Effect of Double Branching in α,ω-Substituted Oligothiophenes on Thermal Solid-State Properties

Article abstract of DOI:10.1002/ejoc.201700046

A systematic series of septi-, noni- and undecithiophenes and the corresponding pre-oligomers with five different dendrimer-like branched end-groups have been synthesized and their thermal solid-state properties investigated. The substituents vary in terms of the lengths of the linkers between the silicon branching points. Comparison of the compounds in the series reveals that the linker connecting the oligomeric core with the first branching point has the strongest effect on the thermal properties. Furthermore, the relatively large volume of the substituents causes surprisingly low overall transition enthalpies and entropies for the oligomers of 10–20 kJ mol^–1 and 15–40 J mol^–1 K^–1, respectively, whereas the pre-oligomers with interrupted conjugation display values in the range of 15–40 kJ mol^–1 and 40–100 J mol^–1 K^–1, respectively. Polarizing optical microscopy (POM) revealed textures pointing to smectic and columnar liquid-crystalline phases but X-ray and AFM data of a representative example are typical of cubic phases.

Full text of DOI:10.1002/ejoc.201700046

A Journal of
Accepted Article
Title: Effect of Double Branching in α,ω-Substituted Oligothiophenes
on Thermal Solid-State Properties
Authors: Ulrich Ziener, Jochen Gülcher, Roman Vill, Markus
Braumüller, Khosrow Rahimi, Wim H. de Jeu, and Ahmed
Mourran
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201700046
Link to VoR: http://dx.doi.org/10.1002/ejoc.201700046
Supported by

European Journal of Organic Chemistry
10.1002/ejoc.201700046
FULL PAPER
Effect of Double Branching in α,ω-Substituted Oligothiophenes
on Thermal Solid-State Properties
[
a]
[a]
[a]
[b]
[b]
Jochen Gülcher, Roman Vill, Markus Braumüller, Khosrow Rahimi, Wim H. de Jeu, Ahmed
[
b]
[a]
Mourran, and Ulrich Ziener*
Abstract: A systematic series of septi-, nona- and undecithiophenes
and corresponding pre-oligomers with five different dendrimer-like
branched end groups were synthesized and their thermal solid-state
properties were investigated. The substituents vary in terms of
length of the linkers between the silicon branching points.
Comparison of the series reveals that the linker connecting the
oligomeric core with the first branching point has the strongest effect
on the thermal properties. Furthermore, the relatively large volume of
the substituents causes surprisingly low overall transition enthalpies
reports are concentrating on solution properties of the electronic
materials. The improvement of processing is in the focus of their
application but a weakening of the π-π interactions of the
functional core as origin for the enhancement of solubility is
often overlooked. In turn, the weakening might have a strong
effect on solid-state structures and, thus, electronic properties in
(thin film) applications. Transition-temperature engineering of
liquid crystalline oligothiophenes can be achieved by
desymmetrization of the end groups or by varying the number of
-
1
and entropies for the oligomers of 10 – 20 kJ mol and 15 – 40 J
methyl substituents in both branched alkyl end groups,
-
1
-1
[9]
mol K , respectively, while the pre-oligomers with interrupted
respectively.
The
ordering
properties
of
organic
-
1
conjugation display values in the range of 15 – 40 kJ mol and 40 –
semiconductors in the liquid crystalline state is widely employed
-
1
-1
[10-13]
1
00 J mol K , respectively. Polarizing optical microscopy (POM)
in materials science and described in excellent reviews.
displays textures pointing to smectic and columnar liquid crystalline
phases but x-ray and AFM data of a representative example are
typical for cubic phases.
There are some reports on the influence of the side chain on the
molecular organization and charge transport performance of
(co)polymers
like
diketopyrrolopyrrole-quaterthiophene
The crystalline solid-state order of
[
14]
copolymers (PDQTs).
[
1]benzothieno[3,2-b]benzothiophenes could be fine-tuned by
variation of the end groups between the bulky single branched
Introduction
substituents isopropyl, t-butyl and trimethylsilyl (TMS), leading to
[
15]
high-mobility organic semiconductors.
The principle of
Semi-conducting organic materials for electronic applications
like organic field-effect transistors (OFETs), organic solar cells
branching in substituents by introducing silicon is described
[16]
many times in literature but mainly for polymeric materials. It
(
OSCs) or organic light emitting diodes (OLEDs) require a subtle
can be also used to generate further topologies of the oligomers
fine-tuning of the intermolecular interactions for efficient charge
[17-18]
like dendrimers or multipods.
Apart from the few references
[
1-4]
transport.
