A bolaamphiphilic sexithiophene with liquid crystalline triangular honeycomb phase

Article abstract of DOI:10.1039/c3cc38859j

A new bolaamphiphile comprising a 5,5′′′′′- diphenyl-sexithiophene core with glycerol groups at each end and four lateral decyl chains was synthesized, which self-assembles into a liquid crystalline phase representing a nanoscale honeycomb composed of qua

Full text of DOI:10.1039/c3cc38859j

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A Bolaamphiphilic Sexithiophene with Liquid Crystalline Triangular
Honeycomb Phase
Wei Bu,a Hongfei Gao,a Xiaoping Tan,a Xing Dong,a Xiaohong Cheng, * a Marko Prehm,b Carsten
Tschierske*b
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
bolaamphiphile possessing four lateral decyl chains (see Fig. 1).
This compound, which represents the longest oligothiophene
based LC bolaamphihpile reported yet, selfꢀassembles into a LC
honeycomb composed of regular triangular cylinder cells with a
55 sideꢀlength of 4.0 to 4.4 nm.
A
new bolaamphiphile comprising
sexithiophene core with glycerol groups at each end and four
10 lateral decyl chains was synthesized which self-assembles into
liquid crystalline phase representing nanoscale
a 5,5’’’’’-diphenyl-
a
a
honeycomb composed of quasi-infinite triangular cylinders of
Scheme 1 describes the synthesis of the target bolaamphipile
6T/10 by using Kumada and Suzuki coupling reactions as key
steps. Accordingly, 3ꢀdecylthiophene 2,17 was monobrominated
with one equivalent NBS in THF at RT.18 The obtained 2ꢀbromoꢀ
60 3ꢀdecylthiophene 3 was then transferred to the Grignard reagent 4
with 1.2 equivalent Mg turnings at T < 60 °C, followed by 1h
reflux to complete the reaction. Grignard reagent 4 was then
coupled with 4ꢀ(5ꢀbromothienꢀ2ꢀyl)anisole 6, which was obtained
in the monocoupling reaction between 2,5ꢀdibromothiophene and
65 4ꢀmethoxybenzene boronic acid19 under standard Suzuki
condition with Pd(PPh3)4.20 The resulting dithiophene 7 was
monobrominated with one equivalent NBS18 in THF at 30 °C.
π-conjugated sexithiophenes.
The spatial organization of πꢀconjugated molecules plays a
15 crucial role for optoelectronic devices such as OLEDs, TFTs and
PVs based on organic semiconducting materials. However, the
design of materials with predictable arrangement of the molecules
in well defined assemblies, driven by nonꢀcovalent interactions
that control and direct their selfꢀassembly, still remains a major
20 challenge. In this context it is of interest to consider the
possibility of liquid crystalline (LC) phases formed by πꢀ
conjugated rods, which have the advantage of annealing defects
due to their fluidity.1,2,3 Sexithiophene and other oligothiophenes4
belong to the most intensively investigated πꢀconjugated rods.5,6
25 LC oligothiophenes in most cases form smectic phases7,8 and
there are only rare cases of columnar and spheroidic cubic
phases.9 Polar functional end groups have recently been
recognized as controlling units for selfꢀassembly of πꢀconjugated
rods in gels and on surfaces.10,11 We used polar glycerol endꢀ
30 groups in combination with flexible nonꢀpolar side groups to
assemble πꢀconjugated rods into polygonal honeycombs.3,12 In
these honeycombs the πꢀconjugated rods stack parallel and on top
of each other, in this way forming walls, and these walls are
interconnected by hydrogen bonding networks between the
35 terminal glycerol groups, running along the edges of the resulting
polygonal cylinders forming the honeycomb. The prismatic cells
inside the honeycomb represent channels of different shape and
size which are filled with the laterally attached chains.12,13 In
previous work we have reported Tꢀshaped and Xꢀshaped
40 bisthiophenes14,15 forming triangular and square cylinders and a
Xꢀshaped tetrathiophene forming square cylinders. 16
The thus obtained bromide
8 was coupled with nꢀdecyl
magnesium bromide to give the methoxysubstituted
4
70 terthiophene 9. Demethylation of 9 using BBr3 at ꢀ78 °C21 yielded
the phenol 10; here it is essential that the reaction is quenched by
adding ice water as soon as the reaction was finished (TLC). The
obtained phenol 10 was then allylated with allybromide followed
by dihydroxylation of the double bonds with catalytic amounts of
75 osmium tetroxide and NꢀmethylmorpholineꢀNꢀoxide as
reoxydant22 to yield the glycerol ether 12. Protection of the diol
group with 2,2ꢀdimethoxypropane produced the acetonide 13
which was then oxidatively dimerized with nꢀBuLi and
anhydrous CuCl2 to yield the sexithiophene 14. In the final step
80 the acetonide protecting groups at both ends were cleaved (10%
HCl in CH3OH) and the obtained bolaamphiphile 6T/10 was
purified by repeated crystallization from ethyl acetate/methanol
(10:5). Detailed synthetic procedures and analytical data are
given in the electronic supporting information (ESI †).
