surface
constraints like the one used in surface-stabilized FLCs
(SSFLCs).4 Early experiments performed on a classic
FLC molecule, (S)-2-methylbutyl N-(4-n-decyloxyben-
zylidene)-4′-aminocinnamate (DOBAMBC),3 confirmed
the potential use of FLCs for nonlinear optics, although
the NLO susceptibility turned out to be extremely
small.5 Walba and co-workers6 were the first to realize
that FLCs with enhanced NLO effects could be obtained
if a NLO chromophore was aligned in the direction of
the polarization, perpendicular to the long axis of the
molecule. Therefore, they synthesized a low molecular
weight FLC I (Figure 1), in which an electron-accepting
nitro group was introduced in the ortho position of the
F igu r e 1. Ferroelectric liquid crystals designed for nonlinear
optics (I and II) and the NLO active part 4-((R or S)-1-
methylalkoxy)-3-nitrophenyl (III).
chiral moiety, with the specific purpose of increasing
the second-order optical nonlinearity. This compound
showed a second harmonic generation (SHG) coefficient
(d22) of 0.6 pm/V.7 In 1993, Schmitt et al.,8 in an attempt
to increase the SHG signal, synthesized a four-ring
compound in which an electron-donating amino group
was introduced in the molecule in the para position to
the electron-accepting nitro group (Figure 1, compound
II). Their NLO properties were studied, and a large
SHG coefficient (d22) of 5pm/V was obtained.9 Based on
the work of Walba and Schmitt, several liquid crystal-
* To whom all correspondence should be addressed.
10.1021/ma010290j CCC: $22.00 © 2002 American Chemical Society
Published on Web 01/26/2002

1664 Busson et al.
Macromolecules, Vol. 35, No. 5, 2002
line systems containing the NLO moiety III, 4-((R or
S)-1-methylalkoxy)-3-nitrophenyl, have been prepared.
Thus, dimers,10 dimesogenic oligosiloxanes,11 cyclic oli-
gomers,12 side-chain polymers,8b,13 and main-chain poly-
mers,14 including III, have been synthesized for NLO
purposes. In addition, partially cross-linked15 and densely
cross-linked16 pyroelectric polymers, based on ferroelec-
tric acrylate monomers of type I, have been prepared
by our group in order to improve the mechanical
properties and long-term stability of the NLO materials.
Lately, thermotropic LC materials with dendritic
architecture have received a lot of attention, and both
LC hyperbranched polymers17 and LC dendrimers18
have been prepared by several groups. Dendritic liquid
crystalline polymers (DLCPs) offer new synthetic and
structural alternatives to side-chain and main-chain
liquid crystalline polymers. Recently, we presented the
preparation of ferroelectric LC dendrimers19 based on
aliphatic dendritic scaffolds functionalized with me-
sogen-containing units. Although there are some ex-
amples of hyperbranched polymers20 and dendrimers21
with NLO properties in the literature, to our knowledge,
no other ferroelectric dendritic liquid crystalline systems
designed for NLO purposes have been prepared so far.
Herein, we report the functionalization of a second
generation dendritic aliphatic polyester, bearing 12
hydroxyl groups on its surface, with two different
mesogen-containing units incorporating the NLO active
group III. The preparation and characterization of both
the mesogen-containing units and the mesogen-func-
tionalized dendrimers are described in detail. In addi-
tion, the liquid crystalline properties of the dendrimers
are reported, and initial results concerning the elec-
trooptical and nonlinear optical properties are shortly
presented.
generation dendrimer. For these reasons, G#2-(OH)12
was used as dendritic scaffold in this study.
(b) Syn th esis of th e Mesogen -Con ta in in g Un its.
Two different molecules were prepared, both possessing
a carboxylic acid terminal group required for the
coupling to the dendritic scaffold. The mesogenic core
of 4′′-[10-(hydroxycarbonyl)decyloxy]phenyl 4-[4′-(2-(R)-
octyloxy)-3′-nitrophenyl]benzoate (10a ) consists of a
three-aromatic-ring system, whereas 4′′-[10-(hydroxy-
carbonyl)decyloxy]biphenyl 4-[4′-(2-(R)-octyloxy)-3′-ni-
trophenyl]benzoate (10b) contains four aromatic rings.
The mesogen-functionalized dendrimer Nitr oBG#2 is
therefore expected to show higher phase transition
temperatures than Nitr oAG#2.8 The synthesis of 10a
and 10b involves several selective reactions, described
in detail in the next paragraph.
The synthetic pathways used in the preparation of
10a and 10b are shown in Scheme 1.
Compounds 10a and 10b were synthesized according
to the same procedure. Therefore, only the preparation
of 10b is described in detail. The synthesis of 10b was
divided into two parts 4 and 8b, which were coupled in
a low-temperature esterification procedure using N,N′-
dicyclohexylcarbodiimide (DCC) and 4-(dimethylamino)-
pyridine (DMAP) to yield the intermediate 9b. Com-
pound 4 was synthesized in four steps starting by the
protection via esterification of 4′-hydroxy-4-biphenyl-
carboxylic acid with ethanol to give 1. Nitration of the
para-substituted phenol 1 using a two-phase system
described by Keller gave exclusively the ortho-nitrated
compound 2.23 2 was etherified by (S)-2-octanol in the
presence of diethylazodicarboxylate (DEAD) and tri-
phenylphosphine (TPP) using the Mitsunobu reaction
to yield the intermediate 3.24 This step proceeds by in-
version of configuration of the chiral center, changing
the S-alcohol to a R-ether. Compound 3 was subsequent-
ly deprotected by saponification with KOH to give 4.
Resu lts a n d Discu ssion
Syn th esis. Both mesogen-functionalized dendrimers
were prepared according to a general strategy described
earlier.18a,19 Their preparation is divided into three
parts: (a) synthesis of the dendritic scaffold, G#2-(OH)12,
with 12 terminal hydroxyl groups; (b) preparation of the
mesogen-containing units possessing a carboxylic acid
terminal group; (c) coupling of the respective mesogen-
containing units to the dendritic scaffold via acid
chloride reaction yielding the mesogen-functionalized
dendrimers Nitr oAG#2 and Nitr oBG#2.