In the past, research activities on electronic organic
described herein there is hardly any systematic investigation on
the effect of end or side group structures on solid-state
properties of organic materials in literature. We have reported on
the effect of varying branching topology on solid-state properties
of long oligothiophenes (septithiophenes and longer) with single
materials were mostly dedicated to the tailoring of the π
[
5]
functional moieties and extending the conjugated core. On the
other side, preferred processing technologies for those materials
from organic solution like printing require sufficient solubility,
which is usually provided by introducing solubilizing (alkyl) side
chains in oligomers and polymers or end groups in oligomers.
While linear substituents contribute only a little to enhancing the
solubility branched equivalents are much more effective. The
more bulky the substituents the stronger the effect on solubility
is. Therefore, bulky end groups like medium sized polystyrene
[19-22]
branched end groups.
The present contribution is a logic extension of the previous
reports by introducing further branching points in the
substituents. In total, five new substituents were synthesized
and introduced in septi-, nona- and undecithiophenes with
systematic variation of the linkers between the branching points
leading to dendrimer-like structures (Scheme 1). This causes an
increased competition between bulkiness of the substituents and
π–π interactions of the oligomeric cores, which has a substantial
effect on thermodynamic properties of the oligomers in solid-
state like total transition enthalpy and entropy and clearing
temperature. This competition is also made responsible for the
appearance of liquid crystalline phases in accordance with
reports on septithiophenes with more crowded single branched
substituents versus less crowded substituents in bulk and thin
[
6]
(
degree of polymerization 30) in an undecithiophene, and
poly(benzylether) dendrons in oligo(p-phenylenevinylene) (OPV)
[
7]
[8]
gelators
and in oligothiophenes
were described. Those
[
a]
b]
J. Gülcher, R. Vill, M. Braumüller, U. Ziener
Institut für Organische Chemie III
Universität Ulm
Albert-Einstein-Allee 11, D-89081 Ulm, Germany
E-mail: ulrich.ziener@uni-ulm.de, http://www.uni-
ulm.de/nawi/institut-fuer-organische-chemie-iii/
K. Rahimi, W. H. de Jeu, A. Mourran
[
19]
film. For the sake of readability the five different substituents
are called by letters or by their carbon linker lengths,
respectively. The first number gives the linker between the
thiophene core and the first branching point (1. linker), the
second one describes the linker between the two branching
[
DWI‒Leibniz Institute for Interactive Materials
Forckenbeckstrasse 50, D-52056 Aachen, Germany.
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

European Journal of Organic Chemistry
10.1002/ejoc.201700046
FULL PAPER
points (2. linker) and the third denotes the hexyl end groups
separable. Therefore, we employed the literature known N-
[
23-24]
(
Scheme 1).
heterocyclic carbene complex (ICy)Pt(dvtms)
(Scheme 2)
leading to quantitative formation of the desired regioisomer.
Furthermore, the catalyst reacts selectively with terminal double
bonds and additions to rearranged double bonds, occasionally
found for the Karstedt catalyst, were not observed for
O
O
S
S
S
R
R
R
R
7
,9,11
3,4,5
3
,4,5
(
ICy)Pt(dvtms). Subsequently, the chlorine atoms were
substituted with in situ generated Grignard reagents from allyl,
hexenyl and undecenyl bromide, respectively, resulting five
different pre-substituents 1TnSiAlkene (Scheme 2). Finally, the
alkenyl end groups were hydrosilylated with hexyldimethylsilane
delivering the mono-substituted thiophenes 1TR with the
Si
Si
∗
Si
11
3
6
(R
C
)
substituents 3-3-6 (R
A B E D
), 6-3-6 (R ), 3-11-6 (R ), 3-6-6 (R ) and
1
1-3-6 (R ) (Scheme 1 and Scheme 2). The thiophenes 1TR could
C
be mostly obtained in altogether reasonable yields between 70
and 80% for the various steps.
Si
Si
Variation of
length of
st linker
∗
1
Si
BuLi
6
3
6
(R
B
)
+
Br
S
S
n
n
1
1
TAll (n = 1)
Si
THex (n = 4)
R =
∗
3
Si
1TUnd (n = 9)
HSiCl CH3
2
3
6
(R
A
)
Si
SiCl CH3
2
(ICy)Pt(dvtms)
S
n
Si
Si
1T3Si (n = 1)
1T6Si (n = 4)
T11Si (n = 9)
1
∗
3
Si
Variation of
length of
2nd linker
6
6
(R
D
)
m
HSi
BrMg
Si
n
S
n
(ICy)Pt(dvtms)
Si
Si
1
1
1
1
T3SiAll (n = 1, m = 1)
T6SiAll (n = 4, m = 1)
T11SiAll (n = 9, m = 1)
T3SiHex (n = 1, m = 4)
m
∗
Si
3
11
6
(R
E
)
1T3SiUnd (n = 1, m = 9)
Si
Scheme 1. Schematic structures of the oligomers and pre-oligomers and
substituents with varying branching topology, respectively.
m
Si
S
n
m
Results and Discussion
Si
1
1
1
1
1
TRA (n = 1, m = 1)
TRB (n = 4, m = 1)
TRC (n = 9, m = 1)
TRD (n = 1, m = 4)
TRE (n = 1, m = 9)
The series of oligomers with different branched aliphatic end
groups were synthesized by metal catalysed coupling chemistry.
