Liquid-crystalline functional carbazole and naphthalene platforms

Article abstract of DOI:10.1039/c0sm00547a

Two novel families of highly functionalized molecules consisting of a central carbazole or naphthalene core carrying actionable acid functions and linked to gallate platforms equipped with three long alkoxy chains have been rationally designed. The presence of amide tethers and chelating rigid fragments generate a new class of luminescent mesomorphic materials. Platforms bearing long paraffin chains (n = 12 and 16) self-organize into columnar liquid crystalline phases in which the columns are arranged according to a 2D oblique, rectangular or hexagonal lattice symmetry as deduced from powder XRD experiments. FT-IR studies confirm that the common driving force for aggregation and micro-segregation in the mesophase is due to the occurrence of a tight intermolecular H-bonded network. Spectroscopic measurements show that these platforms are luminescent in solution and in the solid state. Due to the synthetic availability of carbazole and naphthalene rigid cores and the simplicity by which these platforms can be graphed, this methodology represents a practical alternative to the production of fluorescent and mesomorphic materials.

Full text of DOI:10.1039/c0sm00547a

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PAPER
www.rsc.org/softmatter | Soft Matter
Liquid-crystalline functional carbazole and naphthalene platforms†
a
Franck Camerel, Bertrand Donnio and Raymond Ziessel
b
a
*
*
*
Received 17th June 2010, Accepted 9th September 2010
DOI: 10.1039/c0sm00547a
Two novel families of highly functionalized molecules consisting of a central carbazole or naphthalene
core carrying actionable acid functions and linked to gallate platforms equipped with three long alkoxy
chains have been rationally designed. The presence of amide tethers and chelating rigid fragments
generate a new class of luminescent mesomorphic materials. Platforms bearing long paraffin chains
(n ¼ 12 and 16) self-organize into columnar liquid crystalline phases in which the columns are arranged
according to a 2D oblique, rectangular or hexagonal lattice symmetry as deduced from powder XRD
experiments. FT-IR studies confirm that the common driving force for aggregation and micro-
segregation in the mesophase is due to the occurrence of a tight intermolecular H-bonded network.
Spectroscopic measurements show that these platforms are luminescent in solution and in the solid
state. Due to the synthetic availability of carbazole and naphthalene rigid cores and the simplicity by
which these platforms can be graphed, this methodology represents a practical alternative to the
production of fluorescent and mesomorphic materials.
Recently, we have investigated the synthesis of functional non-
Introduction
discotic mesogenic platforms able to self-assemble into columnar
liquid crystalline structures.10 These platforms were constructed
from the grafting of lipophilic gallate derivatives on central
2,6-diaminotoluene molecules functionalized by an acid function
or an iodine atom in the 4-position (Chart I). The introduction of
hydrogen bonding donor–acceptor groups through the forma-
tion of amide functions was found to stabilize strongly supra-
molecular organisations in the solid state, in the mesomorphic
state and to some extend in solution via aggregation processes.11
The introduction of grafting sites such as an acid function or an
iodine atom has allowed the introduction of various function-
alities on these mesogenic platforms through the formation of
ester or amide links or directly by Sonogashira cross-couplings to
produce functional liquid crystalline matter.12 More recently,
luminescence was introduced by the grafting of organic lumi-
nophores, displaying exceptional optical properties,13 or by the
anchorage of platinum complexes, as triplet emitters.14 Several
types of chelating agents were also introduced on the platforms
such as polypyridine fragments or crown ethers leading to
functional metallomesogens after metal chelation.12,15
Over the past few years, chemists have made significant efforts in
the design and synthesis of function-integrated molecules leading
to soft materials with predictable and stimuli-responsive prop-
erties such as luminescence, charge transport, catalytic activity
and macroscopic ordering.1 A great deal of attention has been
paid to the generation of self-assembled soft nanostructures
originating in most cases from weak interactions (dipolar,
hydrophobic, hydrogen bonding.) between preprogrammed
building blocks.2 Amongst these materials, liquid crystals are of
particular interest since they combine order and fluidity and
produce well-defined anisotropic and soft self-assembled struc-
tures from functional molecules.3 For instance, discotic liquid
crystals possess the ability to self-organize into ordered columnar
structures and such one-dimensional assemblies offer great
potential as molecular wires in electronic applications.4 Due to
their intriguing charge mobility, the self-assembly of p-conju-
gated molecules into linear structures has attracted much atten-
tion for its potential applications in photonics and
optoelectronics devices, such as field-effect transistors (FETs),5
organic light emitting diodes (OLEDs),6 organic light emitting
transistors (OLETs)7 and solar cells.8 Such one-dimensional
molecular assemblies can be constructed in the solid state or in
solution9 through weak intermolecular hydrogen bonding, p–p
stacking, electrostatic, van der Waals forces and/or solvophobic
interactions.
The motivation for the present work consists of the incorpo-
ration of additional functionalities, such as luminescence and
charge transport properties, directly onto the mesogenic plat-
forms, while maintaining the shape and number of amide func-
tions and leaving the grafting site unchanged, to generate novel
aLaboratoire de Chimie Moleꢀculaire et Spectroscopies Avanceꢀes (LCOSA,
Web: http://www-lmspc.u-strasbg.fr/lcosa) Ecole Chimie, Polymeꢁres,
Mateꢀriaux (ECPM), Universiteꢀ de Strasbourg-CNRS (UMR 7515), 25
rue Becquerel, F-67008 Strasbourg Cedex, France. E-mail: fcamerel@
chimie.u-strasbg.fr; ziessel@unistra.fr
bInstitut de Physique et Chimie des Mateꢀriaux de Strasbourg (IPCMS),
ꢀ
Universite De Strasbourg-CNRS (UMR 7504), 23 rue du Loess, BP 43,
F-67034 Strasbourg Cedex 2, France. E-mail: bdonnio@ipcms.u-strasbg.fr
† Electronic supplementary information (ESI) available: X-ray
diffractograms of the mesomorphic compounds Fig. S1-S9. See DOI:
10.1039/c0sm00547a
Chart 1 Diamino molecules carrying an acid fragment at the tip used for
the synthesis of functional mesogenic platforms.
412 | Soft Matter, 2011, 7, 412–428
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families of unconventional materials able to nano-segregate and
form supramolecular organized structures. For this purpose,
carbazole and naphthalene derivatives have been targeted and
designed to replace the central toluene core (Chart I).
450 ꢀC. The samples were examined at a scanning rate of
10 K minꢁ1 by applying two heating and one cooling cycles. The
ꢀ
apparatus was calibrated with indium (156.6 C). Phase behav-
iour was studied by polarized light optical microscopy (POM) on
a Leica DMLB microscope equipped with a Linkam LTS350
hot-stage and a Linkam TMS94 central processor. X-Ray scat-
tering measurements were carried out with two different exper-
imental set-ups. In both cases, a linear monochromatic Cu–Ka1
Carbazole and naphthalimide molecules have both been
selected as flat central cores due to the possibility of introducing
two amine functions at 120ꢀ around the periphery of the core,
whilst an acid function can be inserted at the tip on the nitrogen
atom of the carbazole or on the imide function of the naphtha-
lene molecule (Chart I). These two functionalized molecules were
also selected for their good luminescent and charge transport
properties. Carbazole-based molecules have been the subject of
numerous studies in the OLED technology, essentially due to
their excellent photoconductive properties and inherent electron-
donating nature arising from the nitrogen atom (p type
conductor). The carbazole unit is tolerant to functionalization
and as such has been largely incorporated into small molecular16
and macromolecular materials.17 The naphthalimide moiety also
displays good luminescence properties and has been extensively
used as fluorescence probes for anions detection18 and biological
labelling.19 Such p-conjugated aromatic fragments are also
electron-deficient and can be used as n type charge carriers in
optoelectronic devices.20 Both skeletons are chemically robust
and amenable to functionalization. Little effort has been made
up to now to generate liquid crystalline materials with these
building blocks.21
ꢂ
beam (l ¼ 1.5405 A) was obtained using a sealed-tube generator
(900W) equipped with a bent monochromator. In the first set, the
transmission Guinier geometry was used, whereas a Debye–
Scherrer-like geometry was used in the second experimental set-
up. In all cases, Lindemann glass capillaries of 1 mm diameter
and 10 mm wall thickness were filled with the crude powder.
Microwave irradiation experiments were performed using
a multi-mode MARS System from CEM Corporation using
standard Pyrex vessels (capacity 50 mL). The temperature
profiles for microwave experiments were recorded using a fiber-
optic probe protected by a sapphire immersion tube well inserted
directly into the reaction mixture. Pressure profiles were recorded
with a pressure sensor directly connected to the reaction vessel.
Synthetic procedures
Syntheses of 3,4,5 trialkyloxybenzoic chlorides with C12 and C16
chains have already been reported.22
Herein, we report on the syntheses and thermotropic and
luminescent properties of new functional mesogenic platforms
with fluorescent central naphthalene or carbazole cores carrying
an acid function as the grafting site and two structured lateral
gallate fragments.
Compound 1. A solution of 3,4,5-tridodecyloxybenzoic chlo-
ride (1.25 g, 1.8 mmol) in distilled THF (25 mL) was slowly
added to a distilled THF solution (50 mL) containing 3,6-dia-
minocarbazole (0.18 g, 0.9 mmol) and triethylamine (0.5 mL,
3.6 mmol). After complete addition, the reaction mixture was
stirred at room temperature under argon for 17 h. After removal
of the solvent, the crude product was dissolved in dichloro-
methane, washed with water and dried over anhydrous MgSO4.
After evaporation of the solvent, purification was performed by
chromatography on alumina gel with CH2Cl2–MeOH (100/0 to
99.8/0.2) and followed by crystallization from CH2Cl2–CH3CN
(0.66 g, 48%). 1H NMR (CDCl3, 300 MHz) d 0.88 (m, 18H, CH3),
0.99–1.60 (m, 108 H, CH2), 1.60–1.94 (m, 12H, CH2), 3.73–4.13
(m, 12H, OCH2), 6.91 (d, 2H, 3J ¼ 8.46 Hz), 7.23 (s, 4H), 7.28 (d,
Experimental
NMR Spectra (300.1 (1H) and 75.5 MHz (13C)) were recorded at
room temperature using perdeuterated solvents as internal
standards. FT-IR spectra were recorded using a Perkin-Elmer
‘‘spectrum one’’ spectrometer equipped with an ATR ‘‘diamond’’
apparatus. UV–vis spectra were recorded using a Shimadzu UV-
3600 dual-beam grating spectrophotometer with a 1 cm quartz
cell. Fluorescence spectra were recorded on a HORIBA Jobin-
Yvon fluoromax 4P spectrofluorimeter with a 1 cm quartz cell for
solutions or an optical fiber for solids. Temperature-dependent
luminescence measurements were performed on thin films thank
to the HORIBA Jobin-Yvon fluoromax 4P spectrofluorimeter
equipped with an optical fiber and a heating stage (Linkam
LTS350 hot-stage and a Linkam TMS94 central processor). All
fluorescence spectra were corrected. The fluorescence quantum
yield (Fexp) was calculated from eqn (1). Here, F denotes the
integral of the corrected fluorescence spectrum, A is the absor-
bance at the excitation wavelength, and n is the refractive index
of the medium. The reference system used was rhodamine 6G in
methanol (Fref ¼ 0.78, lexc ¼ 488 nm).
3
2H, J ¼ 8.85 Hz), 7.57 (s, 2H), 8.37 (s, 1H), 8.57 (s, 2H) ppm.