85
Compound 6T/10 was investigated by polarizing microscopy
(PM), differential scanning calorimetry (DSC) and Xꢀray
diffraction (XRD). The thermotropic phase sequence and the
transition temperatures are collated in Fig. 1. 6T/10 melts at T =
109 °C, ‡ forming a LC phase which transforms into an isotropic
HO
C10H21
S
C10H21
HO
S
O
OH
OH
S
S
S
S
O
C10H21
C10H21
6T/10
90 liquid at T = 148 °C. The relatively low enthalpy of the transition
to the isotropic liquid state (ꢀH = 3.5 kJ molꢀ1) is in line with the
presence of a LC phase. On cooling the LC phase is formed from
the isotropic liquid at approximately the same temperature, but no
crystallization can be observed down to room temperature. At 20
95 °C the LC phase is stable for prolonged periods of time (about
one hour) before it crystallizes.
45
Cr 109 °C [34.1 kJmolꢀ1] Colhex/p6mm 148 °C [3.5 kJmolꢀ1] Iso
Fig.1 Compound 6T/10 with transition temperatures with associated
enthalpy values as determined by DSC (peak temperatures, 10 K minꢀ1) ‡;
abbreviations: Cr = crystalline solid; Colhex/p6mm = hexagonal columnar
LC phase with p6mm lattice; Iso = isotropic liquid state.
50
Herein we report the first example of a sexithiophene
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C10H21
C10H21
ii
10
5
Br
Br
Br
S
S
S
3
2
vii
iv
i
iii
Br
C10H21
C10H21
S
Br
+
S
O
OCH3
MgBr
S
S
S
4
6
S
v
11
12
13
C10H21
S
C10H21
viii
OH
OH
5
OCH3
C10H21
S
S
O
7
S
ii
S
C10H21
S
C10H21
ix
OCH3
O
Br
S
C10H21
S
O
O
8
9
S
3
iii, v
S
C10H21
OCH3
O
10
C10H21
S
x
S
S
C10H21
S
C10H21
C10H21
vi
O
S
O
O
S
C10H21
S
S
S
S
OH
O
O
14
S
C10H21
C10H21
S
xi
6T/10
10
C10H21
15
Scheme 1 Synthesis of compound 6T/10; Reagents and conditions: i) CnH2n+1MgBr, Ni(dppp)Cl2, THF, reflux, 15 h; ii) NBS, THF, 30 °C, 15 h; iii) Mg,
THF, reflux, 1 h; iv) 4ꢀmethoxybenzene boronic acid, Pd(PPh3)4, NaHCO3, glyme, H2O, reflux, 15 h; v) Ni(dppp)Cl2, THF, reflux, 15 h; vi) BBr3, ꢀ78 °C,
CH2Cl2, RT, 12 h; vii) K2CO3, CH3CN, allylbromide, reflux, 2 h; viii) OsO4, NMMNO, H2O, acetone, RT, 24 h; ix) Me2C(OMe)2, PPTS‚ TosOH, RT, 12
h; x) nꢀBuLi, THF, CuCl2，ꢀ60 °C, 15 h; xi) 10% HCl, CH3OH, reflux, 6 h.
