Star-shaped conjugated compounds forming nematic discotic systems

Article abstract of DOI:10.1016/j.tet.2004.06.012

Star-shaped compounds, having a benzene (9a,b) or a 1,3,5-triazine (11a,b) core and stilbenoid arms were prepared. Hexyloxy chains, attached in the middle of the arms, provide nematic discotic phases N_D, which are unusual for such systems. The

Full text of DOI:10.1016/j.tet.2004.06.012

Tetrahedron 60 (2004) 6881–6888
Star-shaped conjugated compounds forming nematic
discotic systems
*
Herbert Meier, Matthias Lehmann, Hans Christof Holst and Dirk Schwoppe
¨
Institute of Organic Chemistry, Johannes Gutenburg—University of Mainz, Duesbergweg 10-14, D-55099 Mainz, Germany
Received 2 April 2004; accepted 3 June 2004
Available online 4 July 2004
Abstract—Star-shaped compounds, having a benzene (9a,b) or a 1,3,5-triazine (11a,b) core and stilbenoid arms were prepared. Hexyloxy
chains, attached in the middle of the arms, provide nematic discotic phases ND, which are unusual for such systems. The position of the
sidechains prevents the micro-segregation, which is valid for star-shaped discs of columnar phases. The stilbenoid character of 9a,b and
11a,b guarantees a high light sensitivity. Apart from the statistical CC bond formation by irradiation in solution or in the LC phases, a
topochemically controlled chemo-, regio- and stereoselective photocyclodimerization 11a!12 was found in the crystalline state. The
structure determination of 12 is based on different two-dimensional NMR techniques (COSY, NOESY, HMQC, HMBC).
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
2. Results and discussion
Molecules with an arene or hetarene core and three or
more conjugated arms, which consist of oligo(1,4-phenyl-
enevinylene) arms (OPV) or oligo(1,4-phenylene-
ethynylene) arms (OPE), form (in the time average) planar
discs and represent, therefore, suitable mesogens for
discotic liquid crystals (LC). Most common are benzene
cores1–17 and 1,3,5-triazine or pyrazine cores18–23 and
long, flexible alkyl or alkoxy chains at the periphery. Such a
molecular design provokes the formation of hexagonal or
rectangular columnar LC phases having a micro-segregation
between the region of the p electron systems and the region
of the saturated chains. However, the attachment of alkoxy
chains in the middle of the arms should prevent such an
arrangement, so that nematic mesophases, formed by single
discs or two or more weakly aggregated discs, can be
expected. Moreover, we attached CN groups at the
periphery of the arms in order to generate a donor–acceptor
or an acceptor–donor–acceptor character of the arms. The
multipolarity should increase the interaction between the
discs. Thus, the molecular concept was based on benzene or
1,3,5-triazine cores with three corresponding stilbenoid
arms—as shown for the compounds 9a,b and 11a,b in
Scheme 1.
2.1. Synthesis of star-shaped compounds
1,4-Dihexyloxybenzene (1) represents an electron-rich
arene which enters a twofold electrophilic substitution by
an uncatalyzed reaction with bromine.24–26 The obtained
1,4-dibromo-2,5-dihexyloxybenzene (2) can be transformed
by a Bouveault reaction to the monoaldehyde 3. Acetal
formation with trimethoxymethane in the presence of
Dowex furnishes high yields of the corresponding dimethyl
acetal 4, which gives in a second Bouveault process the
mono-protected terephthalaldehyde 5. The Wittig–Horner
reaction of 5 and phosphonate 6a27 or 6b28 leads to the (E)-
stilbenes 7a and 7b, respectively. The protected aldehyde
function is deprotected by acidic work-up (Scheme 1). After
the purification of 7a,b by column chromatopraphy, the
amount of (Z)-isomer is below the limit of detection (3%) in
the 1H and 13C NMR spectroscopy. The subsequent Wittig–
Horner reaction of the triphosphonate 813,29 with 7a,b yields
the target compounds 9a,b. In contrast to mesitylene, 2,4,6-
trimethyl-1,3,5-triazine (10) shows with the aldehydes 7a,b
a smooth threefold condensation reaction, which yields the
target compounds 11a,b. Particularly 7b, which contains an
electron-withdrawing CN group, gives high yields of the
star-shaped compound 11b.
2.2. Spectroscopic characterization
The compounds 9a and 9b generate yellow solutions
in CH2Cl2 with lmax¼405 nm (1max¼1.24£105 L mol21
cm21) and lmax¼418 nm (1max¼1.39£105 L mol21 cm21),
Keywords: Condensation; Liquid crystals; Photoreactivity.
*
Corresponding author. Tel.: þ49-6131-3922605; fax: þ49-6131-
3925396; e-mail address: hmeier@mail.uni-mainz.de
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.06.012

6882
H. Meier et al. / Tetrahedron 60 (2004) 6881–6888
Scheme 1. Preparation of the star-shaped compounds 9a,b and 11a,b.
respectively. Due to the 1,3,5-trisubstitution at the central
benzene ring, these values correspond to absorptions of 1,4-
distyrylbenzenes;30 the effect of the cross-conjugation can
be neglected. The 1,3,5-triazine systems 11a and 11b
exhibit bathochromically shifted absorption maxima at
431 and 435 nm, respectively [1max¼(1.23^0.1)£105
L mol21 cm21]. Each arm of 11a can be regarded as an
acceptor–donor (A–D) system and of 11b as an A–D–A
system.