13C{1H} DEPT NMR (75.47 MHz, CDCl3) d 14.09 (CH3), 22.70
(CH2), 26.18 (CH2), 26.22 (CH2), 29.41 (CH2), 29.49 (CH2),
29.56 (CH2), 29.73 (CH2), 29.78 (CH2), 29.81 (CH2), 30.45
(CH2), 31.96 (CH2), 69.27 (OCH2), 73.53 (OCH2), 105.91 (CH),
110.57 (CH), 113.97 (CH), 121.14 (CH), 122.91 (Cq), 129.26
(Cq), 129.76 (Cq), 137.75 (Cq), 141.13 (Cq), 153.14 (Cq), 166.21
(C]O) ppm. UV–vis (CH2Cl2, 23 ꢀC): lmax (3, Mꢁ1 cmꢁ1) ¼ 259
(32750), 301 (51600). IR (ATR): 3275 (nNH), 2920, 2852, 1640
(nCO), 1578, 1530, 1490, 1467, 1441, 1425, 1381, 1337, 1221,
1115, 1002, 847, 805 cmꢁ1. EI-MS: m/z (%) ¼ 1510.1 (100) [M]+.
Anal. calcd for C98H163N3O8: C, 77.88; H, 10.87; N, 2.78; Found
C, 77.55; H, 10.53; N, 2.51.
È
À
ÁÉ
F 1 ꢁ exp ꢁ Aref ln10 n2
Fref f1 ꢁ expðꢁ Aln10Þgnr2ef
Fexp ¼ Fref
(1)
Compound 2. To a distilled THF solution (50 mL) containing
3,6-diaminocarbazole (0.26 g, 1.0 mmol) and triethylamine
(0.55 mL, 4.0 mmol), a solution of 3,4,5-trihexadecyloxybenzoic
chloride (1.72 g, 2.0 mmol) in distilled THF (25 mL) was added
Differential scanning calorimetry (DSC) was performed on
a Netzsch DSC 200 PC/1/M/H Phoxꢀ instrument equipped with
an intracooler, allowing measurements from ꢁ65 ꢀC up to
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Soft Matter, 2011, 7, 412–428 | 413

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dropwise. After complete addition, the reaction mixture was
stirred at room temperature under argon for 16 h. After evapo-
ration of the solvent, the crude product was dissolved in
dichloromethane, washed with water and the organic layers dried
over anhydrous MgSO4. Purification was performed by chro-
matography on alumina gel with CH2Cl2–MeOH (100/0 to 99.7/
0.3) and followed by crystallization from CH2Cl2–CH3CN
(1.02 g, 55%). 1H NMR (CDCl3, 300 MHz) d 0.87 (m, 18H, CH3),
1.06–1.57 (m, 156 H, CH2), 1.66–1.90 (m, 12H, CH2), 4.01 (m,
12H, OCH2), 7.15 (s, 4H), 7.21 (d, 2H, 3J ¼ 13.71 Hz), 7.48 (d,
2H, 3J ¼ 12.03 Hz), 7.94 (s, 2H), 8.17 (s, 2H), 8.32 (s, 1H) ppm.
13C{1H} DEPT NMR (75.47 MHz, CDCl3) d 14.11 (CH3), 22.70
(CH2), 26.20 (CH2), 29.40 (CH2), 29.47 (CH2), 29.55 (CH2),
29.70 (CH2), 29.77 (CH2), 29.78 (CH2), 30.44 (CH2), 30.90
(CH2), 31.95 (CH2), 69.30 (OCH2), 73.53 (OCH2), 105.84 (CH),
110.64 (CH), 113.85 (CH), 121.02 (CH), 123.05 (Cq), 129.42
(Cq), 129.82 (Cq), 137.75 (Cq), 141.16 (Cq), 153.16 (Cq), 166.16
(C]O) ppm. UV–vis (CH2Cl2, 23 ꢀC): lmax (3, Mꢁ1 cmꢁ1) ¼ 259
(29800), 301 (48600). IR (ATR): 3285 (nNH), 2916, 2850, 1641
(nCO), 1581, 1538, 1493, 1467, 1425, 1380, 1335, 1223, 1117,
1014, 992, 953, 861, 847 cmꢁ1. EI-MS: m/z (%) ¼ 1847.1 (100) [M]
+. Anal. calcd for C122H211N3O8: C, 79.29; H, 11.51; N, 2.27;
found C, 78.95; H, 11.34; N, 1.98.
exposure to light and air. The crude product is extremely sensi-
tive to air and light and was used without further purification. 1H
NMR (d6-DMSO, 300 MHz) d 1.19 (t, 3H, 3J ¼ 5.27 Hz), 4.11 (q,
2H, CH2, 3J ¼ 5.40 Hz), 4.71 (br, 4H, NH2), 5.02 (s, 2 H, CH2),
7.84 (dd, 2H, CH, 3J ¼ 6.40 Hz, 4J ¼ 1.51 Hz), 7.10 (m, 4H, CH)
ppm. 13C{1H} DEPT NMR (75.47 MHz, d6-DMSO) d 14.96
(CH3), 44.99 (NCH2), 61.51 (OCH2), 104.86 (CH), 109.99 (CH),
115.48 (CH), 123.65 (Cq), 135.11 (Cq), 141.95 (Cq), 170.17
(C]O) ppm. UV–vis (CH2Cl2, 23 ꢀC): lmax (3, Mꢁ1 cmꢁ1) ¼ 235
(24250), 319 (9100), 373 (3100). IR (ATR): 3382 (nNH), 3194,
2957, 2924, 2848, 1731, 1677, 1618, 1580, 1498, 1474, 1441, 1422,
1368, 1326, 1261, 1238, 1189, 1151, 1120, 1070, 1030, 934, 869
cmꢁ1. EI-MS: m/z (%) ¼ 284.1 (100) [M]+. Anal. calcd for
C16H17N3O2: C, 67.83; H, 6.05; N, 14.83; found C, 67.57; H,
5.64; N, 14.64.
Compound 5. To a solution of N-ethyl-(3,6-diamino-carba-
zolyl)-acetate (0.2 g, 0.7 mmol) in 20 mL of distilled dichloro-
methane was added 2 equivalents of 3,4,5 tridodecyloxybenzoic
chloride (0.98 g, 1.4 mmol) and 4 equivalents of triethylamine
(0.4 mL, 2.8 mmol). The mixture was stirred at room tempera-
ture for 16 h. After removal of the solvent, the crude product was
redissolved in dichloromethane, washed with water and dried
over anhydrous MgSO4. Purification was performed by chro-
matography on alumina gel with CH2Cl2–MeOH (100/0 to 99.5/
0.5) and followed by crystallization from CH2Cl2–CH3CN
(0.53 g, 47%). 1H NMR (CDCl3, 300 MHz) d 0.87 (m, 18H, CH3),
1.13–1.42 (m, 99 H, CH3 + CH2), 1.42–1.55 (m, 12H, CH2), 1.68–
1.91 (m, 12 H, CH2), 4.04 (m, 12H, OCH2), 4.20 (q, 2H, 3J ¼ 7.15
Hz, CH2), 4.95 (s, 2H, CH2), 7.13 (s, 4H), 7.27 (d, 2H, 3J ¼ 8.67
Hz), 7.67 (dd, 2H, 3J ¼ 8.67 Hz, 4J ¼ 1.89 Hz), 7.97 (s, 2H), 8.24
Compound 3. 3,6-Dinitrocarbazole (0.5 g, 1.9 mmol) was stir-
red with sodium hydride (77.8 mg (60% in oil), 1.9 mmol) in
20 mL of freshly distilled N,N-dimethylformamide under argon
for 30 min at room temperature before ethyl bromoacetate
(0.35 mL, 1.5 equiv.) was added. The reaction mixture was stirred
at room temperature for 20 h. The reaction was quenched with
water and the formed precipitate triturated for 1 h. The precip-
itate was filtered, washed with water and dried under vacuum to
yield a yellow powder (549 mg, 82%), which was used without
further purification. 1H NMR (d6-DMSO, 300 MHz) d 1.23
(t, 3H, 3J ¼ 5.25 Hz), 4.19 (q, 2H, CH2, 3J ¼ 5.36 Hz), 5.56 (s, 2
4
(d, 2H, J ¼ 1.86 Hz) ppm. 13C{1H} DEPT NMR (75.47 MHz,
CDCl3) d 14.11 (CH3), 22.69 (CH2), 26.12 (CH2), 29.37 (CH2),
29.40 (CH2), 29.44 (CH2), 29.61 (CH2), 29.66 (CH2), 29.71
(CH2), 29.76 (CH2), 30.36 (CH2), 31.93 (CH2), 31.94 (CH2),
45.03 (CH2), 61.74 (OCH2), 69.46 (OCH2), 73.58 (OCH2), 105.83
(CH), 108.66 (CH), 113.17 (CH), 120.30 (CH), 123.24 (Cq),
130.09 (Cq), 130.63 (Cq), 138.42 (Cq), 141.38 (Cq), 153.26 (Cq),
165.70 (C]O), 168.32 (C]O) ppm. UV–vis (CH2Cl2, 23 ꢀC):
lmax (3, Mꢁ1 cmꢁ1) ¼ 261 (30100), 301 (45700). IR (ATR): 3299
(nNH), 2921, 2852, 1741, 1641 (nCO), 1582, 1535, 1489, 1467,
1426, 1378, 1335, 1311, 1208, 1113, 1072, 1025, 1004, 954, 861
cmꢁ1. EI-MS: m/z (%) ¼ 1596.2 (100) [M]+. Anal. calcd for
3
H, CH2), 7.84 (d, 2H, CH, J ¼ 6.81 Hz), 8.35 (d, 2H, CH,
3J ¼ 6.81 Hz), 9.36 (s, 2H, CH) ppm. 13C{1H} DEPT NMR
(75.47 MHz, d6-DMSO) d 14.87 (CH3), 45.64 (NCH2), 62.38
(OCH2), 111.74 (CH), 119.27 (CH), 122.92 (Cq), 123.47 (CH),
142.44 (Cq), 145.75 (Cq), 168.69 (C]O) ppm. UV-vis (CH2Cl2,
23 ꢀC): lmax (3, Mꢁ1 cmꢁ1) ¼ 267 (27125), 286 (18800), 358
(16900). IR (ATR): 3098, 2981, 2925, 2853, 1744, 1671, 1629,
1606, 1586, 1513, 1479, 1430, 1396, 1375, 1331, 1305, 1201, 1148,
1136, 1098, 1010, 910, 862, 819 cmꢁ1. EI-MS: m/z (%) ¼ 343.1
(100) [M]+. Anal. calcd for C16H13N3O6: C, 55.98; H, 3.82; N,
12.24; found C, 55.67; H, 3.47; N, 11.87.
C
102H169N3O10: C, 76.69; H, 10.66; N, 2.63; found C, 76.94; H,
10.93; N, 3.04.
Compound 6. Distilled dichloromethane (50 mL) containing
0.16 g of N-ethyl-(3,6-diamino-carbazolyl)-acetate (0.55 mmol),
0.95 g of 3,4,5-trihexadecyloxybenzoic chloride (2 equiv.,
1.1 mmol) and 0.23 g of triethylamine (0.31 mL, 4 equiv.,
2.2 mmol) was stirred for 24 h under argon. The solvent was
removed and the crude product was redissolved in dichloro-
methane, washed with water and dried over anhydrous MgSO4.