Both mesogen-containing units, 4′′-[10-(hydroxycar-
bonyl)decyloxy]phenyl 4-[4′-(2-(R)-octyloxy)-3′-nitro-
phenyl]benzoate (10a ) and 4′′-[10-(hydroxycarbonyl)-
decyloxy]biphenyl 4-[4′-(2-(R)-octyloxy)-3′-nitrophenyl]-
benzoate (10b), incorporating the NLO active group III,
are expected to exhibit a chiral smectic C mesophase
and promising nonlinear optical properties.6,8
(a ) Syn th esis of th e Hyd r oxyl F u n ction a l Den -
d r im er . The second generation hydroxyl functional
aliphatic dendrimer, G#2-(OH)12, was prepared accord-
ing to a previously described procedure.22 In our previ-
ous work on ferroelectric LC dendrimers,19b we under-
lined that the electrooptical properties of the materials
were independent of the generation number. However,
electrooptical measurements were easier to perform on
ferroelectric LC dendrimers of higher generation (gen-
erations 2 and 3) as compared to the first generation
LC dendrimer. Moreover, the preparation of the third
generation aliphatic dendritic scaffold requires more
synthetic steps than the preparation of the second
The synthesis of the other half of the molecule was
also divided into two parts 6 and 5. 4,4′-Dihydroxybi-
phenyl was mono protected with benzyl bromide under
basic conditions to give 6. The tert-butyl ester 5 was
prepared by reaction of 11-bromoundecanoic acid with
isobutylene according to the procedure described by
Anderson and Callahan.25 Attempts to prepare 5 from
11-bromoundecanoic acid and tert-butyl alcohol using
standard esterification procedures failed to give the
desired compound in reasonable yields. 7b was obtained
by etherification of 6 with 5 in the presence of potassium
carbonate and a catalytic amount of 18-crown-6. This
reaction proceeded without affecting the tert-butyl ester
group of 5. Finally, the benzyl ether protective group of
7b was removed by catalytic hydrogenolysis to yield
compound 8b. This method did not affect the ester
function in 7b. 9b was obtained by coupling 4 with 8b,
and the tert-butyl group was removed by acid-catalyzed
hydrolysis using trifluoroacetic acid to finally give the
meson-containing unit 10b.26 This reaction proceeded
without any adverse effects on the central ester bond
and other functional groups. 10a was prepared in a
similar way. However, commercially available 4-benzyl-
oxyphenol was used instead of 6.
(c) Syn th esis of th e Mesogen -F u n ction a lized
Den d r im er s (Sch em e 2). These compounds were
prepared according to a previously described method.19
Coupling of the mesogen-containing units to the den-
dritic scaffolds was performed via acid chloride reaction
in the presence of triethylamine (TEA) and DMAP.

Macromolecules, Vol. 35, No. 5, 2002
Mesogen-Functionalized Dendrimers 1665
Sch em e 1. Syn th esis of Mesogen -Con ta in in g Un its 10a a n d 10b a n d Its Acid Ch lor id e Der iva tives 11a a n d 11b
Compound 10a (10b) was reacted with oxalyl chloride
in the presence of a catalytic amount of DMF to give
the corresponding acid chloride 11a (11b ). For every
terminal hydroxyl function, a 1.15 molar excess amount
of 11a (11b) was used to ensure full substitution of the
second generation dendritic scaffold. The products,
Nitr oAG#2 and Nitr oBG#2, were highly soluble in
dichloromethane, chloroform, and THF but insoluble in
methanol, ethanol, and water. The final purification was
performed by precipitation of a solution of the dendrimer
in dichloromethane into a large volume of methanol.
This procedure was repeated until no starting mesogen-
containing unit was detected by H NMR spectroscopy.
Both materials were isolated as slightly yellow powders.
1
Gen er a l Ch a r a cter iza tion . The chemical structures
1
of Nitr oAG#2 and Nitr oBG#2 were confirmed by H
NMR, size exclusion chromatography (SEC), and el-
emental analysis.
1H NMR spectroscopic data of all compounds were in
agreement with the structures proposed (see Experi-
1
mental Section). Figure 2 shows the H NMR spectrum
of Nitr oAG#2. The disappearance of the signal around

1666 Busson et al.
Macromolecules, Vol. 35, No. 5, 2002
Sch em e 2. Syn th esis of Mesogen -F u n ction a lized
Den d r im er s Nitr oAG#2 a n d Nitr oBG#2; Th e Cir cle
Rep r esen ts th e Den d r itic Sca ffold
to the differences in the hydrodynamic volume of linear
polystyrene standards and dendrimers. At present, it
is known that dendrimers, because of their compact
globular shape, have smaller hydrodynamic volume as
compared to that of linear polymers.27
Finally, additional information from elemental analy-
sis confirmed the high purity and individuality of
Nitr oAG#2 and Nitr oBG#2 (see Experimental Sec-
tion).
Liqu id Cr ysta llin e P r op er ties. The mesomorphic
and thermal properties of Nitr oAG#2 and Nitr oBG#2
were investigated by differential scanning calorimetry
(DSC) and optical microscopy. The transition temper-
atures of the compounds are listed in Table 2.
The DSC scans of the two materials showed a second-
order phase transition (glass transition) and two first-
order phase transitions. Both dendrimers exhibit liquid
crystalline behavior. As can be seen from the data in
Table 2, Nitr oBG#2 showed a higher glass transition
temperature (Tg) than Nitr oAG#2. Moreover, it ap-
peared that the temperature corresponding to the
transition between the liquid crystalline state and the
isotropic phase, TLC-I, was dramatically higher in the
case of Nitr oBG#2 than in the case of Nitr oAG#2. It
is known that an increase in the length of the mesogens
elevates both the transition from the glass to the liquid
crystalline phase and the transition from the liquid
crystalline to the isotropic phase. The upper transition
is usually affected more, and thereby the stability of the
liquid crystalline phase region is enhanced. Such changes
have also been observed in side-chain liquid crystalline
polyacrylates obtained from monomers similar to 10a
and 10b.8b
The optical textures of both compounds were exam-
ined by optical microscopy by preparing thin liquid
crystal films sandwiched between a clean glass slide and
a coverslip. In the case of Nitr oAG#2, coexistence of
focal-conic fan and homeotropic textures appeared at
82 °C when slowly cooling (0.5 °C/min) the sample from
the isotropic state. These macroscopic textures suggest
that a smectic A* (SmA*) phase is formed.28 Those
textures were unchanged until 69 °C. At this temper-
ature, a different liquid crystalline phase was formed.