At first the various substitution patterns were prepared at a
single thiophene unit (Scheme 2) followed by the built-up of the
oligomers (Scheme 3) similar to previous publications on
N
N
Si
Si
Pt
O
[
21-22]
oligomers with mono-branched substituents.
lithiated and alkylated with bromoalkene and in
hydrosilylation step reacted with dichloromethylsilane resulting
TnSi (Scheme 2). It turned out that the usage of the quite
Thiophene was
(
ICy)Pt(dvtms)
a
a
1
A E
Scheme 2. Synthesis of 1TR with the double branched substituents R to R .
common Karstedt catalyst does not give full control over the
regiochemistry with partial formation of the Markovnikov adduct
instead of the anti-Markovnikov product, which are hardly
Subsequently, 1TR was reacted in Stille- or Suzuki-type
coupling with 2-bromothiophene, 2-bromobithiophene and 2-
This article is protected by copyright. All rights reserved.

European Journal of Organic Chemistry
10.1002/ejoc.201700046
FULL PAPER
bromoterthiophene, respectively, leading to the corresponding
monosubstituted bi-, ter- and quaterthiophenes nTR (Scheme 3).
Finally, the nTR oligomers were again stannylated and coupled
to the diketal synthon BrdialBr delivering symmetrically
substituted pre-oligomers RnTdialnTR. Although the solubility of
the pre-oligomers is much higher than for corresponding
All the final oligomers RnTR and the corresponding pre-
oligomers RnTdionnTR show multiple thermal phase transitions
with variable temperature ranges depending on the structure of
the substituents. All thermal data are summarized in Table S 1 in
Supporting Information. Figure
thermogram of septithiophene R
more in detail (see below).
1
shows exemplarily the
, which will be explored
A
7TR
A
[
25-27]
oligomers with mono-branched or even linear substituents,
it turned out that the usage of the diketo synthon (see Scheme 3)
instead of plain 2,2’’-dibromoterthiophene is advantageous
C
especially for substituent 11-3-6 (R ) with the long linker
between the thiophene core and the first branching point. This
finding is related to the solubility, which is lowest for oligomers
with substituent
C
R . The diketal pre-oligomers were then
subjected to acidic deprotection of the diketo functionality
yielding the diketo functionalized pre-oligomers RnTdionnTR
and ring closure reaction with Lawesson reagent to form the final
septi-, nona- and undecithiophenes RnTR (Scheme 3). While for
R7TR and R9TR the oligomer series with all five substituents
could be obtained after purification by column chromatography
C
and recrystallization, the solubility of substituent R was again
too low (see above) to prepare the corresponding
undecithiophene in acceptable purity. Hence, in total 14 new
oligomers were synthesized in moderate to good yields.
A A
Figure 1. DSC thermogram of R 7TR as representative example for various
series of oligothiophenes.
H
Br
S 1
-3
1
. BuLi
This behaviour is quite similar to the monobranched
nTBr
counterparts with varying position of the branching point
R
[M]
R
S
S
Pd cat.
[22]
2
. [M]X
c
reported earlier. Looking at the temperatures T of the highest
1
TR
M1TR
thermal transition to the isotropic phase the two additional
bishexylmethylsilyl groups in the present substituents cause a
lowering of the thermal transition of around 40 K (e. g. T
77 °C (R’7TR’) and 270 °C (R’9TR’) for R’
c
=
=
1
. BuLi
1
H
R
-4
[22]
Me Sn
R
-4
C
H
Si(CH
R9TR) for R
)(C10
H
)
vs. T
c
= 138 °C (R7TR) and 225 °C
S
3
3
6
3
21
2
2
. Me SnCl
S
2
3
2
(
E
(Figure 2)). This is expected as the additional
nTR
SnnTR
branching causes an increase of the volume of the branch and
thus the volume ratio v(branch):v(linker), introduced earlier as
O O O O
[
22]
the so-called packing parameter P. An increasing P was found
to decrease the intermolecular forces and, thus, to lower, e. g.,
transition temperatures. Correspondingly, it is no surprise that
O
O
O
O
S
S
Br
R
BrdialBr
S
3-5
S
Pd cat.