Purification was performed by chromatography on alumina gel
with CH2Cl2–MeOH (100/0 to 99.7/0.3) and followed by crys-
tallization from CH2Cl2–CH3CN (0.44 g, 40%). 1H NMR
(CDCl3, 300 MHz) d 0.87 (m, 18H, CH3), 1.10–1.42 (m, 147 H,
CH3 + CH2), 1.42–1.63 (m, 12H, CH2), 1.68–1.92 (m, 12 H,
Compound 4. A mixture of N-(3,6-dinitro-carbazolyl)-ethyl
acetate (0.5 g, 1.45 mmol), 10% palladium on carbon (250 mg, 33
wt %), methanol (100 mL) and glacial acetic acid (10 mL) was
hydrogenated at atmospheric pressure under a balloon for 14 h.
The mixture was filtered through a cake of celite and the meth-
anol removed by rotary evaporation under reduced pressure.
Saturated aqueous NaHCO3 solution was added to neutralize
the acetic acid and the crude suspension was extracted with
chloroform. The combined organic layers were washed with
saturated aqueous NaHCO3 solution and dried over anhydrous
MgSO4. Evaporation of the solvent under reduced pressure
yielded 0.34 g (82%) of a yellow solid, which darkens rapidly on
3
CH2), 4.05 (m, 12H, OCH2), 4.20 (q, 2H, J ¼ 7.10 Hz, CH2),
414 | Soft Matter, 2011, 7, 412–428
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3
4.98 (s, 2H, CH2), 7.11 (s, 4H), 7.30 (d, 2H, J ¼ 8.67 Hz), 7.69
form. UV–vis (CH2Cl2, 23 ꢀC): lmax (3, Mꢁ1 cmꢁ1) ¼ 261 (34100),
300 (47700). IR (ATR): 3259 (nNH), 2914, 2850, 1732, 1641
(nCO), 1583, 1535, 1492, 1467, 1427, 1379, 1336, 1275, 1260,
1212, 1118, 1011, 987, 954, 848 cmꢁ1. EI-MS: m/z (%) ¼ 1905.0
(100) [M]+, 1845.5 (30) [Mꢁ(CH2COOH)]+. Anal. calcd for
3
4
(dd, 2H, J ¼ 8.67 Hz, J ¼ 1.32 Hz), 7.90 (s, 2H), 8.25 (s, 2H)
ppm. 13C{1H} DEPT NMR (75.47 MHz, CDCl3) d 14.10 (CH3),
22.69 (CH2), 26.14 (CH2), 26.17 (CH2), 29.37 (CH2), 29.45
(CH2), 29.50 (CH2), 29.70 (CH2), 29.75 (CH2), 30.39 (CH2),
31.93 (CH2), 61.72 (OCH2), 69.42 (OCH2), 73.56 (OCH2), 105.95
(CH), 108.51 (CH), 113.43 (CH), 120.59 (CH), 123.09 (Cq),
129.73 (Cq), 130.47 (Cq), 138.36 (Cq), 141.36 (Cq), 153.19 (Cq),
165.88 (C]O), 168.38 (C]O). UV–vis (CH2Cl2, 23 ꢀC): lmax
(3, Mꢁ1 cmꢁ1) ¼ 261 (33100), 301 (50700). IR (ATR): 3303
(nNH), 2919, 2851, 1741, 1643 (nCO), 1582, 1534, 1489, 1467,
C
124H213N3O10: C, 78.14; H, 11.26; N, 2.20; Found C, 77.98; H,
11.55; N, 2.32.
Compound 9. 3,6-Dinitro-1,8-naphthalic anhydride (2.0 g,
6.9 mmol) and glycinoethylester hydrochloride (1.1 g, 7.6 mmol)
were added to a 250 mL flask containing 70 mL of dry acetoni-
trile. Triethylamine (1.15 mL, 8.3 mmol) was added drop by drop
to give a violet solution that was heated to 90 ꢀC for 20 h. After
cooling the solution to room temperature, the solvent was
removed by rotary evaporation and the solid obtained purified
by chromatography on alumina gel with CH2Cl2–MeOH (100/
0 to 99.6/0.4) and followed by crystallization from hot CH3CN
1427, 1375, 1335, 1309, 1207, 1115, 1070, 1022, 956, 859 cmꢁ1
EI-MS: m/z (%)
1933.2 (100) [M]+. Anal. calcd for
126H217N3O10: C, 78.25; H, 11.31; N, 2.17; found C, 78.72; H,
.
¼
C
11.67; N, 2.55.
Compound 7. A mixture of N-ethyl-(3,6-bis(3,4,5-tridodecy-
loxybenzoylamido)-carbazoyl)-acetate (0.19 g, 0.12 mmol) and
KOH (33 mg, 0.6 mmol) in 50 mL THF–H2O (90/10 v/v) was
refluxed overnight. After complete consumption of the starting
material, the pH of the hot mixture was adjusted to 2 with 10% v/
v dilute HCl solution. After removal of the solvents, the crude
product was dissolved in dichloromethane and washed with
water. The organic layers were combined and dried over anhy-
drous MgSO4. After crystallization from a CH2Cl2–CH3CN
mixture, the product was isolated in a fair yield as a white powder
(0.10 g, 54%). Due to the low solubility of N-(3,6-bis(3,4,5-tri-
dodecyloxybenzoylamido)-carbazoyl)-acetic acid in all common
deuterated solvents, even in the presence of base, NMR experi-
ments could not be performed. However, an esterification reac-
tion with H2SO4 in ethanol on this product led to the formation
of the starting material N-ethyl-(3,6-bis(3,4,5-tridodecylox-
ybenzoylamido)-carbazoyl)-acetate. This result confirms the
formation and the integrity of the platform in acid form. UV–vis
(CH2Cl2, 23 ꢀC): lmax (3, Mꢁ1 cmꢁ1) ¼ 260 (32000), 301 (49200).
IR (ATR): 3246 (nNH), 2921, 2852, 1730, 1638 (nCO), 1583,
1536, 1491, 1467, 1426, 1387, 1337, 1261, 1213, 1193, 1116, 1013,
954, 845 cmꢁ1. EI-MS: m/z (%) ¼ 1568.2 (100) [M]+. Anal. calcd
for C100H165N3O10, H2O: C, 75.66; H, 10.60;N, 2.65; found C,
75.87; H, 10.80; N, 2.87.
1
(1.3 g, 50%). H NMR (d6-DMSO, 300 MHz) d 1.23 (t, 3H,
3J ¼ 7.15 Hz), 4.19 (q, 2H, CH2, 3J ¼ 7.03 Hz), 4.88 (s, 2 H, CH2),
9.12 (d, 2H, CH, 4J ¼ 2.07 Hz), 9.82 (d, 2H, CH, 4J ¼ 2.07 Hz).
13C{1H} DEPT NMR (75.47 MHz, d6-DMSO) d 14.47 (CH3),
42.12 (NCH2), 61.84 (OCH2), 124.05 (Cq), 127.02 (CH), 131.44
(Cq), 131.96 (Cq), 132.57 (CH), 147.70 (Cq), 161.87 (C]O),
167.96 (C]O). UV–vis (CH2Cl2, 23 C): lmax (3, Mꢁ1 cmꢁ1) ¼
ꢀ
269 (40700), 331 (7400). IR (ATR): 1758, 1716, 1666, 1614, 1595,
1553, 1533, 1435, 1418, 1405, 1377, 1347, 1337, 1244, 1211, 1174,
1119, 1064, 1019, 985, 959, 930, 908, 866, 832, 814 cmꢁ1. EI-MS:
m/z (%) ¼ 373.1 (100) [M]+, 286.2 (20) [Mꢁ(CH2COOH)]+. Anal.
calcd for C16H11N3O8: C, 51.48; H, 2.97; N, 11.26; found C,
51.28; H, 2.60; N, 10.82.
Compound 10. To a solution of N-ethyl-(3,6-dinitro-1,8-
naphthalyl)-acetate (0.30 g, 0.8 mmol) dissolved in 25 mL of
EtOH was added ammonium formiate (1.0 g, 16.0 mmol) and
palladium on carbon (10 w%) (60 mg, 1/10th of the mass of
N-ethyl-(3,6-dinitro-1,8-naphthalyl)-acetate per nitro function).
The mixture was heated at 120 ꢀC with stirring for 15 min in
a 50 mL reactor vessel under microwave irradiations (300 W).
The crude reaction mixture was filtered hot on a glass frit to
remove the Pd/C. Upon cooling, the product crystallized in
ethanol as a yellow crystalline powder, which was filtered,
washed with cold ethanol and dried under vacuum (0.23 g, 91%).
1H NMR (d6-DMSO, 300 MHz) d 1.20 (t, 3H, 3J ¼ 7.07 Hz), 4.15
(q, 2H, CH2, 3J ¼ 7.09 Hz), 4.74 (s, 2 H, CH2), 5.72 (s, 4H, NH2),
Compound 8. A mixture of N-ethyl-(3,6-bis(3,4,5-trihex-
adecyloxybenzoylamido)-carbazoyl)-acetate (0.25 g, 0.13 mmol)
and KOH (36 mg, 0.65 mmol) in 50 mL THF–H2O (90/10 v/v)
was refluxed overnight. After complete consumption of the
starting material, the pH of the hot mixture was adjusted to 2
with 10% v/v dilute HCl solution. After removal of the solvents,
the crude product was dissolved in dichloromethane and washed
with water. The organic layers were combined and dried over
anhydrous MgSO4. After crystallization from a CH2Cl2–CH3CN
mixture, the product was isolated in a fair yield as a white powder
(0.13 g, 53%). Due to the low solubility of N-(3,6-bis(3,4,5-tri-
hexadecyloxybenzoylamido)-carbazoyl)-acetic acid in all
common deuterated solvents, even in the presence of base, NMR
experiments could not be performed. However, an esterification
reaction with H2SO4 in ethanol on this product led to the
formation of the starting material N-ethyl-(3,6-bis(3,4,5-trihex-
4
4
6.97 (d, 2H, CH, J ¼ 2.07 Hz), 7.60 (d, 2H, CH, J ¼ 2.07 Hz)
ppm. 13C{1H} DEPT NMR (75.47 MHz, d6-DMSO) 14.49
(CH3), 41.52 (NCH2), 61.44 (OCH2), 110.54 (CH), 114.94 (Cq),
117.68 (CH), 122.21 (Cq), 136.09 (Cq), 148.16 (ꢀCq), 164.08
(C]O), 168.64 (C]O) ppm. UV–vis (CH2Cl2, 23 C): lmax (3,
Mꢁ1 cmꢁ1) ¼ 250 (37800), 412 (8000). IR (ATR): 3361 (nNH),
1741, 1699, 1657, 1618, 1573, 1526, 1458, 1406, 1381, 1350, 1318,
1276, 1261, 1211, 1177, 1115, 1017, 984, 932, 871 cmꢁ1. EI-MS:
m/z (%) ¼ 313.0 (100) [M]+, 226.1 (20) [Mꢁ(CH2COOH)]+. Anal.
calcd for C16H15N3O4.H2O: C, 58.00; H, 5.17; N, 12.68; found:
C, 57.84; H, 4.94; N, 12.43.
Compound 11. Dry dichloromethane (100 mL) containing
210 mg of N-ethyl-(3,6-diamino-1,8-naphthalyl)-acetate
adecyloxybenzoylamido)-carbazoyl)-acetate.