20
The texture of the LC phase observed by PM between crossed
polarizers is characterized by spherulitic domains which indicate
the presence of a LC phase with 2D lattice (columnar phase, see
assumed. This number was calculated for a hypothetical unit cell
from the experimental 2D lattice parameters and an assumed
height of oneꢀmolecule thickness of 0.44 ꢀ 0.46 nm (average
Fig. 2b). Some regions appear optically isotropic,§ in these 55 maximum of the diffuse wide angle scattering, see Tab. S1) from
regions the column long axes are perpendicular to the substrate
the volume of this unit cell (Vcell) and the volume of a molecule
(Vmol, calculated using crystal volume increments23) according to
ncell = Vcell/Vmol as ncell ~ 3 (the density calculated with this value
is 1.0 ꢀ 1.1 g cmꢀ3, see Tab. S1). Since there are three walls per
25 surfaces and the fact that no birefringence is found in these
regions indicates that this mesophase is optically uniaxial, as
typical for square and hexagonal columnar mesophases. Shearing
the sample leads to flow which removes this texture; this 60 unit cell, the calculated average thickness of the walls (nwall
=
confirms the LC state of the material.
ncell/3) is about one rodꢀlike core.
30
Fig. 2a shows the XRD pattern of the LC phase at T = 40 °C
(supercooled state) and at T = 140 °C. The diffuse scattering in
the wide angle region confirms the fluid liquid crystalline state of
the material. The position of the wide angle scattering between d
= 0.44 (T = 40 °C) and d = 0.46 nm (T = 140 °C) is typically
35 observed as average of the mean distances between the aliphatic
chains and the aromatic cores. There is no additional reflection in
the wide angle range. The ratio of the positions of the small angle
reflections is 1: 31/2 : 2 at all temperatures, confirming a
hexagonal lattice and excluding a square lattice. The lattice
40 parameter ahex is strongly temperature dependent and grows from
ahex = 4.03 nm at T = 140 °C to ahex = 4.38 nm at T = 40 °C.
Overall the lattice parameter is in the range of the molecular
length L = 4.1 nm and this is in line with a triangular cylinder
honeycomb structure of this hexagonal columnar phase. In this
45 case the position and direction of the rodꢀlike cores coincide with
the hexagonal lattice (see Fig. 2c,d), the hydrogen bonding
networks incorporating six glycerol units are located at the 6ꢀfold
nodes of the (36)ꢀnet (blue columns in Fig. 2d) and the triangular
prismatic cells are filled with the alkyl chains. Fig 2c indicates
50 that satisfactory space filling is achieved in the proposed structure
if a thickness of the walls corresponding to ~1 molecule is
65
70
75 Fig. 2 Compound 6T/10: a) XRD patterns of the Colhex/p6mm phase at T
= 40 and 140 °C; b) texture between crossed polarizers at T = 140 °C; c)
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CPK models showing the organization of the molecules in the cross
‡ In the first heating scan here are crystalꢀcrystal transitions at 51 °C and
section of two adjacent triangular cylinders (one 2D unit cell); d) shows a 60 76 °C before the melting point at 109 °C, the given enthalpy is the total of
model of the triangular honeycomb phase and e) (36)ꢀnet.
all three transitions.
§ The dark red color of the material is also dominating in the optical
isotropic areas.
¶ The orientation of the optical axis can in this case not be determined
65 with certainty by observing the birefringence color shift using a lambda
retarder plate, due to the color of the material covering the birefringence.
An alternative honeycomb formed by hexagonal cylinders can
be excluded as this would provide insufficient space filling of the
larger hexagonal cells and would require a lattice parameter of
ahex= 31/2 L which is much larger than the experimental
determined value. If the rodꢀlike units would be arranged parallel
to the column long axis and surrounded by the fluid alkyl chains
5
1
(a) I. Mcculloch, M. Heeney, C. Bailey, K. Genevicius, I. Macdonald,
M. Shkunov, D. Sparrowe, S. Tierney, R. Wagner, W. M. Zhang, M.
L. Chabinyc, R. J. Kline, M. D. McGehee and M. F. Toney, Nat.
Mater., 2006, 5, 328ꢀ333; (b) M. M. Ling and Z. N. Bao, Chem.
Mater., 2004, 16, 4824ꢀ4840.
