Discotic liquid crystals through molecular self-assembly

Article abstract of DOI:10.1021/ja9631108

We have created self-assembled disk-like aggregates of predictable stoichiometry which form discotic liquid crystalline phases. Attempts to assemble multiple molecules of one compound radially about a second acting as a template failed, presumably owing t

Full text of DOI:10.1021/ja9631108

VOLUME 119, NUMBER 18
MAY 7, 1997
©
Copyright 1997 by the
American Chemical Society
Discotic Liquid Crystals through Molecular Self-Assembly†
Ralf Kleppinger, C. Peter Lillya,* and Changqing Yang‡
Contribution from the Department of Chemistry, UniVersity of Massachusetts, Box 34510,
Amherst, Massachusetts 01003-4510
X
ReceiVed September 4, 1996
Abstract: We have created self-assembled disk-like aggregates of predictable stoichiometry which form discotic
liquid crystalline phases. Attempts to assemble multiple molecules of one compound radially about a second acting
as a template failed, presumably owing to the existence of a stable crystalline phase of the template. This difficulty
was obviated by the choice of tetrakis(n-alkoxy)-6(5H)-phenanthridinones (1a-c), which were expected to form
disk-like dimers by analogy with pyridones. All three of these compounds form columnar hexagonal liquid crystalline
phases as shown by DSC, POM, and X-ray diffraction experiments. Infrared measurements show that 1a-c exist as
hydrogen-bonded aggregates to temperatures well above their clearing points. Intercolumnar spacing and density
considerations require the discotic entities to be dimers.
Liquid crystalline phases (mesophases) formed by rodlike
calamitic) molecules have been known for more than 100
columnar mesophase formation by well-defined disklike su-
pramolecules.
(
years.1 More recently mesophase formation by disklike mol-
Self-assembly of non-disklike molecules to form columnar
6
2
3
mesophases was first noted for neat soaps, not a discotic system.
ecules (discotics) was predicted and verified. Both nematic
and columnar organizations are known.4 While there are many
More closely related to simple discotics are examples like
7
diisobutylsilanediol, Lattermann’s monoaryl esters of cis, cis-
examples of calamitic mesogens that are formed by self-
8
9
1
,3,5-cyclohexanetriol, and Praefcke’s inositol derivatives.
5
assembly via hydrogen bonding, there was no precedent for
These molecules associate to form columnar mesophases
primarily owing to amphiphilic interactions including hydrogen
bonding. Percec’s examples of large wedge-shaped molecules,
which assemble into columns in emulation of tobacco mosaic
virus, are the highest development of this type of self-assembly.
The “endo recognition”, which builds the column cores, is
†
Presented in part at the 209th National Meeting of the American
Chemical Society, Anaheim, CA, April 2-6, 1995, paper No. 103 (ORG).
Taken in part from the Ph.D. Dissertation of Changqing Yang, University
of Massachusetts, 1995.
‡
Current address: Cubist Pharmaceuticals, Inc., 24 Emily Street,
Cambridge, MA 02139.
X
Abstract published in AdVance ACS Abstracts, April, 1, 1997.
(5) (a) Gray, G. W.; Jones, B. J. Chem. Soc. 1953, 4179. (b) Gray, G.
W.; Jones, B. J. Chem. Soc. 1954, 683. (c) Goodby, J. W. Mol. Cryst. Liq.
Cryst. 1984, 110, 205. (d) Kato, T.; Fr e´ chet, J. M. J. J. Am. Chem. Soc.
1989, 111, 8533. (e) Kato, T.; Fujishima, A.; Fr e´ chet, J. M. J. Chem. Lett.
1990, 919. (f) Paleos, C. M.; Tsionvas, D. Angew. Chem., Int. Ed. Engl.
1995, 34, 1696.
(6) Cf.: Spegt, P. A.; Sokolius, A. E. Acta Crystallogr. 1966, 21, 892
and references therein.
(7) Bunning, J. D.; Goodby, J. W.; Gray, G. W.; Lydon, J. E. In Liquid
Crystals of One- and Two-Dimensional Order; Helfrich, W., Heppke, G.,
Eds.; Springer-Verlag: Berlin, 1980; p 397.
(1) (a) Reinitzer, F. Monatsh. Chem. 1888, 9, 421. (b) Kelker, H.; Hatz,
R.; Handbook of Liquid Crystals; Verlag Chemie: Deerfield, FL, 1980.
c) Toyne, A. J. In Thermotropic Liquid Crystals, Gray, G. W., Ed.; John
Wiley & Sons: New York, 1987; p 28.
(
(
2) Ishihara, A. J. Chem. Phys. 1951, 19, 141.
(3) Chandrasekhar, S.; Sadashiva, B. K.; Suresh, K. A. Pramana 1977,
9
, 471. See also: Destrade, C.; Mondon, M. C.; Malthete, J. J. Phys. Colloq.
Paris) 1979, 40B, C3.
4) For reviews, see: (a) Chandrasekhar, S. In AdVanced Liquid Crystals;
Brown, G. H., Ed.; Academic Press, Inc.: New York, 1982; Vol. 5, p 49.
b) Chandrasekhar, S. Liq. Cryst. 1993, 14, 3. (c) Chandrasekhar, S. Liquid
(
(
(
(8) (a) Lattermann, G. Liq. Cryst. 1987, 2, 723. (b) Lattermann, G.;
Staufer, G. Liq. Cryst. 1989, 4, 347. (c) Ebert, M.; Kleppinger, R.; Soliman,
M.; Wolf, M.; Wendorff, J. H.; Lattermann, G.; Staufer, G. Liq. Cryst. 1990,
7, 553.