This
result
confirms the formation and the integrity of the platform in acid
(0.7 mmol), 1.0
g
of 3,4,5-tridodecyloxybenzoic chloride
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(1.4 mmol) and 0.4 mL triethylamine (2.8 mmol) was stirred for
20 h under argon. The solvent was removed and the crude
product was redissolved in dichloromethane, washed with water
and dried over anhydrous MgSO4. Purification was performed
by flash chromatography on silica gel with CH2Cl2–MeOH (100/
0 to 99/1) and followed by crystallization from CH2Cl2–CH3CN
(0.42 g, 38%). 1H NMR (CDCl3, 300 MHz) d 0.87 (m, 18H, CH3),
1.12–1.57 (m, 111H, CH2 + CH3), 1.68–1.89 (m, 12 H, CH2), 4.02
temperature, removal of the THF led to the precipitation of the
product. The white powder obtained was washed with water,
dried and recrystallized from CH2Cl2–CH3CN (0.13 g, 88%).
Due to the low solubility of N-ethyl-(3,6-bis(3,4,5-
tridodecyloxybenzoylamido)-1,8-naphthalyl)-acetic acid, only
1H NMR experiments could have been performed in CDCl3 in
the presence of deuterated methanol. 1H NMR (CDCl3
+
MeOD, 300 MHz) d 0.67 (m, 18H, CH3), 0.93–1.24 (m, 96H,
CH2), 1.24–1.40 (m, 12 H, CH2), 1.48–1.73 (m, 12 H, CH2), 3.88
(m, 12H, OCH2), 4.70 (s, 2H, CH2), 7.10 (s, 4H), 8.29 (d, 2H,
4J ¼ 1.89 Hz), 8.47 (d, 2H, 4J ¼ 1.86 Hz). The disappearance of
the quadruplet around 4.2 ppm (CH2 of the ethyl function) is
a clear sign of the efficiency of the saponification. Due to the
presence of methanol, the amide functions are not visible in the
3
(m, 12H, OCH2), 4.23 (q, J ¼ 7.1 Hz, 2H, CH2), 4.84 (s, 2H,
CH2), 7.21 (s, 4H), 8.20 (s, 2H), 8.23 (s, 2H), 8.81 (s, 2H) ppm.
13C{1H} DEPT NMR (75.47 MHz, CDCl3) d 14.09 (CH3), 22.68
(CH2), 26.18 (CH2), 29.39 (CH2), 29.47 (CH2), 29.54 (CH2),
29.71 (CH2), 29.76 (CH2), 29.79 (CH2), 30.44 (CH2), 31.93
(CH2), 62.18 (OCH2), 69.44 (OCH2), 73.55 (OCH2), 103.53 (Cq),
106.13 (CH), 121.48 (Cq), 121.67 (Cq), 123.03 (CH), 123.53
(CH), 128.98 (Cq), 137.00 (Cq), 141.82 (Cq), 153.28 (Cq), 162.94
(C]O), 166.42 (C]O), 169.34 (C]O) ppm. UV–vis (CH2Cl2,
23 ꢀC): lmax (3, Mꢁ1 cmꢁ1) ¼ 278 (59400), 291 (60000), 376
(12800), 388 (12600). IR (ATR): 3336 (nNH), 2921, 2852, 1709,
1655 (nCO), 1629, 1582, 1548, 1537, 1498, 1467, 1398, 1378, 1333,
1266, 1217, 1177, 1115, 1023, 933, 899, 867, 802 cmꢁ1. MS
(FAB+, mNBA): m/z (%) ¼ 1626.3 (100) [M]+. Anal. calcd for
1H NMR spectrum. UV–vis (CH2Cl2, 23 ꢀC): lmax (3, Mꢁ1 cmꢁ1
)
¼ 278 (60800), 290 (60600), 378 (13500), 388 (13200). IR (ATR):
3303 (nNH), 2921, 2852, 1706, 1650 (nCO), 1582, 1546, 1517,
1495, 1467, 1426, 1389, 1377, 1333, 1292, 1220, 1180, 1114, 1003,
934, 904, 854 cmꢁ1. Anal. calcd for C100H163N3O12: C, 75.10; H,
10.27; N, 2.63; found C, 75.38; H, 10.29; N, 2.72.
Compound 14. A mixture of N-ethyl-(3,6-bis(3,4,5-tridodecy-
loxybenzoylamido)-1,8-naphthalyl)-acetate (0.25 g, 0.12 mmol)
and KOH (34 mg, 0.60 mmol) in 50 mL THF–H2O (90/10 v/v)
was refluxed overnight. After complete consumption of the
starting material, the pH of the hot mixture was adjusted to 2
with 10% v/v dilute HCl solution. After cooling to room
temperature, removal of the THF led to the precipitation of the
product. The white powder obtained was filtered, washed with
water, dried and recrystallized from CH2Cl2–CH3CN (0.20 g,
82%). Due to the low solubility of N-(3,6-bis(3,4,5-trihex-
adecyloxybenzoylamido)-1,8-naphthalyl)-acetic acid, only 1H
NMR experiments could be performed in CDCl3 in the presence
of deuterated methanol. 1H NMR (CDCl3 + MeOD, 300 MHz)
d 0.66 (m, 18H, CH3), 0.89–1.23 (m, 144H, CH2), 1.23–1.41 (m,
12 H, CH2), 1.48–1.73 (m, 12 H, CH2), 3.87 (m, 12H, OCH2),
4.69 (s, 2H, CH2), 7.08 (s, 4H), 8.30 (d, 2H, 4J ¼ 1.86 Hz), 8.50 (d,
2H, 4J ¼ 1.68 Hz). The disappearance of the quadruplet around
4.2 ppm (CH2 of the ethyl function) is a clear sign of the efficiency
of the saponification. Due to the presence of methanol, the amide
functions are not visible in the 1H NMR spectrum. UV–vis
(CH2Cl2, 23 ꢀC): lmax (3, Mꢁ1 cmꢁ1) ¼ 278 (53350), 290 (53500),
378 (13600), 388 (13400). IR (ATR): 3303 (nNH), 2918, 2850,
1707, 1657 (nCO), 1582, 1548, 1517, 1496, 1467, 1426, 1392, 1378,
1333, 1288, 1221, 1179, 1116, 987, 934, 904, 854 cmꢁ1. Anal. calcd
for C124H211N3O12: C, 76.93; H, 10.99; N, 2.17; found C, 77.18;
H, 11.37; N, 2.54.
C102H167N3O12: C, 75.28; H, 10.34; N, 2.58; found: C, 75.54; H,
10.66; N, 3.17.
Compound 12. To a solution of N-ethyl-(3,6-diamino-1,8-
naphthalyl)-acetate (0.16 g, 0.5 mmol) in 50 mL of distilled
dichloromethane was added 2 equivalents of 3,4,5-trihex-
adecyloxybenzoic chloride (0.86 g, 1.0 mmol) and 4 equivalents
of triethylamine (0.28 mL, 2.0 mmol). The mixture was stirred at
room temperature for 16 h. After removal of the solvent, the
crude product was redissolved in dichloromethane, washed with
water and dried over anhydrous MgSO4. Purification was per-
formed by flash chromatography on silica gel with CH2Cl2–
MeOH (100/0 to 99/1) and followed by crystallization from
1
CH2Cl2–CH3CN (0.34 g, 34%). H NMR (CDCl3, 300 MHz)
d 0.87 (m, 18H, CH3), 1.10–1.57 (m, 159H, CH2 + CH3), 1.69–
1.89 (m, 12 H, CH2), 4.02 (m, 12H, OCH2), 4.24 (q, 3J ¼ 7.15 Hz,
2H, CH2), 4.85 (s, 2H, CH2), 7.21 (s, 4H), 8.22 (s, 2H), 8.27 (s,
2H), 8.76 (s, 2H) ppm. 13C{1H} DEPT NMR (75.47 MHz,
CDCl3) d 14.09 (CH3), 22.68 (CH2), 26.19 (CH2), 29.37 (CH2),
29.47 (CH2), 29.55 (CH2), 29.68 (CH2), 29.74 (CH2), 29.77
(CH2), 30.43 (CH2), 31.93 (CH2), 62.14 (OCH2), 69.46 (OCH2),
73.56 (OCH2), 103.80 (Cq), 106.12 (CH), 121.54 (Cq), 121.75
(Cq), 123.57 (CH), 124.25 (CH), 128.98 (Cq), 137.03 (Cq), 141.83
(Cq), 153.30 (Cq), 162.98 (C]O), 166.40 (C]O), 169.28 (C]O)
ppm. UV–vis (CH2Cl2, 23 ꢀC): lmax (3, Mꢁ1 cmꢁ1) ¼ 277 (54300),
290 (54400), 376 (11200), 388 (10800). IR (ATR): 3336 (nNH),
2920, 2852, 1709, 1651 (nCO), 1628, 1583, 1547, 1497, 1467, 1394,
1377, 1264, 1217, 1177, 1116, 1022, 933, 902, 869 cmꢁ1. EI-MS:
m/z (%) ¼ 1963.0 (100) [M]+. Anal. calcd for C126H215N3O12: C,
77.05; H, 11.03; N, 2.14; found C, 77.34; H, 11.54; N, 2.27.
Compound
15.
N-(3,6-Bis(3,4,5-trihexadecyloxy-
benzoylamido)-1,8-naphthalyl)-acetic acid (0.13 g, 0.07 mmol)
and dimethylaminopyridine (DMAP) (17 mg, 0.14 mmol) were
introduced in 50 mL of distilled CH2Cl2 in a Schlenck flask under
argon. The mixture was stirred until complete solubilisation of
Compound 13. A mixture of N-ethyl-(3,6-bis(3,4,5-tridodecy-
loxybenzoylamido)-1,8-naphthalyl)-acetate (0.15 g, 0.09 mmol)
and KOH (25 mg, 0.45 mmol) in 50 mL THF–H2O (90/10 v/v)
was refluxed overnight. After complete consumption of the
starting material, the pH of the hot mixture was adjusted to 2
with 10% v/v dilute HCl solution. After cooling to room
the
acid.
Finally
1-[3-(dimethyl-amino)propyl]-3-ethyl-
carbodiimide hydrochloride (EDCI) (27 mg, 0.14 mmol) and
ethylenediamine (840 mg, 14 mmol) were added to the clear
solution which was stirred overnight. The solvent was removed
and the crude product was redissolved in dichloromethane,
washed with water and dried over anhydrous MgSO4.
416 | Soft Matter, 2011, 7, 412–428
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Purification was performed by crystallization from CH2Cl2–
1
CH3CN (0.11 g, 81%). H NMR (CDCl3 + MeOD, 300 MHz)
synthetic procedures for compounds 1–8 containing carbazole
cores. Compounds 1 with n ¼ 12 and 2 with n ¼ 16 were readily
obtained by reaction of the 3,6-diaminocarbazole with 3,4,5-
trialkyloxybenzoic acid chloride (n ¼ 12, 16) under anhydrous
conditions. Unfortunately, reactions of the anions of
compounds 1 and 2 with ethylbromoacetate did not allow
introduction of the ester function onto the nitrogen atom.