10 as recently proposed for the rodꢀbundle phases, 24 then ahex should
be significantly less than 3.6 nm. 27 This value is much smaller
than the experimentally observed lattice parameter and was
estimated from twice the length of the lateral chain (1.35 nm in
all-trans conformation) plus twice the diameter of the aromatic
15 core (0.45 nm).
70
75
2
3
M. O’Neill and S. M. Kelly, Adv. Mater., 2011, 23, 566–584.
X. Zeng, R. Kieffer, B. Glettner, C. Nürnberger, F. Liu, K. Pelz, M.
Prehm, U. Baumeister, H. Hahn, H. Lang, G. A. Gehring, C. H. M.
Weber, J. K. Hobbs, C. Tschierske and G. Ungar, Science, 2011, 331,
1302ꢀ1306.
The shrinkage of the trigonal cylinders with rising temperature
can be explained by the increasing mobility of the molecules and
especially the alkyl chains with increasing temperature and this is
typically observed for columnar phases and especially for
20 polygonal honeycomb phases.12,13 The thermal expansion occurs
predominately along the cylinder long axis which reduces the
coreꢀcore packing density along this direction. This is in line with
the shift of the position of the diffuse wide angle scattering from
d = 0.44 nm at T = 40 °C to d = 0.46 nm at T = 140 °C. Also in
25 line with the enhanced mobility is the significant broadening of
the small angle scatterings with rising temperature (Fig. 2a). This
indicates a continuously decreasing correlation length of the
hexagonal lattice with rising temperature which might be due to
the incorporation of a growing number of rhombic cells.15 These
30 rhombic cells can be formed by fusion of two adjacent triangular
cells and hence provide more space for the lateral chains. These
cells also allow an enhanced flexibility, as in contrast to triangles
the rhombs can more easily change the angles. This leads to a
reduced correlation length of the hexagonal lattice. At T = 148 °C
35 the 2Dꢀlattice becomes short range at the phase transition to the
isotropic liquid state which is assumed to be composed of small
disordered segments of the previous honeycomb.
In Summary, the first example of a sexithiophene based
bolaamphiphile decorated with four lateral decyl chains and two
40 terminal glycerol groups was synthesized. It represents the
bolaamphiphilic mesogens with the longest πꢀconjugated
oligothiophene core so far, which selfꢀassembles into a triangular
honeycombꢀlike LC phase over a broad temperature region. This
mode of selfꢀassembly is different to all previously reported
45 sexithiophenes and opens new possibilities for the directed
organization of πꢀconjugated organic materials into complex
superstructures. Further work will be focused on modification of
the πꢀconjugated core to achieve closer πꢀstacking along the
honeycomb walls. Such optimized compounds could be of
50 interest for selfꢀassembled nanoꢀscale organic electronic devices.
4
D. Fichou, J. Mater. Chem., 2000, 10, 571–588; S. Hotta and
K.Waragai, Adv. Mater., 1993, 5, 896–908; F. Garnier, A. Yassar, R.
Hajlaoui, G. Horowitz, F. Deloffre, B. Servet, S. Ries and P. Alnot, J.
Am. Chem. Soc., 1993, 115, 8716–8721; M. Halik, H. Klauk, U.
Zschieschang, G. Schmid, S. Ponomarenko, S. Kirchmeyer and W.
Weber, Adv. Mater., 2003, 15, 917–922.
(a) G. Horowitz, D. Fichou, X. Peng, Z. Xu and F. Garnier, Solid
State Commun., 1989, 72,381ꢀ384; (b) H. E. Katz, Z. Bao and S. L.
Gilat, Acc. Chem. Res., 2001, 34, 359ꢀ369.
A. Mishra, C.ꢀQ. Ma, and P. Bäuerle, Chem. Rev., 2009, 109, 1141ꢀ
1276.
J. Ma, Q. Li, in Self-organized Organic Semiconductors: From
Materials to Device Applications, Ed. Q. Li, John Wiley & Sons,
Hoboken NJ, 2011.
80
5
85
6
7
90
8
9
A. Dell’Aquila, P. Mastrorilli, C. F. Nobile, G. Romanazzi, G. P.
Suranna, L. Torsi, M. C. Tanese, D. Acierno, E. Amendola and P.
Morales, J. Mater. Chem., 2006, 16, 1183–1191.