The 1H and 13C NMR data of 2–5 and 9a, 9b, 11a, 11b are
summarized in the Tables 1 and 2, respectively. The
1
assignment of the signals to certain H and 13C nuclei is
based on two-dimensional measurements (HMQC and
HMBC).31 The (E)-configurations of the CC double bonds
3
are certified by coupling constants J (H,H)¼16.2^0.2 Hz
for the olefinic AB spin systems. The IR and MS data of
2–5, 9a,b and 11a,b as well as IR, NMR and MS data of the
stilbenes 7a and 7b are listed in Section 4.
1
Table 1. H and 13C NMR data of 2-5 (solvent: CDCl3, TMS as internal standard)
Compound
C-1
C-2
HC-3
C-4
C-5
HC-6
a-CH2
b-CH2
g-CH2
d-CH2
1-CH2
CH3
R 1, R 2
2
3
7.06
118.5
7.19
7.06
118.5
7.27
3.92
70.4
3.98
69.5
69.9
3.93
69.4
70.1
3.96
4.04
68.9
69.2
1.78
29.1
1.78
29.0
1.41
25.6
1.41
25.6
1.31
31.5
1.31
31.5
1.31
22.5
1.31
22.6
0.89
14.0
0.88
14.0
111.2
124.3
150.1
155.6
111.2
121.0
150.1
149.9
10.38/188.9 (CHO)
118.5
110.7
4
5
7.07
117.4
7.05
112.6
1.76
29.2
1.45
25.7
1.31
31.5
1.31
22.6
0.88
14.0
3.36/54.2 (OCH3)
5.54/99.3 (CH)
126.8
124.7
151.0
156.1
112.6
134.7
149.6
150.5
7.28
7.17
1.78
29.2
1.43
25.7
1.31
31.5
1.31
22.6
0.88
14.0
10.44/189.6 (CHO)
3.40/54.6 (OCH3)
5.58/99.3 (CH)
109.8
112.1

H. Meier et al. / Tetrahedron 60 (2004) 6881–6888
Table 2. H and 13C NMR data of the star-shaped compounds 9a, 9b, 11a and 11b (CDCl3, TMS an internal standard)
6883
1
Compound
Positions (shown in Scheme 1)
a
b
c
d
e
f
g
h,h0
i,i0
j
k
9a
7.26
127.2
—
7.37
128.6
7.62
7.54
126.6
7.59
—
138.1
—
7.15
129.0
7.13
7.51
123.7
7.60
—
127.1
—
7.15/7.16
111.0/111.2
7.12/7.15
—
151.3/151.3
—
—
127.1
—
7.55
124.3
7.53
9b
119.1
7.27
127.6
—
132.4
7.36
128.6
7.63
132.5
126.9
7.55
126.5
7.56
126.8
142.6
—
137.7
—
142.2
127.4
7.18
129.9
7.17
127.8
126.9
7.49
123.3
7.58
127.3
125.9
—
129.2
—
127.9
111.0/111.2
7.16/7.23
110.0/111.3
7.13/7.23
110.9/111.8
151.2/151.6
—
150.9/152.3
—
151.2/152.2
128.2
—
125.1
—
126.1
124.2
8.60
136.3
8.59
136.2
11a
11b
119.1
1
m
—
138.7
—
138.6
—
171.5
—
171.5
n
a-CH2
b-CH2
1.90
29.5/29.6
1.89
29.5
g-CH2
1.56
25.9/26.0
1.55
26.0
d-CH2
1.40
31.6/31.7
1.38
31.6
1.38
31.6
1.37
31.6
1-CH2
1.40
22.6
1.38
22.6
1.38
22.6
1.37
22.6
CH3
0.88/0.93
14.0
0.87/0.92
14.0
0.85/0.92
14.0
9.84/0.91
14.0
CN
—
—
—
119.1
—
—
—
119.1
9a
7.21
128.9
7.22
129.5
7.21
126.7
7.22
127.0
7.59
124.0
7.56
124.2
—
4.06/4.10
69.7/69.8
4.07/4.08
69.6/69.8
4.04/4.11
69.4/69.6
4.05/4.10
69.3/69.6
9b
11a
11b
1.90
1.55
—
—
29.3/29.4
1.90
29.3
25.8/25.9
1.54
25.8/25.9
2.3. Formation of liquid crystalline phases
107 8C (DH¼35 kJ mol21). The acceptor–donor–acceptor
(A–D–A) character of 11b leads to a strong increase of the
phase transition temperatures. A nematic phase is obtained
at Tg¼210 8C and disappears at 236 8C (DH¼49.8
kJ mol21). The cooling curve of 11b shows the formation
of the nematic phase at 213 8C; the undercooling effect for
11a is so high and the rate of the phase transitions so low,
that the DSC of 11a does not exhibit an endothermic peak in
the cooling curve. These observations and the high DH
Star-shaped compounds, which consist of stilbenoid build-
ing blocks and long flexible chains in peripheral positions,
can generate thermotropic mesophases. In contrast to earlier
studied systems,23,32 the compounds 9a, 9b, 11a and 11b
bear hexyloxy chains in the middle of the three arms—and
not at the periphery. Thus, the usual micro-segregation
between the p-electron regions and the aliphatic regions
cannot be realized. Consequently, nematic discotic phases
can be expected instead of columnar phases. The differential
scanning calorimetry (DSC) of 9a reveals in the second
heating curve (rate 108 per min) a glass transition (Tg¼8 8C)
to a first nematic discotic phase ND. A second mesophase
ND0 is formed at 114 8C. The small endothermic peak for the
latter transition corresponds to a low transition enthalpy of
0.2 kJ mol21. Finally, the isotropic molten phase is reached
at 126 8C (DH¼0.4 kJ mol21). The first (and second)
cooling curve exhibits only one nematic discotic phase,
which is formed at 126 8C (DH¼0.4 kJ mol21) and
disappears at Tg¼2 8C. The structural difference between
the two nematic phases is not known. The polarized optical
microscopy shows typical nematic ‘Schlieren’ textures33,34
for both phases, which have a low viscosity. Moreover, at
114 8C a homeotropic reorganization becomes visible in the
microscope. Possibly, the ND phase consists of molecular
pairs (or higher aggregates), whereas the ND0 phase consists
of single discs.
