Molecular design of benzothienobenzothiophene-cored columnar mesogens: Facile synthesis, mesomorphism, and charge carrier mobility

Article abstract of DOI:10.1039/c7tc05315k

Benzothienobenzothiophene (BTBT) liquid-crystalline semiconductors are arousing a lot of interest due to their long-range ordered, self-organizational abilities and high-charge carrier transport properties. In this work, we report the design and the straightforward synthesis of a homologous series of compounds containing the BTBT substructure by the successive Suzuki cross-coupling and FeCl₃ oxidative Scholl cyclodehydrogenation reaction. Target π-conjugated aromatic, H-shaped sanidic mesogens self-organize into a classical hexagonal columnar mesophase over wide temperature ranges as deduced from polarized optical microscopy (POM), differential scanning calorimetry (DSC), and small-angle X-ray scattering (SAXS) investigations. UV/Vis absorption and photoluminescence spectra, measured in both solution and films, revealed strong photoluminescence with high quantum yields. The charge carrier mobility measured by the time-of-flight (TOF) technique showed a balanced ambipolar hole and electron mobility in the range of 10^-3 cm² V^-1 s^-1 between 100 and 230 °C in the mesophase. These BTBT-based columnar liquid crystals may represent attractive candidates to be incorporated within one-dimensional organic optoelectronic devices.

Full text of DOI:10.1039/c7tc05315k

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ARTICLE
Molecular Design of Benzothienobenzothiophene‐Cored
Columnar Mesogens: Facile Synthesis, Mesomorphism, and
Charge Carrier Mobility
Received 00th January 20xx,
Accepted 00th January 20xx
Chun‐Xia Liu,a Hu Wang,a Jun‐Qi Du,a Ke‐Qing Zhaoa*, Ping Hu,a Bi‐Qin Wang,a Hirosato Monobe,b*
Benoît Heinrich,c Bertrand Donnio,c*
DOI: 10.1039/x0xx00000x
www.rsc.org/
Benzothienobenzothiophene (BTBT) liquid‐crystalline semiconductors are arousing a lot of interest due to their long‐range
ordered, self‐organizational abilities and high‐charge carrier transport properties. In this work, we report the design and the
straightforward synthesis of a homologous series of compounds containing the BTBT substructure by the successive Suzuki
cross‐coupling and FeCl3 oxidative Scholl cyclodehydrogenation reaction. The target ‐conjugated aromatic, H‐shaped
sanidic mesogens self‐organize into a classical hexagonal columnar mesophase over wide temperature ranges as deduced
from polarized optical microscopy (POM), differential scanning calorimetry (DSC), and small‐angle X‐ray scattering (SAXS)
investigations. UV/Vis absorption and photoluminescent spectra, measured in both solution and film, revealed strong
photoluminescence with high quantum yields. The charge carrier mobility measured by time‐of‐flight (TOF) technique
showed a balanced ambipolar hole and electron mobility in the range of 10‐3 cm2 V‐1 s‐1 between 100 to 230°C in the
mesophase. These BTBT‐based columnar liquid crystals may represent attractive candidates to be incorporated within one‐
dimensionnal organic optoelectronic devices.
Compared with crystalline and amorphous molecular
semiconducting materials, mesomorphous semiconductors
combine features of both, i.e. self‐organizational tendency,
fluidity and molecular dynamics which help to self‐heal defects,
and high charge carrier mobility.23‐28 Molecular design and
straight synthesis of novel mesophase semiconductors are
highly desirable due to their controllable anisotropy with one‐
or two‐dimensional charge transport property and outstanding
thin‐film device performance.26,27
Among the large amount of S‐containing aromatics reported so
far in the literature, benzothienobenzothiophene (BTBT)
derivatives have been found to display lamellar columnar
mesophases,29 as well as high ordered layered smectic
mesophases.30‐32 The former systems show time‐of‐flight (TOF)
charge drift mobility in 10‐3 cm2 V‐1 s‐1 range, whereas the latter
ones display higher TOF mobility as well as excellent OFET
device’ performances in their high ordered crystalline phase,
which is templated by slowly cooling from the fluid high‐
temperature smectic liquid crystalline phase,32 or just by
solution process.31
Introduction
Thiophene‐based materials are ubiquitous as organic
semiconductors.1‐6 The sulfur‐containing aromatic heterocycle
possesses
a versatile and unique chemistry, and the
investigation of thiophene‐containing oligomers,7 dendrimers8
and polymers,9 as well as polycyclic aromatics1‐6 are becoming
a vivid part of contemporary chemistry, including synthetic and
materials chemistries. Potentially more interesting, are the
related two‐dimensional, conjugated thiophene‐fused
aromatics.10‐22 They have been found to prefer ordered
arrangements stabilized by π‐π intermolecular interactions with
large molecular orbital overlaps, which result in the
enhancement of the charge carrier mobility. As such, these
fused thiophene molecular materials are being extensively
investigated in organic thin‐film electronics and optoelectronic
devices such as organic field‐effect transistors (OFETs),10
photovoltaic solar cells (OPVs),11 and light‐emitting diodes
(OLEDs).12
However, discotic columnar mesomorphic materials possess
one‐dimensional π‐π stacked columnar mesophase, and charge
carriers hopping along the discotic columns, whereas the
peripheral alkyl chains play the role of insulator. Such
supramolecular columns appear therefore as ideal one‐
dimensional pathway for charge carrier transport.33‐36 The
charge carrier mobility, according to Marcus’s electronic
transfer theory of small molecules,37 is determined mainly by
two parameters: the reorganization energy and the charge
transfer integral, both parameters being related to the
a. College of Chemistry and Material Science, Sichuan Normal University, Chengdu
610066, China. E‐mail: kqzhao@sicnu.edu.cn
b. Inorganic Functional Materials Research Institute, National Institute of Advanced
Industrial Science and Technology (AIST), Ikeda, Osaka 5638577, Japan. E‐mail:
monobe‐hirosato@aist.go.jp
c. Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), CNRS‐
Université de Strasbourg (UMR 7504), 67034 Strasbourg, France. E‐mail:
bertrand.donnio@ipcms.unistra.fr
Electronic Supplementary Information (ESI) available: Experimental techniques,
synthetic details, 1H NMR, HMRS, POM, DSC, TGA, SAXS, indexation tables. See
DOI: 10.1039/x0xx00000x
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molecular chemical structure and to the molecular packing The preparation of M1 was achieved in three steps, starting
morphology in mesophase.38 Therefore, it is expected that from precursory biphenylene derivatives (Supplementary
BTBT‐containing columnar mesogens are also suitable Information, SI, and in reference 35), and consisted of the
candidate for one‐dimensional mesophase semiconductors.
