Synthesis and specific features of mesomorphic behavior of new polysubstituted triphenylenes

Article abstract of DOI:10.1007/s11172-005-0028-7

Previously unknown 2,3,6,7,10,11-hexakis(dodecyloxy)triphenylene and -(tetradecyloxy)triphenylene were synthesized. The structures of the synthesized compounds were proved by elemental analysis and spectral methods. Polymesomorphism was found for the first time and studied for substances of the hexaalkoxytriphenylene homologic series, as well as liotropic mesomorphism in a series of organic solvents.

Full text of DOI:10.1007/s11172-005-0028-7

Russian Chemical Bulletin, International Edition, Vol. 53, No. 8, pp. 1743—1748, August, 2004
1743
Synthesis and specific features of mesomorphic behavior
of new polysubstituted triphenylenes
ꢀ
O. V. Zemtsova and K. N. Zheleznov
Institute of Solutions Chemistry, Russian Academy of Sciences,
1 ul. Akademicheskaya, 153045 Ivanovo, Russian Federation.
Fax: +7 (093 2) 37 8509. Eꢀmail: vap@iscꢀras.ru
Previously unknown 2,3,6,7,10,11ꢀhexakis(dodecyloxy)triphenylene and ꢀ(tetradecylꢀ
oxy)triphenylene were synthesized. The structures of the synthesized compounds were proved
by elemental analysis and spectral methods. Polymesomorphism was found for the first time
and studied for substances of the hexaalkoxytriphenylene homologic series, as well as liotropic
mesomorphism in a series of organic solvents.
Key words: synthesis, 2,3,6,7,10,11ꢀhexakis(dodecyloxy)triphenylene, 2,3,6,7,10,11ꢀhexaꢀ
kis(tetradecyloxy)triphenylene, polymesomorphism, phase transitions, textures, liotropic mesoꢀ
morphism.
Scheme 1
Discotic compounds with columnar or nematic mesoꢀ
morphism are being intensely studied recently. These
compounds can be used in optoelectronics,1—3 sensor deꢀ
vices,4 and other areas.5,6 The synthesis of the mesogenic
core of discotics and purification of target products are
rather laborꢀconsuming. The main steps of the synthesis
have been described previously.7—10
Hexaalkoxytriphenylenes can be synthesized by difꢀ
ferent methods,11—17 including the oxidative condensaꢀ
tion of benzene derivatives in concentrated sulfuric acid
using chloranil (tetrachloroꢀpꢀbenzoquinone)11 or anhyꢀ
drous iron chloride as oxidants.12 However, these methꢀ
ods do not give triphenylene derivatives in appropriate
yields.
In this work, we used a previously developed method18
for the synthesis of hexamethoxytriphenylene (Scheme 1)
to synthesize representatives of the hexaalkoxytriꢀ
phenylene homologic series.
In the first step, pyrocatechol was alkylated by alkyl
bromides in an alcoholꢀalkaline medium. Compounds
1а—l trimerized in the second step. A phaseꢀtransfer cataꢀ
lyst, С16Н33NMe3Br, which can be recovered from washꢀ
ing waters after the separation of target products, was
introduced into the reaction medium to enhance the yield
of triphenylenes 2а—l. The reaction occurred under hetꢀ
erogeneous conditions at room temperature in hexane as
a solvent. When the alkyl substituent length increased, we
had to prolong the duration of the synthesis to achieve
appropriate yields of the target products, which were
20—30% in the case of compounds 2k,l synthesized for
the first time. Since it is known11 that only triphenylene
derivatives with a certain arrangement of substituents are
formed under the reaction conditions, the elemental
Reagents and conditions: i. RBr, KOH, EtOH. ii. Chloranil,
С16Н33NMe3Br, H2SO4, hexane.
R = nꢀCmH2m+1, m = 1 (а), 2 (b), 3 (c), 4 (d), 5 (e), 7 (f), 8 (g), 9 (h),
10 (i), 11 (j), 12 (k), 14 (l)
analysis data (Table 1) and coincidence of the phase tranꢀ
sition temperatures with the published data11 confirm
unambiguously the structures of the compounds synꢀ
thesized.