The introduction of cyano groups causes a push–pull
character of the arms; the phase transition temperatures and
the corresponding DH values of 9b are much higher. The
second heating curve (heating rate 108 per min) reveals a
transformation of the crystalline phase to a nematic discotic
phase at 209 8C (DH¼40 kJ mol21) and the formation of
the isotropic phase at 232 8C (DH¼1 kJ mol21). The
cooling curve confirms this phase behavior; at 232 8C
(DH¼21 kJ mol21) the nematic phase is found and at
201 8C (DH¼237 kJ mol21) the crystalline phase. Figure 1
shows the typical nematic textures of 9b and 11a. The 1,3,5-
triazine 11a exhibits in the second heating curve an ND
phase (Tg¼95 8C) before the isotropic melt is reached at
Figure 1. Nematic ‘Schlieren’ textures obtained by polarization
microscopy. Upper part: measurement of 11a at 99 8C; lower part:
measurement of 9b at 224 8C.

6884
H. Meier et al. / Tetrahedron 60 (2004) 6881–6888
values for the isotropization of 11a and 11b are an
indication for Ncol phases.35
In contrast to the statistical CC bond formation, 11a shows
in the crystalline state a selective photodimerization.
Daylight or monochromatic irradiation with l¼366 nm
provokes a chemoselective [2pþ2p] cycloaddition of the
inner, more polar olefinic double bonds. The NMR studies
reveal a regioselective head-to-tail dimerization with a
stereoselective syn arrangement of head and tail and a
preservation of the trans configuration, which is originally
present at the olefinic CC bonds (Scheme 3). The chemo-,
regio- and stereoselectivity can be explained by a
topochemical control. Amorphous 11a does not exhibit
this photocyclodimerization.
2.4. Photochemistry
Stilbenoid compounds like 9a,b and 11a,b are light-
sensitive.36 The major irreversible process in solution as
well as in the LC phases consists of CC bond formations
between the original olefinic centers (Scheme 2). Mono-
chromatic irradiation with l¼366 nm or even an extended
absorption of daylight is sufficient for the break-down of the
LC phases of 9a,b and 11a,b. Finally crosslinked oligomers
and polymers are generated, in which four-membered rings
and CC bonds in different directions are generated. The
process can be used as imaging technique with liquid
crystals.
The structure elucidation of 12 is based on one- and two-
dimensional NMR techniques (COSY, NOESY, HMQC and
1
HMBC).31 The integration of the H NMR signals proves
that only one four-membered ring is formed. The symmetry
1
of the dimer is manifested in the number of H and 13C
NMR signals. The chemoselective reaction of the inner CC
double bonds in 11b becomes obvious (HMBC) by the
couplings of 1-H (d¼4.87) and 2-H (d¼5.27) with the
quaternary carbon atom OCq (d¼151.2) of the adjacent
benzene ring and the carbon atom NCq (d¼178.2) of the
1,3,5-triazine ring. The syn head-to-tail cycloaddition is
revealed by the through-space interactions (NOESY) of the
substituents on C-1 and C-4 of 12.
Scheme 2. Photochemical CC bond formation between olefinic centers of
stilbenoid compounds.
The protons on the four-membered ring constitute an
AA0MM0 spin system. Figure 2 shows the measured and
Scheme 3. Topochemically controlled photodimerization of 11a.

H. Meier et al. / Tetrahedron 60 (2004) 6881–6888
6885
Figure 2. 1H NMR signals of the protons at the four-membered ring of 12, representing an AA0MM0 spin pattern. Upper part: measured signals in CDCl3; lower
3
3
3
4
4
part: calculated spectrum38 (3JAM¼ JA M ¼10.7 Hz, JAM ¼ JA M¼7.2 Hz, l JAA l¼0.5 Hz, l JMM l¼0.8 Hz).