R
R
the temperatures T
increase with increasing length of the linker
c
RnTdialnTR
3-5
(
3 à 6 à 11) between the thiophene core and the first
c A c B c C
branching point (T (R ) < T (R ) < T (R )) (red filled symbols in
O
O
Figure 2). The relative effect of the first branch is almost
independent of the number of thiophene units, only the absolute
temperatures are affected. An incremental increase of the
transition temperatures with ca. 75 to 100 K per two thiophene
units can be deduced regardless of the type of substituent which
HCl
S
3-5
RnTdionnTR
S
R
R
3-5
T: thiophene
is slightly lower than that found for less branched or even linear
L. R.
[27]
n: number of thiophene rings
R: R , R , R , R , (for 7T,
substituents (ca. 50-60 K per thiophene unit).
Consequently,
R
,9,11
R
S
one would expect that for the double branched substituents an
increase of the second linker between first and second
A
B
D
E
7
RnTR
9T, 11T) and RC (for 7T, 9T)
A D E
branching point (3 (R ) à 6 (R ) à 11 (R )) should cause a
[
M]X: ((CH ) SnCl or
3 3
decrease of the transition temperatures as it increases the
volume of the branched part of the substituent. In contrast,
increasing the length of the second linker leads to an increase of
(
(CH ) CO) BOCH(CH )
3 2 2 3 2
L.R.: Lawesson reagent
Scheme 3. Synthesis of the symmetrically substituted septi-, nona- and
the isotropization temperatures
T
c
,
too, although less
undecithiophenes RnTR.
This article is protected by copyright. All rights reserved.

European Journal of Organic Chemistry
10.1002/ejoc.201700046
FULL PAPER
pronounced than for the first linker (blue open symbols in Figure
room temperature (for compounds in the crystalline state at rt) or
lower (-50 °C for compounds in a mesophase at rt) and the
isotropic state were summed up regardless of the number and
nature of (first order) phase transitions according to Hess’s law.
The numbers deliver the thermodynamic data of the transition
between the solid state phase with the lowest energy and the
isotropic liquid phase and, thus, can be compared with each
other based on the similarity of the molecular structures. Please
note that the temperature dependence of the entropy is
neglected as it will be rather minor and the data evaluation is
2
). Here, the influence of the length of the second linker
decreases with increasing number of thiophene moieties and
becomes almost negligible for R11TR (Figure 2). This means that
a closer branch disturbs more efficiently the order of the
oligomeric core than a branch further apart. These findings are
valid not only for the oligomers RnTR but also for the
monosubstituted 4TR and even the pre-oligomers RnTdionnTR
meaning that these thermal properties are following a general
[
22]
principle as postulated in our previous report.
This is also
[
28]
supported by the lower transition temperatures of the pre-
oligomers RnTdionnTR compared to the fully conjugated
oligomers RnTR because of the non-planar 1,4-diketo moieties
and, thus, disturbed intermolecular π-π interactions of the pre-
oligomers.
done only in comparison to similar oligomers.
It should be
further mentioned that some of the compounds show second
order transitions (glass transitions) marked by black circles in
Figure 3 characteristic for only semi-crystalline phases. Hence,
the thermodynamic data might be underestimated for these
compounds but this effect should be also rather negligible in the
overall evaluation as the similarities and differences in the
various series are comparable regardless of the presence or
absence of glassy states. The glass transitions demonstrate a
strong kinetic hindrance of crystallization owing to the bulky end
groups.
a)
a)
b)
b)
Figure 2. Clearing temperatures T
and corresponding pre-oligomers (b) with five different branched substituents.
Red filled symbols refer to substituents R , R , R and blue open symbols to
, R , R , respectively.
c
for septi-, nona- and undecithiophenes (a)
A
B
C
R
A
D
E
In order to get more insight into the thermodynamic properties
and better understanding of the structure-property
a
relationships we have evaluated the phase transition enthalpies
and entropies of the oligomers RnTR, pre-oligomers
RnTdionnTR and monosubstituted 4TR (Figure 3). The
enthalpies and entropies of all detectable transitions between
This article is protected by copyright. All rights reserved.

European Journal of Organic Chemistry
10.1002/ejoc.201700046
FULL PAPER
c)
f)
g)
h)
d)
e)
Figure 3. Sum of phase transition enthalpies and entropies between lowest
crystalline and isotropic liquid state for 4TR (a), RnTR (b, c, d) and
RnTdionnTR (e, f, g); h) phase transition enthalpies and entropies for the
oligomers averaged over the substituents R
A B C
, R , R (red filled symbols) and
R
A
, R , R (blue open symbols), respectively. Black circles indicate oligomers
D
E
with glass transitions.
A view on the enthalpies and entropies for the RnTR series
(
Figure 3 b, c, d) reveals that (i) there is only a slight increase with
increasing length of the linkers, (ii) the data for the first linker are
always slightly smaller than for the second, (iii) the length of the
oligomer core plays a minor role and (iv) the absolute values are
surprisingly low in comparison to other α,ω-substituted
This article is protected by copyright. All rights reserved.