The focal-conic fan and homeotropic textures were
replaced by broken focal-conic fan and sanded schlieren
textures. These optical textures are characteristic of the
chiral smectic C (SmC*) phase. According to these
observations, one can suppose that Nitr oAG#2 displays
the following phase transitions: g T SmC* T SmA* T
I. Nitr oBG#2 displayed comparable liquid crystalline
properties. However, as mentioned before, the phase
transition temperatures were higher. Parts a and b of
Figure 3 show the optical textures of Nitr oBG#2 in the
smectic A* and smectic C* phase, respectively. It is
important to note that, in both cases, large mono-
domains could be obtained between the glass plates by
slowly cooling the samples from the isotropic state.
3.6 ppm in the 1H NMR spectrum of Nitr oAG#2 (which
corresponds to the methylene group close to the hy-
droxyl function of the partially substituted dendrimer)
and the appearance of a signal at 4.22 ppm (which
corresponds to the methylene group f of the fully
substituted dendrimer) confirmed that all hydroxyl
groups were functionalized. Moreover, the lack of a
signal at 2.35 ppm in the 1H NMR spectrum (which
corresponds to the methylene group close to the car-
boxylic acid function in 10a ) proved that the final
product was not contaminated with no unreacted me-
sogen-containing unit. Instead, a signal appeared at 2.28
ppm (h ) in the fully substituted dendrimer. Finally, it
is important to note that the signals corresponding to
the mesogenic aromatic protons in Nitr oAG#2 shifted
upfield as compared to the corresponding signals in the
mesogen-containing unit 10a . Such subtle changes could
be attributed to the intramolecular and steric interac-
tions between the mesogen-containing units in the
dendrimer. Similar observations have been made in
other mesogen-functionalized dendrimers.19b
A similar 1H NMR spectrum was obtained for
Nitr oBG#2. However, it showed two additional signals
(two doublets) corresponding to the aromatic protons of
the fourth aromatic ring present in the mesogen.
SEC analyses showed that only narrow monodisperse
peaks were shown for both LC dendrimers. The obtained
data are reported in Table 1. The molar masses of
Nitr oAG#2 and Nitr oBG#2 determined by SEC were
not in agreement with the theoretical molar masses.
Such behavior is common for dendrimers and is related
Observation of both smectic A* and smectic C* phases
in the materials indicates that the mesogen-containing
units are not oriented radially around the dendritic
scaffold but form a cylinder-like structure with the
mesogens oriented upward and downward. A possible
model explaining the formation of smectic layers by such
dendritic structures has recently been proposed by
others and us.19b,29
To get additional information on the properties of the
SmC* phase displayed by Nitr oAG#2 and Nitr oBG#2,

Macromolecules, Vol. 35, No. 5, 2002
Mesogen-Functionalized Dendrimers 1667
F igu r e 2. 1H NMR spectrum of Nitr oAG#2.
Ta ble 1. SEC Da ta of th e LC Den d r im er s
in the LC dendrimers increases the viscosity of the
materials. Similar effects have also been observed in
side-chain and main-chain liquid crystalline polymers.
However, initial measurements were performed on the
films of best optical quality.
M(calcd)
(g/mol)
Mh (SEC)
(g/mol)
Mh (SEC)
(g/mol)
LC dendrimer
Mh /Mh
Nitr oAG#2
Nitr oBG#2
8898
9810
10 900
13 100
10 000
12 000
1.09
1.09
(a ) F er r oelectr ic P r op er ties. After filling of the
cells, the films were cooled to the temperature region
corresponding to the SmC* phase. Both LC dendrimers
showed ferroelectric switching. Typical current and
optical responses to an applied triangular electric field
in the SmC* phase of Nitr oBG#2 are depicted as an
example in Figure 4.
The materials were subjected to electrooptical studies,
including spontaneous polarization (Ps) and tilt angle
(θ) measurements. As we observed in ferroelectric
dendrimers previously reported,19b determination of the
electrooptical properties of the materials was not pos-
sible in the full temperature range of the SmC* phase.
Both spontaneous polarization and tilt angle measure-
ments were affected by the high viscosity of the materi-
als. In fact, measurements could only be performed in
a narrow temperature region under the transition from
the SmA* to the SmC* phase. Herein, we report the
maximal values obtained at a given reduced tempera-
ture Tr defined as
Ta ble 2. P h a se Tr a n sition Tem p er a tu r es of th e LC
Den d r im er sa
LC dendrimer
Tg (°C)
transition temp (°C)
Nitr oAG#2
Nitr oBG#2
34
70
SmC* 69 SmA* 82 I
SmC* 152 SmA* 208 I
a
Tg ) glass transition temperature, SmA* ) chiral smectic A
phase, SmC* ) chiral smectic C phase, I ) isotropic liquid.
the compounds were subjected to electrooptical studies.
Moreover, nonlinear optical properties of Nitr oBG#2
were preliminarily characterized.
F er r oelectr ic a n d Non lin ea r Op tica l P r op er ties.
The setups and methods used in the characterization
of the electrooptical and nonlinear optical properties of
the LC dendrimers have been previously described.30,31
Commercial 4 µm glass cells (EHC, J apan) with both
sides pretreated with indium tin oxide (ITO) and rubbed
polyimide were used in the determination of the afore-
mentioned properties. Each compound was heated to a
temperature region close the isotropization temperature
and was subsequently soaked into the glass cell by
capillary forces. It is worth noting that below the narrow
temperature region we used filling of the cells did not
occur, and above this temperature region wetting of the
surfaces was poor, leaving large air bubbles in the film.
In fact, the two materials turned out to be extremely
viscous, and good parallel-aligned samples were difficult
to obtain. The presence of a strong lateral polar group
Tr ) T - Ttr
(1)
where Ttr corresponds to the SmA*-SmC* transition
temperature in Nitr oAG#2 and Nitr oBG#2. T is the
temperature at which the spontaneous polarization and
tilt angle measurements were performed. Nitr oAG#2
showed a maximal spontaneous polarization Ps of 18 nC/
cm2 at Tr ) -6 °C. However, determination of the tilt

1668 Busson et al.
Macromolecules, Vol. 35, No. 5, 2002
of the samples. One alternative could be the use of glass
cells pretreated with a uniaxial Teflon monolayer.14a
Nitr oBG#2, which appeared as the most promising
material, was subjected to second-harmonic generation
(SHG) measurements.