0
0
0
0
0
0
the calculated signal pattern. A head-to-tail addition with
anti orientation would lead to an A2M2 spin system with a
completely different pattern.37
technique. The elemental analyses were determined in the
Microanalytical Laboratory of the Chemistry Department of
the University of Mainz.
4.1.1. 1,4-Dibromo-2,5-dihexyloxybenzene (2). Prepar-
ation according to the literature.24–26
3. Conclusion
The star-shaped compounds 9a,b having a benzene core and
11a,b having a 1,3,5-triazine core could be obtained by
Wittig–Horner reactions and alkaline condensation reac-
tions, respectively. Due to the attachment of hexyloxy
chains in the middle of the arms, nematic LC phases are
formed-and no columnar phases, which require extended
micro-segregations. The stilbenoid character of the arms
provokes a high photoreactivity. The LC phases are
transformed isothermally by irradiation to isotropic melts
by statistical photochemical CC bond formations. This
irreversible process provides an imaging technique with
liquid crystals. A chemo-, regio- and stereoselective
photocyclodimerization was found for 11a in the crystalline
state. The topochemically controlled reaction works already
in the daylight; amorphous particles of 11a do not show this
process.
4.1.2. 4-Bromo-2,5-dihexyloxybenzaldehyde (3). To
80.0 g (0.18 mol) 2, dissolved in 300 mL dry diethylether,
71.9 mL (0.20 mol) of a 2.7 M solution of n-BuLi in
n-heptane were slowly added under argon at 220 8C. After
1 h stirring at this temperature, the reaction mixture was
brought to room temperature and treated tropwise with dry
DMF till the reaction came to the end. After stirring for
another hour, 30 mL 6 M HCl was added. The organic layer
was separated, washed two times with the equivalent
amount of water, dried with Na2SO4 and evaporated. The
residue was purified by column filtration (10£15 cm SiO2,
CCl4); 31.1 g (44%) aldehyde 3 could be obtained as a
colorless solid, which melted at 58 8C. (Apart from the main
fraction 3.0 g (5%) of 2,5-dihexyloxyterephthaldialdehyde
could be isolated). 3: IR (KBr): n (cm21)¼2970, 2850,
˜
1670, 1590, 1490, 1470, 1380, 1260, 1200, 1020, 990, 970,
880, 750; FD MS: m/z (%)¼385 (100) [MþHþ], Br isotope
pattern. Anal. Calcd for C19H29O3Br (385.3): C, 59.22; H,
7.59; Br 20.74. Found: C, 59.51; H, 7.41; Br, 20.35.
4. Experimental
4.1. General remarks
4.1.3. 4-Bromo-2,5-dihexyloxybenzaldehyde dimethyl
acetal (4). Aldehyde 3 (24.0 g, 62.3 mmol), trimethoxy-
methane (19.83 g, 190 mmol) and 3.0 g Dowex 50 W-X8
were refluxed for 10 h. After stirring for 10 min with 2.5 g
(23.6 mmol) Na2CO3 at room temperature, the reaction
mixture was filtered and evaporated. The residue was boiled
with 50 mL dry n-hexane for 10 min and immediately
filtered. After removal of the volatile parts, 24.13 g (90%) of
Melting points were measured on a Bu¨chi melting point
apparatus and are uncorrected. The phase transitions of 9a,b
and 11a,b were studied with a Perkin Elmer DSC 7. The
polarization microscopy was performed with a Zeiss
Jenapol equipped with a Linkam TMS 93 and a digital
camera CC12, Soft Imaging System. The 1H and 13C NMR
spectra were recorded with the Bruker spectrometers AMX
400, ARX 400 and Avance 600. The UV/Vis spectra were
obtained with a Zeiss MCS 320/340. A Perkin Elmer GX
was used for the measurement of the IR spectra in
transmission, whereas a Nicolet 5 SXB with a LOT-Oriel
Golden-Gate ATR unit served for the measurements in
reflection. The mass spectra were obtained on a Finnigan
MAT 95 spectrometer with the field desorption (FD)
an oil was obtained. IR (film): n (cm21)¼2930, 2850, 1490,
˜
1460, 1370, 1200, 1090, 1050, 980, 880, 750; FD MS: m/z
(%)¼430 (100) [Mþ]. Anal. Calcd for C21H35O4Br (431.4):
C, 58.47; H, 8.18; Br, 18.52. Found: C, 58.80; H, 7.95; Br,
18.02.
4.1.4. 2,5-Dihexyloxy-4-dimethoxymethylbenzaldehyde
(5). To 23.13 g (53.36 mmol) 4 in 300 mL dry diethylether,

6886
H. Meier et al. / Tetrahedron 60 (2004) 6881–6888
23.80 mL (64.40 mmol) of a 2.7 M solution of n-BuLi were
dropped at 225 8C. After 2 h dry DMF was dropwise added
at room temperature till the reaction stopped. Water
(50 mL) was added, the organic layer was separated and
the water phase several times extracted with diethylether.