Crystals; Cambridge University Press: 1977. (d) Tinh, N. H.; Gasparoux,
H.; Destrade, C. Mol. Cryst. Liq. Cryst. 1981, 68, 101. (e) Tinh, N. H.;
Destrade, C.; Gasparoux, H. Phys. Lett. 1979, 72A, 251.
S0002-7863(96)03110-1 CCC: $14.00 © 1997 American Chemical Society

4098 J. Am. Chem. Soc., Vol. 119, No. 18, 1997
Kleppinger et al.
essentially amphiphilic; while the “exo recognition”, responsible
1
0
for the column peripheries, is based on shape recognition. In
the preceding examples, the factors that determine the number
of units that will constitute “one disk” in the aggregated state
remain to be elucidated completely, and confident a priori
prediction of this number is usually not possible. Percec et al.
cited an example in which a column stratum comprises an
average of 5.8 wedge-crown ether units.1
0b
Others have used association mechanisms that lead to
predictable stoichiometry. Thus, Matsunaga et al. employed
hydrogen bonding, which is directed along the column axis to
11
stabilize columnar mesophases, Lehn et al. reported cases of
complementary base pairing,12 and Malth eˆ te et al. have de-
1
3
scribed a case involving carboxyl dimer formation. In the
latter two cases clearly defined dimers are generated and then
stack to form columns. But the resulting discotic mesophases
are formed by simulation of disks by two dimers that pack side
by side, a behavior not easily predictable on the basis of
molecular structure.
Our contribution, described below, provides an example of
rational molecular design of self-assembled disklike supramol-
ecules with predictable stoichiometry that, in turn, form
columnar mesophases. We have used pyridone dimerization,
Figure 1. Potential hydrogen-bonded complex of trisalkoxystilbazoles
with trimesic acid. R ) n-octyl, n-decyl, and n-dodecyl.
14
which is extensively documented in solution and the solid state
and was elegantly employed by Wuest et al. as the basis for
hexacarboxylic acid), in 3:1 or 6:1 mole ratio, respectively, in
THF or pyridine followed by evaporation, infrared and melting
point criteria revealed formation of new compounds. The
trimesic acid-stilbazole complexes chromatographed on silica
gel TLC plates as single compounds of unique Rf which lacked
the characteristic fluorescence of the pure stilbazoles. Optical
microscopy, however, revealed that these solid state complexes
decomposed at a temperature above the melting point of pure
stilbazoles to give heterogeneous mixtures in which crystals
floated on an isotropic melt.
their construction of highly associated solids using a concept
they call molecular techtonics.1
4,15
To provide sufficiently large
central planar cores for our discotics, we choose to study 6(5H)-
phenanthridinones 1. This is not expected to affect dimerization,
since compound 1 itself exists as the hydrogen-bonded dimer
in its crystalline state.16
In a second case, we attempted to prepare a 3:1 bis(n-
19
decyloxy)phthalimide -melamine complex (Figure 2). In this
case no evidence of compound formation was observed. The
bis(n-decyloxy)phthalimide melted at its characteristic melting
point of 139 °C to give melamine crystals suspended in
phthalimide melt.
Failure of these experiments is probably caused by the
existence of very stable crystalline phases of the pure polycar-
boxylic acids and of melamine, rendering complex formation
thermodynamically noncompetitive. Thus, we changed to the
pyridone/phenanthridinone strategy obviating at once this
problem and the requirement that two different compounds form
a single phase. The thermodynamic driving force for dimer
formation, ∆G° ) -2.7 kcal/mol and ∆H° ) -5.9 kcal/mol
for pyridone itself in chloroform at 25c°C, led us to expect
dimerization in the neat melt at temperatures below 200 °C.
Synthesis of 2,3,8,9-Tetrakis(n-alkoxy)-6(5H)-phenanthri-
dinones. Originally, we synthesized tetraalkoxy-9-fluorenone
Results and Discussion
Our initial attempts to create self-assembled disks used central
templates around which several molecules of a second com-
1
7
pound were intended to assemble in radial fashion. When
alkoxystilbazoles1 were mixed with trimesic acid (benzene-
8
1
,3,5-tricarboxylic acid, Figure 1) or mellitic acid (benzene-
2
0
(
9) Praefcke, K.; Marquardt, P.; Kohne, B.; Stephan, W.; Levelut, A.-
M.; Wachtel, E. Mol. Cryst. Liq. Cryst. 1991, 203, 149.
10) (a) Percec, V.; Heck, J.; Lee, M.; Ungar, G.; Alvarez-Castillo, A.
(
J. Mater. Chem. 1992, 2, 1033. (b) Percec, V.; Johansson, G.; Heck, J.;
Ungar, G.; Gatty, S. V. J. Chem. Soc., Perkin Trans. 1 1993, 1411. (c)
Percec, V.; Heck, J.; Tomazos, D.; Falkenberg, F.; Blackwell, H.; Ungar,
G. J. Chem. Soc., Perkin Trans. 1 1993, 2799. (d) Johansson, G.; Percec,
V.; Ungar, G.; Abramic, D. J. Chem. Soc., Perkin Trans. 1 1994, 447. (e)
Percec, V.; Heck, J. A.; Tomazos, D.; Ungar, G. J. Chem. Soc., Perkin
Trans 2 1993, 2381. (f) Percec, V.; Tomazos, D.; Heck, J.; Blackwell, H.;
Ungar, G. J. Chem. Soc., Perkin Trans. 2 1994, 31.