European Journal of Organic Chemistry
10.1002/ejoc.201700046
FULL PAPER
oligothiophenes. The enthalpies vary between ca. 10 and 20 kJ
1 and Table S 1) suggest the existence of liquid crystalline (lc)
states. Indeed, temperature dependent polarizing optical
microscopy (POM) of the septi- and nonathiophene series
reveals after cooling from the isotropic phase and shearing
experiments fluid behaviour typical for lc phases (not shown). A
similar behaviour is assumed for the undecathiophene series but
the transition temperatures were too high to obtain reproducible
results as the samples partially decomposed under the
microscope although they proved to be stable in the DSC
measurements up to the isotropic state. Figure 4 and Figure S 1
display representative POM images with crossed polarizers of
the septi- and nonathiophene series at various temperatures.
The phase behavior of the oligomers proves partially quite
-
1
-1
-
mol while the entropies are found between 15 and 40 J mol
K
1
.
In contrast, the linear eicosyl substituent in a septithiophene
-
1
leads to a total enthalpy of 121 kJ mol and an entropy of 268 J
-
1
-1 [27]
mol
K .
For shorter oligomers (quaterthiophene to
sexithiophene) and substituents (decyl) the values are still in the
-
1
-1
-1
range of 50 to 80 kJ mol and 80 to 200 J mol
K
for the
Branching of the
substituents causes a lowering of the values but they still
[
28]
enthalpy and entropy, respectively.
-
1
-1
-1
amount to 33 and 48 kJ mol and 60 to 115 J mol
K
for
Interestingly, a small second branch by
introducing a 2-ethylhexyl group reduces the enthalpy further to
[
27]
septithiophenes.
-
1
-1
-1
2
0 kJ mol and the entropy to 37 J mol K . Hence, the much
more bulky double branched substituents in the present
contribution consistently cause even lower values. This finding
can be interpreted as weaker intermolecular forces in a less
ordered and/or less dense packing originating from the larger
bulkiness of the substituents. It is in accordance with the minor
influences of the core and linker lengths as the bulky
substituents weaken the overall intermolecular interaction so
effectively that additional thiophene units do not add much
attractive forces. The higher entropy gains and enthalpy losses
of the heating phase transitions for the second linker than the
first one underlines the importance of the first branching point
over the second one as found in the higher transition
temperatures, too (see Figure 2). The values for the
monosubstituted quaterthiophene (Figure 3 a) are slightly larger
presumably because of the presence of just one bulky
substituent compared to the RnTR series. Because of the similar
transition enthalpies and entropies we have averaged the values
over the different linkers for each RnTR series and the results
are summarized in Figure 3 h (left side).
A A
complex. Hence, we will focus on R 7TR with the most easily
accessible phase transitions among the whole bunch of
compounds (Figure 1 and Figure 4). Cooling from the isotropic
phase POM reveals clear birefringence with a fan-like texture
and striation across the fans just below the onset of the high T
-
transition at 112 °C (Figure 4 a). The low enthalpy of ca. 8 kJ mol
1
(Figure 1 and Figure S 1) is in accordance with the fluidity of the
texture upon shearing. Further cooling of the same texture
region until 80 °C (Figure 4 b-d) leads to a color change of some
fan domains from red to green. In the vicinity of the low T
transition at 65 °C (Figure 4 e) straight dark lines with an angle of
ca. 80° appear across the fans until the crystalline phase is
formed below ca. 45 °C (Figure 4 f). It shall be noted that the solid
at rt is smeary, which points to a weakly ordered crystal,
[
29]
potentially
a
soft crystal phase.
The textures of the
mesophase are ambiguous and might indicate the presence of
[
30]
smectic phases,
oligomers in our previous investigations.
various columnar phases might show similar textures as
presumably SmC in analogy to related
[
21]
On the other side,
[
31-34]
For the pre-oligomers RnTdionnTR the picture is quite different.
The enthalpies and entropies are significantly larger and range
described in literature.
For the other compounds of the
septi- and nonathiophene series further morphologies with
maltese crosses and fern-like textures are found (Figure S 1),
which are indicative of columnar phases, too. In contrast to most
of our previously reported monobranched oligothiophenes,
-
1
-1
-1
from ca. 15 to 40 kJ mol and from 40 to 100 J mol
K (Figure 3
e, f, g), respectively. Furthermore, the impact of the length of the
linkers is more expressed and the trends are non-uniform. While
for R3Tdion3TR the values are slightly increasing, for
R4Tdion4TR they are strongly decreasing and for R5Tdion5TR
they are strongly increasing with increasing length of the linkers.