The electronic absorption spectra of compounds 1k
and 2k contain two absorption bands corresponding to
the π—π*ꢀtransitions of the aromatic moieties (Fig. 1). In
the spectrum of compound 2k, a shorterꢀwave band has
λmax = 279 nm (ε = 33100) and is characterized by a
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1676—1681, August, 2004.
1066ꢀ5285/04/5308ꢀ1743 © 2004 Springer Science+Business Media, Inc.

1744
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 8, August, 2004
Zemtsova and Zheleznov
Table 1. Elemental analysis data for compounds 2a—l
Table 2. Electronic absorption spectra of compounds 2a,e—l
Comꢀ
pound
Found
Calculated
Molecular
formula
Comꢀ
λ /nm
λ /nm
λ /nm
(max)
λ /nm
(max) (shoulder)
λ /nm
5
1
2
3
4
(%)
Н
pound (shoulder) (max)
[logε ]
[logε ]
[logε ]
[logε ]
[logε ]
1
2
3
4
5
С
2а
2е
2f
303
[5.51]
290
[4.46]
307
[4.09]
308
[4.35]
307
[4.20]
290
[4.45]
307
[4.38]
308
[3.37]
306
279
[5.71]
282
[4.27]
278
[4.74]
280
[4.90]
277
[4.88]
280
[4.92]
278
[5.05]
279
[4.52]
278
270
[5.60]
275
[4.10]
270
[4.56]
271
[4.82]
273
[4.75]
272
[4.76]
270
[4.85]
271
[4.34]
272
260
[5.43]
265
[4.10]
260
[4.36]
262
[4.60]
265
[4.58]
263
[4.58]
260
[4.68]
263
[4.15]
262
—
—
2a
2b
2c
2d
2e
2f
70.58
5.92
5.95
7.37
7.48
8.39
8.51
9.15
9.28
9.74
С24H24O6
С30H36O6
С36H48O6
С42H60O6
С48H72O6
С60H96O6
С66H108O6
С72H120O6
С78H132O6
С84H144O6
С90H156O6
С102H180O6
69.73
73.15
74.25
74.97
76.09
76.33
77.37
77.38
79.47
78.95
80.52
79.46
80.01
79.94
80.24
80.35
81.52
80.71
80.71
81.02
81.02
81.54
82.76
250
[3.79]
252
[4.30]
257
2g
2h
2i
[4.30]
—
8.79
10.61
9.72
2j
250
[4.38]
253
[3.78]
252
2g
2h
2i
10.91
11.04
11.18
11.35
11.41
10.69
11.61
11.75
11.78
11.96
12.07
12.24
2k
2l
[3.48]
[4.54]
[4.32]
[4.20]
[3.81]
2j
Note. For known compounds (2а—j), the constants are preꢀ
sented in Refs 11 and 12.
2k
2l
spectra of earlier described11 compound 2f and compound
2k are similar (see Fig. 1, curves 2 and 3).
The spectral parameters of triphenylene derivatives
2a,e—l are presented in Table 2. The IR spectra of comꢀ
pounds 2c—j synthesized in this work agree well with the
published data.19
vibrational structure. In the spectrum of compound 1k, a
longerꢀwave band lies at λmax = 278 nm (ε = 34700). The
increase in the intensity of the absorption bands and their
bathochromic shift indicate the appearance of a new chroꢀ
mophore with a higher degree of conjugation, namely, a
triphenylene moiety, because the electronic absorption
A comparison of the IR spectra of compounds 1k
and 2k confirmed additionally the structure of triphenylꢀ
Table 3. Comparative characterization of the main absorption
bands in the IR spectra of compounds 1k and 2k
A
Type of vibrations
ν/cm–1
1.1
1k
2k
0.9
ν(СH arom.)
3005 sh (v.w)
2980
3080 (w)
2956
2920
2880
2852
3
as
ν (CH3)
as
ν (CH2)
2966
2880
2856
0.7
s
ν (CH3)
s
ν (CH2)
0.5
0.3
0.1
2
ν(С—С arom.)