(15) (a) Gallant, M.; Phan Viet, M. T.; Wuest, J. D. J. Org. Chem. 1991,
56, 2284. (b) Persico, F.; Wuest, J. D. J. Org. Chem. 1993, 58, 95. (c)
Boucher, EÄ .; Simard, M.; Wuest, J. D. J. Org. Chem. 1995, 60, 1408. (d)
Gallant, M.; Phan Viet, M. T.; Wuest, J. D. J. Am. Chem. Soc. 1991, 113,
721. (e) Simard, M.; Su, D.; Wuest, J. D. J. Am. Chem. Soc. 1991, 113,
4696. (f) Wang, X.; Simard, M.; Wuest, J. D. J. Am. Chem. Soc. 1994,
116, 12119.
(16) (a) Sen, D. K. Acta Crystallogr. 1970, B26, 1629. (b) Sen, D. K. J.
Cryst. Mol. Struct. 1976, 6, 153.
(17) Yang, C. Ph.D. Dissertation, University of Massachusetts, Amherst,
MA, 1995.
(
11) (a) Kawamata, J.; Matsunaga, Y. Mol. Cryst. Liq. Cryst. 1993, 231,
9 and previous publications. (b) Malth eˆ te, J.; Levelut, A.-M.; Li e´ bert, L.
AdV. Mater. 1992, 4, 36.
12) Brienne, M.-J.; Gabard, J.; Lehn, J.-M.; Stibor, I. J. Chem. Soc.,
7
(
Chem. Commun. 1989, 1868. See also: Lehn, J.-M. Makromol. Chem.,
Makromol. Symp. 1993, 69, 1.
(18) Synthetic details and spectral data for several alkoxystilbazoles are
provided in the Supporting Information.
(19) Synthetic details and spectral data for 4,5-bis(n-decyloxy)phthalimide
are provided in the Supporting Information.
(
(
13) Malth eˆ te, J.; Collet, A.; Levelut, A.-M. Liq. Cryst. 1989, 5, 123.
14) Cf.: Wuest, J. D. In Mesomolecules, From Molecules to Materials;
Mendenhall, G. D., Greenberg, A., Liebman, J., Eds.; Chapman and Hall:
New York, NY, 1995; p 107.
(20) Hammes, G. G.; Park, A. C. J. Am. Chem. Soc. 1969, 91, 956.

Discotic Liquid Crystals through Molecular Self-Assembly
J. Am. Chem. Soc., Vol. 119, No. 18, 1997 4099
Table 1. DSC Results for
Tetrakis(n-alkoxy)-6(5H)-phenanthridinones
1
a
1b
1c
-
K Ma
-
M Ia
-
K Ma
-
M Ia
-
a
- a
K M
M I
heating (°C)
H (J/g)
cooling (°C)
114.2b
98.8
66.7
118.4
2.8
104.7
2.7
88.3
40.5
69.3
57.9
108.0
1.8
103.1
2.0
∆
68.0b
90.4
66.0
111.2 78.8
2.3 69.0
∆
H, (J/g)
a
K: crystalline phase. M: mesophase. I: isotropic phase. b K-I
transitions. Heating and cooling rates: 10 °C.
Following Dow’s route, with the key step a modified
2
3
Negishi-type coupling, biphenyl ester 4 was obtained and
quantitatively converted to nitrobiphenyl ester 5, which was then
demethylated (BBr3) and quenched with methanol to give crude
methyl ester 6. Subsequent alkylation with alkyl bromide,
potassium carbonate, and catalytic amounts of potassium iodide
in refluxing methyl isobutyl ketone followed by chromatography
yielded 7a-c with minor impurities deduced to be the ethyl
1
and octyl/decyl/dodecyl esters by H NMR spectroscopy.
Figure 2. Potential hydrogen-bonded complex of bis(n-decyloxy)ph-
thalimide with melamine.
Reduction of the crude 7a-c followed by recrystallization or
flash chromatography afforded the desired alkoxyphenanthri-
dinones 1a-c in 20-25% overall yield from nitroester 5. The
Scheme 1. Synthesis of Phenanthridinone Derivativesa
1
final products were chromatographically pure, and their IR, H,
13
and C NMR spectra are in accord with the proposed structures.
High-resolution mass spectrometry results were in agreement
2
4
with calculated exact molecular masses.
Thermal Phase Behavior. Thermal phase behavior of
tetrakis(n-alkoxy)-6(5H)-phenanthridinones 1a-c was studied
using differential scanning calorimetry (DSC), polarizing optical
microscopy (POM), and X-ray diffraction. Results of the DSC
studies, which used heating and cooling rates of 10 °C/min,
are presented in Table 1.
Each of the compounds exhibited two, apparently first order,
transitions. The lower temperature transitions exhibit large
enthalpy changes, 40 to 70 J/g, and super-cooling, 19 to 24 °C,
characteristic of melting or crystallization. The higher temper-
ature transitions exhibit small enthalpy changes, 2-3 J/g,
consistent with clearing (mesophase-isotropic) transitions. Super-
cooling results are irregular: small for 1c, and unexpectedly
large but reproducible for 1b. The mesophase for 1a is observed
only on cooling; thus this compound forms a monotropic
mesophase. Two reproducible crystal-crystal endotherms were
observed for 1c below the melting transition.