In analogy to the oligomers RnTR the values were also
averaged over the different linkers and are displayed in Figure 3 h
[
21]
which display almost exclusively smectic phases,
the more
bulky double branched substituents seem to favour the
formation of columnar phases. Recently, we have reported on a
series of septithiophenes with increasing bulkiness and
transition from a layered structure to a columnar/bicontinuous
[
19]
(
right side). Obviously the intermolecular forces of the pre-
cubic in thin films. Corresponding columnar structures for the
present series would be also in accordance with the low values
for the enthalpy and entropy because of the reduced π-π overlap
(see above).
oligomers in the solid are stronger than for the final oligomers.
This is rather surprising as the diketo unit interrupts the linear
coplanar arrangement of the thiophene moieties in the core. On
the other side, it gives more flexibility to the stiff core and can,
thus, support a closer and tighter packing. Interestingly, the
RnTdionnTR series hardly display glass transitions while for
B D C E
RnTR either R and R or R and R cause kinetically hindered
crystallization (see Table S 1 in SI), which we attribute also to
the lower flexibility of the fully conjugated molecules. The
varying trends with increasing length of the linkers show a subtle
dependence of the packing from the length of the core.
The overall low transition enthalpies and entropies of the final
oligomers RnTR and the presence of multiple phases (see Figure
This article is protected by copyright. All rights reserved.

European Journal of Organic Chemistry
10.1002/ejoc.201700046
FULL PAPER
This broad peak is observed in all phases, from crystalline to
isotropic. Two other peaks are observed in both the solid and
the liquid-crystalline phase, though at somewhat different
positions. In the liquid-crystalline phase (data at 80 °C) the peak
positions obey very precisely the simple ratio: 1.15 : 1.63 : 2.00
a)
b)
d)
=
A A
1: √2 : √3. Obviously, these results for R 7TR fit to a simple
[
35]
cubic phase (either primitive or bcc).
[
36]
Percec et al. have reported extensively on a series of wedge-
shaped monodendrons that self-assemble into spherical
Pm3n
supramolecular dendrimers that form, in turn, a
three-
c)
dimensional cubic lattice. In these cases the diameter of the
dendrimer – that determines the cubic lattice spacing – is about
A A
twice the length of a wedge-shaped molecule. For R 7TR , in
the absence of other peaks we cannot discriminate against any
of these more complicated cubic phases. In our case, the
molecules have a branched end group at each side of the
thiophene core, leading rather to a dumbbell shape. We can
make an analogy to wedge-shaped units and imagine the
dumbbell compounds also to assemble into dendrimers that are
close to spherical. This would again provide an explanation for
the cubic structures. However, our dendrimers are (i) expected
to be less rigid, and (ii) to have a diameter of about the length of
a single molecule, in agreement with the lowest-angle x-ray
peak. The assumption of stable, but still loosely associated
complexes explains the presence of the broad lowest-angle
peak in all phases.
e)
f)
Figure 4. POM images from the same area of R
temperatures upon cooling from the isotropic state: a) 112 °C, b) 100°C, c) 90
C, d) 80°C, e) 65 °C, f) 45 °C; the image sizes are 765 µm x 765 µm.
A
7TR
A
at different
The comparison with R
complications. In principle the structure of the x-ray spectrum is
similar as for R 7TR , with two main peaks now at slightly
B B D D
7TR and R 7TR presents some
°
A
A
shifted positions. In addition some higher orders appear.
However, now the peaks do not obey the simple relation for a
Based on all these arguments one is tempted to assign mainly
columnar mesophases to the present oligothiophene series. Still,
an unambiguous assignment requires more detailed information
A A D D
cubic phase as for R 7TR . Nevertheless for R 7TR they are
exactly in the proportion √2 : √3, but without a fit to the
fundamental. The main scattering unit in the molecules are the
thiophene core and the Si atoms. Hence the shift in position of
the two main peaks to lower Q-values can in principle be
attributed to the increased distance between the core and the Si
atoms. Qualitatively the following overall picture emerges. The
compounds form loosely associated complexes in all phases. In
the liquid crystalline phases these assemble into cubic-like
structures that are distorted/disordered such that the surface
diagonal (√2) and the inner diagonal (√3) tend to be unaffected.
from x-ray diffraction. We considered R , R
A
7TR
A
B B
7TR and
R
D
7TR as series of compounds with a representative
D
a
variation of the structure (see Scheme 1) and typical x-ray
scattering data were obtained as a function of temperature.
Measuring the WAXS-region in a reflective Bragg-Brentano
geometry, the low-angle part provides the basic structural
information. First data were taken for increasing temperatures,
subsequently the sample was cooled down from the isotropic
phase mimicking the process in POM (see Figure 4). At each
measurement temperature an equilibration time of 30 minutes
B B D D
In R 7TR and R 7TR in addition some new peaks develop at
was applied. For R
crystalline phase is expected between 112 °C and 73 °C (Figure
and Table S 1). The peaks are somewhat broadened due to
the relatively large beam size needed to get data in
A A
7TR according to DSC and POM a liquid-
-
1
about Q = 2.8 nm . This could indicate a transition to other
structures as a result of increasing distortions.