Consequently, the ester function was introduced onto the 3,6-
dinitrocarbazole starting material. Compound 3 was obtained,
in good yield, by addition of a DMF solution of ethyl-
bromoacetate containing the anion of 3,6-dinitrocarbazole
preformed by reaction with sodium hydride. Reduction of the
nitro fragments on palladium/carbon in methanol with glacial
acetic acid afforded compound 4 in 82% yield. The amide-
functionalized platforms 5 and 6, carrying an ester function at
the tip, were obtained by amidation with 3,4,5-trialkoxybenzoic
acid chloride (n ¼ 12, 16) in dry dichloromethane in the pres-
ence of triethylamine. Saponification of the ester function under
basic conditions afforded the targeted functional acid platforms
7 (n ¼ 12) and 8 (n ¼ 16). Purification of the compounds was
achieved by chromatography on silica gel followed by crystal-
lization in a CH2Cl2–CH3CN mixture. Purity of the samples
was probed by 1H and 13C NMR, mass spectroscopy and
elemental analysis.
d 0.74 (m, 18H, CH3), 0.97–1.30 (m, 144 H, CH2), 1.30–1.46
(m, 12 H, CH2), 1.56–1.79 (m, 12 H, CH2), 2.74 (s, 2H, CH2
ethylamino), 3.58 (s, 2H, CH2 ethylamino), 3.95 (m, 12 H,
OCH2), 4.73 (s, 2H, CH2), 7.15 (s, 4H, CH), 8.39 (s, 2 H, CH),
8.67 (s, 2 H, CH) ppm. Due to the presence of methanol, the
amide and amine functions are not visible in the 1H NMR
spectrum. 13C{1H} NMR (75.47 MHz, CDCl3 + MeOD, 50 ꢀC)
d 13.67, 22.45, 26.00, 26.07, 29.15, 29.37, 29.43, 29.60, 30.27,
31.75, 69.50, 73.57, 106.75, 108.58, 121.87, 122.14, 122.22,
123.39, 124.18, 129.00, 132.90, 137.69, 137.78, 141.83, 153.06,
163.85, 166.79 ppm. UV–vis (CH2Cl2, 23 C): lmax (3,Mꢁ1cmꢁ1
)
ꢀ
¼ 279 (52700), 289 (53100), 376 (12100), 388 (11700). IR (ATR):
3235 (nNH), 2919, 2850, 1698, 1648 (nCO), 1584, 1525, 1497,
1467, 1426, 1379, 1335, 1220, 1179, 1115, 984, 938, 899, 857, 804
cmꢁ1. EI-MS: m/z (%) ¼ 1978.2 (100) [M] +. Anal. calcd for
C126H217N5O11: C, 76.51; H, 11.06; N, 3.54; found C, 76.34; H,
11.07; N, 3.57.
Compound
16.
N-(3,6-Bis(3,4,5-trihexadecyloxy-
benzoylamido)-carbazoyl)-acetic acid (86 mg, 0.045 mmol) and
dimethylaminopyridine (DMAP) (11 mg, 0.09 mmol) were
introduced into 20 mL of distilled CH2Cl2 in a Schlenck flask
under argon. The mixture was stirred until complete solubilisa-
tion of the acid. Finally 1-[3-(dimethyl-amino)propyl]-3-ethyl-
carbodiimide hydrochloride (EDCI) (17 mg, 0.09 mmol) and
N-(2-aminoethyl)-(3,6-bis(3,4,5-trihexadecyloxybenzoylamido)-
1,8-naphthalyl)-acetamide (51 mg, 0.03 mmol) were added to the
clear solution which was stirred overnight. The solvent was
removed and the crude product was redissolved in dichloro-
methane, washed with water and dried over anhydrous MgSO4.
Purification of the product was performed by chromatography
on alumina gel with CH2Cl2–MeOH (100/0 to 95/5) and followed
by crystallization from CH2Cl2–CH3CN (53 mg, 53%). 1H NMR
(CDCl3 + MeOD, 300 MHz) d 0.84 (m, 36 H, CH3), 0.95–1.60
(m, 312 H, CH2), 1.62–1.90 (m, 24 H, CH2), 2.63 (s, 4 H, CH2),
4.03 (m, 24 H, OCH2), 5.30 (s, 4 H, CH2), 7.05–7.36 (m, 10 H,
CH), 7.44 (s, 2 H, CH), 7.48–7.73 (m, 2 H, CH), 8.05–8.23 (m,
2 H, CH), 8.50 (s, 2 H, CH) ppm. Due to the presence of
methanol, the amide and amine functions are not visible in the 1H
NMR spectrum. 13C{1H} NMR (75.47 MHz, CDCl3 + MeOD)
13.90, 22.59, 26.04, 26.10, 29.29, 29.39, 30.26, 31.85, 69.29, 73.62,
106.07, 106.33, 108.43, 110.72, 113.53, 120.95, 121.53, 122.92,
123.04, 123.55, 124.58, 128.97, 129.59, 129.95, 137.77, 137.91,
138.30, 140.93, 141.10, 141.38, 152.97, 153.00, 163.77, 166.71,
166.95 ppm. UV–vis (CH2Cl2, 23 ꢀC): lmax (3, Mꢁ1 cmꢁ1) ¼ 298
(100500), 388 (7700). IR (ATR): 3298 (nNH), 2918, 2850, 1702,
1651 (nCO), 1582, 1533, 1497, 1467, 1426, 1379, 1334, 1273, 1261,
1220, 1116, 1034, 1013, 987, 951, 897, 855 cmꢁ1. Anal. calcd for
A similar synthetic route was used to build the luminescent
naphthalene core, containing an acid function at the tip and
two amido-gallate fragments as peripheral structural fragments
(Scheme 2). The starting compound 3,6-dinitro-1,8-naphthalic
anhydride was synthesized according to literature procedures.24
Introduction of the ethylacetate fragment was achieved using
glycine ethylester hydrochloride under basic conditions
affording compound 9 in reasonable yield. Reduction of the
nitro functions was efficiently performed under microwave
irradiation in the presence of palladium on carbon (10 wt%)
and ammonium formiate as a solid source of hydrogen.25 The
mixture was heated at 120 ꢀC with stirring for 15 min in
a 50 mL reactor vessel under microwave irradiation (300 W).
After crystallization, compound 10 was isolated in an almost
quantitative yield.
Reaction of compound 10 with 3,4,5-trialkoxybenzoic acid
chloride (n ¼ 12, 16) in dry dichloromethane and triethylamine
afforded the naphthalene based platforms 11 (n ¼ 12) and 12
(n ¼ 16) containing an ester function at the tip and two lateral
amido-gallate fragments. Finally, the targeted naphthalene
platforms 13 (n ¼ 12) and 14 (n ¼ 16) containing an acid function
were obtained by saponification with KOH. Purification of the
compounds was achieved by chromatography on silica gel and
1
the purity determined by H and 13C NMR, mass spectroscopy
and IR spectroscopy. In order to further extend and modify the
functionality of the platform, compound 14 was reacted with
excess ethylenediamine in the presence of 1-[3-(dimethylami-
no)propyl]-3-ethylcarbodiimide hydrochloride (EDCI) and
dimethylamino pyridine (DMAP) to afford the modified plat-
form 15 carrying a flexible amine function at the central position.
In a final trial the linkage of compounds 8 and 15 was achieved
using classical peptide chemistry with EDCI in the presence of
DMAP in dry dichloromethane. The flexible dyad 16 containing
a naphthalene core and a carbazole residue was produced in 53%
isolated yield (Scheme 3).
C250H428N8O20: C, 77.67; H, 11.16; N, 2.90; found: C, 78.04; H,
11.26; N, 3.17.
Results and discussion
Synthesis and characterisation
3,6-Dinitrocarbazole and 3,6-diaminocarbazole were synthe-
sized according to reported procedures.23 Scheme 1 outlines the
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Scheme 1 Synthesis of the functional carbazole platforms: i) Pd/C (10 w%), glacial acetic acid, MeOH, H2 (gas, 1 atm), 14 h, rt, 82% for 4 and 80% for
3,6-diaminocarbazole; ii) Et3N (4 eq.), THF, rt, 17 h, 48% (n ¼ 12), 55% (n ¼ 16); iii) NaH (1 eq.), DMF, 30 min, rt, then ethylbromoacetate (1.5 eq.), 20
h, rt, 82%; iv) CH2Cl2, Et3N (4 eq.), rt, 24 h, 47% (n ¼ 12), 40% (n ¼ 16); v) KOH (5 eq.), THF–H2O (90/10 v/v), reflux, 16 h, 54% (n ¼ 12), 53% (n ¼ 16).
Spectroscopic properties in solution
bands, each displaying two close maxima at 388/376
(3 z 12 000 Mꢁ1cmꢁ1) and 290/278 nm (3 z 55 000 Mꢁ1cmꢁ1),
respectively (Fig. 1b). The low energy bands are due to transi-
tions mainly localized on the naphthalene core whereas the high
energy bands are likely due to p–p* and n–p* transitions
localized on the naphthalene core and the alkoxyphenyl frag-
ments. The nature of the substituent on the diimide fragment did
not affect the positions or the absorption coefficients of these
bands. The absorption spectrum of dyad 16 displays a broad and
intense absorption band presenting a maximum at 299 nm and
a weaker absorption peak with a maximum at 380 nm. The
absorption spectrum of compound 16 is almost a linear combi-
nation of the absorption spectra of compounds 8 and 15 (Fig. 2).
Excitation of the carbazole compounds 1–2 and 5–8 in the
lowest energy bands at 301 nm leads to a broad emission band
peaking at 400 nm and extending up to 700 nm with low
quantum yields (Fig. 1a). In some cases, a second broad emission
band centred at 510–520 nm, which appears as a shoulder on the
main emission band, can also be detected. In light of previous
work,13,27 this additional broad emissive band is due to aggre-
gates. Whereas the nitro compound 3 is non luminescent, exci-
tation in the lowest energy absorption band of the
Spectroscopic data for compounds 1 to 16 in diluted dichloro-
methane solutions are gathered in Table 1. All the absorption
spectra of the functional carbazole-based platforms 1–2 and 5–8
show a main absorption band with two maxima at 301 nm
(3 z 50 000 Mꢁ1 cmꢁ1) and at 261 nm (3 z 30 000 Mꢁ1 cmꢁ1
)
(Fig. 1a). These absorption bands are assigned to p–p* and n–p*
transitions localized on the carbazole core and the alkoxyphenyl
fragments, respectively. The absorption properties are not
sensitive to the nature of the substituent on the nitrogen atom. In
contrast the spectra of precursors 3 and 4 appear to be quite
different and show several absorption bands in the 230–400 nm
range (Table 1). Introduction of amino functions on the carba-
zole core in compound 4 leads to the appearance of a charge
transfer band centred at 373 nm. The absorption spectrum of the
starting nitro naphthalene derivative 9 displays two main
absorption bands at 331 nm (3 z 7 000 Mꢁ1 cmꢁ1) and at 269 nm
(3 z 40 000 Mꢁ1 cmꢁ1). Conversion of the nitro functions into
amino functions leads to a bathochromic shift of 80 nm of the
low energy absorption band and a hypsochromic shift of the high
energy absorption band of 20 nm. Absorption spectra of naph-
thalene platforms 11–15 display two main broad absorption
418 | Soft Matter, 2011, 7, 412–428
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Scheme 2 Synthesis of the functional naphthalene platforms: i) glycine ethylester (1.1 eq.), Et3N (1.2 eq.), CH3CN, 20 h, 90 ꢀC, 50%; ii) Pd/C (10 w%),
EtOH, NH4COOH (20 eq.), 300 W, 15 min, 120 ꢀC, 91%; iii) CH2Cl2, Et3N (4 eq.), 20 h, rt, 38% (n ¼ 12), 34% (n ¼ 16); iv) KOH (5 eq.), THF–H2O (90/
10 v/v), reflux, 16 h, 88% (n ¼ 12), 82% (n ¼ 16); v) ethylenediamine (100 eq.), EDCI (2 eq.), DMAP (2 eq.) in dichloromethane at rt, 16 h, 81%.
diaminocarbazole derivative 4 at 373 nm leads to a strong
emission centred at 424 nm with a quantum yield of 0.25. As for
compound 3, the naphthalene-dinitro compound 9 is not lumi-
nescent. This is not very surprising because it has been previously
reported that a nitro function is easily reduced, and that when
coupled to a chromophore (e.g; cyanines, Bodipy, pyrene and
naphthalene.) a photo-induced electron transfer from the
excited dye to the nitro residues occurs.28 Excitation of
compound 10 at 412 nm leads to a broad emission centred at 483
nm with a quantum yield of 0.36. As observed above for the
amino derivatives 4 and 10, the electron donating ability of
the amino functions improves the luminescent properties of the
aromatic core. It was found that compounds 11–16 have a strong
tendency to form aggregated species in solution at concentra-
tions above 10ꢁ5 M and, upon excitation at 380 nm, broad
emission bands with multiple contributions and that extended
from 400 up to 700 nm, were observed. At lower concentrations,
the aggregation feature of these dyes is clearly highlighted by
excitation at 380 nm leading to a dual emission band centred at
430 nm with an additional broad emission band tailing-off up to
700 nm (Fig. 1b). This is a clear signature of the high tendency of
these dyes to aggregate, as would be expected by the design and
the presence of a flat core, and amide vectors which likely
promote intermolecular hydrogen bonding. The quantum yields
determined for this series of compounds lie in the range
0.9–1.3%.