Polarizing optical microscopy observations confirmed the
existence of viscous fluid birefringent phases at temperatures
between the DSC melting and clearing temperatures. Heating
from the crystalline phase into the mesophase region gave focal
conic textures consistent with columnar organization25 for
compounds 1b and 1c. Upon cooling from the isotropic phase,
all three compounds exhibit dendritic mesophase growth,26
which is a common feature of columnar mesophase formation,
e.g., for triphenylene derivatives. All the samples exhibited
homeotropic regions.
X-ray diffraction from an unoriented sample of 1b at room
temperature produced numerous sharp reflections characteristic
a
(
a) KMnO
c) (i) n-butyllithium, ether, -78 to 0 °C; (ii) ZnCl
Pd(PPh Cl , DIBAL-H, THF, reflux, 54%. (d) HNO
temperature, 99%. (e) (i) BBr ; (ii) MeOH. (f) RBr, K CO
-methyl-2-pentanone. (g) Fe, HOAc, 100 °C; 20-24% for three steps.
4
, NaOH, 75 °C, 88%. (b) EtOH, H
, THF, 0 °C; (iii) 3,
, HOAc, room
, KI, reflux,
2 4
SO , reflux, 94%.
(
2
3
)
2
2
3
3
2
3
4
derivatives and attempted to convert them into the desired
phenanthridinone derivatives via a final Beckmann or Schmidt
rearrangement. Although 9-fluorenone itself undergoes Beck-
mann or Schmidt rearrangement to give 6(5H)-phenanthridinone
in reasonable yield, our attempts were not successful under
various conditions.
2
7
21
1
7
(23) Negishi, E.-I.; Takahashi, T;, King, A. O. In Organic Syntheses;
Dow has reported synthesis of 2,3,8,9-tetrahydroxy-6(5H)-
phenanthridinone via tetramethoxybiphenyl ester 4.22 Modifica-
tion of this route as described in Scheme 1 led to the desired
tetrakis(n-alkoxy)-6(5H)-phenanthridinones (1a-c).
Freeman, J. P., et al., Eds.; John Wiley & Sons: New York, 1993; Collect.
Vol. VIII, p 430.
(
24) Mass spectrometry data were obtained from Midwest Center for
Mass Spectrometry, University of NebraskasLincoln.
25) Billard, J. In Liquid Crystals of One- and Two-Dimensional Order;
(
Helfrich, W., Heppke, G., Eds.; Springer-Verlag: Berlin, 1980; p 383.
(26) Kleppinger, R.; Lillya, C. P.; Yang, C. Angew. Chem., Int. Ed. Engl.
1995, 34, 1637.
(
21) Keene, B. R.; Tissington, P. AdV. Heterocycl. Chem., 1971, 13, 315.
(
22) Dow, R. L., PCT Int. Appl. WO 92 21,660 (Cl. C07D221/12), Dec
1
0, 1992, US Appl. 706,629 29, May 1991; 64 pp. We thank Dr. Dow for
(27) Billard, J.; Dubois, J. C.; Tinh, N. H.; Zann, A. NouV. J. Chim.
1978, 2, 535.
providing us the experimental details for related syntheses.

4100 J. Am. Chem. Soc., Vol. 119, No. 18, 1997
Kleppinger et al.
Figure 3. X-ray scattering diagrams of the unoriented mesophase and
isotropic phase of 2,3,8,9-tetrakis(n-decyloxy)-6(5H)-phenanthridinone
Figure 4. X-ray scattering diagram for the mesophase of 2,3,8,9-
tetrakis(n-decyloxy)-6(5H)-phenanthridinone (1b). The radial intensity
distribution I(s) display reflections from inter- and intracolumnar order.
(1b) from 110 to 180 °C.
-
1
The insert shows the azimuthal intensity distribution I(f, s ) 0.25 Å
)
of a well-ordered crystalline phase; however, elevation of the
temperature to the mesophase region left only two prominent
reflections. The sharp, intense small angle reflection, which
corresponds to intercolumnar spacing, and the broad halo at 4.5
Å, which corresponds to disordered, liquid-like side chains are
presented as a function of temperature in Figure 3. The sharp
reflection at small angle does not disappear suddenly at the
clearing temperature, 120 °C. Rather it broadens in a roughly
continuous fashion as the temperature increases, persisting even
at 180 °C, more than 60 °C above the thermodynamic and
optical clearing temperature. This behavior, which suggests that
local stacking of disks persists above Tc, has been reported
of the intracolumnar reflections, derived from a densitometer-scan,
performed on a flat-chamber X-ray diagram. The original X-ray pattern
was taken from an oriented sample at 110 °C in the mesophase region.
28
previously for Lattermann’s cyclohexane-1,3,5-triol monoesters.
At longer exposure, an unoriented sample of 1b mesophase
revealed sharp reflections corresponding to Bragg spacings of
26, 15, and 13 Å (Figure 4), consistent with hexagonal ordering
of columns. The low intensity of higher order reflections
observed here is in accord with expectation for a columnar
hexagonal organization as pointed out by Levelut29 but not with
a simple lamellar organization. In addition, a broad shoulder,
which we assigned to the 3.6 Å average spacing between disks
in a column, appeared on the wide angle side of the 4.5 Å halo.