T.Yasuda, H. Ooi, J. Morita, Y. Akama, K. Minoura, M. Funahashi,
T. Shimomura and T. Kato, Adv. Funct. Mater., 2009, 19, 411–419.
95
10 (a) K. Yoosaf, A. R. Ramesh, J. George, C. H. Suresh, and K. G.
Thomas, J. Phys. Chem. C, 2009, 113, 11836ꢀ11843; (b) S. K.
Samanata, A. Pal and S. Bhattacharya, Langmuir, 2009, 25, 8567ꢀ
8578.
11 (a) A. Jatsch, E.ꢀK. Schillinger, S. Schmid and P. Bäuerle, J. Mater.
Chem., 2010, 20, 3563–3578; (b) S. Schmid, E. MenaꢀOsteritz, A.
Kopyshev and Peter Bäuerle, Org. Lett., 2009, 11, 5098ꢀ5101.
12 C. Tschierske, Chem. Soc. Rev., 2007, 36, 1930ꢀ1970; C. Tschierske,
C. Nürnberger, H. Ebert, B. Glettner, M. Prehm, F. Liu, X. Zeng and
G. Ungar, Interface Focus, 2012, 2, 669ꢀ680.
100
105
13 X. H. Cheng, M. Prehm, M. K. Das, J. Kain, U. Baumeister, S. Diele,
D. Leine, A. Blume and C. Tschierske, J. Am. Chem. Soc., 2003, 125,
10977–10996.
110 14 X. H. Cheng, X. Dong, G. H. Wei, M. Prehm and C. Tschierske,
Angew. Chem., 2009, 121, 8158ꢀ8161; Angew. Chem. Int. Ed., 2009,
48, 8014ꢀ8017.
15 H. F. Gao, Y. F. Ye, X. H. Cheng, M. Prehm, H. Ebert and C.
Tschierske, Soft matter 2012, 8, 10921ꢀ10931
115 16 (a) M. Prehm, G. Götz, P. Bäuerle, F. Liu, X. B. Zeng, G. Ungar and
C. Tschierske, Angew. Chem. Int. Ed., 2007, 46, 7856ꢀ7859.
17 C. V. Pham, H. B. Mark, and H. Zimmer, Synth. Commun., 1986, 16,
689ꢀ696.
18 (a) T.A. Chen, X.M.Wu and R. D.Rieke, J. Am. Chem. Soc., 1995,
120
117, 233ꢀ244; (b) R. D. McCullough, R. D. Lowe, M. Jayaraman and
D. L.Anderson, J. Org. Chem., 1993, 58, 904ꢀ912.
Notes and references
19 Y. Huang, X. Dong, T. Zheng, L. J. He and X. H. Cheng, Yunnan
Unversity (Natural Science Edition), 2007, 29, 398ꢀ400.
20 N. Miyaura and A. Suzuki, Chem. Rev., 1995, 95, 2457ꢀ2483.
a Chemistry Department, Yunnan University, Kunming, Yunnan 650091,
P. R. China. Fax: (+86) 871 5032905; E-mail: xhcheng@ynu.edu.cn
b Institute of Chemistry Organic Chemistry, Martin-Luther University
55 Halle-Wittenberg, Kurt-Mothes Str. 2, 06120 Halle/Saale, Germany. Fax:
(+49) 345 55 27346; E-mail: carsten.tschierske@chemie.uni-halle.de
† Electronic Supplementary Information (ESI) available: [Synthesis,
analytical data and XRD data]. See DOI: 10.1039/b000000x/
125 21 J. F. W. McOmie, D. E. West, Organic Syntheses, Wiley: New York,
1973, Coll. Vol. V, p. 412.
22 V. Van Rheenen, D. Y. Cha and W. M. Hartley, Org. Synth., 1978,
58, 43ꢀ51.
23 A. Immirzi and B. Perini, Acta Cryst. Sect. A., 1977, 33, 216ꢀ218.
This journal is © The Royal Society of Chemistry [year]
Journal Name, [year], [vol], 00–00 | 3

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24 M. Prehm, F. Liu, X. Zeng, G. Ungar and Carsten Tschierske, J. Am.
Chem. Soc., 2011, 133, 4906–4916.
4
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