1590, 1516
1464, 1450 sh
1392, 1380 sh
1260
1592, 1518, 1476
1465, 1452
1392, 1384
1258
as
as
δ (CH2), δ (CH3)
s
s
δ (CH2), δ (CH3)
ν(C—O—C)
1
δ(C—H arom.)*
1220
1124
1225
1122
s
ν (Ar—O)
ν(C—O—C)
δ(C—H arom.)**
δ((СH2)n)
1050
812
736
1064
856
740
46
42
38
34
ν•10–3/cm–1
Fig. 1. Electronic absorption spectra of compounds 1k (1),
2k (2), and 2f (3). C = 3.10•10–4 (1), 2.99•10–5 (2), and
1.30•10–5 mol L–1 (3).
* Plane vibrations.
** Outꢀofꢀplane vibrations.

Hexaalkoxytriphenylenes
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 8, August, 2004
1745
Table 4. Temperatures of phase transitions (PT) and textures of
mesophases for compounds 2a—l, determined by polarization
microscopy
ene 2k (Table 3). The absorption bands in the reꢀ
gions of stretching (2960—2850 cm–1) and bending
(1465—1392 cm–1) vibrations of the Me and CH2 groups
confirm that compound 2k contains hydrocarbon subꢀ
stituents. A slight difference in positions of the absorption
bands is observed only in the region of asymmetric stretchꢀ
ing vibrations of the Me and CH2 groups, which occurs
due to a high shift of the electron density to the triꢀ
phenylene ring in compound 2k, compared to the benꢀ
zene moiety of compound 1k, and thus decreases the
force constant of the С—Н bond. The presence of a
С—О—С group is confirmed by absorption bands at
1260—1050 cm–1 in the spectra of both compounds, indiꢀ
cating that ether bonds are retained in compound 2k.
Rocking vibrations of CH2 groups in hydrocarbon subꢀ
stituents are observed in the IR spectra of both comꢀ
Comꢀ
pound
PT
Т*/°С
Texture
2а
2b
2c
2d
Cr → I
Cr → I
Cr → I
310
247
176
86
145
68
123
67
92
64
85
56
75
57
67
54
65
55
58
63
55
—
—
—
Cr → Col
Col → I
Cr → Col
Col → I
Cr → Col
Col → I
Cr → Col
Col → I
Cr → Col
Col → I
Cr → Col
Col → I
Cr → Col
Col → I
Cr → ColX
Mosaic
2e
2f
Mosaic
Bandedꢀmosaic
(fingerꢀshaped**)
Flower
2g
2h
2i
pounds at 736—740 cm–1
.
Bandedꢀmosaic
Flower
Substantial spectral distinctions are observed in an
absorption region of stretching and bending outꢀofꢀplane
vibrations of the С—Н groups of the aromatic ring. Very
weak absorption bands of stretching vibrations of the C—H
groups are observed at 3005 cm–1 in the case of the benꢀ
zene derivative (1k), while, after the benzene rings
trimerized to the triphenylene cycle (compound 2k), the
band intensity increased and the bands shifted toward a
highꢀfrequency spectral region (see Table 3). The absorpꢀ
tion band of bending vibrations of the С—Н groups shifts
in the same direction, which indicates a stronger conjuꢀ
gated system of the triphenylene ring compared to the
benzene ring.
2j
Flower
(fingerꢀshaped**)
Brokenꢀfan (55 °С),
basket (58 °С)
2k
1
ColX → ColX
ColX12 → I
2
2
2l
Cr → ColX
Filiformꢀcellular (55 °С),
filiformꢀ
1
ColX → ColX
58
64
ColX12 → I
reticulate (58 °С)
Note. Cr is crystal, Col is the columnar phase, and I is the
isotropic liquid. The textures were identified in the cooling reꢀ
gime. For compounds 2а—j, textural studies are presented
in Ref. 11.
* The PT temperatures were determined in the heating regime.
** The texture is formed near the PT and characteristic of
mesophases with columnar hexagonal supramolecular structures.
The mesomorphic behavior of the synthesized comꢀ
pounds was studied by thermal polarization microscopy.
It was found that only compounds 2а—с do not form a
thermotropic liquidꢀcrystalline phase (Table 4).