The combined organic phases were dried with Na2SO4 and
evaporated. Column filtration (15£10 cm SiO2, CH2Cl2–
triethylamine 99:1) yielded 18.40 g (90%) of a yellow oil.
4.1.7. all-(E)-1,3,5-Tris{2-[2,5-dihexyloxy-4-(2-phenyl-
ethenyl)phenyl]ethenyl}benzene (9a). Tri-phosphonate
813 (0.42 g, 0.79 mmol) and aldehyde 7a (1.00 g,
2.45 mmol) were dissolved in 10 mL dry THF and dropped
at 0 8C under Ar to 0.25 g (6.3 mmol) NaH (60% in paraffin)
suspended in 40 mL dry THF. The reaction mixture was
warmed to room temperature and stirred for 2H, before it
was poured on 50 g crushed ice; 50 mL 2 M HCl was added.
The precipitate was filtered off, dried and dissolved in
CH2Cl2 (10 mL). Portionwise addition of ethanol yielded
0.36 g (35%) of a yellow solid with the clearing point
IR (film): n (cm21)¼2950, 2840, 1670, 1600, 1480, 1460,
˜
1410, 1380, 1200, 1150, 1070, 980, 950, 880; FD MS: m/z
(%)¼380 (100) [Mþ]. Anal. Calcd for C22H36O5 (380.5): C,
69.44; H, 9.54. Found: C, 69.10; H, 9.84.
T ¼126 8C. IR (KBr): n (cm21)¼3030, 2950, 2920, 2860,
˜
cl
1590, 1570, 1200, 970, 755, 695; UV/Vis (CH2Cl2):
lmax¼405 nm, 1¼1.24£105 L mol21 cm21; FD MS: m/z
(%)¼1293 (100) [MþHþ]. Anal. Calcd for C90H114O6
(1291.9): C, 83.68;H, 8.89. Found: C, 83.47;H, 8.82.
4.1.5. (E)-2,5-Dihexyloxy-4-(2-phenylethenyl)benzalde-
hyde (7a). Diethyl benzylphosphonate (6a)27 (1.23 g,
5.4 mmol) and 5 (2.00 g, 5.3 mmol) were dissolved in
20 mL dry THF and dropped under Ar at 0 8C to 0.30 g
(12.5 mmol) NaH in 40 mL dry THF. After 24 h 0.20 g
(8.33 mmol) NaH in 30 mL dry THF was added and the
stirring continued at room temperature for further 24 h. The
mixture was cooled to 0 8C before 50 mL H2O were slowly
added. The product was extracted with 100 mL CHCl3 and
the solution vigorously stirred with 20 mL 2 M HCl for 2 h.
The organic layer was separated, washed with 50 mL
saturated NaHCO3 and 50 mL H2O. The organic phase was
dried with MgSO4 and evaporated. Column chromato-
graphy [20£10 cm SiO2, petroleum (bp 40–70 8C)/ethyl–
acetate 25:1] yielded 1.80 g (84%) of a yellow oil. IR (film):
4.1.8. all-(E)-1,3,5-Tris(2-{4-[2-(4-cyanophenyl)ethenyl]-
2,5-dihexloxyphenyl}ethenyl)benzene (9b) or all-(E)-4-
[2-(4-{2-[3,5-bis(2-{4-[2-(4-cyanophenyl)ethenyl]-2,5-
dihexyloxyphenyl}ethenyl)phenyl]ethenyl}-2,5-dihexyl-
oxyphenyl)ethenyl]benzonitrile (9b). According to the
preparation of 9a, 0.26 g (25%) of pure 9b was obtained
from 1.00 g (2.3 mmol) 7b, 0.40 g (0.8 mmol) 8 and 0.25 g
(6.3 mmol) NaH. The raw product (about 1.0 g) was first
purified on a column [10£15 cm SiO2, toluene–ethyl
acetate 2:1] before it was recrystallized from CH2Cl2/
C2H5OH as described for 9a. The yellow solid 9b has a
n (cm21)¼3050, 3020, 2940, 2920, 2860, 1655, 1595, 1205,
clearing point T ¼232 8C. IR (KBr): n (cm21)¼3020, 2940,
˜
˜
cl
1
970, 750, 690; H NMR (CDCl3): d¼0.90 (m, 6 H, CH3),
2910, 2850, 2220, 1615, 1580, 1200, 960, 855, 815; UV/Vis
(CH2Cl2): lmax¼418 nm, 1¼1.39£105 L mol21 cm21; FD
MS: m/z (%)¼1368 (100) [MþHþ]. Anal. Calcd for
C93H111N3O6 (1366.9): C, 81.72;H, 8.18; N, 3.07. Found:
C, 81.34;H, 7.90; N, 2.91.
1.24–1.56 (m, 12H, CH2), 1.83 (m, 4H, CH2), 4.01 (t, 2H,
OCH2), 4.10 (t, 2H, OCH2), 7.16 (s, 1H, 3-H), 7.31 (s, 1H,
3
6-H), 7.22/7.46 (AB, J¼16.6 Hz, 2H, olefin. H), 7.29 (m,
1H, p-H, phenyl), 7.36 (m, 2H, m-H, phenyl), 7.53 (m, 2H,
o-H, phenyl), 10.43 (s, 1H, CHO); 13C NMR (CDCl3);
d¼13.9 (CH3), 22.5–31.5 (CH2, partly superimposed), 69.2,
69.4 (OCH2), 110.3, 110.8, 123.7, 126.9, 128.2, 128.7,
132.3 (aromat. and olefin. CH), 124.5, 134.4, 137.3 (aromat.