(b ) Non lin ea r Op t ica l P r op er t ies. A film of
Nitr oBG#2 was prepared as mentioned above and was
cooled to 150 °C, where appropriate switching of the
ferroelectric liquid crystalline dendrimer was estab-
lished. A complete unwinding of the helix axis of the
ferroelectric phase could not be induced by surface forces
alone, and at low electric fields the switching originated
mainly from the deflection of the optic axis. This
deflection was attributed to the deformation of the helix.
Above a critical electric field (the threshold field) a sharp
shift in birefringence color occurred, and this was taken
as a confirmation of the unwinding of the helix axis
(ferroelectric switching mode). An electric field with an
amplitude of 6.5 V/µm (square wave, 5 Hz) gave a
purple-pink birefringence color at 150 °C (birefringence
0.14, ferroelectric switching mode) and a yellowish color
at 140 °C (birefringence 0.08, deformed helix switching
mode). The birefringence was estimated from the Mich-
el-Levy chart and was correct within approximately
20%. The lowering of the temperature was accompanied
by a sharp shift in birefringence color due to increased
viscosity, which caused the threshold field to increase
above 6.5 V/µm. After these findings, a static electric
field of 20 V/µm was applied at 150 °C, and the heating
of the oven was turned off. The birefringence color
changed from purple-pink at high temperature to light
blue-cyan on reaching room temperature (birefringence
0.18). The tilt angle was close to 45° at room tempera-
ture. The electric field was then removed, and the SHG
measurements were performed at room temperature
without external electric field.
F igu r e 3. (a, top) Polarized photomicrograph of Nitr oBG#2
in the SmA* at T ) 160 °C. (b, bottom) Polarized photomicro-
graph of Nitr oBG#2 in the SmC* at T ) 138 °C.
The unwound SmC* liquid crystal phase belongs to
the C2 symmetry group in which the second-order
reduced susceptibility tensor, d , contains four indepen-
dent coefficients under the assumption of Kleinman
symmetry conditions:32
d14
d16
0
0
0
0
d16 d22 d23
d14
d )
0
d23
0
d14
(2)
[
]
0
0
0
0
Values obtained for the second harmonic coefficients d23
and d16 were of the same order of magnitude, which is
in agreement with data reported on nitro-substituted
ferroelectric liquid crystals.33 d23 and d16 were estimated
to be 0.03 pm/V and 0.025 pm/V, respectively. The
inaccuracy of the given values of d23 and d16 due to the
weak contribution of d22 is approximately 20%. In
addition, the accuracy is decreased by the lack of
information on the dispersion relation of the refractive
index (inaccuracy estimated to 10%). However, from the
measurements and the analysis accounted for here, we
conclude that the d coefficients on the ferroelectric liquid
crystalline dendrimer Nitr oBG#2, as determined by
SHG, are d23 ) 0.03 ( 0.007 pm/V and d16 ) 0.025 (
0.006 pm/V.
F igu r e 4. Typical optical and current responses (bottom and
middle, respectively) to an applied triangular electric field (top)
in the SmC* phase of Nitr oBG#2 (T ) 143 °C).
angle of this material was not possible due to poor
alignment. The maximal spontaneous polarization ob-
tained for Nitr oBG#2 was 66 nC/cm2 at Tr ) -11 °C.
Moreover, a tilt angle value of 32.5° was obtained at Tr
) -36 °C. These initial results confirm that the pres-
ence of an electron-accepting nitro group placed per-
pendicular to the long axis of the molecule improves the
electrooptical properties of the materials. In fact, for the
second generation ferroelectric liquid crystalline den-
drimer reported previously (LC dendrimer without polar
nitro group in the mesogen), the value of the spontane-
ous polarization determined at Tr ) -11 °C was
approximately 25 nC/cm2.
Con clu sion s
Novel liquid crystalline dendrimers have been suc-
cessfully prepared. Two different mesogen-containing
units incorporating a nitro group perpendicular to their
long axis were synthesized and subsequently coupled
Further investigation of the electrooptical properties
may be achieved by realizing a better parallel alignment

Macromolecules, Vol. 35, No. 5, 2002
Mesogen-Functionalized Dendrimers 1669
17.66 mmol), and (S)-2-octanol (2.30 g, 17.66 mmol) in dry THF
(40 mL). The reaction mixture was stirred for 12 h at room
temperature, and the solvent was evaporated under vacuum.
The remaining product was purified by column chromatogra-
phy (silica gel, hexane/EtOAc as eluent) to give a yellow oil.
Yield: 5.91 g (84%). 1H NMR (CDCl3): δ ) 0.89 (t, 3H,
-(CH2)5CH3), 1.27-1.45 (m, 14H, -ArArOCH(CH3)CH2(CH2)4-
CH3 and -OCH2CH3), 1.60-1.88 (m, 2H, -ArArOCH-(CH3)-
CH2-), 4.40 (q, 2H, -OCH2CH3), 4.55 (m, 1H, -ArArOCH(CH3)-
CH2-), 7.14 (d, 1H, 5′-H), 7.60 (d, 2H, 3-H and 5-H), 7.74 (dd,
1H, 6′-H), 8.04 (d, 1H, 2′-H), 8.10 (d, 2H, 2-H and 6-H).
4-[3′-Nitr o-4′-(2-(R)-octyloxy)p h en yl]ben zoic Acid (4).
Compound 3 (7.04 g, 17.64 mmol) and KOH (85%) (2.32 g,
35.28 mmol) were stirred in ethanol (95%) (100 mL) under
reflux for 3 h. The solution was allowed to cool, acidified by
HCl (2 M), and poured into water. The mixture was extracted
three times with CH2Cl2, and the combined organic phases
were washed with water, dried over MgSO4, and filtered. The
solvent was evaporated to give a yellow solid. Yield: 6.41 g
(98%). 1H NMR (CDCl3): δ ) 0.88 (t, 3H, -(CH2)5CH3), 1.30-
1.50 (m, 11H, -ArArOCH(CH3)CH2(CH2)4CH3), 1.60-1.88 (m,
2H, -ArArOCH(CH3)CH2-), 4.57 (m, 1H, -ArArOCH(CH3)-
CH2-), 7.16 (d, 1H, 5′-H), 7.66 (d, 2H, 3-H and 5-H), 7.76 (dd,
1H, 6′-H), 8.07 (d, 1H, 2′-H), 8.19 (d, 2H, 2-H and 6-H).