Suzuki coupling between thieno[3,2‐b]thiophen‐2‐ylboronic
BTBT derivatives with 2,7‐disubstitution normally exhibit acid and the 2‐bromo‐1,1’‐biphenyl precursor (1‐1) to yield the
smectic phases,30‐32 but the synthesis of BTBT‐cored key precursor 1‐2 (75%), followed by a first FeCl3 oxidation to
compounds with six to eight peripheral alkyl chains to induce yield 1‐3 in 81%, which was then immediately reacted with
discotic columnar mesophase is still regarded as challenging. 3,3’,4,4’‐tetra(pentyloxy)biphenyl by the second FeCl3 oxidative
The construction of useful mesophase semiconductors by cross coupling to yield M1 in 43% yield. The cross‐
higher efficient synthetic methods is a crucial objective,39‐44 and cyclodehydrogenation resulted in 4 C‐H bonds cleavage and two
introducing BTBT‐unit into discotic columnar mesophase would C‐C bond formation in one‐pot, which is highly efficient. This
provide
semiconductor materials.
a
new and exciting class of one‐dimensional multiple‐step synthetic method is however time‐consuming
(three steps), affords a low overall yield (26%), and the isolation
Here, we report the design and the straightforward synthesis of of the pure target compounds was difficult, and systematically
BTBT‐unit containing columnar mesogens by two different required several purifications by column chromatography.
synthetic routes involving either intermolecular or Despite the repeated purification procedures, this strategy is
intramolecular FeCl3 oxidative Scholl cyclodehydrogenation nevertheless very interesting and could be implemented to the
reaction as key step reactions (Scheme 1). Both approaches synthesis of unsymmetrical BTBT‐based “Janus” mesogens
have their own assets and specificities. The intermolecular decorated by aliphatic chains of different lengths or by chains
cross‐oxidative Scholl reaction is a linear strategy (Route 1, of different chemical natures, when, for example different
Scheme 1) specifically dedicated for the construction of functional biphenyls are used, of relevance for the construction
unsymmetrical BTBT‐containing compounds, i.e. with a “Janus” of original self‐assembled functional materials.
structure, by, for example, associating similar building block,
but bearing alkyl chains of different lengths, of by combining
Route 1
Route 2
hydrophilic/hydrophobic
or
fluorophilic/fluorophobic
peripheries, which would impact on their self‐assembly,
thermal, solubility and surface properties. It is nonetheless a
time‐consuming solution, as it also requires tedious
purifications. The intramolecular approach (Route 2, Scheme 1)
is more direct and straightforward, and highly efficient to
produce symmetrical structures by orthogonal coupling in high
yield, with also much simpler purification processes. All the
BTBT‐containing molecules prepared thereafter are
symmetrical, and the homogeneous alkyl periphery was
increased from pentyl to dodecyl chains to tune the liquid
crystalline temperature ranges and transition temperatures.
The liquid crystalline properties of these compounds have been
carefully investigated by POM, DSC, and SAXS. Their optical
properties (UV/Vis absorption and photoluminescence)
measured in both solution revealed strong photoluminescence
with high quantum yields. Furthermore, the charge carrier
mobility of one representative material, measured by the time‐
of‐flight (TOF) transient photocurrent technique, exhibited
ambipolar hole and electron drift mobility above 10‐3 cm2 V‐1 s‐
1, showing a great potential as mesomorphous semiconductors.
OC5H11
OR
OR
Br
Br
S
Br
Br
C5H11
O
O
+
(HO)2B
S
RO
RO
Br
THF/H2O,
K2CO3,
Pd(PPh3)4
C5H11
1-1
OC5H11
RO
OR
S
B(OH)2
Pd(PPh3)4
K2CO3,
RO
S
THF/H2O
S
S
OR
OC5H11
OR
C5H11
O
O
OR
D2: R=C6H13 (92.9%)
D3: R=C8H17 (72.6%)
D4: R=C10H21 (73.0%)
D5: R=C12H25 (62.3%)
S
FeCl3,
CH3NO2
CH2Cl2
S
C5H11
1-2 (75%)
OC5H11
OR
OC5H11
OC5H11
FeCl3,
CH3NO2/
CH2Cl2
OR
RO
RO
OR
OR
S
OC5H11
S
C5H11
O
O
OC5H11
OC5H11
OR
S
OR
M1: R=C5H11 (43.0%)
M2: R=C6H13 (82.5%)
M3: R=C8H17 (74.7%)
M4: R=C10H21 (71.3%)
M5: R=C12H25 (83.9%)
Results and Discussion
Methodology, Synthesis and Characterization
FeCl3,
CH3NO2,
CHCl3
S
C5H11
OC5H11
The two different synthetic methods were tested with success
1-3 (81%)
Scheme 1. Synthesis of the fused thieno[3,2‐b]thiophene H‐shaped
liquid crystals, and precursors (D2 ), by Suzuki coupling and i)
intermolecular (Route 1, M1) or ii) intramolecular (Route 2, M2 ) Scholl
cyclodehydrogenation reaction, nomeclature, and yields (Details shown
in SI).
for the fabrication of the H‐shape fused thiophenes, M1‐5: the
intermolecular cross‐oxidative Scholl reaction afforded
compound M1 (Route 1, Scheme 1), whereas the other terms of
the series, M2‐5, were obtained in high yields by the direct
‐
5
‐5
intramolecular cross‐oxidative Scholl reaction (Route 2, Scheme
1).