To verify the columnar structure, we oriented a sample of 1b
in the mesophase by allowing it to flow down the wall of a
quartz X-ray capillary. The insert in Figure 4 presents the
azimuthal intensity distribution of this broad reflection, which
demonstrated that it is orthogonal to the column axes, which
aligned in the flow direction. Final confirmation of hexagonal
ordering of columns was obtained by orienting the flow direction
parallel to the X-ray beam. In this case, the diffraction pattern
revealed six hexagonally arranged reflections, (Figure 5).
Monomers or Dimers? We next consider whether the
discotic entity is a monomeric tetrakis(n-alkoxy)-6-(5H)-
phenanthridinone, a dimeric, or a higher aggregate. The small-
angle reflections we have observed correspond to a interco-
lumnar spacing of 31 ( 1 Å. This does not fit monomeric
Figure 5. Diffraction pattern from the oriented mesophase of 1b. The
flow direction is approximately parallel to the X-ray beam.
diameter within the limit of experimental uncertainty. Com-
bination of this value with the 3.6-Å intracolumnar disk spacing
-
21
-1
yields a value of 3.0 × 10
cm for the volume of the unit
cell that comprises one discotic entity. If this is a single
phenanthridinone molecule, it leads to the unreasonably low
calculated mesophase density of 0.45 g cm , while if it is a
dimer a reasonable density of 0.90 g cm at 110 °C is
calculated. The same analysis eliminates higher aggregates.
Thus, the discotic entity must be the expected phenanthridinone
dimer.
-
3
-
3
Several related observations are consistent with this conclu-
sion. First, tetrakis(n-decyloxy)-9-fluorenone synthesized in our
17
tetrakis(n-decyloxy)phenanthridinone, a molecule of the size of
laboratory, which approximates the shape of monomeric 1a-c
but lacks hydrogen-bonding sites, exhibits no mesophase. More
persuasive, however, are the results of a variable-temperature
infrared study of 1c from 70 to 170 °C, a range which spans
crystalline, mesotropic, and isotropic phases. The amide I band
2
2
1 × 33 Å . It would require the side chains to be fully
extended in the mesophase, and without interpenetration in
neighboring columns. An additional diffraction experiment with
the tetrakisdodecyl derivative 1c yielded an identical column
-1
at ca. 1670 cm underwent only minor shifts in frequency over
this temperature range. No high-frequency band indicative of
non-hydrogen bonded amide carbonyl was detected.30 N-H
(
28) Festag, R.; Kleppinger, R.; Soliman, M.; Wendorff, J. H.; Latter-
mann, G.; Staufer, G. Liq. Cryst. 1992, 11, 699.
29) Levelut, A. M. J. Phys. Lett. (Paris) 1979, 40, L81.
(

Discotic Liquid Crystals through Molecular Self-Assembly
J. Am. Chem. Soc., Vol. 119, No. 18, 1997 4101
absorption appeared as a broad featureless band near 3200-
Ethyl 2-Bromo-4,5-dimethoxybenzoate (3). A mixture of 2-bromo-
4,5-dimethoxybenzoic acid (2.6 g, 10 mmol), absolute ethanol (50 mL),
and concentrated H
SO (5 mL) was heated at reflux with stirring under
2 4
dry argon overnight. Excess ethanol was removed on a rotary
evaporator, and the residue was dissolved in ethyl acetate. The solution
-1
3
300 cm throughout the entire temperature range. Had a few
percent of monomer been present, this should have been
-
1 30
observed as a small sharp N-H band near 3440 cm .
was washed with water (3×), saturated NaHCO
dried (Na SO ). Solvent was evaporated to afford ethyl 2-bromo-4,5-
dimethoxybenzoate as white powder (2.7 g, 94%), mp 88.5-89 °C.
3
, water, and brine and
Conclusion
2
4
In several attempts to produce self-assembling discotics in
which four to seven molecules comprising two chemical
components were required to associate, we were unable to
observe mesophase formation. Causes for failure may be
manifold, but prominent among them is the existence of a very
stable crystalline phase for one of the components. This
problem was obviated by use of tetrakis(n-alkoxy)-6-(5H)-
phenanthridinones. The octyloxy, decyloxy, and dodecyloxy
derivatives all dimerize as predicted to give discotic entities
which form hexagonal columnar mesophases.
-
1
1
IR (KBr): 1720 cm (CdO str). H NMR (CDCl
3
): δ 7.40 (s, 1H,
2
3
H
-
6
), 7.10 (s, 1H, H
OCH ), 3.91 (s, 3H, -OCH
3
), 4.39 (q, J ) 7 Hz, 2H, -OCH ), 3.92 (s, 3H,
3
3
3
), 1.41 (t, J ) 7 Hz, 3H, -OCH
2
1
CH
3
).
3
Ethyl 3′,4,4′,5-Tetramethoxybiphenyl-2-carboxylate (4). To a
78 °C solution of 4-bromoveratrole (1.50 g, 6.92 mmol) in 10 mL of
-
anhydrous ethyl ether was added n-butyllithium (3.00 mL, 2.5 M in
hexane, 7.5 mmol) to produce a thick white slurry under dry argon.
This slurry was allowed to warm to 0 °C and stirred under argon at
this temperature for 30 min. Anhydrous THF (5 mL) was then added
to the mixture, and the white slurry was transferred slowly with a dry
2
syringe to a cold (0 °C) stirred solution of ZnCl (1.10 g, 8.07 mmol,
fused immediately prior to use) in THF (10 mL). The resulting turbid
solution was stirred at 0 °C for 30 min.