ter t-Bu tyl 11-Br om ou n d eca n oa te (5). Isobutylene was
passed through a stirred solution of 11-bromoundecanoic acid
(10.6 g, 40 mmol) in CH2Cl2 (50 mL) containing concentrated
H2SO4 (0.5 mL) for 3 h at room temperature. After standing
an additional 12 h at room temperature, the solvent was
evaporated, and the remaining crude product was dissolved
in hexane and extracted with a mixture of saturated NaHCO3
and brine (1:1) and then with water. The organic phase was
dried over MgSO4 and filtered, and the solvent was evap-
to a second generation aliphatic dendrimer possessing
12 terminal hydroxyl groups. The two compounds,
Nitr oAG#2 and Nitr oBG#2, showed SmA* and SmC*
phases, and ferroelectric response was observed in the
SmC* phase. Moreover, the second harmonic generation
coefficients d23 and d16 of Nitr oBG#2 were measured
at room temperature, and the values obtained were 0.03
pm/V and 0.025 pm/V, respectively. Thus, mesogen-
functionalized dendrimers offer a new alternative for
the preparation of NLO active materials.
Exp er im en ta l Section
Gen er a l P r oced u r es. All the chemicals were purchased
from Aldrich, Lancaster, and Acros Organics and used without
further purification. 1H NMR spectra were recorded on a
Bruker AM 400 at 400 MHz using CDCl3 and DMSO-d6 as
solvents. The solvent signal was used as internal standard.
All purifications were performed by medium-pressure liquid
chromatography as described by Baeckstro¨m et al.,34 unless
specified. Size exclusion chromatography (SEC) measurements
were performed on a Waters GPC system using a solvent
delivery system (M510), automatic injector (WISP 710B), and
a differential refractometer (Waters 410) as a detector. All
measurements were made at 25 °C with a 10 µm mixed B
column from Polymer Labs. THF was used as eluent at a flow
rate of 1.0 mL/min. The molecular weights were computed
using a calibration curve constructed by linear polystyrene
standards with narrow molecular weight distribution. Elemen-
tal analysis was performed at the Analytische Laboratorien
GmbH, Lindlar, Germany. Transition temperatures were
determined by differential scanning calorimetry on a Mettler
Toledo DSC 820 under a nitrogen atmosphere (80 mL/min).
In all cases, heating and cooling rates were 10 °C/min. Optical
texture studies were made using a Leitz Ortholux POL BK II
polarized optical microscope equipped with a Mettler Hot Stage
FP 82 and a FP 80 central processor. Equipment and tech-
niques used to determine the electrooptical30 and the NLO31
properties have been previously described.
1
orated to afford a colorless oil. Yield: 11.56 g (90%). H NMR
(CDCl3): δ ) 1.27 (m, 12H, -CH2(CH2)6CH2-), 1.43 (s,
9H, -COOC(CH3)3), 1.55 (m, 2H, -OOCCH2CH2-), 1.84 (m,
2H, BrCH2CH2-), 2.19 (t, 2H, -OOCCH2-), 3.40 (t, 2H,
BrCH2-).
4′-Ben zyloxy-4-h yd r oxybip h en yl (6). 4,4′-Dihydroxybi-
phenyl (3.72 g, 20 mmol) and sodium hydroxide (0.8 g, 20
mmol) were dissolved in EtOH (30 mL), and the solution was
heated to boiling. Once the solution turned dark green, benzyl
bromide (3.42 g, 20 mmol) was added all at once, and the
reaction was refluxed for 3 h. The solution was allowed to cool
to ambient temperature and subsequently acidified with HCl
(2 M). The resulting precipitate was collected by filtration,
washed with EtOH, dried in a vacuum, and recrystallized from
a mixture of EtOH (95%)/acetic acid to give a white crystalline
powder. Yield: 4.25 g (77%). 1H NMR (DMSO-d6): δ ) 4.37
(bd, 1H, -ArArOH), 5.13 (s, 2H, -OCH2ArH), 6.81 (d, 2H, 3-H
and 5-H), 7.04 (d, 2H, 3′-H and 5′-H), 7.33-7.50 (m, 9H,
-OCH2ArH, 2-H, 6′-H, 2-H, and 6-H).
Syn th esis. Eth yl 4-(4′-Hyd r oxyp h en yl)ben zoa te (1). 4′-
Hydroxy-4-biphenylcarboxylic acid (5 g, 23.36 mmol), concen-
trated sulfuric acid (few drops), ethanol (99,5%) (41 mL), and
benzene (13 mL) were charged in a single-necked 250 mL
round-bottom flask equipped with a Dean-Stark trap. The
mixture was stirred under reflux for 36 h. After cooling to room
temperature, most of the solvent was evaporated under
vacuum. The residue was dissolved in CH2Cl2, and the organic
phase washed with aqueous NaHCO3 solution (10%) and then
with water. The organic phase was dried over MgSO4 and
filtered, and the solvent was evaporated to give a white
1
crystalline powder. Yield: 5.2 g (92%). H NMR (CDCl3): δ )
1.42 (t, 3H, -OCH2CH3), 4.42 (q, 2H, -OCH2CH3), 6.07 (b,
1H, -OH), 6.97 (d, 2H, 3′-H and 5′-H), 7.52 (d, 2H, 2′-H and
6′-H), 7.61 (d, 2H, 3-H and 5-H), 8.09 (d, 2H, 2-H and 6-H).
Eth yl 4-(3′-Nitr o-4′-h yd r oxyp h en yl)ben zoa te (2). Com-
pound 1 (3.3 g, 13.64 mmol) dissolved in Et2O (60 mL) and
CH2Cl2 (30 mL) was added to a stirred solution of NaNO3 (1.16
g, 13.64 mmol), water (20 mL), and concentrated HCl (10 mL).