1
a
reasonable time. Fehler! Verweisquelle konnte nicht
gefunden werden.a gives an overview over the full Q-range, a
blow-up of the low-angle data is shown in Fehler!
Verweisquelle konnte nicht gefunden werden. b. For all three
compounds in the liquid crystalline phase essentially three main
A A
peaks are observed (Figure 5 c), for R 7TR at Q = 1.15, 1.63
-
1
and 2.00 nm . There is no evidence for any peaks at lower Q-
values.
For R
.16 nm corresponding to d = 2π/Q = 5.4 nm. This value is
approximately equal to the longest dimension of the molecules.
A A
7TR first we note a broad low-angle peak around Q =
-
1
1
This article is protected by copyright. All rights reserved.

European Journal of Organic Chemistry
10.1002/ejoc.201700046
FULL PAPER
underestimated because of compression by the AFM tip – we
associate these ‘blobs’ with the spherical dendrimers forming the
cubic structure. If we assume the dendrimer units to be still
stable at higher temperatures, this would explain the persistence
-
1
of the broad peak at Q = 1.15 nm in the isotropic phase due to
short-range structures.
a)
b)
c)
A A
Figure 6. Scanning force microscopy images of a bulk sample of R 7TR at rt.
a) Overview, b) and c) detailed views.
Conclusions
We have reported on the synthesis of highly systematic series of
α,ω-substituted septi-, nona- and undecithiophene with double
branched substituents and varying length of the alkyl linkers.
The compounds were characterized by their thermal properties
and exhibit multiple phases showing
a clear dependence
between linker length and highest thermal transition temperature.
The overall phase transition enthalpies and entropies are
surprisingly low pointing to weakly ordered solid phases. For
corresponding pre-oligomers the values are in the expected
range found in literature for similar compounds. The
thermodynamic data together with textures from polarizing
optical microscopy suggest that mainly columnar phases are
formed in contrast to smectic phases found for oligomers with
linear or monobranched substituents. Instead, exemplary
temperature dependent x-ray data of one member from the
septithiophene series reveals the presence of cubic phases.
This finding is further supported by AFM investigations of the rt
phase. The construction of the substituents allows fine-tuning of
the thermal properties and adjustment to appropriate
applications for e. g. molecular electronics.
Figure 5. (a) Overview and (b) low-angle WAXS region for the compound
A A
R 7TR at various temperatures in the solid phase (23 °C and 28 °C), in the
liquid crystalline phase (80 °C) and in the isotropic state (115 °C). (c)
Comparison of the low-angle WAXS range of the liquid-crystalline phase at
1
A A B B D D
20 °C for R 7TR , R 7TR and R 7TR .
Figure 6 shows results from scanning force microscopy of the
surface of a bulk sample of R 7TR at room temperature. First,
we note in the overview terraces with step heights of 3.4 nm
Figure 6 a). A detailed view on the surface of a terrace reveals a
structure of elongated ‘bands’ with a width of around 5 nm (Figure
b). At further magnification one can distinguish a substructure
A
A
(
6
of ‘blobs’ of about the same size. As those magnitudes agree
roughly with the cubic dimension – the step height might be
Experimental Section
This article is protected by copyright. All rights reserved.

European Journal of Organic Chemistry
10.1002/ejoc.201700046
FULL PAPER
General: n-Butyllithium (2.5 M in n-hexane), 2-bromothiophene (98%),
performed with standard silicon cantilevers (Nano world, NCH-W point
probe).
succinylchloride
dichloromethylsilane (99%), Lawesson reagent (97%), 2-isopropoxy-
,4,5,5-tetramethyl-1,3,2-dioxaborolane (98%), allylbromide (99%),
(95%)
(all
Acros),
thiophene
(99+%),
,
4
Detailed information on the synthesis of the new compounds, further
POM images and complete data of the thermal transitions are presented
in SI.
trimethylstannylchloride (97%), 1-bromohexane (98%), platinum(0)-1,3-
divinyl-1,1,3,3-tetramethyldisiloxane (2% in xylene), p-toluenesulfonic
acid monohydrate (98,5%), tetrafluoroboric acid (48% in
2
H O),
Pd(dppf)Cl *CH Cl , Pd (dba)3*CHCl , tris(o-tolyl) phoshine (97%) (all
2
2
2
2
3
Aldrich), bromo-1-undecene (Alfa Aesar, 95%), magnesium (>90%), N-
bromosuccinimide (>99%), 5-hexen-1-ol (>90%), triphenylphosphane
Acknowledgements
(
>99%), ethylene glycol (>99%), aluminium chloride (>98%), potassium t-
butanolate (98%), sodium hydrogencarbonate (99.5%), cyclohexylamine
99%), glyoxal (40% in H O), potassium carbonate (99%) (all Merck),
Pd(PPh (Strem, 99%), HCl (VWR BDH Prolabo, 37%), sodium chloride
VWR BDH Prolabo, 99%) and the solvents THF, acetone, ethylacetate,
We gratefully acknowledge financial support of the present work
by the Deutsche Forschungsgemeinschaft (ZI567/4-3 and
MO982/2-3).