As for the next terms of the series with longer peripheral chains,
they were prepared in two steps, starting from
2 | J. Name., 2012, 00, 1‐3
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Apart from D2, the other tetraarylthioeno[3,2‐b]thiophenes exhibit
a complex solid state behavior, with the formation of a metastable
solid phase on cooling the samples from the isotropic liquid, that
crystallizes on subsequent heating (cold crystallization). The
isotropization temperature is also found to decrease with chain‐
length (Figure 1, Table 1). The rapid rotation around the sigma bond
axis of the four appending bulky dialkoxyaryl units connected to the
central thieno[3,2‐b]thiophene is thought to be the main cause for
this solid‐state thermal behavior and for the absence of
mesomorphism in this series, as probably detrimental to cohesive
stacking into columns.
tetrabromothieno[3,2‐b]thiophene (obtained in quantitive
yields from direct bromination of thieno[3,2‐b]thiophene in
excess of bromine, Scheme S1) by Suzuki cross‐coupling with
various 3,4‐dialkoxyphenyl)boronic acids to yield the
corresponding tetraarylthieno[3,2‐b]thiophenes D2
Oxidative cyclodehydrogenation of D2 by FeCl3/MeNO2
produced the target fused mesogens M2 in good yields
(71 84%). The compounds were isolated by simple filtration
‐5 (62‐93%).
‐
5
–
5

and purified by crystallization, without tedious column
chromatography purifications. It is stressed that this
intramolecular cyclodehydrogenation resulted in 4 C‐H bonds
cleavage and two C‐C bond formation in one‐pot, and no
After cyclodehydrogenation, the substituted phenyls and the central
1
isomeric compounds were isolated, as confirmed by H‐NMR
thieno[3,2‐b]thiophene core fuse into
a large, co‐planar π‐
(Figures S25‐29, SI).
conjugated discotic aryl‐containing molecule. Consequently, the self‐
organization process is strongly affected, and an enantiotropic Colhex
mesophase (SAXS) is induced for all M1‐5 compounds, at rather
elevated temperatures though, consistent with stronger π‐π
intermolecular interactions and the substantial increase of the
isotropization temperatures (by more than 200°C on average, Figure
1) with respect to the corresponding D terms: the I‐to‐Colhex
transition temperatures is maximal for M1 (309°C) and continuously
decreases in the series with the dilution of the mesogenic cores,
down to 226°C as the peripheral chain length increases to dodecyl.
Melting also decreases steadily with chain‐length. The variation of
All the
characterized by H NMR (Figures S11‐S29, SI) and the fused
compounds (M1 ) were further analyzed by high resolution
mass spectra (HRMS, Figures S30‐S34, SI). The results were in
agreement with the molecular structures. Detailed synthesis of
all precursors is given in SI.
D and M (and some intermediate) compounds were
1
‐
5
Thermal stability and Mesomorphism TGA, DSC, POM
The thermal stability of the targeted H‐shaped sanidic mesogens was
measured by thermal gravimetric analysis (TGA): compounds M2‐5
exhibited very high thermal stability, displaying thermal
decomposition temperatures higher than 380oC (Figure S5, SI). The
thermal behavior and liquid crystalline properties of intermediates
1‐n and D2‐5 and target compounds M1‐5 (Table 1) were
investigated by polarized optical microscopy (POM, Figures S1‐2, SI)
and by differential scanning calorimetry (DSC, Figures S3‐4, SI). As
expected from some previous work, neither compounds 1‐2 and 1‐
3,35 nor any of the precursory compounds D2‐5 were
mesomorphous, whereas all final compounds exhibit
mesomorphism, over large temperature ranges (Figure S4, SI). The
sanidic compounds display typical fan‐shaped optical textures, long
linear defects and large homeotropic domains (Figure S2, SI), which
are characteristics of a hexagonal columnar mesophase.
the chain lengths proved
a maximum extension of the
mesomorphous range for the derivatives with eight octyl and decyl
side chains, M3 and M4 (Table 1).