Samples of compounds 2d—l were shown to transit on
melting to a very viscous birefringent phase, and the
sample viscosity decreases to form a mesophase with the
typical finely domain texture with the further temperature
increase. Such a texture is characteristic of columnar (Col)
twoꢀdimensionally ordered phases. The phase transition
temperatures of compounds 2a—j (see Table 4) agree satꢀ
isfactorily with the published data.11
Based on both textural and Xꢀray diffraction studies,20
the authors found that compounds 2d—j form only one
hexagonal columnar mesophase with an ordered arrangeꢀ
ment of molecules in columns. We have shown (see
Table 4) that the further elongation of the hydrocarbon
substituent results in the appearance of two mesomorphic
transitions of compounds 2k,l, i.e., polymesomorphism
appears.
cooling each element of the flower texture formed lateral
branches, and the nuclei resembled snowflakes with
rounded ends.
It has previously been shown21—24 that the appearance
of fingerꢀshaped nuclei of regular shape near the phase
transition from the isotropic liquid to the mesophase (the
study was carried out in the nonpolarized light) allows
one to assign the mesophase to the columnar type with
hexagonal packing of columns.
In this work, we showed that samples of compounds
2k,l, except for textures characteristic of columnar hexꢀ
agonal mesophases, form textures, whose analogs are unꢀ
known. These textures obtained in the cooling regime are
presented in Figs 2 and 3. In the case of compound 2k, a
basket texture is formed (see Fig. 2, a), whereas comꢀ
pound 2l is characterized by a filiformꢀreticulate texture
(see Fig. 3, a). On further cooling of the sample, the first
texture is transformed into a brokenꢀfan texture (see
Fig. 2, b), while the second texture forms a filiformꢀcelluꢀ
lar one (see Fig. 3, b). Under a shear deformation of a
All types of textures characteristic of compounds 2d—l
are indicated in Table 4. Fingerꢀshaped domains appeared
upon very slow cooling near the phase transition from the
isotropic liquid (I) to the mesophase. Nuclei had a proꢀ
nounced shape of a regular hexagon, and upon further

1746
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 8, August, 2004
Zemtsova and Zheleznov
a
a
b
b
Fig. 2. Textures of a sample of compound 2k obtained in the
cooling regime (crossed polarizers, magnification ×160): basket
of the columnar phase (ColX ) (a) and brokenꢀfan of the columꢀ
Fig. 3. Textures of a sample of compound 2l obtained in the
cooling regime (crossed polarizers, magnification ×200): filiꢀ
formꢀreticulate of the columnar phase (ColX ) (a) and filiformꢀ
nar phase (ColX ) (b) at 58 a2nd 55 °С, respectively.
cellular of the columnar phase (ColX ) (b)2at 58 and 55 °С,
1
1
respectively.
sample of compound 2k, the basket texture is modified to
a texture of the parquet type.
ColX →ColX (55 °C), ColX →Cr (49 °C) for compound 2l
2
1
1
At this stage of studies, the mesophases mentioned
above can be identified as columnar with an unknown
packing type of both columns themselves (СolX) and molꢀ
(Сr is the crystalline phase).
It should be mentioned that the type of supramolecuꢀ
lar packings of thermotropic mesogens can be concluded
from the ability to form liotropic mesophases.20,25 In
this work, liotropic mesomorphism of compounds
2a—c,f,h—j,l has been studied for the first time in systems
with normal and cyclic alkanes, cyclohexene, benzene,
and chloroform. For this purpose, we used the method of
contact preparations. Liotropic mesomorphism was found
only for compounds 2f,h—j,l (thermotropic mesomorꢀ
phism). It was found that the liotropic systems are charꢀ
acterized by the appearance of a brokenꢀfan texture and
confocal domains in addition to textures characteristic of
the thermotropic liquidꢀcrystalline state.
All samples demonstrate the formation of the same
type of a liomesophase with different variants of the texꢀ
ture characteristic of hexagonal columnar phases, dependꢀ
ing on the concentration gradient. Compounds 2f,h—j,l
possess a liomesophase, as a rule, with a nongeometric
texture already at room temperature. At a high solvent
concentration, i.e., nearer to the zone of isotropic liquid,
ecules in the columns (ColX , y = 1, 2). It should be
y
emphasized that the results of preliminary prediction of
columnar mesomorphism initiated our intention to synꢀ
thesize compounds 2k,l with the number of C atoms in
the alkyl substituent >11.