Cq), 150.9, 156.3 (CqO), 189.0 (CHO); FD MS: m/z
(%)¼408 (100) [Mþ]. Anal. Calcd for C27H36O3 (408.6):
C, 79,37;H, 8.88. Found: C, 79.40;H, 8.74.
4.1.9. all-(E)-2,4,6-Tris{2-[2,5-dihexyloxy-4-(2-phenyl-
ethenyl)phenyl]ethenyl}-1,3,5-triazine (11a). Aldehyde
7a (0.5 g, 1.22 mmol), dissolved in 7 mL dry THF, was
added to 45.2 mg (0.37 mmol) 10 and 180 mg (1.60 mmol)
KOC(CH3)3 in 7 mL dry THF. After stirring for 5 d at
ambient temperature, the raw product was precipitated by
the addition of methanol. Column chromatography
(4£40 cm SiO2, toluene) yielded 153 mg (32%) of a yellow
4.1.6. (E)-4-[2-(4-Formyl-2,5-dihexyloxyphenyl)-
ethenyl]benzonitrile (7b). 137 g (5.4 mmol) diethyl
4-cyanobenzylphosphonate (6b),28 2.00 g (5.3 mmol) 5
and 0.60 g (25.0 mmol) NaH in 40 mL dry THF were
reacted as described for 7a. The corresponding work-up and
the column chromatography [petroleum (bp 40–70 8C)/
ethyl–acetate 15:1] yielded 2.00 g (88%) of a yellow oil
which was used without further purification for the
following reaction step. Spectroscopic characterization. IR
solid; T ¼107.5 8C. IR (ATR): n (cm21)¼3081, 3057,
˜
cl
3025, 2953, 2928, 2869, 2857, 1623, 1601, 1504, 1467,
1422, 1376, 1288, 1251, 1207, 1030, 986, 964, 873, 852,
753, 692; UV/Vis (CH2Cl2): lmax¼431 nm, log 1¼5.0; FD
MS: m/z (%)¼1296 (100) [MþHþ]. Anal. Calcd for
C87H111N3O6 (1294.9): C, 80.70;H, 8.64; N, 3.25. Found:
C, 80.48;H, 8.84; N, 3.21.
(film): n (cm21)¼3040, 2940, 2920, 2840, 1665, 1600,
4.1.10. all-(E)-2,4,6-Tris(2-{4-[2-(4-cyanophenyl)-
ethenyl]-2,5-dihexyloxyphenyl}ethenyl)-1,3,5-triazine
(11b) or all-(E)-4[2-(4-{2-[4,6-bis(2-{4-[2-(4-cyano-
phenyl)ethenyl]-2,5-dihexyloxyphenyl}ethenyl)-1,3,5-
triazin-2-yl]ethenyl}-2,5-dihexyloxyphenyl)ethenyl]-
benzonitrile (11b). According to the preparation of 11a,
257 mg (94%) of 11b was obtained from 286 mg
(0.66 mmol) 7b, 24.5 mg (0.20 mmol) 10 and 67.5 mg
(0.60 mmol) KOC(CH3)3 in 15 mL dry THF. After refluxing
for 2 d, the purification was performed by column
chromatography [4£40 cm SiO2, petroleum (bp 40–70 8C/
ethyl–acetate 7:1] and crystallization from CH2Cl2/
˜
1
1415, 1205, 970, 865; H NMR (CDCl3): d¼0.88 (m, 6H,
CH3), 1.23–1.51 (m, 12H, CH2), 1.83 (m, 4H, CH2), 4.01 (t,
2H, OCH2), 4.08 (t, 2H, OCH2), 7.14 (s, 1H, aromat. H),
3
7.31 (s, 1H, aromat. H), 7.20/7.55 (AB, J¼16.6 Hz, 2H,
olefin. H), 7.58/7.63 (AA0BB0, 4H, aromat. H), 10.43
(CHO); 13C NMR (CDCl3): d¼14.0 (CH3), 22.5-31.5
(CH2, partly superimposed), 69.1, 69.3 (OCH2), 110.3/
111.1 (aromat. CH and C-1), 127.1, 126.7, 130.1, 132.5
(aromat. and olefin. CH), 118.9 (CN), 125.0, 132.8, 141.7
(aromat. Cq), 151.0, 156.0 (aromat. CqO), 189.0 (CHO); FD
MS: m/z (%)¼433 (100) [Mþ].

H. Meier et al. / Tetrahedron 60 (2004) 6881–6888
6887
2. Ebert, M.; Jungbauer, D. A.; Kleppinger, R.; Wendorff, J. H.;
Kohne, B.; Praefcke, K. Liq. Cryst. 1989, 4, 53.