Table 1. Mesophases, transition temperatures and enthalpy changes for
compounds D and M (heating and cooling rate of 5‐10 oC∙min‐1)a
Second heating [first cooling] / oC (ΔH, kJ∙mol‐1)
D2
D3
Cr 91.8(87.5) I [I 73.1(‐85.7) Cr]
Cr* 44(‐40) Cr 57.0(‐) Cr’ 73.5(74.3) I
[I 65.4(‐20.8) Cr’ 53.0(‐) Cr*]
Cr* 44(‐50.0) Cr 71.4(122.2) I
[I 52.5(‐11.1) Cr 41(‐25) Cr*]
D4
Cr 8(11.0) Cr* 38(‐60.0) Cr’ 71(130.5) I
[I 48(‐64.1) Cr’ 1(‐8.0) Cr]
D5
Cr 111(5.0) Cr’ 179(‐) Cr” 189(29.6)† Colhex 309(6.8) I
[I 307(‐6.2) Colhex 161(‐24.3) Cr 90(‐10.0) Cr’]
Cr 125(4.0) Cr’ 161(‐) Cr” 168(14.7)† Colhex 297(8.4) I
[I 295(8.5) Colhex 150(‐34.7) Cr’ 122(‐4.0) Cr]
Cr 109(‐) Cr’ 125(‐) Cr” 133(11.5)† Colhex 280(6.1) I
[I 279(‐3.4) Colhex 107(56.9) Cr’ 97(‐) Cr]
Cr ‐11(4.0) Cr’ 104(‐) Cr” 111(44)† Colhex 261(9.7) I
[I 260(‐9.7) Colhex 87(96.2) Cr’ ‐10(‐) Cr]
Cr 79(55.0) Cr’ 98(56.7) Colhex 226(4.5) I
[I 222(‐4.1) Colhex 61(‐127.7) Cr]
M1
M2
M3
M4
M5
aCr, Cr’, Cr”: crystalline phases; Cr*: metastable crystalline phase, or mixture
of (partially or conformationnally disordered) crystalline and amorphous
solids; Colhex: hexagonal columnar mesophase; I: isotropic liquid. †Cumulated
enthalpy.
Figure 1. Phase diagram of BTBT‐cored mesogens
non‐mesomorphic precursors
M and of their
D
.
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crystalline phase for D2, and the co‐existence of crystalline and
amorphous phases (for D3‐5), in agreement with their complex
thermal behavior detected by DSC (and POM). On the contrary, all
the fused thieno[3,2‐b]thiophene compounds self‐organize into a
Colhex mesophase at high temperature, constituted by
supramolecular columns of stacked mesogens (spacing from
scattering signal: h = 3.73‐3.82 Å, Figure 2), arranged at the nodes
of a hexagonal array, and separated from each other by a continuum
of molten chains (liquid‐like lateral distances between molten chains,
ch, from broad maximum: hch  4.5 Å, Figure 2). The long‐range
correlated two‐dimensional columnar lattices are characterized by a
relatively large number of reflections and thus by quite sharp
interfaces with the continuum, obviously in relation with a strongly
cohesive stacking (five reflections (hk) visible for M1/M2 and still
three for the longest chain homologues M4/M5, Table S1, Figures 2,
S6‐9). The cause might be the reinforced interactions from
thienothiophene segments, whose presence further confers an ovoid
shape and zones devoid of side‐chains to mesogens. Yet, the
hexagonal symmetry implies that columns have an average
cylindrical shape with a regular distribution of aliphatic tails along
their periphery. The mesogens must therefore adopt various (non‐
preferential) orientations along the stacking directions and be tilted
Figure 2. Representative SAXS pattern of compounds
M (M5 at 180°C)
Characterization of the mesophase by small‐angle X‐ray scattering
(SAXS)
The SAXS patterns were recorded for all samples, at various
temperatures (Figures 2 and S6‐9, Tables 2 and S1). The absence of
mesomorphism was confirmed for compounds D2‐5. In these cases,
the SAXS patterns, recorded below the isotropic phase, revealed a
Figure 3. Stacking features and supramolecular model of the fused thieno[3,2‐b]thiophene cores stacked into cylindrical columns, with tilt and non‐
preferential orientations of the mesogen cores (in blue); hexagonal lattice in red (Models were reconstructed from single crystal structures of
2,3,6,7,10,11‐hexaethoxytriphenylene (CSD‐XEFTAD),49 and thieno[3,2‐b]thiophene (CSD‐THIPHT)50). The molten chains continuum between the
columns is not shown for clarity.
Table 2. Mesophase parameter of the Colhex of compounds M1‐5†
Cpds
M1
M2
M3
M4
M5
T
Vmol
a
A[Z]
hmol
Acore
181
165
167
161
165
Dcyl
Sch,cyl
24.7
26.2
25.7
26.0
25.3
qch,cyl
1.02
1.07
1.06
1.08
1.07

Vch
h

25
34
33
36
33
240
230
210
200
180
1982 0.95
2258 0.91
2722 0.90
3194 0.88
3635 0.88
0.62(2) 23.5 478[1] 4.14
0.66(4) 23.7 488[1] 4.60
0.72(5) 26.7 616[1] 4.48
0.76(7) 28.4 700[1] 4.64
0.79(8) 31.3 847[1] 4.45
3.76
3.82
3.76
3.76
3.73
15.2
14.5
14.6
14.3
14.5
†T, temperature of the measure in °C; Vmol, molecular volume (Å3) and,
(accuracy ca. 4%); V,ch, aliphatic volume fraction (
V,ch = Vch/Vmol); lattice parameter (a, Å), area (A = 2a2/√3, Å2) and Z, number of columns par lattice
(Z = 1); columnar slice thickness (Å) hmol = Vmol/(Z×A); h, stacking distance from SAXS pattern (missing value for terms was estimated to ca. 3.8 Å);
, out‐of‐ plane tilt angle of mesogens inside columns VchA/Z; Dcyl (Å),
= arcos(h/hmol) (°); Acore, cross‐sectional area of columnar cores (Å2): Acore
diameter of equivalent cylinder of cross‐sectional area Acore; Sch,cyl, cylinder area per chain (Å2): Sch,cyl
Dcyl×hmol/nch, nch being the number of chains
ch being the cross‐sectional area of a molten chain.