Acetic anhydride (0.5 mL) was then added. The reaction
mixture was stirred for 4 h, and the organic layer was
separated off. The aqueous phase was extracted once with
Et2O. The combined etheral phases were extracted once with
brine, and the solvent was evaporated. The brown crystalline
product was dissolved in a minimum amount of EtOH (95%)
at 60 °C, and water was added to the mixture. The voluminous
precipitate was filtered off, washed well with water, and dried
under vacuum to give a yellow crystalline solid. Yield: 3.83 g
(98%). 1H NMR (CDCl3): δ ) 1.42 (t, 3H, -OCH2CH3), 4.42
(q, 2H, -OCH2CH3), 7.27 (d, 1H, 5′-H), 7.63 (d, 2H, 3-H and
5-H), 7.86 (dd, 1H, 6′-H), 8.13 (d, 2H, 2-H and 6-H), 8.37 (d,
1H, 2′-H), 10.25 (b, 1H, -ArArOH).
ter t-Bu t yl 11-(4-(Ben zyloxy)p h en yloxy)u n d eca n oa t e
(7a ). A mixture of 4-benzyloxyphenol (2.00 g, 10 mmol),
anhydrous K2CO3 (1.45 g, 10.5 mmol), and 18-crown-6 (cata-
lytic amount) in acetone (100 mL) was stirred at 60 °C for 1
h. To the resulting white suspension was added a solution of
compound 5 (3.53 g, 11 mmol) in dry acetone (10 mL), and
stirring was continued at 60 °C for 36 h. The mixture was
allowed to cool to room temperature, and the solvent was
evaporated. The residue was dissolved in CH2Cl2 and extracted
three times with brine. The organic phase was dried over
MgSO4 and filtered, and the solvent was evaporated. The
resulting brown powder was recrystallized from EtOH
(95%) to give white crystals. Yield: 4.05 g (92%). 1H NMR
(CDCl3): δ ) 1.29 (m, 12H, -CH2(CH2)6CH2-), 1.44 (s, 9H,
-COOC(CH3)3), 1.57 (m, 2H, -OOCCH2CH2-), 1.74 (q, 2H,
-ArOCH2CH2-), 2.20 (t, 2H, -OOCCH2-), 3.89 (t, 2H,
-ArOCH2-), 5.01 (s, 2H, -OCH2Ar), 6.81 (d, 2H, 2-H and 6-H),
6.90 (d, 2H, 3-H and 5-H), 7.37 (m, 5H, -OCH2ArH).
ter t-Bu tyl 11-(4′-(Ben zyloxy)bip h en yloxy)u n d eca n oa te
(7b). Compound 7b was synthesized according to the proce-
dure described for compound 7a starting from 6 and 5. Yield:
2.27 g (88%). 1H NMR (CDCl3): δ ) 1.29 (m, 12H, -CH2-
(CH2)6CH2-), 1.44 (s, 9H, -COOC(CH3)3), 1.55 (m, 2H,
Eth yl 4-[3′-Nitr o-4′-((R)-2-octyloxy)ph en yl]ben zoate (3).
TPP (4.63 g, 17.66 mmol) was added all at once to a stirred
solution of DEAD (3.07 g, 17.66 mmol), compound 2 (5.07 g,

1670 Busson et al.
Macromolecules, Vol. 35, No. 5, 2002
-OOCCH2CH2-), 1.79 (q, 2H, -ArArOCH2CH2-), 2.20 (t, 2H,
-OOCCH2-), 3.98 (t, 2H, -ArArOCH2-), 5.10 (s, 2H, -OCH2-
ArH), 6.94 (d, 2H, 3-H and 5-H), 7.03 (d, 2H, 3′-H and 5′-H),
7.33-7.50 (m, 9H, -OCH2ArH, 2′-H, 6′-H, 2-H, and 6-H).
2H, 3-H and 5-H), 7.77 (dd, 1H, 6′-H), 8.08 (d, 1H, 2′-H), 8.26
(d, 2H, 2-H and 6-H).
4′′-[10-(Hyd r oxyca r bon yl)d ecyloxy]bip h en yl 4-[4′-(2-
(R)-Octyloxy)-3′-n itr op h en yl]ben zoa te (10b). Compound
10b was synthesized according to the procedure described for
compound 10a . Yield: 2.15 g (98%). 1H NMR (CDCl3): δ )
0.89 (t, 3H, -(CH2)5CH3), 1.30-1.45 (m, 23H, -ArArOCH-
(CH3)CH2(CH2)4CH3 and -CH2(CH2)6CH2-), 1.52-1.85 (m,
6H, -ArArOCH(CH3)CH2-, -ArArOCH2CH2-, and HOO-
CCH2CH2-), 2.35 (t, 2H, HOOCCH2-), 4.00 (t, 2H, -ArAr-
OCH2-), 4.57 (m, 1H, -ArArOCH(CH3)CH2-), 6.97 (d, 2H,
3′′-H and 5′′-H), 7.17 (d, 1H, 5′-H), 7.28 (d, 2H, 3′′′-H and 5′′′-
H), 7.52 (d, 2H, 2′′-H and 6′′-H), 7.60 (d, 2H, 2′′′-H and 6′′′-H),
7.70 (d, 2H, 3-H and 5-H), 7.78 (dd, 1H, 6′-H), 8.09 (d, 1H,
2′-H), 8.29 (d, 2H, 2-H and 6-H).
4′′-[10-(Ch lor oca r bon yl)d ecyloxy]p h en yl 4-[4′-(2-(R)-
Octyloxy)-3′-n itr op h en yl]ben zoa te (11a ). Oxalyl chloride
(0.51 g, 4 mmol) was added drop by drop to a solution of 10a
(1.29 g, 2 mmol) and 3 drops of DMF in CH2Cl2 (20 mL). The
reaction was allowed to reach completion for 3 h at room
temperature. The excess of oxalyl chloride was removed on the
rotary evaporator to give a slightly yellow solid that was used
without any further purification. Yield: 1.33 g (quantitative).
1H NMR (CDCl3): δ ) 0.88 (t, 3H, -(CH2)5CH3), 1.30-1.45
(m, 23H, -ArArOCH(CH3)CH2(CH2)4CH3 and -CH2(CH2)6-
CH2-), 1.51-1.85 (m, 6H, -ArArOCH(CH3)CH2-, -ArOCH2-
CH2-, and ClOCCH2CH2-), 2.89 (t, 2H, ClOCCH2-), 3.96 (t,
2H, -ArOCH2-), 4.57 (m, 1H, -ArArOCH(CH3)CH2-), 6.93
(d, 2H, 3′′-H and 5′′-H), 7.13 (d, 2H, 2′′-H and 6′′-H), 7.17 (d,
1H, 5′-H), 7.68 (d, 2H, 3-H and 5-H), 7.77 (dd, 1H, 6′-H), 8.08
(d, 1H, 2′-H), 8.26 (d, 2H, 2-H and 6-H).
ter t-Bu tyl 11-[4-(Hydr oxy)ph en yloxy]u n decan oate (8a).