Experimental Section
General Data. All chemical reagents and solvents were purchased
from Aldrich Chemical Company or Fisher Scientific unless specified
and were used without prior purification, unless otherwise stated. Dry
tetrahydrofuran and dry diethyl ether were distilled from sodium
benzophenone. Dry methylene chloride was distilled from calcium
hydride.
In another flask, diisobutylaluminum hydride (0.25 mL × 1.0 M in
2 2 3 2 2
CH Cl ) was added to a solution of Pd(PPh ) Cl (121 mg, 0.25 mmol)
in anhydrous THF (5 mL) via a dry syringe to give a deep black
solution. After all yellow Pd(II) crystals disappeared, ethyl 2-bromo-
,5-dimethoxybenzoate (1.00 g, 3.46 mmol) was added, and the
4
resulting solution was transferred with a dry syringe to the arylzinc
chloride solution at 0 °C. After the mixture was brought to room
temperature, a condenser was attached, and the mixture was heated at
reflux for 40 h. After cooling to room temperature, the mixture was
poured into ice-cold 1 M HCl solution. The organic materials were
extracted with ethyl acetate, washed with water (3×), saturated
Thin layer chromatography was performed on Whatman flexible
plates (PE SIL G/UV) or Baker-Flex plates (Silica Gel IB2-F). Flash
chromatography was performed using 60 Å, 200-400 mesh silica gel,
1
purchased from Aldrich, under dry nitrogen pressure. H NMR and
13
C NMR spectra were obtained from Brucker AC200 and MSL300
instruments at 200 and 75 MHz, respectively, with tetramethylsilane
as internal standard. Routine IR spectra were obtained on a Perkin-
Elmer 1420 ratio recording infrared spectrometer. Mass spectrometry
was performed by the Midwest Center for Mass Spectrometry,
University of NebraskasLincoln following the FAB method with a
3 2 4
NaHCO , and brine, and dried (Na SO ). The solvent was evaporated,
and the residue was purified by flash chromatography (30% ethyl acetate
in hexane, 250 g of silica gel) to afford ethyl 3′,4,4′,5-tetramethoxy-
biphenyl-2-carboxylate as a yellowish-white solid (645.1 mg, 54%).
-1
1
IR (KBr): 1706, 1730 cm (CdO str) H NMR (CDCl ): δ 7.39 (s,
3
3
-NBA matrix.
3
3
1
)
3
H, H
3
), 6.89 (d, J ) 10 Hz, 1H, H5′), 6.88 (bs, 1H, H2′), 6.83 (d, J
Differential scanning calorimetry was performed with a Perkin-Elmer
3
10 Hz, 1H, H6′), 6.82 (s, 1H, H
6
), 4.08 (q, J ) 7 Hz, 2H, -OCH
), 3.93 (s, 3H, -OCH
), 1.02 (t, J ) 7 Hz, 3H, -OCH CH ).
Ethyl 2′-Nitro-4,4′,5,5′-tetramethoxybiphenyl-2-carboxylate (5).
2
),
DSC 7 Series instrument at heating and cooling rates of 10 °C/min. A
nitrogen atmosphere was maintained over ca. 5-mg samples. Daily
calibration of temperature and enthalpy was performed with an indium
standard. Polarizing optical microscopy was performed with a Leitz
microscope equipped with a LINKAM heating stage. Samples were
placed between clean glass slides and observed under crossed polarizers
as they were heated at the rate of 5 °C/min.
Wide angle X-ray scattering was performed on a Siemans D-500
goniometer, using Cu KR radiation (λ ) 1.54 Å) operating in the
reflection mode. Heating was maintained with a home-made heating
stage. Flat chamber exposures on samples, annealed just below the
clearing temperature, were performed with a Statton camera, using an
X-ray beam collimated with a 200-mm pinhole.
.96 (s, 3H, -OCH
.88 (s, 3H, -OCH
3
), 3.94 (s, 3H, -OCH
3
3
),
3
3
3
2
3
To a stirred solution of ethyl 3′,4,4′,5-tetramethoxybiphenyl-2-car-
boxylate (600 mg, 1.73 mmol) in glacial acetic acid (10 mL) was added
concentrated nitric acid (25 drops, about 0.4 mL). After being stirred
for about 10 min, the reaction mixture was poured onto ice, and the
bright yellow solid was extracted with ethyl acetate. The organic phase
2 2 4
was washed with H O, 20% NaOH, and brine and dried (Na SO ).
Removal of solvent afforded ethyl 2′-nitro-4,4′,5,5′-tetramethoxybi-
phenyl-2-carboxylate as a bright yellow powder (668 mg, 98.5%), mp
22
1
25-127 °C (lit. mp 126-128 °C). IR (KBr): 1710 (CdO str), 1515
1 1
-
and 1340 cm (N-O str). H NMR (CDCl
.61 (s, 1H, H3′ or H6′), 6.66 (s, 1H, H ), 6.65 (s, 1H, H6′ or H3′), 4.08
-), 4.01 (s, 3H, -OCH ), 3.99 (s, 3H,
), 3.91 (s, 3H, -OCH ), 1.09 (t, J ) 7
3
): δ 7.73 (s, 1H, H
3
),
2
-Bromo-4,5-dimethoxybenzoic Acid (2). A solution of KMnO
4
7
(
-
6
(1.11 g, 7.0 mmol) in water was added to a mixture of 6-bromovera-
3
q, J ) 7 Hz, 2H, -CO
2
CH
), 3.93 (s, 3H, -OCH
CH CH ).