An Xꢀray diffraction study of the oriented samples is
needed to establish more exactly the structural organizaꢀ
tion of these mesophases. At this stage, we studied a misꢀ
cibility of triphenylene 2l with compounds that possess
columnar mesomorphism according to published data. In
addition, lamination was found on mixing compounds 2k
and 2l.
Thus, the thermal microscopic observations performed
in the framework of this study made it possible to establish
the phase transition temperatures for compounds 2k,l in
both the heating (see Table 4) and cooling regimes:
I→ColX (58 °C), ColX →ColX (56 °C), ColX →Cr
2
(50 °C) for compound2 2k an1d I→ColX (59 1 °C),
2

Hexaalkoxytriphenylenes
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 8, August, 2004
1747
Table 5. Clarification temperatures (Tc) of compounds 2f,h—j,l
in contact preparations with different solvents
a Leitz Laborlux 12 Pol microscope with a Mettler FP 82 heatꢀ
ing stage. The heating rate was 2 °С min–1. Photographs of
textures were obtained by a microphotoattachment (24×36 mm2)
of a Wild MPS 51 camera.
Solvent
Tc/°С
Phase transition temperatures were determined in heating
and cooling regimes, using different rates of temperature change
in both regimes. Samples were prepared as a thin film between
the objectꢀplate and cover glass.
2f
2h
2i
2j
2l
Hexane
Decane
Cyclohexane
Cyclohexene
Benzene
50
50
72
70
50
50
49
40
49
46
49
48
55
54
52
40
49
58
46
45
51
40
55
20
58
59
45
57
48
46
For the structural identification of mesophases of some comꢀ
pounds, we additionally used the shear deformation method,26
which makes it possible to reveal specific features of textures of
mesogenic samples by miscibility.11 Liotropic mesomorphism
was studied using contact preparations.27 Solvents used for studꢀ
ies of liotropic mesomorphism and chromatography were addiꢀ
tionally dried and distilled. Alkyl bromides were purified chroꢀ
matographically on Al2O3 (hexane or benzene as eluants).
1,2ꢀBis(dodecyloxy)benzene (1k) is commercially available.
Pyrocatechol (reagent grade) was recrystallized from an
EtOH—H2O mixture. Synthesized compounds were puriꢀ
fied by column chromatography on silica gel L (100—250 or
40—100 µm) or Al2O3 (activity grade II according to Brockmann)
using gradient elution with mixtures of organic solvents (CHCl3,
hexane, benzene, CCl4); for more detail, see purification
of compound 2k. Ethers 2a—k were additionally recrystalꢀ
lized (EtOH—benzene) to constant temperatures of phase tranꢀ
sitions.
2,3,6,7,10,11ꢀHexakis(dodecyloxy)triphenylene (2k). Freshly
distilled hexane (215.0 mL) and 1,2ꢀbis(dedecyloxy)benzene (1k)
(8.0 g, 0.1 mol) were mixed in a conic 500ꢀcm3 flask with a
magnetic stirrer and a reflux condenser. Sulfuric acid (44.6 mL,
81%, d = 1.83 g cm–3) and then С16Н33NMe3Br (0.61 g,
0.69 mol) were added. Chloranil (44.6 g, 50.2 mol) was added to
the mixture with stirring. After gaseous HBr stopped evolving
(in ~1 h), the flask was equipped with a reflux condenser, and
the reaction mixture was magnetically stirred at ~20 °С. The
color of the reaction mixture changed from yellowꢀpink to green
and then to dark blue. After 10—12 days, the reaction mixture
was neutralized on cooling with an aqueous solution of NH4OH,
and the organic layer was separated, washed with water to the
neutral reaction, and dried with calcined Na2SO4. After excess
solvent was distilled off, the product was isolated by column
chromatography on silica gel (using hexane and then hexꢀ
ane—benzene—ССl4 (1 : 1 : 1) and hexane—benzene (1 : 1)
mixtures are eluents). The first hexane fraction containing comꢀ
pound 1k was rejected. Other fractions were combined, and the
solvent was distilled off almost to dryness. An airꢀdry residue
was dissolved in benzene with weak heating, and 95% EtOH was
added until a white flaky precipitate began to form. After some
time (~5 min), the precipitate that formed was filtered off and
washed with a small amount of a 95% EtOH—benzene (1 : 1)
mixture and then with EtOH. After drying in vacuo, compound
2k was obtained in 25—30% yield (3.5—4.2 g). Recrystallization
was repeated until constant phase transition temperatures were
achieved. 1Н NMR, δ: 0.86 (t, 18 Н, Me, J = 6.1 Hz); 1.25—1.93
(m, 120 Н, CH2); 4.21 (t, 12 Н, СН2О, J = 6.1 Hz); 7.82
(s, 6 Н, Ar).