0.53 g of Pd/C (10%) was added to a solution of compound 7a
(5.3 g, 12.04 mmol) in EtOAc (150 mL). The round-bottom flask
was evacuated from air and filled with H2. The mixture was
stirred overnight at room temperature. The Pd/C was filtered
off and carefully washed with EtOAc. The filtrate was evapo-
rated to give white crystals. Yield: 4.11 g (98%). 1H NMR
(CDCl3): δ ) 1.28 (m, 12H, -CH2(CH2)6CH2-), 1.44 (s, 9H,
-COOC(CH3)3), 1.57 (m, 2H, -OOCCH2CH2-), 1.74 (m, 2H,
-ArOCH2CH2-), 2.20 (t, 2H, -OOCCH2-), 3.89 (t, 2H,
-ArOCH2-), 4.79 (b, 1H, -ArOH), 6.76 (s, 4H, 2-H, 6-H, 3-H,
and 5-H).
ter t-Bu tyl 11-[4′-(Hyd r oxy)bip h en yloxy]u n d eca n oa te
(8b). Compound 8b was synthesized according to the proce-
dure described for compound 8a . Yield: 1.85 g (99%). 1H NMR
(CDCl3): δ ) 1.29 (m, 12H, -CH2(CH2)6CH2-), 1.46 (s, 9H,
-COOC(CH3)3), 1.59 (m, 2H, -OOCCH2CH2-), 1.81 (q, 2H,
-ArArOCH2CH2-), 2.22 (t, 2H, -OOCCH2-), 3.98 (t, 2H,
-ArArOCH2-), 5.50 (b, 1H, -ArArOH), 6.89 (d, 2H, 3′-H and
5′-H), 6.94 (d, 2H, 3-H and 5-H), 7.42 (d, 2H, 2′-H and 6′-H),
7.45 (d, 2H, 2-H and 6-H).
4′′-[10-(ter t-Bu tyloxyca r bon yl)d ecyloxy]p h en yl 4-[4′-
(2-(R)-Octyloxy)-3′-n itr op h en yl]ben zoa te (9a ). A solution
of compound 8a (3.5 g, 10 mmol), compound 4 (3.71 g, 10
mmol), DCC (2.47 g, 12 mmol), and DMAP (0.12 g, 1 mmol) in
CH2Cl2 (50 mL) was stirred at room temperature for 24 h. The
reaction mixture was then cooled to -5 °C, and the white
precipitate of 1,3-dicyclohexylurea was filtered from the solu-
tion. The solvent was evaporated, and the resulting product
was purified by column chromatography (silica gel, hexane/
EtOAc as eluent) to give a yellow liquid crystalline material.
Yield: 5.06 g (72%). 1H NMR (CDCl3): δ ) 0.88 (t, 3H,
-(CH2)5CH3), 1.30-1.45 (m, 32H, -ArArOCH(CH3)CH2(CH2)4-
CH3, -CH2(CH2)6CH2-, and -COOC(CH3)3), 1.51-1.85 (m,
6H, -ArArOCH(CH3)CH2-, -ArOCH2CH2-, and -OOCCH2-
CH2-), 2.20 (t, 2H, -OOCCH2-), 3.96 (t, 2H, -ArOCH2-),
4.57 (m, 1H, -ArArOCH(CH3)CH2-), 6.93 (d, 2H, 3′′-H and
5′′-H), 7.13 (d, 2H, 2′′-H and 6′′-H), 7.17 (d, 1H, 5′-H), 7.68 (d,
2H, 3-H and 5-H), 7.77 (dd, 1H, 6′-H), 8.08 (d, 1H, 2′-H), 8.26
(d, 2H, 2-H and 6-H).
4′′-[10-(Ch lor oca r bon yl)d ecyloxy]bip h en yl 4-[4′-(2-(R)-
Octyloxy)-3′-n itr op h en yl]ben zoa te (11b). Compound 11b
was synthesized according to the procedure described for
compound 11a . Yield: 1.48
g
(quantitative). 1H NMR
(CDCl3): δ ) 0.89 (t, 3H, -(CH2)5CH3), 1.30-1.45 (m, 23H,
-ArArOCH(CH3)CH2(CH2)4CH3 and -CH2(CH2)6CH2-), 1.61-
1.85 (m, 6H, -ArArOCH(CH3)CH2-, -ArArOCH2CH2-, and
ClOCCH2CH2-), 2.89 (t, 2H, ClOCCH2-), 4.00 (t, 2H, -ArAr-
OCH2-), 4.57 (m, 1H, -ArArOCH(CH3)CH2-), 6.97 (d, 2H,
3′′-H and 5′′-H), 7.17 (d, 1H, 5′-H), 7.28 (d, 2H, 3′′′-H and 5′′′-
H), 7.52 (d, 2H, 2′′-H and 6′′-H), 7.60 (d, 2H, 2′′′-H and 6′′′-H),
7.70 (d, 2H, 3-H and 5-H), 7.78 (dd, 1H, 6′-H), 8.09 (d, 1H,
2′-H), 8.29 (d, 2H, 2-H and 6-H).
Nitr oAG#2. Compound 11a (1.294 g, 2 mmol), diluted in a
small amount of THF, was added dropwise to a solution of
G#2-(OH)12 dendrimer (0.195 g, 0.145 mmol), DMAP (0.106 g,
0.87 mmol), and TEA (0.264 g, 2.609 mmol) in THF (10 mL)
at 0 °C. After stirring at 0 °C for 1 h, the mixture was allowed
to reach ambient temperature and stirred for a further 24 h.
The solvent was then evaporated under vacuum, and the
brown residue was dissolved in CH2Cl2. The solution was first
extracted three times with saturated NaHCO3, then three
times with HCl (2 M), and finally with brine. The organic
phase was dried over MgSO4 and filtered, and the solvent was
evaporated. Finally, the solid was dissolved in a minimum
amount of CH2Cl2 and precipitated from methanol. The
precipitated powder was filtered off and dried under vacuum.