2
3
traldehyde (1.22 g, 5.0 mmol) and water (20 mL) at 75 °C over a period
of 20 min. The reaction mixture was heated at this temperature for 2
h with vigorous stirring. Aqueous KOH (20%) was then added until
the reaction mixture was strongly alkaline. The mixture was filtered
hot, and the residue was washed thoroughly with hot water. The
combined filtrate and washings were cooled to room temperature, and
unreacted aldehyde (121 mg) was removed by gravity filtration. The
clear colorless filtrate was then acidified using concentrated HCl to
pH 2. The white precipitate was collected by filtration and washed
with cold water to afford 2-bromo-4,5-dimethoxybenzoic acid as a white
powder (1.03 g, 88% adjusted for recovered aldehyde), mp 190.5-
3
OCH
3
3
3
Hz, 3H, -CO
2
2
3
Methyl 2′-Nitro-4,4′,5,5′-tetrahydroxybiphenyl-2-carboxylate (6).
To a solution of ethyl 2′-nitro-4,4′,5,5′-tetramethoxybiphenyl-2-car-
boxylate (100 mg, 0.256 mmol) in anhydrous CH Cl was added boron
2 2
tribromide (0.12 mL, 0.32 g, 1.3 mmol) at -78 °C via a syringe. The
resulting dark red solution was brought to room temperature and stirred
at room temperature for 2 h. Ten milliliters of anhydrous methanol
was injected with caution through another dry syringe. The solution
was heated at reflux with stirring overnight; then most of the solvent
along with the trimethyl borate generated was distilled. Dry methanol
was added to the residue. The mixture was heated at reflux for 2 h
and methanol and methylborate were removed by distillation. This
1
91.5 °C. This chromatographically and spectrally pure sample was
-
1
1
not further purified. IR (KBr): 1710 cm (CdO str). H NMR
CDCl ): δ 7.60 (s, 1H, H ), 7.14 (s, 1H, H ), 3.95 (s, 3H, -OCH ),
.93 (s, 3H, -OCH ).
(
3
3
6
3
3
was repeated one more time, and the residue was further concentrated
3
1
in Vacuo to afford a deep brown colored solid. H NMR (acetone-d
6
)
(
30) Conley, R. T. Infrared Spectroscopy; Allyn and Bacon: Boston,
MA, 1966; pp 150 and 164.
(31) Adopted from the method of Dow, see ref 22.

4102 J. Am. Chem. Soc., Vol. 119, No. 18, 1997
Kleppinger et al.
revealed no aryl methyl ether signals. This crude methyl 2′-nitro-
,4′,5,5′-tetrahydroxybiphenyl-2-carboxylate was used in the subsequent
alkylation.
,3,8,9-Tetrakis(n-decyloxy)-6(5H)-phenanthridinone (1b).
mixture of crude methyl 2′-nitro-4,4′,5,5′-tetrahydroxybiphenyl-2-
carboxylate, K CO (5 g), KI (0.1 g), 1-bromodecane (0.50 mL, 0.53
7.42 (s, 1H, H
1
), 6.77 (s, 1H, H
(quin, J ) 7 Hz, 8H, -OCH CH
). C NMR (CDCl
4
), 4.24-4.07 (m, 8H, -OCH
), 1.3 (m, 40H, -CH -), 0.89 (t, J
): δ 162.2 (C ); 153.7, 151.3,
2
-), 1.90
3
3
4
2
2
2
13
) 6 Hz, 12H, -CH
149.0, and 145.4 (C2,3,8,9); 130.9 (C4a); 129.8, 118.3, and 111.4
(C6a,10a,10b); 109.9, 108.8, 104.3, and 100.7 (C1,4,7,10); 71.0, 69.3, and
3
3
6
2
A
2
3
69.2 (-OCH -); 31.8, 29.6, 29.4, 29.3, 29.2, 26.1, and 22.7
2
g, 2.4 mmol), and 25 mL of methyl isobutyl ketone was heated at reflux
under dry argon with vigorous stirring for 4 days. At the end of the 4
day period, the mixture was filtered hot, and the residue was washed
with hot Skelly C (bp 88-99 °C). The combined filtrate was
concentrated in Vacuo, the concentrate was dissolved in ethyl acetate,
(-CH
2
-); 14.1 (-CH
3
). MS: Calcd for C45
H73NO
5
:
707.5489.
+
+
Found: [M ] 707.5487, [M + 1] 708.5548.
2,3,8,9-Tetrakis(dodecyloxy)-6(5H)-phenanthridinone (1c): 24%
from 5, K 88 °C M 108 °C I. IR (KBr): 3400 (br, N-H str), 1670
cm-1 (CdO str).