X-ray diffraction (SA-XRD). The measured transition temper-
atures and enthalpy values are gathered in Table 2, whilst the
mesophase parameters are gathered in Table 3.
Thermal behaviour of the carbazole derivatives 1–8. Both
carbazole compounds 1 and 2 (with chain-length n ¼ 12 and n ¼
16, respectively) behave quite similarly and display two reversible
thermal transitions, as detected by DSC (Table 2). POM obser-
vations revealed that the high transition temperature, at about
100 ꢀC for both samples, corresponds to the cooling temperature.
Upon cooling, DSC traces evidenced a slight supercooling of the
ꢀ
transition, at about 80 C, as observed by POM. The materials
are still fluid at this temperature and birefringence can be induced
by mechanical stress, suggesting the formation of a liquid crys-
talline mesophase. On further cooling, a broad transition is
detected by DSC which is likely attributed to crystallization of
aliphatic chains, through the hardening of the material. X-Ray
patterns recorded in the temperature range from 20 to 120 ꢀC
confirmed the above observations and allowed the identification
of the mesophases for both compounds. In the temperature
intervals delimited by DSC and POM, and which correspond to
mesophase stability, one intense and several weak, sharp, small-
angle diffraction peaks along with broad wide-angle diffuse
bands were detected. For compound 1 (Fig. 3), reflections, with
spacings in the ratio 1:O3:O4:O9:O13 could be indexed unequiv-
ocally as the hk reflections (10), (11), (20), (30), (31) of a hexag-
onal lattice with p6mm plane symmetry. In the wide angle part,
ꢂ
the very intense halo centred at 4.6 A was associated with the
Thermal studies
molten chains in the isotropic state, and the two weak diffusions
ꢂ
The liquid crystalline properties of compounds 1–2, 5–8, 11–14,
15 and 16, carrying amido-gallate fragments with long alkoxy
chains, were investigated by polarizing optical microscopy
(POM), differential scanning calorimetry (DSC) and small-angle
at 3.8 and 7.5 A, to some intermolecular interactions (vide
supra). For 2, the same wide-angle features were observed (h, h0,
hch), but only two sharp small-angle peaks were detected, indexed
by analogy to 1 as (10) and (30) reflections of the hexagonal
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Scheme 3 Chemical structure of the functional dyad. Key: i) EDCI (2 eq.), DMAP (2 eq.) in dichloromethane at rt, 16 h, 53%.
ꢂ
4.5 A for 6, were detected, which suggested amorphous solids
lattice. Although, the phases assignment as Colh is not
unequivocal (the small-angle reflections are indeed compatible
with a smectic phase too), it is nevertheless more reasonable to
consider the columnar morphology because of the semi-disc-like
shape of the compound and to the recognized columnar meso-
phase nature of its lower-chain counterpart. Such an assumption
is also strongly supported and consistent with the behaviour
reported for other structurally related bent hexacatenar liquid
crystals.29 Thus, both compounds exhibit a Colh phase, with
with partial ordering.
The initial DSC heating curves of compounds 7 and 8, the acid
parents of 5 and 6, respectively, displayed broad transitions, due
to some internal rearrangement and melting of the aliphatic
chains. After thermal treatment, compound 7 displays a single
broad reversible transition centred at 23 ꢀC, corresponding to
melting. As for 8, after the first heating curve, the compound did
not show any thermal transition from ꢁ20 ꢀC up to 110 ꢀC; POM
observations revealed its non-mesomorphic nature in the
explored temperature range. Thus, among the six carbazole
derivatives, only the non-substituted carbazoles, 1 and 2, are
mesomorphic, exhibiting a Colh mesophase, showing that small
modifications of the core’s tip is detrimental to the emergence of
liquid crystallinity.
ꢀ
ꢂ
lattice parameters at 80 C of 44.4 and 49.2 A for 1 and 2,
respectively, which are quasi invariant with temperature
(Table 3).
The corresponding ester carbazole derivatives 5 (n ¼ 12) and
6 (n ¼ 16), exhibit a completely different thermal behaviour.
The ꢀDSC traces of 5 display an endothermic peak centred at
112 C, and a broad exothermic peak centred at 82 ꢀC on the
heating and cooling curves, respectively. By POM, 5 is in the
isotropic state at 112 ꢀC, and below 82 ꢀC on cooling, turns
slightly birefringent but no readily developed texture occurs.
DSC traces of compound 6 reveal the presence of a single broad
reversible thermal transition centred at 86 ꢀC on heating,
associated to the isotropization (POM). Both compounds
exhibit strong supercooling. XRD demonstrated in both cases
the absence of a liquid crystalline phase, despite the birefrin-
gence exhibited by both samples. Instead, only broad and
Thermal behaviour of the naphthalene derivatives 11–16. In
contrast to the thermal behaviour of the carbazole-based
compounds, most of the compounds derived from the naphtha-
lene core were mesomorphic. At room temperature, compound
11 (with dodecyl chains) with a naphthalene core carrying an
ester function appears as a birefringent sticky material. DSC
traces displayed two reversible thermal transitions centred at
161 ꢀC and 221 ꢀC (Fig. 4a), the higher one corresponding to the
transition to the isotropic liquid (above 221 ꢀC, the compound is
an isotropic fluid).
ꢂ
intense reflections, seen at ca 27 and 4.5 A for 5 and ca 35 and
420 | Soft Matter, 2011, 7, 412–428
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Table 1 Optical data measured in dichloromethane solution at 298 K
a
FF
Compd
labs/nm (3/Mꢁ1 cmꢁ1
)
lF/nm @ lex/nm
1
2
3
301 (51 600)
259 (32 750)
301 (48 600)
259 (29 800)
358 (16 900)
267 (27 200)
286 (18 800)
373 (3 100)
319 (9 100)
235 (24 250)
301 (45 700)
261 (30 100)
301 (50 700)
261 (33 100)
301(49 200)
260 (32 000)
300 (47 700)
261 (34 100)
331 (7 400)
269 (40 700)
412 (8 000)
250 (37 800)
388 (12 600)
376 (12 800)
291 (60 000)
278 (59 400)
388 (10 800)
376 (11 200)
290 (54 400)
277 (54 300)
388 (13 200)
377 (13 500)
290 (60 600)
278 (60 800)
388 (13 400)
378 (13 600)
290 (53 500)
278 (53 350)
388 (11 700)
376 (12 100)
289 (53 100)
279 (52 700)
388 (7 700)
298 (100 500)
416 @ 301
513 @ 301
395 @ 301
513 @ 301
—
<0.01
<0.01
—
4
424 @ 373
399 @ 301
0.25
5
<0.01
<0.01
<0.01
<0.01
—
6
417 @ 301
517 @ 301
398 @ 301
7
8
398 @ 301
520 @ 301
—
9
10
11
483 @ 390
429 @ 390
0.36
0.013
12
13
14
15
431 @ 380
428 @ 380
429 @ 380
430 @ 380
429 @ 380
0.012
0.013
0.01
Fig. 1 a) Absorption spectra of compounds 1–2 and 5–8 in dichloro-
methane and an emission spectrum of compound 1 (lex ¼ 301 nm) in
dichloromethane (c z 1.0 ꢂ 10ꢁ6 mol Lꢁ1) as a typical example (arbitrary
unit); b) absorption spectra of compounds 11–15 in dichloromethane and
an emission spectrum of compound 11 (lex ¼ 380 nm) in dichloromethane
(c z 1.0 ꢂ 10ꢁ6 mol Lꢁ1) as a typical example (arbitrary unit).
0.011
16
0.009
a
Determined in dichloromethane solution (c
z
10ꢁ7 M) using
Rhodamine 6G as reference (FF ¼ 0.78 in water, lexc ¼ 488 nm).26 All
FF are corrected for changes in refractive index.
On cooling of the isotropic liquid, the compound becomes
birefringent and broken-fan shaped textures and large homeo-
tropic domains, typical of a hexagonal columnar phase, were
observed (Fig. 5a). The fluid nature of the material confirms its
liquid-crystalline nature. Below the low-temperature transition
(145 ꢀC), the homeotropic domains become birefringent and the
birefringence properties and the size of the fan-shaped domains
are concomitantly strongly affected (Fig. 5b).
Fig. 2 Absorption spectra of compounds 8, 15 and dyad 16 in
dichloromethane.
Such changes in the birefringence and textural properties are
usually attributed to a high-to-low symmetry phase trans-
formation (e.g. a hexagonal/rectangular lattice phase trans-
formation). The homologous derivative with hexadecyl chains,
12, has a thermal behaviour close to 11, with two reversible
thermal transitions visible by DSC. Above 192 ꢀC, the material is
an isotropic liquid. Cooling below 189 ꢀC leads to the formation
of a mosaic-like texture with pseudo-fan shapes typical of
a hexagonal columnar mesophase, and below 141 ꢀC the textural
changes indicate the formation of another columnar mesophase,
likely with a rectangular symmetry, as above. On further cooling,
two othꢀer additional reversible thermal transitions centred at 33
and 25 C were detected by DSC. Based on POM, these transi-
tions are likely attributed to mesophase/crystal and crystal/
crystal phase transitions, respectively. XRD confirmed the
existence of two mesophases for each compounds, namely a
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Table 2 Thermal behaviour of compounds 1–2, 5–8, 11–14, 15 and 16.a
Onset transition temperatures/ꢀC (DH ¼ enthalpy/kJ molꢁ1
)
Compd
2nd Heating
1st Cooling
1
2
5
6
7
8
11
12
Cr 29 (13.8) Colh 100 (26.15) Iso
Cr 57.5 (42.3) Colh 98 (21.8) Iso
M 112 (13.7) Iso
M 86 (66.9) Iso
Cr 23 (56.2) Iso
Iso 82 (ꢁ21.5) Colh 22(ꢁ13.75) Cr
Iso 81 (ꢁ21.4) Colh 52 (ꢁ31.05) Cr
Iso 82 (ꢁ6.9) M
Iso 16 (ꢁ63.4) M
Iso 20 (ꢁ55.6) Cr
ꢁ20 Iso 110
110 Iso ꢁ20
Colr 161 (19.4) Colh 221 (7.5) Iso
Iso 219 (ꢁ7.5) Colh 145 (ꢁ16.9) Colr
Cr 28 (18.5) Cr0 42 (27.7) Colo 120 (-) Colr 150 (15.5) Colh 192 (7.5) Iso
Iso 189 (ꢁ6.9) Colh 141 (ꢁ14.1) Colr 50 (-) Colo 33 (ꢁ27.9)
Cr0 25 (ꢁ18.3) Cr
13
14
15
16
Colh 235 (4.3) Iso
Iso 228 (ꢁ4.2) Colh
Cr 28 (89.8) Colh 209 (6.8) Iso
Cr 21 (71.4) Colh 230 (30.1) iso
Cr 31 (179.8) Colh 110 (-) Iso
Iso 204 (ꢁ5.6) Colh 22 (ꢁ91.2) Cr
Iso (24.3) 230 Colh 19 (ꢁ71.8) Cr
Iso (-) 105 Colh 24 (ꢁ175.1) Cr
a
Cr, crystalline phase; Iso, isotropic liquid; Colh, hexagonal columnar mesophase; Colr, rectangular columnar mesophase; Colo: oblique columnar
phase; M, amorphous solid.
high-temperature Colh phase and a Colr at lower temperature.