, density (g cm‐3) calculated from partial volumes of reference substances


Mn


= 
=

per molecule (nch = 8); qch,cyl, chain packing ratio: qch,cyl = Sch,cyl/ch, 
4 | J. Name., 2012, 00, 1‐3
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inside and between columns, as similarly occurring for rod‐like with the interface area offered by stacked mesogens, i.e. that the
mesogens in the Colhex phases of polycatenar compounds (Figure ratio qch,cyl of both areas does not deviate too much from unity.47‐48
3).45‐46
This ratio is indeed lying between 1.02 and 1.08, meaning that the
The values of hmol (columnar slice thickness obtained from the ratio chains are compactly packed and quasi‐stretched, close to well‐
between the molecular volume, Vmol, and the lattice area, S, Table 2) defined interfaces. Such nearly ideal packing is however the result of
the self‐optimization of the molecular organization, the interface
expansion just required by chains being reached through the tilting
of the mesogens out of the columnar plane ( ≈ 28‐36°). This strongly
cohesive, rotated and tilted packing (Figure 3) combines with the
periodicities of several mesogens along and between neighboring
columns, and explains the appearance of additional broad signals D1,
D2 from a local‐range three‐dimensional superstructure. It must be
stressed that this model is just a schematic view of how molecules
may stack by compromising the average tilt and the hexagonal
symmetry. The bulkiness of the sulphur atoms prevents
configurations with exact superposition of stacked mesogens, which
could be at the origin of the shifts and the rotations along the
columns, and ultimately of their average cylindrical shape and of
their arrangement into the hexagonal lattice.
shows a substantial shift from h, which indicates a tilted stacking of
the flat cores along the columnar axis (by ca. 28‐36°, deduced from
ratio of h and molecular slice thickness hmol, Table 2). A further
condition for the emergence of columnar mesophases is that the
overall cross‐sectional area of the peripheral chains is compatible
UV‐Vis absorption and photoluminescent properties
The synthesized H‐shaped sanidic compounds are large π‐conjugated
polycyclic aromatic hydrocarbon (PAHs) and as expected show strong
light absorption and photo‐induced light emission, as measured by
UV/vis absorption and photoluminescence (Figure 4 and Table 3).
The main, broad absorption of compounds D2‐5 in solution is located
below 400 nm. In contrast, the fused compounds M1‐5 display two
fine, well‐resolved absorption bands with four peaks, all located
below 400 nm. The absorption spectra of all fused compounds are
red‐shifted and increased in intensity (molar coefficient), due to the
π‐conjugated system extension. The thin‐film photoluminescence of
all compounds is constituted of only one broad and intense peak,
located between 430444 nm for D2‐5, and at 450 nm with a
shoulder and long tail for M1‐5. However, the solution
photoluminescence of M1‐5 is better resolved and exhibit three
separated peaks, blue‐shifted compared to their film emissions. They
emit blue light in THF solution. The light‐emitting efficiency
(quantum yield, QY) was measured for both series: the tetraaryl‐
substituted compounds D display lower quantum yields, around
10%, than the fused aromatics M, which show higher
photoluminescence, with efficiency of about 23%. The alkyl chain
length do not seem to impact on the photoluminescence of the fused
mesogens.
It is conventional that the solid‐state emission is red‐shifted
compared to the emission of the samples in diluted solution, due to
the molecular aggregation in the former, resulting in orbital overlap
and therefore narrowed HOMO‐LUMO energy gap. The fused
aromatics M compounds display emission QY values higher than that
of the D‐compounds, which can be explained by the difference of the
aromatic cores and the decrease of the conjugation. Another factor
contributing to the lowering of the QY of compounds D might be due
to the tetraaryl groups surrounding the thienothiophene core that
rotate around the Ar‐Ar’ sigma bonds in solution, such rotating
motions forcing the molecules to relax from excited to ground states,
and causing partially fluorescence quenching.
Figure 4. UV/Vis absorption spectra (A), photoluminescence in diluted
solution (B) and in solid thin‐films (C), respectively, of compounds
(open symbols) and (filled symbols).
D
M
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and, poly‐crystalline grain boundaries start to form, which act as
deep traps for charge carriers, and dispersed transient
Table 3. Photo‐physical properties of the BTBT‐containing compounds.
Quantum yields were measured with solution concentration of 1×10‐5 mol L‐
1 in THF excited at 300 nm.
a
photocurrent curve is observed. The TOF charge mobility of M4 is
located in the range of 10‐4  0.1 cm2 V‐1 s‐1, similar to the charge
transport rate for reported other one‐dimensional columnar
mesophases. The columnar phase of this thiophene‐fused mesogen
therefore acts as an ambipolar semiconductor as both electron and
hole mobilities have been realized.
One‐dimensional semiconductor made from discotic columnar
mesogenic materials normally show TOF mobility in the range of 10‐
4 to 10‐1 cm2 V‐1 s‐1. According to the Marcus’s theory,37 the kinetics
of electronic charge carrier hopping between two identical
molecules, in small molecular semiconductors, is determined by two
parameters: i) the reorganization energy and ii) the charge transfer
integral, which are both related to the molecular structure and
crystalline or supramolecular morphology. As predicted in the
Marcus theory, larger π‐conjugated aromatics possess lower
reorganization energies and higher electronic transfer integrals,
therefore higher rates of charge hopping must be displayed.