3. Bengs, H.; Ebert, M.; Karthaus, O.; Kohne, B.; Praefcke, K.;
Ringsdorf, H.; Wendorff, J. H.; Wu¨stefeld, R. Adv. Mater.
1990, 2, 141.
CH3OH. The orange solid has a clearing point at
˜
T ¼235.8 8C. IR (ATR): n (cm21)¼3060, 2926, 2856,
cl
2222, 1679, 1623, 1601, 1483, 1467, 1423, 1374, 1337,
1320, 1285, 1253, 1204, 1173, 1029, 987, 968, 855, 817,
726, 666; UV/Vis (CH2Cl2): lmax¼435, log 1¼5.09; FD
MS: m/z (%)¼1371 (100) [MþHþ]. Anal. Calcd for
C90H108N6O6 (1369.9): C, 78.91;H, 7.95; N, 6.13. Found:
C, 78.74;H, 8.13; N, 6.09.
4. Praefcke, K.; Kohne, B.; Singer, D. Angew. Chem. 1990, 102,
200. Angew. Chem., Int. Ed. Engl. 1990, 29, 177.
5. Heppke, G.; Ranft, A.; Sabaschus, B. Mol. Cryst. Liq. Cryst.,
Lett. Sect. 1991, 8, 17.
¨
¨
6. Ebert, M.; Frick, G.; Bahr, C.; Wendorff, J. H.; Wustefeld, R.;
4.1.11. all-(E)-1r,3t-Bis(4,6-bis{2-[2,5-dihexyloxy-4-(2-
phenylethenyl)phenyl]ethenyl}-1,3,5-triazin-2-yl)-2c,4t-
bis[2,5-dihexyloxy-4-(2-phenylethenyl)phenyl]cyclo-
butan (12). A saturated solution of 129 mg (0.1 mmol) 11a
in CHCl3 was spread on a glass surface; the solvent was
slowly vaporized and crystallization of 11a started.
Irradiation of the ready thin crystalline layer with
monochromatic light (l¼366 nm) or with day light led to
the dimerization, which was followed by TLC control
(SiO2, toluene).Column chromatography (20£3 cm SiO2,
toluene) yielded up to 84 mg (65%) of 12, which melted at
Ringsdorf, H. Liq. Cryst. 1992, 11, 293.
7. Kruerke, D.; Kitzerow, H.-S.; Heppke, G.; Vill, V. Ber.
Bunsen-Ges. Phys. Chem. 1993, 97, 1371.
8. Booth, C. J.; Kruerke, D.; Heppke, G. J. Mater. Chem. 1996, 6,
927.
9. Deb, S. K.; Maddux, T. M.; Yu, L. J. Am. Chem. Soc. 1997,
119, 9097.
10. Meier, H.; Lehmann, M. Angew. Chem. 1998, 110, 666.
Angew. Chem., Int. Ed. 1998, 37, 643.
11. Lehmann, M.; Schartel, B.; Hennecke, M.; Meier, H.
Tetrahedron 1999, 55, 13377.
160 8C. IR (ATR): n (cm21)¼2954, 2932, 2870, 2858,
˜
1624, 1600, 1518, 1467, 1424, 1378, 1288, 1251, 1207,
1030, 991, 962, 753, 691; 1H NMR (CDCl3): d¼0.77 (t, 6H,
CH3), 0.79 (t, 6H, CH3), 0.80 (t, 12H, CH3), 0.90 (t, 12H,
CH3), 1.14–1.58 (m, 72H, CH2), 1.84 (m, 24H, CH2), 3.70
(m, 2H, OCH2), 3.78 (m, 2H, OCH2), 3.88 (m, 4H, OCH2),
4.01 (t, 8H, OCH2), 4.05 (t, 8H, OCH2), 4.87 (AA0 of
AA0MM0, 2H, 1-H, 3-H), 5.27 (MM0, 2H, 2-H, 4-H), 6.86 (s,
2H, aromat. H), 6.91/7.31 (AM, 3J¼16.4 Hz, 4H, olefin. H),
12. Kumar, S.; Varshney, S. K. Angew. Chem. 2000, 112, 3270.
Angew. Chem., Int. Ed. 2000, 39, 3140.
13. Meier, H.; Lehmann, M.; Kolb, U. Chem. Eur. J. 2000, 6,
2462.
14. Meier, H.; Lehmann, M.; Schnorpfeil, C.; Fetten, M. Mol.
Cryst. Liq. Cryst. 2000, 352, 85.
15. Meier, H.; Karpouk, E.; Lehmann, M.; Schollmeyer, D.;
Enkelmann, V. Z. Naturforsch. B., Chem. Sci. 2003, 58, 775.
16. See also Meier, H.; Holst, H. C. Adv. Synth. Catal. 2003, 345,
1005, and references therein.