1
H NMR (CDCl ): δ 9.89 (bs, 1H, NH), 7.88 (s,
3
washed with 10% K
2
3
CO , water, and brine, and dried (Na
2
SO
4
), and
1H, H ), 7.49 (s, 1H, H ), 7.41 (s, 1H, H ), 6.73 (s, 1H, H ), 4.24-
7
10
1
4
the solvent was evaporated. Flash chromatography (ethyl acetate-
hexane (1:10) as eluent) afforded methyl 2′-nitro-4,4′,5,5′-tetrakis(n-
decyloxy)biphenyl-2-carboxylate (7b) as a light yellow solid (117.9
4.06 (m, 8H, -OCH ), 1.90 (quin, J ) 7 Hz, 8H, -OCH CH -),
3
3
2
2
2
J ) 6 Hz, 12H, -CH3). 13C NMR
1.5-1.3 (m, 72H, -CH -), 0.88 (t,
2
(CDCl ): δ 162.2 (C ); 153.7, 151.3, 149.0, and 145.4 (C2,3,8,9); 130.8
3
8
mg) with minor impurities. IR (KBr): 1720 cm (CdO str). 1H NMR
-1
4a
(C ); 129.7, 118.4, and 111.4 (C6a,10a,10b); 110.0, 108.9, 104.3, and 100.7
(
CDCl
3
): δ 7.69 (s), 7.58 (s), 6.62 (s), 4.0 (m), 3.63 (s), 1.8 (m), 1.3
(C1,4,7,10); 71.0, 69.3, and 69.2 (-OCH -), 31.9, 29.72, 29.68, 29.53,
2
(m), 0.8 (m).
29.46, 29.39, 29.2, 26.1, and 22.7 (-CH -); 14.1 (-CH ). MS: Calcd
2
3
To this ester (7b) was added glacial acetic acid (10 mL). About 1
for C H105NO5: 931.7993. Found: [M
+
] 931.8028, [M
+
+ 1]
61
mL of dry THF was added to make sure the ester 7b was totally
dissolved. Fine iron powder (250 mg, 4.5 mmol) was added to the
solution, and the mixture was heated under argon with vigorous stirring
at 100 °C overnight. When the reaction mixture was cooled to room
temperature, excess iron was removed with the magnetic stir bar and
the white suspension was poured onto ice to produce a white precipitate.
The white precipitate was collected by filtration and washed with cold
water. The crude product was subjected to flash chromatography on
a silica gel column (ethyl acetate-hexane 5:95) to afford 2,3,8,9-
tetrakis(n-decyloxy)-6(5H)-phenanthridinone (1b) as a white powder
932.8101.
Acknowledgment. We thank the donors of the Petroleum
Research Fund, administrated by the American Chemical
Society, and the University of Massachusetts Materials Research
Laboratory, funded by the National Science Foundation, for
grants to support this work. R.K. acknowledges the Deutsche
Forschungsgemeinscheft for a fellowship grant (KL 954/1-1).
We thank Professors S. L. Hsu and R. S. Porter, Department of
Polymer Science and Engineering, Professor H. H. Winter,
Department of Chemical Engineering, and the Materials Re-
search Science and Engineering Center, University of Mas-
sachusetts for use of instruments. Dr. R. L. Dow, Pfizer Inc.,
generously supplied details of his related synthesis. Both C.P.L.
and C.Y. enjoyed the hospitality of the Institut f u¨ r Organische
Chemie der Universit a¨ t, Mainz, Germany, during the course of
this work.
(
3
50 mg, 24% from 5 in three steps), K 99 °C M 118 °C I. IR (KBr):
-
1
1
400 (br, N-H str), 1670 cm (CdO str). H NMR (CDCl
), 7.49 (s, 1H, H10), 7.41 (s, 1H, H
), 4.2-4.0 (m, 8H, -OCH ), 1.9 (m, 8H, -OCH CH
3
): δ 9.53
(
6
s, 1H, -NH), 7.86 (s, 1H, H
7
1
),
.69 (s, 1H, H
.5-1.2 (m, 56H, -(CH
): δ 162.0 (C
30.8 (C4a); 129.7, 118.4, and 111.4 (C6a,10a,10b); 110.0, 108.9, 104.3,
4
2
2
2
13
),
C
3
1
2
)
7
-), 0.88 (t, J ) 7 Hz, 12H, -CH
3
).
NMR (CDCl
1
3
6
); 153.7, 151.3, 149.1, and 145.4 (C2,3,8,9);
and 100.6 (C1,4,7,10); 71.0, 69.3, and 69.2 (-OCH -); 31.9, 29.6, 29.5,
2
2
C
9.2, 26.1, and 22.7 (-CH
2
-); 14.1 (-CH
3
). MS: Calcd for
: 819.6741. Found: [M ] 819.6741, [M + 1] 820.6797.
+
+
53
H89NO
5
Anal. Calcd for C53
7.35; H, 11.27; N, 2.02.
The following compounds were obtained by using the same
procedure:
5
H89NO : C, 77.60; H, 10.96; N, 1.71. Found: C,
Supporting Information Available: Synthetic details for
4-(3′,4′,5′-tris(n-alkoxy)styryl)pyridines and 4,5-bis(n-decylox-
y)phthalimide; IR, H, C, and high-resolution mass spectra
for 1a-c; DSC traces for 1a-c and partial variable temperature
FT-IR spectra for 1c (20 pages). See any current masthead page
for ordering and Internet access instructions.
7
1
13
2,3,8,9-Tetrakis(n-octyloxy)-6(5H)-phenanthridinone (1a): 20%
from 5, mp 114 °C; purified by recrystallization from ethyl acetate. IR
-
1
1
(
(
KBr): 3400 (br, N-H str), 1670 cm (CdO str). H NMR
CDCl ): δ 10.23 (bs, 1H, NH), 7.89 (s, 1H, H ), 7.50 (s, 1H, H10),
3
7
JA9631108