λabs
ε
λem
solution
λem
film
Solution
QY (%)
(nm) (L mol ‐1 cm‐1)
D2
D3
D4
D5
355
354
353
353
248
280
365
391
249
280
367
390
249
280
367
390
249
280
367
390
4.05 x 104
3.38 x 104
2.91 x 104
2.94 x104
9.79 x 104
9.93 x 104
5.86 x 104
6.54 x104
9.73 x 104
9.96 x 104
5.83 x 104
6.40 x 104
9.73 x 104
9.96 x 104
5.83 x 104
6.40 x 104
9.73 x 104
9.96 x 104
5.83 x 104
6.40 x 104
437
437
437
437
412
434
460
444
443
445
438
9.90
9.28
8.90
12.44
M1
M2
M3
M4
450
450
450
450
21.30
22.78
22.23
22.50
412
434
460
412
434
460
412
434
460
The SAXS results of the pseudo‐discotic mesogens M1‐5 show
aromatic core‐core separations in the 3.7‐3.8 Å range in the columns
(h, Table 2), much larger than the 3.5 Å found for the stacking of
conventional discotic systems (e.g. triphenylenes).51 Such a large
249
9.73 x 104
412
280
367
390
9.96 x 104
5.83 x 104
6.40 x 104
434
460
M5
450
21.91
Charge carrier mobility
As seen above, all thieno[3,2‐b]thiophene‐fused molecules M1‐5
display a hexagonal columnar mesophase with a high clearing
temperatures, and a strong tendency for alignment (Figure S10 in SI).
They are therefore expected to possess good electronic transport
properties. The transient photocurrent time‐of‐flight (TOF)
technique was used here as a direct, simple, and reliable method to
obtain both electron and hole mobilities of the liquid crystalline
materials and to measure the charge transport mobility rates.
For the measurement of the charge carrier mobility, M4 was chosen
as a representative example. The liquid crystal cell for the TOF study
(cell thickness is 16.4 μm) was filled by capillary attraction from the
isotropic liquid phase (ca 260°C). The cell, consisting of two ITO
glasses sandwiching M4 sample, was then slowly cooled from the
isotropic liquid to guaranty a good homeotropic alignment of the
sample into mono‐domain. An electric field strength of 2000050000
V cm‐1 was applied. The results are shown in Figure 5: i) the transient
photocurrent decay curves of holes and electrons with an N2 laser
(337 nm) irradiation are shown in Figure 5A‐B; ii) the double‐
logarithm plots Figure 5C‐D were used to directly read out the transit
time of charge carriers for mobility calculation (the non‐dispersed
photocurrent decay curves for both holes and electrons imply the
high purity of the liquid crystal sample and the good eletrochemical
stability); and iii) Figure 5E‐F demonstrate that between 230100oC,
both electron and hole mobility were higher than 10‐3 cm V‐1 s‐1.
Below 100oC, the sample starts to crystallize in the cell (Figure S10)
Figure 5. Charge carrier mobility of M4 measured by TOF technique (at
120°C): A, Transient photo‐current (hole) decay cures; B, Transient
photo‐current (electron) decay curve; C, Double‐logarithm plot of hole
transport decay curves; D, Double‐logarithm plot of electron transport
decay curves; E,F, Temperature‐dependence of hole mobility and
electron mobility.
spacing implies obviously lesser degree of orbital overlap, and
consequently lower carrier mobility. As shown above, this large
6 | J. Name., 2012, 00, 1‐3
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ARTICLE
4. M. E. Cinar and T. Ozturk, Chem. Rev., 2015, 115, 3036‐3140.
5. A. Mishra, C.‐Q. Ma and P. Bauerle, Chem. Rev., 2009, 109
1141‐1276.
6. K. Takimiya, I. Osaka, T. Mori and M. Nakano. Acc. Chem. Res.,
2014, 47, 1493‐1502.
separation is due to unfavorable factors such as the molecular shape,
which possesses two void areas in the centre, and the molecular
rotation in the column, which overall result in the decrease of charge
transport magnitude.
,
7. (a) Y. Geng, A. Fechtenkotter and K.Mullen, J. Mater. Chem.,
2001, 11, 1634‐1641; (b) T. Yasuda, H. Ooi, J. Morita, Y.
Akama, K. Minoura, M. Funahashi, T. Shimomura and T.
Kato, Adv. Funct. Mater., 2009, 19, 411‐419; (c) M. Prehm,
G. Gotz, P. Bauerle, F. Liu, X. Zeng, G. Ungar and C.
Tschierske, Angew Chem Int. Ed., 2007, 46, 7856‐7859. (e)
N. Hu, R. Shao, Y. Shen, D. Chen, N. A. Clark and D. M. Walba,
Adv. Mater., 2014, 26, 2066‐2071.
Despite the modest values of the charge mobility presented by this
family of compound, this new molecular system presents however
some favorable features that can be further optimized by molecular
design, such as an enlarged π‐conjugated system and the
[1]benzothieno[3,2‐b][1]benzothiophene substructure (BTBT),6,29‐32
which otherwise possesses the highest carrier mobility recorded in
crystalline and liquid crystalline phases. The synthesized mesogen
M4 compared with conventional BTBT has larger π‐conjugated
system, smaller reorganization energy and higher charge carrier
mobility, according to the Marcus theory predictions.37,38 The other
beneficial factor for charge transport property is the strong tendency
for homeotropic alignment of this material in the liquid crystal cell
with thickness of 16.4 μm (Figure S10 SI), which provides the long
range charge carrier hopping along the discotic molecular column. In
summary, the molecular design of these new BTBT‐substructure‐
containing columnar mesogen has been successful as M4 displays
unambiguous hole and electron transport ability in the
mesomorphosu temperature range.
8. (a) C. Xia, X. Fan, J. Locklin and R. Advincula, Org. Lett., 2002,
12, 2067‐2070; (b) W. J. Mitchell, N. Kopidakis, G. Rumbles,
D. S. Ginley and S. E. Shaheen, J. Mater. Chem., 2005, 15
,
4518‐4528; (c) F. Lincker, B. Heinrich, R. De Bettignies, P.