3
7.03 (s, 2H, aromat. H), 7.08/8.47 (AX, J¼16.2 Hz, 8H,
olefin. H), 7.11 (s, 4H, aromat. H), 7.16/7.48 (AM,
3J¼16.2 Hz, 8H, olefin. H), 7.16 (s, 4H, aromat. H), 7.25
(m, 6H, aromat. H), 7.37 (m, 12H, aromat. H), 7.53 (m, 12H,
aromat. H); 13C NMR (CDCl3): d¼14.0 (12 CH3), 22.6 (12
CH2), 25.7–25.9 (12 CH2), 29.2–29.4 (12 CH2), 31.5–31.9
(12 CH2), 40.5 (C-1, C-3), 49.5 (C-2, C-4), 69.4 (4 OCH2),
69.5 (4 OCH2), 70.1 (2 OCH2), 109.0 (2 aromat. CH), 110.5
(4 aromat. CH), 111.8 (4 aromat. CH), 114.4 (2 aromat.
CH), 123.4 (4 olefin. CH), 123.9 (2 olefin. CH), 124.9 (2
aromat. Cq,) 125.0 (4 aromat. Cq), 126.3 (4 aromat. CH),
126.5 (4 olefin. CH), 126.6 (8 aromat. CH), 126.9 (2 aromat.
CH), 127.6 (2 olefin. CH), 127.6 (4 aromat. CH), 128.5 (4
aromat. CH), 128.7 (8 aromat. CH), 129.1 (4 aromat. Cq),
129.7 (4 olefin. CH), 130.6 (2 aromat. Cq), 136.1 (4 olefin.
CH), 137.8 (4 aromat. Cq), 138.2 (2 aromat. Cq), 150.6 (2
aromat. CqO), 150.9 (4 aromat. CqO), 151.2 (2 aromat.
CqO), 152.3 (4 aromat. CqO), 170.9 (4 CqN), 178.2 (2 CqN);
FD MS: m/z (%)¼1295 (100) [M2þ], 2590 (88) [Mþ]. Anal.
Calcd for C174H222N6O12 (2589.7): C, 80.70;H, 8.64; N,
3.25. Found: C, 80.57;H, 8.91; N, 3.32.
17. Meier, H.; Lehmann, M.. In Encyclopedia of Nanoscience and
Nanotechnology; Nalwa, H. S., Ed.; ASP: Stevenson Ranch,
California, USA, 2004; vol. 10, 95–106.
18. Meier, H.; Stalmach, U.; Fetten, M.; Seus, P.; Lehmann, M.;
Schnorpfeil, C. J. Inf. Recording 1998, 24, 47.
19. Lee, C.-H.; Yamamoto, T. Tetrahedron Lett. 2001, 42, 3993.
20. Lee, C.-H.; Yamamoto, T. Bull. Chem. Soc. Jpn 2002, 615.
21. Pieterse, K.; Lauritsen, A.; Schenning, A. P. H. J.; Vekemans,
J. A. J. M.; Meijer, E. W. Chem. Eur. J. 2003, 5597.
22. Meier, H.; Holst, H. C.; Oehlhof, A. Eur. J. Org. Chem. 2003,
4173.
23. Holst, H. C.; Pakula, T.; Meier, H. Manuscript in preparation.
24. Hu, Q.-S.; Huang, W.-S.; Vitharana, D.; Zheng, X.-F.; Pu, L.
J. Am. Chem. Soc. 1997, 119, 12454.
25. Detert, H.; Sugiono, E. J. Prakt. Chem. 1999, 341, 358.
26. Huang, W.-S.; Hu, Q.-S.; Pu, L. J. Org. Chem. 1999, 64, 7940.
27. Mouysset, G.; Bellon, J.; Payard, M.; Tisne-Versailles, J.
Farmaco Ed. Sci. 1987, 42, 805.
28. Kagan, F.; Birkenmeyer, R. D.; Strube, E. J. Am. Chem. Soc.
1959, 81, 3026.
29. Malkes, L. Y.; Kovalenko, N. P. Zh. Org. Khim. 1966, 2, 297.
Chem. Abstr. 1996, 65, 2188a.
Acknowledgements
30. Oelkrug, D.; Rempfer, K.; Prass, E.; Meier, H. Z. Naturforsch.
A 1988, 43, 583.
We are grateful to the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie for financial
support.
31. Hesse, M.; Meier, H.; Zeeh, B. Spektroskopische Methoden in
der organischen Chemie; 6th ed. Thieme: Stuttgart, 2002.
32. Holst, H. C. Dissertation, Mainz, 2003.
33. Dierking, I. Textures of Liquid Crystals; Wiley-VCH:
Weinheim, 2003; pp 51.
References and notes
34. Handbook of Liquid Crystals; Demus, D., Goodby, J., Gray,
G. W., Spiess, H.-W., Vill, V., Eds.; Wiley-VCH: Weinheim,
1998.
1. Kohne, B.; Praefcke, K. Chimia 1987, 41, 196.

6888
H. Meier et al. / Tetrahedron 60 (2004) 6881–6888
35. See for example Attias, A.; Cavalli, C.; Donnio, B.; Guillon,
ˆ
D.; Hapiot, P.; Malthete, J. Chem. Mater. 2002, 14, 375.
37. A comparison of the NMR results shown here and the
measurements for the photodimer of 2,4,6-tristyryltriazines
revealed equivalent dimerization routes.32
36. Meier, H. Angew. Chem. 1992, 104, 1425. Angew. Chem., Int.
Ed. Engl. 1992, 31, 1399.
38. Software MestRe—C 2.3.a.