Chloroform
Note. For all samples, only Tc are presented, because crystallizaꢀ
tion temperatures lie in a lowꢀtemperature region.
the textures look like enlarged broken fans. In addition,
the experimental data indicate that the solvent nature
exerts no substantial effect on the texture type. A thermoꢀ
tropic polymorphic samples of compound 2l do not change
the number of phases when a solvent is added, and only
the clarification temperature decreases considerably and
the interval of mesophase existence extends (Table 5).
The data presented in Tables 4 and 5 indicate that the
solvent nature has an aligning effect on the clarification
temperatures, which range, as a rule, from 40 to 59 °С.
Only when cyclohexane or cyclohexene is added to comꢀ
pound 2f, the clarification temperature decreases insigꢀ
nificantly compared to that of the thermotropic samples.
It should be noted that the addition of solvents to
samples of compounds 2f,h—j,l extends substantially the
intervals of existence of columnar mesophases without
significant rearrangements of their supramolecular strucꢀ
tures.
Thus, new triphenylene derivatives, viz., compounds
2k,l, were synthesized in this work, and their polymesoꢀ
morphism was shown. It was found that, for binary sysꢀ
tems of organic solvents with samples of compounds
2f,h—j,l, the temperatures of liomesophase formation
shift considerably to the lowꢀtemperature region, and the
destruction of the supramolecular structure of the iniꢀ
tial columnar thermotropic mesophase is observed in
some cases.
Experimental
Electronic absorption spectra were recorded on a Specord
UV—VIS spectrophotometer (200—750 nm) in petroleum ether
(fraction with b.p. ~58 °С). IR spectra were recorded on a
Specord Мꢀ80 spectrometer at 400—4000 cm–1 in a thin film or
1
in KBr pellets. Н NMR spectra were obtained in CDCl3 on a
Bruker ACꢀ200 spectrometer (200.13 MHz) using Me4Si as an
internal standard.
Thermal polarization microscopy studies were carried out
on a BIOLAR polarization interference microscope with a heatꢀ
ing stage of original design and a Zorkii photoattachment and on
Compounds 2a—j,l were synthesized using a similar proꢀ
cedure.
2,3,6,7,10,11ꢀHexakis(tetradecyloxy)triphenylene (2l). 1Н
NMR, δ: 0.87 (t, 18 Н, Me, J = 6.1 Hz); 1.25—1.56 (m, 144 Н,
CH2); 4.21 (t, 12 Н, СН2О, J = 6.1 Hz); 7.82 (s, 6 Н, Ar).

1748
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 8, August, 2004
Zemtsova and Zheleznov
The elemental analysis data and physicochemical characterꢀ
istics of the compounds synthesized are presented in Tables 1—4.
12. S. Kumar and M. Manickam, Liq. Cryst., 1999, 26, 1097.
13. H. Gasparoux, C. Destrade, and G. Fug, Mol. Cryst. Liq.
Cryst., 1980, 59, 109.
The authors thank N. V. Usol´tseva and O. B. Akopova
for help and consultation.
14. N. H. Tinh, M. C. Bernaud, G. Sigaud, and C. Destrade,
Mol. Cryst. Liq. Cryst., 1981, 65, 307.
15. I. Tabushi, K. Yamamura, and Y. Okada, Tetrahedron Lett.,
1987, 28, 2269.
16. K. Bechgaard and V. Parker, J. Am. Chem. Soc., 1972,
94, 4749.
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Received January 5, 2003;
in revised form March 29, 2004