Rannou, J. Pécaut, B. Grévin, A. Pron, B. Donnio and R.
Demadrille, J. Mater. Chem., 2011, 21, 5238‐5247; (d) W. W.
H. Wong, C.‐Q. Ma, W. Pisula, A. Mavrinskiy, X. Feng, H.
Seyler, D. J. Jones, K. Mullen, P. Bauerle and A. B. Holmes.
Chem. Eur. J., 2011, 17, 5549‐5560.
9. (a) I. Mcculloch, M. Heeney, C. Bailey, K. Genevicius, I.
Macdonald, M. Shkunov, D. Sparrowe, S. Tierney, R.
Wagner, W. Zhang, M. L. Chabinyc, R. J. Kline, M. D.
Mcgehee and M. F. Toney, Nature Mater., 2006, 5, 328‐333;
(b) D. Zeng, I. Tahar‐Djebbar, Y. Xiao, F. Kameche, N.
Kayunkid, M. Brinkmann, D. Guillon, B. Heinrich, B. Donnio,
D. A. Ivanov, E. Lacaze, D. Kreher, F. Mathevet, A.‐J. Attias,
Macromolecules, 2014, 47, 1715‐1731
10. L. Chen, S. R. Puniredd, Y.‐Z. Tan, M. Baumgarten, U.
Zschieschang, V. Enkelmann, W. Pisula, X. Feng, H. Klauk and
K. Mullen, J. Am. Chem. Soc., 2012, 134, 17869‐17872.
11. Q. Xiao, T. Sakurai, T. Fukino, K. Akaike, Y. Honsho, A. Saeki, S.
Seki, K. Kato, M. Takata and T. Aida, J. Am. Chem. Soc., 2013,
135, 18268‐18271.
12. A. C. Grimsdale, K. L. Chan, R. E. Martin, P. G. Jokisz and A. B.
Holmes, Chem. Rev., 2009, 109, 897‐1091.
13. R. K. Gupta, B. Pradhan, S. K. Pathak, M. Gupta, S. K. Pal and
A. A. Sudhakar, Langmuir, 2015, 31, 8092‐8100.
Conclusions
Five BTBT‐unit containing H‐shaped sanidic mesogen have been
successfully synthesized by Suzuki cross‐coupling reaction and FeCl3
oxidative
intermolecular
and/or
intramolecular
Scholl
cyclodehydrogenation recation. These π‐extended liquid crystals
were isolated by simple filtration and purified by crystallization from
organic solvent. These mesogens self‐organize into hexagonal
columnar mesophases with high clearing temperatures and broad
mesophase temperature ranges. They emit blue light in THF solution
with quantum yield of about 20%. The charge carrier mobility of M4,
chosen as a representative example, measured by the photocurrent
transient TOF technique reveals ambipolar transport properties with
14. A. Demenev, S. H. Eichhorn, T. Taerum, D. F. Perepichka, S.
Patwardhan, F. C. Grozema, L. D. A. Siebbeles and R.
Klenkler, Chem. Mater., 2010, 22, 1420‐1428.
15. D. M. Knawby and T. M. Swager, Chem. Mater., 1997,
9
, 535‐
538.
equal rate, and values in the range of 10‐3 cm2 V‐1 s‐1. Such extended 16. M. J. Cook and A. Jafari‐Fini, J. Mater. Chem., 1997,
7, 5‐7.
17. M. J. Cook and A. Jafari‐Fini, Tetrahedron, 2000, 56, 4085‐
4094.
thieno[3,2‐b]thiophene‐fused columnar mesogens may play an
important role in potential applications as organic optoelectronic
devices and ambipolar semiconductors.
18. A. D. Bromby, W. H. Kan and T. C. Sutherland, J. Mater. Chem.,
2012, 22, 20611‐20617.
19. H. Suzuki, K. Kawano, K. Ohta, Y. Shimizu, N. Kobayashi and M.
Kimura, Chem. Open, 2016, 5, 150‐156.
Acknowledgements
20. J. Luo, B. Zhao, H. S. O. Chan and C. Chi, J. Mater. Chem., 2010,
20, 1932‐1941.
This work was financially supported by the National Nature Science
Foundation of China (grant No. 51773140) and a NSFC‐JSPS joint
project (grant no. 50811140156). BD and BH thank CNRS and
Université de Strasbourg for support.
21. J. Luo, B. Zhao, J. Shao, K. A. Lim, H. S. O. Chan and C. Chi, J.
Mater. Chem., 2009, 19, 8327‐8334.
22. Q. Ye, J. Chang, K.‐W. Huang and C. Chi, Org. Lett., 2011, 13
,
5960‐5963.
23. T. Kato, M. Yoshio, T. Ichikawa, B. Soberats, H. Ohno and M.
Funahashi, Nat. Rev. Mater., 2017, 2, 17001.
24. T. Wöhrle, I Wurzbach, J. Kirres, A. Kostidou, N. Kapernaum, J.
Litterscheidt, J. C. Haenle, P. Staffeld, A. Baro, F.
Giesselmann and S. Laschat, Chem. Rev., 2016, 116, 1139‐
1241.
25. B. R. Kaafarani, Chem. Mater., 2011, 23, 378‐396.
26. S. Sergeyev, W. Pisula and Y. H. Geerts, Chem. Soc. Rev., 2007,
36, 1902‐1929.
References
1. H. E. Katz, Z. Bao and S. L. Gilat, Acc. Chem. Res., 2001, 34, 359‐
369.
2. A. R. Murphy and J. M. J. Frechet, Chem. Rev., 2007, 107
,
1066‐1096.