The Colh phase of both compounds was identified by the pres-
ence of three small-angles, sharp reflections, indexed as hk
reflections (10), (11), (20) of a hexagonal lattice with the p6mm
plane symmetry. In the wide angle part, the very intense halo
ꢂ
centred at 4.6 A was associated with the molten chains in the
ꢂ
isotropic state, and another weak diffusion at 3.5–3.8 A, asso-
reversible broad transition, attributed to the crystallization of the
aliphatic chains, is detected on the DSC traces around 28 ꢀC (on
the heating curve, Fig. 4b). At 209 ꢀC, a low enthalpy transition
is detected and POM observations reveal that this transition is
associated with the isotropization temperature. ꢀA thin mosaic-
like texture is observed by POM in the 50–200 C temperature
range. The hexagonal symmetry of the columnar mesophase was
readily confirmed by XRD where two and three sharp reflections,
(10), (11), (20), were detected in the small angle and three diffuse
scatterings in the wide part, h0, hch and h. As above, for
compounds 1 and 2, respectively, these halos correspond to the
molten state of the alkyl chains (hch) and to some intermolecular
interactions (h, h0, short-range uniaxial stacking periodicity). In
both case, the mesophase lattice parameters are quasi invariant
in the mesomorphic temperature ranges (Table 3).
ciated to the short-range stacking of the naphthalene cores (vide
supra). The lower-temperature mesophase X-ray pattern
exhibited broad diffusions, as above for the Colh phases,
evidencing the molten state of the alkyl chains and the persis-
tence, although short-range, of the stacking, and a series of
sharp, small-angle peaks. Despite the presence of only one single
intense and sharp peak (fundamental reflection), the X-ray
pattern was not compatible with hexagonal and square lattices,
and therefore were excluded. However, considering this single
peak as the 11/20 reflection, indexation of all peaks was in
agreement with a rectangular lattice with the p2gg plane group
(Table 3); this particular rectangular phase, with lattice ratio
a/b ¼ O3 is also known as pseudo-hexagonal phase.30 In addition,
12 exhibits another mesophase at a lower temperature than the
Colr phase that could be detected by XRD only, through the shift
of some of the small-angle reflections and the emergence of new
ones. The absence of any apparent changes on the DSC heating
trace suggests a second order phase transition, occuring at ca
120 ꢀC, but that supercools strongly (transition below 60 ꢀC). On
the basis of the X-ray patterns obtained from this mesophase, the
small-angle reflections could be indexed into an oblique lattice
with the p-1 plane symmetry, i.e. the mesophase is an oblique
columnar phase, Colo; the fluid nature of the phase was also
confirmed by the presence of broad diffuse bands in the wide-
angle area.
ꢀ
Finally, 15 displays two reversible transitions, at 21 C, asso-
ciated with the melting of the hydrocarbon chains, and at 230 ꢀC,
the temperature at which the compound clears into the isotropic
liquid. POM observations revealed that above 21 ꢀC the material
is in a liquid-crystalline state, and mosaic-like textures typical of
hexagonal columnar mesophases are observed. Introduction of
the ethyl-amine arm thus slightly stabilizes the Colh phase with
respect to that of 14, since isotropization occurs at 230 ꢀC. XRD
confirmed the presence of a single mesophase between these two
temperatures, although only one peak could be detected in the
small-angles region, insufficient for a proper mesophase assign-
ment. Supported by POM and by the behaviour of its homo-
logues (12 and 14), the phase is likely columnar and was assigned
ꢂ
as Colh, with a lattice parameter of 44.3 A.
Thermal behaviour of the carbazole-naphthalene dyad 16.
Finally, the dyad 16 resulting from the connection of 8 and 15
displays a single broad and reversible thermal transition on the
DSC traces at 31 ꢀC. As already mentioned, this broad transition
is associated to the melting of the carbon chains. Above this
transition, no texture could be observed by POM. Although,
mechanical constraints on the top glass cover slide induced the
emergence of birefringence. This behaviour can be explained by
the strong tendency of the material to form homeotropic
The pendant naphthalene acid derivatives (13 and 14) appear
also to be mesomorphic too. DSC traces of 13 displayed a single
reversible transition centred at 235 ꢀC, above which the material
is isotropic. Upon cooling, a fluid birefringent phase forms and
a pseudo-fan shaped texture typical of columnar hexagonal
phase readily develops (POM). Lengthening of the chains (14)
allows its crystallization at low temperature and an energetic
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Table 3 X-Ray diffraction data and mesophase parameters
b
bd
ꢂ
dtheo/A
T/ꢀCa
I/L
hkc
Parametersef
ꢂ
dexp/A
1
38.4
22.23
19.17
12.75
10.74
7.5
4.6
3.8
42.75
14.15
7.4
VS (sh)
M (sh)
M (sh)
M (sh)
M (sh)
W (br)
VS (br)
W (br)
VS (sh)
M (sh)
W (br)
VS (br)
W (br)
10
11
20
30
31
38.45
22.20
19.22
12.82
10.66
h0
hch
h
42.6
14.2
h0
T ¼ 80 ꢀC
Colh-p6mm
ꢂ
a ¼ 44.4 A
2
ꢂ
S ¼ 1710 A
3
ꢂ
Vmol ¼ 2610 A
ꢂ
h0 ¼ 3.05 A for Z ¼ 2
2
10
30
T ¼ 80 ꢀC
Colh-p6mm
ꢂ
a ¼ 49.2 A
2
ꢂ
4.6
3.6
hch
h
S ¼ 2095 A
3
ꢂ
Vmol ¼ 3195 A
ꢂ
h0 ¼ 3.05 A for Z ¼ 2
11
29.22
22.5
16.0
13.2
4.7
VS (sh)
VS (sh)
W (sh)
M (sh)
VS (br)
W (br)
11/20
21
12
—
T ¼ 120 ꢀC
22.1
16.2
13.4
hch
h
Colr-p2gg
ꢂ
a ¼ 58.4 A
ꢂ
41
b ¼ 33.72 A
2
ꢂ
S ¼ 984.5 A
3
ꢂ
3.7
Vmol ¼ 3000 A
ꢂ
h0 ¼ 3.05 A for Z ¼ 1
28.9
16.62
14.47
4.6
VS (sh)
S (sh)
M (sh)
VS (br)
M (br)
10
11
20
28.87
16.67
14.43
hch
T ¼ 180 ꢀC
Colh-p6mm
ꢂ
a ¼ 33.3 A
2
ꢂ
S ¼ 965 A
3
ꢂ
3.5
h
Vmol ¼ 3015 A
ꢂ
h0 ¼ 3.1 A for Z ¼ 1
12
33.44
30.75
26.22
21.73
18.29
16.84
14.17
12.75
4.75
3.8
32.8
24.32
18.8
17.85
14.7
4.7
VS (sh)
VS (sh)
S (sh)
11
1–1
20
2-1
1-2
31/22
32
41/1-3
—
—
—
21.2
18.33
16.6/16.7
13.8
12.8
hch
h
—
24.8
18.94
18.2
14.3/15.05
hch
T ¼ 80 ꢀC
Colo-p-1
ꢂ
a ¼ 52.64 A
ꢂ
S (sh)
b ¼ 40.6 A
VS (sh)
W (sh)
W (sh)
W (sh)
VS (br)
M (br)
VS (sh)
VS (sh)
S (sh)
g ¼ 85ꢀ
2
ꢂ
S ¼ 1060 A
3
ꢂ
Vmol ¼ 3500 A
ꢂ
h0 ¼ 3.3 A for Z ¼ 1
11/20
21
31/02
12
32/41
T ¼ 140 ꢀC
Colr-p2gg
ꢂ
ꢂ
a ¼ 65.6 A, b ¼ 37.87 A
2
ꢂ
S (sh)
S ¼ 1242 A
3
ꢂ
M (sh)
VS (br)
M (br)
VS (sh)
S (sh)
Vmol ¼ 3500 A
ꢂ
h0 ¼ 3.05 A for Z ¼ 1
3.7
h
32.3
18.6
16.1
7.8
4.6
3.8
26.86
15.48
8.0
4.7
3.75
10
11
20
32.24
18.61
16.12
h0
hch
h
26.84
15.49
h0
hch
h
T ¼ 160 ꢀC
Colh-p6mm
ꢂ
S (sh)
a ¼ 37.23 A
2
ꢂ
M (br)
VS (br)
M (sh)
VS (sh)
M (sh)
M (br)
VS (br)
M (br)
S ¼ 1200 A
3
ꢂ
Vmol ¼ 3590 A
ꢂ
h0 ¼ 3.0 A for Z ¼ 1
13
14
15
10
11
T ¼ 160 ꢀC
Colh-p6mm
ꢂ
a ¼ 30.99 A
2
ꢂ
S ¼ 830 A
3
ꢂ
Vmol ¼ 2925 A
ꢂ
h0 ¼ 3.5 A for Z ¼ 1
a ¼ 30.63, 30.8, 31.41, and 31.98 at T ¼ 120, 140, 180 and 200 ꢀC
30.05
17.31
14.84
8.0
4.7
3.8
VS (sh)
S (sh)
M (sh)
M (br)
VS (br)
M (br)
10
11
20
29.9
17.26
14.95
h0
hch
h
T ¼ 140 ꢀC
Colh-p6mm
ꢂ
a ¼ 34.52 A
2
ꢂ
S ¼ 1030 A
3
ꢂ
Vmol ¼ 3490 A
ꢂ
h0 ¼ 3.45 A for Z ¼ 1
a ¼ 34.4, 34.6, 34.7, 34.9, 35.1 at T ¼ 120, 140, 160, 180 and 200 ꢀC
38.4
4.7
VS (sh)
VS (br)
10
38.4
hch
T ¼ 100 ꢀC
Colh-p6mm
ꢂ
a ¼ 44.3 A
2
ꢂ
S ¼ 1700 A
3
ꢂ
Vmol ¼ 3490 A
ꢂ
h0 ¼ 4.7 A for Z ¼ 2
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Table 3 (Contd.)
b
bd
ꢂ
dtheo/A
T/ꢀCa
I/L
hkc
Parametersef
ꢂ
dexp/A
16
33.16
19.1
9.0
VS (sh)
M (sh)
M (br)
VS (br)
10
11
h0
33.1
19.1
h0
T ¼ 100 ꢀ
C
Colh-p6mm
ꢂ
a ¼ 38.2 A
2
ꢂ
4.7
hch
hch
S ¼ 1265 A
3
ꢂ
Vmol ¼ 6420 A
ꢂ
h0 ¼ 4.7 A for Z ¼ 1
a
T and T0 in ꢀC, T0 ¼ 25 ꢀC, and T is the experimental temperature. b dexp and dtheo are the experimentally measured and theoretical diffraction spacings.
c
The distances are given in A. [hk] are the indexation of the reflections. Intensity of the reflections: VS: very strong, S: strong, M: medium, W: weak,
ꢂ
VW:very weak; br and sh stand for broad and sharp (diffuse) reflections, respectively. d dtheor is deduced from the lattice parameter a (Colh) from the
following mathematical expressions: a ¼ 2[Shkdhk.(h2 + k2 + hk) ]/O3 ꢂ Nhk where Nhk is the number of hk reflections and S is the lattice area: S ¼ a231/2/2.