This procedure was repeated until no starting mesogen-
4′′-[10-(ter t-Bu tyloxyca r bon yl)d ecyloxy]bip h en yl 4-[4′-
(2-(R)-Octyloxy)-3′-n itr op h en yl]ben zoa te (9b). Compound
9b was synthesized according to the procedure described for
1
compound 9a starting from 8b and 4. Yield: 2.57 g (65%). H
NMR (CDCl3): δ ) 0.89 (t, 3H, -(CH2)5CH3), 1.30-1.45 (m,
32H, -ArArOCH(CH3)CH2(CH2)4CH3, -CH2(CH2)6CH2-, and
-COOC(CH3)3), 1.52-1.85 (m, 6H, -ArArOCH(CH3)CH2-,
-ArArOCH2CH2-, and -OOCCH2CH2-), 2.21 (t, 2H, -OOC-
CH2-), 4.00 (t, 2H, -ArArOCH2-), 4.57 (m, 1H, -ArArOCH-
(CH3)CH2-), 6.97 (d, 2H, 3′′-H and 5′′-H), 7.17 (d, 1H, 5′-H),
7.28 (d, 2H, 3′′′-H and 5′′′-H), 7.52 (d, 2H, 2′′-H and 6′′-H), 7.60
(d, 2H, 2′′′-H and 6′′′-H), 7.70 (d, 2H, 3-H and 5-H), 7.78 (dd,
1H, 6′-H), 8.09 (d, 1H, 2′-H), 8.29 (d, 2H, 2-H and 6-H).
4′′-[10-(Hyd r oxyca r bon yl)d ecyloxy]p h en yl 4-[4′-(2-(R)-
Octyloxy)-3′-n itr op h en yl]ben zoa te (10a ). Compound 9a
(4.78 g, 6.8 mmol) was dissolved in CH2Cl2 (20 mL) and cooled
in an ice bath, whereupon trifluoroacetic acid (TFA) (10.5 mL,
136 mmol) was added dropwise with stirring. The resulting
solution was stirred at this temperature for 1 h and allowed
to warm to ambient temperature over 12 h. The solution was
then concentrated in a vacuum, and the residual TFA was
removed by coevaporation with CH2Cl2 (10 mL) and benzene
(20 mL). Repeating twice this coevaporation procedure gave a
slightly yellow solid. Yield: 4.17 g (95%). 1H NMR (CDCl3): δ
) 0.88 (t, 3H, -(CH2)5CH3), 1.30-1.45 (m, 23H, -ArArOCH-
(CH3)CH2(CH2)4CH3 and -CH2(CH2)6CH2-), 1.51-1.85 (m,
6H, -ArArOCH(CH3)CH2-, -ArOCH2CH2-, and HOOCCH2-
CH2-), 2.35 (t, 2H, HOOCCH2-), 3.96 (t, 2H, -ArOCH2-),
4.57 (m, 1H, -ArArOCH(CH3)CH2-), 6.93 (d, 2H, 3′′-H and
5′′-H), 7.13 (d, 2H, 2′′-H and 6′′-H), 7.17 (d, 1H, 5′-H), 7.68 (d,
1
containing units were detected on by H NMR. Yield: 1.21 g
(68%). 1H NMR (CDCl3): δ ) 0.88 (t, 36H, -(CH2)5CH3), 1.24-
1.49 (m, 303H, -ArArOCH(CH3)CH2(CH2)4CH3, -CH2(CH2)6-
CH2-, and -CH3), 1.51-1.66 (m, 48H, -ArArOCH(CH3)CH2-
and -OOCCH2CH2-), 1.78 (m, 24H, -ArOCH2CH2-), 2.15
(s, 3H, -CH3), 2.28 (t, 24H, -OOCCH2-), 3.93 (t, 24H,
-ArOCH2-), 4.22 (q, 24H, -CH2C-), 4.40 (s, 12H, -CH2C-),
4.56 (m, 12H, -ArArOCH(CH3)CH2-), 6.90 (d, 24H, 3′′-H and
5′′-H), 6.98 (d, 6H, ArH), 7.11 (d, 30H, ArH, 2′′-H, and 6′′-H),
7.15 (d, 12H, 5′-H), 7.65 (d, 24H, 3-H and 5-H), 7.75 (d, 12H,
6′-H), 8.06 (s, 12H, 2′-H), 8.23 (d, 24H, 2-H and 6-H). Anal.
Calcd for C521H654O114N12: C, 70.24; H, 7.4; N, 1.89. Found:
C, 70.32; H, 7.60; N, 1.79.
Nitr oBG#2. This compound was prepared from 11b (1.446
g, 2 mmol), G#2-(OH)12 (0.195 g, 0.145 mmol), DMAP (0.106
g, 0.87 mmol), and TEA (0.264 g, 2.609 mmol) according to

Macromolecules, Vol. 35, No. 5, 2002
Mesogen-Functionalized Dendrimers 1671
the method described for Nitr oAG#2. Yield: 1.27 g (65%). 1H
NMR (CDCl3): δ ) 0.88 (t, 36H, -(CH2)5CH3), 1.24-1.49 (m,
303H, -ArArOCH(CH3)CH2(CH2)4CH3, -CH2(CH2)6CH2-, and
-CH3), 1.51-1.66 (m, 48H, -ArArOCH(CH3)CH2- and -OOC-
CH2CH2-), 1.78 (m, 24H, -ArArOCH2CH2-), 2.15 (s, 3H,
-CH3), 2.28 (t, 24H, -OOCCH2-), 3.93 (t, 24H, -ArArO-
CH2-), 4.22 (q, 24H, -CH2C-), 4.40 (s, 12H, -CH2C-), 4.55
(m, 12H, -ArArOCH(CH3)CH2-), 6.94 (d, 24H, 3′′-H and 5′′-
H), 6.98 (d, 6H, ArH), 7.11 (d, 6H, ArH), 7.15 (d, 12H, 5′-H),
7.24 (d, 24H, 3′′′-H and 5′′′-H), 7.48 (d, 24H, 2′′-H and 6′′-H),
7.57 (d, 24H, 2′′′-H and 6′′′-H), 7.67 (d, 24H, 3-H and 5-H),
7.75 (dd, 12H, 6′-H), 8.06 (d, 12H, 2′-H), 8.25 (d, 24H, 2-H and
6-H). Anal. Calcd for C593H702O114N12: C, 72.52; H, 7.21; N,
1.71. Found: C, 72.61; H, 7.34; N, 1.67.
mond, M.; Mondain-Monval, O.; Coles, H. Macromol. Chem.
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Lagerwall, S. T.; Stebler, B.; Lindstro¨m, J .; Rydlund, O.
Macromolecules 1996, 29, 2590.
Ack n ow led gm en t. This work was supported by the
Swedish Research Council for Engineering Sciences
(TFR, Grant 95-807), the Swedish Natural Science
Research Council (NFR, Grant K-AA/KU01910-312),
and the Defense Material Administration (FMV, Grant
64065-LB108704).
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