3. C. Wang, H. Dong, W. Hu, Y. Liu and D. Zhu, Chem. Rev., 2012,
112, 2208‐2267.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1‐3 | 7
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Please do not adjust margins
Journal of Materials Chemistry C
Page 8 of 9
View Article Online
DOI: 10.1039/C7TC05315K
ARTICLE
Journal Name
27. Y. Shimizu, K. Oikawa, K. Nakayama and D. Guillon, J. Mater.
Chem., 2007, 17, 4223‐4229.
28. M. Funahashi and T. Kato, Liq. Cryst., 2015, 42, 909‐917.
29. S. Mery, D. Haristoy, J. Nicoud, D. Guillon, S. Diele, H. Monobe
and Y. Shimizu, J. Mater. Chem., 2002, 12, 37‐41.
30. H. Monobe, L. L. An, P. Hu, B. Q. Wang, K. Q. Zhao and Y.
Shimizu, Mol. Cryst. Liq. Cryst., 2017, 647, 119‐126.
31. H. Iino, T. Usui and J. Hanna, Nat. Comm., 2015, 6, 6828.
32. L. Mazur, A. Castiglione, K. Ocytko, F. Kameche, R. Macabies,
A. Ainsebaa, D. Kreher, B. Heinrich, B. Donnio, S. Sanaur, E.
Lacaze, J.‐L. Fave, K. Matczyszyn, M. Samoc, J. Weon Wu, A.‐
J. Attias, J.‐C. Ribierre and F. Mathevet, Org. Electr., 2014,
15, 943‐953.
33. K. Q. Zhao, M. Jing, L. L. An, J. Q. Du, Y. H. Wang, P. Hu, B. Q.
Wang, H. Monobe, B. Heinrich and B. Donnio, J. Mater.
Chem. C, 2017, 5, 669‐682.
34. K. Q. Zhao, L. L. An, X. B. Zhang, W. H. Yu, P. Hu, B. Q. Wang, J.
Xu, Q. D. Zeng, H. Monobe, Y. Shimizu, B. Heinrich and B.
Donnio, Chem. Eur. J., 2015, 21, 10379‐10390.
35. K. Q. Zhao, J. Q. Du, X. H. Long, M. Jing, B. Q. Wang, P. Hu, H.
Monobe, B. Henrich and B. Donnio, Dyes Pigm., 2017, 143
252‐260.
,
36. K. Q. Zhao, C. Chen, H. Monobe, P. Hu, B. Q. Wang and Y.
Shimizu, Chem. Commun., 2011, 47, 6290‐6292.
37. R. A. Marcus, Rev. Mod. Phys., 1993, 65, 599‐610.
38. V. Lemaur, D. A. da Silva Filho, V. Coropceanu, M. Lehmann,
Y. Geerts, J. Piris, M. G. Debije, A. M. van de Craats, K.
Senthilkumar, L. D. A. Siebbeles, J. M. Warman, J. L. Bredas
and J. Cornil, J. Am. Chem. Soc., 2004, 126, 3271‐3279.
39. C. Feng, X. Wang, B. Q. Wang, K. Q. Zhao, P. Hu and Z. J. Shi,
Chem. Commun., 2012, 48, 356‐358.
40. C. Feng, X. L. Tian, J. Zhou, S. K. Xiang, W. H. Yu, B. Q. Wang, P.
Hu, C. Redshaw and K. Q. Zhao, Org. Biomol. Chem., 2014,
12, 6977‐6981.
41. C. Feng, Y. H. Ding, X. D. Han, W. H. Yu, S. K. Xiang, B. Q. Wang,
P. Hu, L. C. Li, X. Z. Chen and K. Q. Zhao, Dyes Pigm., 2017,
139, 87‐96.
42. X. D. Han, X. L. Tian, W. H. Yu, S. K. Xiang, P. Hu, B. Q. Wang,
K. Q. Zhao, X. Z. Chen and C. Feng, Liq. Cryst., 2017, 44, 1727‐
1738.
43. K. Q. Zhao, X. Y. Bai, B. Xiao, Y. Gao, P. Hu, B. Q. Wang, Q. D.
Zeng , C. Wang, B. Heinrich and B. Donnio, J. Mater. Chem.
C, 2015, 3, 11735‐11746.
44. K. Q. Zhao, Y. Gao, W. H. Yu, P. Hu, B. Q. Wang, B. Heinrich and
B. Donnio. Eur. J. Org. Chem., 2016, 2802‐2814.
45. A. C. Ribeiro, B. Heinrich, C. Cruz, H. T. Nguyen, S. Diele, M. W.
Schröder and D. Guillon, Eur. Phys. J. E, 2003, 10, 143‐151.
46. B. Donnio, B. Heinrich, H. Allouchi, J. Kain, S. Diele, D. Guillon
and D. W. Bruce, J. Am. Chem. Soc., 2004, 126, 15258‐15268.
47. D. Mysliwiec, B. Donnio, P. J. Chmielewski, B. Heinrich and M.
Stepien, J. Am. Chem. Soc., 2012, 134, 4822‐4833.
48. B. Alameddine, O. F. Aebischer, B. Heinrich, D. Guillon, B.
Donnio and T. A. Jenny, Supramol. Chem., 2014, 26, 125‐
137.
49. The Cambridge Structural Database. T. L. Andresen, F. C.
Krebs, N. Thorup and K. Bechgaard, Chem. Mater., 2000, 12
,
2428‐2433.
50. The Cambridge Structural Database. E. G. Cox, R. J. J. H. Gillot
and G. A. Jeffrey, Acta Crystallogr., 1949,
2
, 356‐363.
51. S. Kumar, Chem. Soc. Rev., 2006, 35, 83‐109.
8 | J. Name., 2012, 00, 1‐3
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Semiconductor Mesogens