½
For the Colr phase, dhk ¼ 1/O(h2/a2 + k2/b2) and S ¼ ab/2. For the Colo phase, a ¼ 2d20/sing and b ¼ A/sing, where A ¼ (2/{(1/d11)2 + (1/d1–1)2 ꢁ (1/
e
2d20)2})1/2 and S ¼ absing/2. h0 is the average intracolumnar repeating distance, deduced directly from the measured molecular volume and the
columnar cross-section according to h0 ¼ ZVmol/S, where Z is the aggregation number or the number of molecular equivalents per stratum of
column. Three diffuse scatterings were measured h, hch, and h0, corresponding to the intermolecular stacking, the molten chains in the liquid state,
f
respectively and h0 is likely connected to h (h0 ¼ 2h). Vmol is the molecular volume: Vmol ¼ (MW/0.6022) ꢂ (VCH2(T)/VCH2(T0)), where MW is the
molecular weight and VCH2 ¼ 26.5616 + 0.02023T
Fig. 3 X-Ray pattern recorded at 80 ꢀC for 1 in the Colh phase.
domains between non treated glass slides. Two sharp small-
angles reflections were measured by SA-XRD, allowing the
unequivocal identification of theꢀ mesophase as Colh, with
ꢂ
a lattice parameter of 38.2 A at 100 C. XRD measurements also
revealed that this compound is in the isotropic liquid phase above
110 ꢀC, although thermal transition at this temperature was not
detected by DSC, suggesting that the mesophase is highly
disordered.
The mesomorphism of all the mesogens described here is
characterized by the formation of columnar mesophases, and
therefore the molecules are likely to stack on top of each other in
order to generate columns with circular cross-sections (Colh
phase) or non-circular cross-sections (Colr and Colo meso-
phases).30 From the experimental data gathered in Table 3, one
can conclude that the supramolecular aggregation into columns
is different in carbazole derivatives and naphthalene materials, as
evidenced by the great variation of the surface lattices areas. For
all organic compounds shown here, a density of 1 g cmꢁ3 was
reasonably considered. For compounds 1 and 2, the formation of
columns necessitates the association of two mesogenic carbazoles
to fill the large hexagonal lattice, likely in a head-to-head
assembly, and to generate ‘‘supramolecular’’ discotic slices
h0-thick that stack on top of each other into columns. The
Fig. 4 DSC traces of compounds 11 (a) and 14 (b) (second heating curve
(black) and first cooling curve (red)).
presence of the short-range periodicities h and h0 suggests an
alternated p/2 stack, with a further slight deviation from the
lattice plane (i.e. the dimer adopts a propeller conformation) to
optimize space filling. For these compounds, 12 diverging
aliphatic chains are therefore required to fill the available space
between hard columnar core hexagonal networks (formed by the
rigid molecular parts). As for the naphthalene derivatives 11–14,
424 | Soft Matter, 2011, 7, 412–428
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hydrogen bonding, as clearly evidenced by the nNH and nCO
stretching vibrations that lie respectively in the range 3230–3340
and 1638–1657 cmꢁ1. Notice that corresponding values for the
free amides are at 3400 cmꢁ1 for nNH and around 1680 cmꢁ1 for
nCO.
13,31 The presence of single nNH, nCO stretching bands in the
IR spectra confirms a well-organized hydrogen bonded network
in which only one type of hydrogen bond is effective. The
frequencies of the bands due to CH2 antisymmetric and
symmetric modes [na(CH2) and ns(CH2)] of the alkyl chains
appear at ca 2914–2921 and ca 2850–2852 cmꢁ1 and indicate that
the hydrocarbon chains are all in trans conformation.32 These
trans peaks at 2920 and 2851 cmꢁ1 shifted to around 2926 and
2855 cmꢁ1, respectively, if the population of the cis form in the
alkyl chains increases.33 FTIR measurements performed at room
temperature in the liquid crystalline or crystalline phases
revealed that the amide functions are involved in hydrogen
bonds. These results confirm that the amide function introduced
on the platforms play a role in the intermolecular interactions
and in the stabilization of the organized phases.
Solid state luminescence
Temperature-dependent fluorescence measurements were per-
formed in the solid state with a spectrofluorometer equipped with
an optical fiber and a heating stage. The carbazole derivatives
were found to be non-luminescent in the solid state at room
temperature. Emission spectra of the naphthalene derivatives
showed a broad emission band centred at 520–540 nm upon
excitation at 388 nm at room temperature, whereas a dual
emission was observed in fluid solution (Fig. 1b). The red-shift
observed on the emission spectra is likely attributed to head-to-
tail orientation or J-aggregates of the naphthalene cores in solid
state.34 The evolution of the luminescence of compound 11 in the
solid state as a function of the temperature is presented in Fig. 6.
Increasing the temperature in the crystalline phase does not
significantly change the shape of the emission band but decreases
the emission intensity due to non-radiation deactivation path-
ways. The emission maximum is slightly blue-shifted by about
25 nm upon heating. In the Colh phase above 160 ꢀC, the
intensity of the luminescence drastically drops and a red-shift of
17 nm is observed. The red-shift observed in the liquid crystalline
phase is likely attributed to efficient intermolecular interactions
inside the aggregates, favoured by the soft nature of this phase.
The fact that the global fluorescence is quenched by increasing
the temperature is not surprising and likely due to collisional
interactions between ground and excited states which favor non-
radiative decay of the fluorescence like in a solid state.35,36 We
thus speculate that in the Colr mesophase (below 160 ꢀC) the
molecules are less prone to deactivation due to a less favorable
structural organization. However, in the Colh mesophase (above
160 ꢀC) the molecules are better organized as dimer or oligomers
which favor a bathochromic shift of the steady state emission but
also a better desactivation in the excited state. Likewise, by
cooling the isotropic melt to the various mesophases the spec-
troscopic behavior is reversible demonstrating the dynamic
nature of the fluorophore organization within the mesophases.
Upon cooling, the reverse process is observed, excluding
decomposition of the materials. At the Colh/crystal transition,
a blue-shift is observed and the intensity of emitted light
Fig. 5 Same area of compound 11 observed by optical microscopy at
190 ꢀC (a) and at 130 ꢀC (b) between crossed-polarizers (symbolized by
the cross in the corner of the picture).
with small lattices sizes, only one mesogen is necessary to form an
elementary columnar slice of thickness h0 (Table 3), i.e. 6
diverging aliphatic chains per slice radiating from the columnar
interface, similarly to single discotic molecules. The different
symmetries of the planar arrangements of the columns result
from a more or less pronounced tilt of the molecular plane with
respect to the lattice planes, thus generating a non-circular
projection of the columnar cross sections onto the lattice plane,
and thus inducing a change in the symmetry.30 The presence of
the two short-range wide-angle periodicities (h and h0) suggests,
as above a local alternated p/2 stack ordering. The connection of
the ethylene diamine fragment yielding 15 results in a change
of the self-organisation process as evidenced by a huge increase
2
ꢂ
of the hexagonal lattice (Table 3, S increases from 1030 A for 14
2
to 1700 A for 15, i.e. about 70% increase, concomitantly with h0
ꢂ
ꢂ
ꢂ
from 3.45 A to 4.7 A). Now, two molecules (12 orthogonal chains
per slice) are needed to form the repeat discotic unit, and, as for
compounds 1 and 2, they are likely arranged in a head-to-head
manner to be able to pave the hexagonal lattice, although this
time the stacking is random, without preferential orientation of
the pairs of molecules. Finally, for the 12-chains-containing dyad
16, only one dimer per h0 (or two per h0) is necessary to generate
the columnar organization; the absence of additional signal in
the wide-angle part of the diffractogram implies that the mole-
cules are randomly stacked into columns.
FT-IR measurements performed in the mesophases or in the
ꢀ
crystalline phases (at 23 C after heating in the isotropic phase)
confirm that the molecular organization is stabilized by hydrogen
bonding interactions. All the amide dipoles are involved in
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Fig. 6 Solid state emission spectra of compound 11 measured at various
temperatures upon heating (lex ¼ 380 nm) (2nd heating cycle).
increases, reaching the value of room temperature. The same
trend was observed for all the naphthalene platforms.
Recently, it has been demonstrated that luminescence prop-
erties of liquid crystalline phases can be exploited to probe the
molecular organization in thin films at the macroscopic scale by
fluorescence microscopy.37 For these reasons, the emission
properties of compound 11 were evaluated by dependence fluo-
rescence experiments with the help of a fluorescence microscope
equipped with a heating stage in the various material states
detected by DSC and XRD. Upon cooling from the isotropic
state, the materials became liquid-crystalline, enabling formation
of homogeneous thin films (Fig. 7a). Well-defined texture can be
observed from droplets of the liquid crystalline material by
optical microscopy under crossed polarizers (Fig. 7b). The fluid
material showed a homogeneous green–yellow luminescence,
which is typical of naphthalene moieties (Fig. 7c). It should be
noted that the compound was still luminescent at elevated
temperatures. Despite the formation of well-defined textures with
compound 11, no domains with different emissions have been
observed at the present stage.
Fig. 7 Drop of compound 11 observed by optical microscopy at 180 ꢀC:
a) with a white light in transmission; b) with a white light in transmission
between crossed-polarizers (symbolized by the cross in the corner of the
picture) (classical texture); c) upon irradiation at 300<lex<350 nm.
Conclusion
Our results show that grafting of trialkoxybenzamide residues to
carbazole or naphthalene skeletons induces liquid crystalline
properties. The nature of the group linking the flat core to the
gallate fragment plays a crucial role in the stabilization of the
thermotropic mesophases. The length of the aliphatic chains has
a small effect on the LC temperature range. A decrease of about
30 ꢀC was found by increasing a single chain length from 12 to 16
carbons. The liquid crystalline properties of the carbazole family
are sensitive to the presence of substituents on the nitrogen atom
present at the tip of the five member ring. In contrast,
compounds of the naphthalene series are more tolerant to
structural chemical transformations, such as the grafting of an
ester, an acid or even of an amide function, and consequently LC
properties are not significantly altered, providing columnar
phases with various lattice symmetries. Interestingly, a dyad,
prepared by connecting a naphthalene template to a carbazole
derivative, led to a liquid crystalline compound over a tempera-
ture range of about 80 ꢀC. These novel compounds are prone to
aggregation in solution but also in the solid state as scrutinized
by absorption and fluorescence studies. Luminescent aggregates
are also observed in the mesophase. In all cases, the amide
functions are engaged in a supramolecular hydrogen-bonded
network, as confirmed by infra-red studies. This work demon-
strates guidelines for programming fluorescent ligands into
self-assembled structures. Such dyads might be suitable for
applications in organic devices since electron rich and electron
poor molecules need to be assembled into nano-segregated
structures for efficient charge separation and charge transport.38
Current work along these lines is in progress in our laboratory.
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