(
2
3 4
)
(
ethanol, methanol, diethylether, n-hexane, toluene, dichloromethane,
chloroform, petrolether (all VWR BDH Prolabo, GPR Rectapur), benzene
Keywords: substituent effects • thermodynamics • oligomers •
(
(
Aldrich, 99.9%), 1,1,2,2-tetrachloroethane (Aldrich, 98%), and DMF
Sigma, 99.9%) were purchased and used without further purification
thiophene
except for reactions involving metal organic species. They were
performed with dry solvents under inert gas conditions. 1-
[
[
[
[
1]
2]
3]
4]
H. Sirringhaus, Adv. Mater. 2014, 26, 1319-1335.
K. A. Mazzio, C. K. Luscombe, Chem. Soc. Rev. 2015, 44, 78-90.
A. Facchetti, Chem. Mater. 2011, 23, 733-758.
[
37]
[38]
[39]
Bromohexene, 2-allylthiophene (1TAll), 5-bromo-2-2'-bithiophene,
[
40]
[39]
5
-bromo-2,2':5',2''-terthiophene,
2,2':5',2''-terthiophene,
2-(hex-5-
N. Thejo Kalyani, S. J. Dhoble, Renewable Sustainable Energy Rev.
[
21]
[21]
enyl)thiophene (1THex),
2-(undec-10-enyl)thiophene (1TUnd),
2
015, 44, 319-347.
J. Mei, Y. Diao, A. L. Appleton, L. Fang, Z. Bao, J. Am. Chem. Soc.
013, 135, 6724-6746.
[
20-21]
[41]
dihexylmethylsilane,
1,4-bis(5-bromothien-2-yl)butane-1,4-dione,
[
[
5]
6]
[
25]
1
,2-bis(2-(5-bromothien-2-yl)1,3-dioxolan-2-yl)ethane,
1,3-
Pt(N,N’-
were
2
[
42]
dicyclohexylimidazolium
tetrafluoroborate,
and
M. A. Hempenius, B. M. W. Langeveld-Voss, J. A. E. H. v. Haare, R. A.
J. Janssen, S. S. Sheiko, J. P. Spatz, M. Möller, E. W. Meijer, J. Am.
Chem. Soc. 1998, 120, 2798-2804.
[
24]
dicyclohexylimidazol-2-ylidene)
(divinyltetramethylsiloxane)
synthesized according to literature procedures.
[
7]
S. S. Babu, V. K. Praveen, K. K. Kartha, S. Mahesh, A. Ajayaghosh,
Chem. Asian J. 2014, 9, 1830-1840.
1
13
H NMR and C NMR spectra were recorded at room temperature, if not
otherwise mentioned, on a Bruker AMX 400 and Bruker AMX 500. All
NMR measurements were done in CDCl or C Cl , respectively with
the solvent residual peak as internal reference [CDCl
[8]
P. R. L. Malenfant, L. Groenendaal, J. M. J. Frechet, J. Am. Chem. Soc.
3
2
D
2
4
1
998, 120, 10990-10991.
1
3
: δ = 7.24 ( H) and
[
[
9]
J. Leroy, N. Boucher, S. Sergeyev, M. Sferrazza, Y. H. Geerts, Eur. J.
Org. Chem. 2007, 1256-1261.
1
3
1
13
2 2 4
δ = 77.0 ( C), C D Cl : δ = 6.00 ( H) and δ = 74.20 ( C) ppm]. Mass
spectrometry was performed on Bruker Reflex III (MALDI-TOF), Bruker
SolariX (HRMS-MALDI-FTICR) and Finnigan Mat SSQ 7000 (CI),
respectively. UV/Vis spectra were taken with a Perkin Elmer Lambda 16.
Elemental composition was determined with an Elementar Vario EL.
10] E.-K. Fleischmann, R. Zentel, Angew. Chem., Int. Ed. 2013, 52, 8810-
827.
[11] J. P. F. Lagerwall, G. Scalia, Curr. Appl. Phys. 2012, 12, 1387-1412.
8
[
[
12] C. Tschierske, Angew. Chem., Int. Ed. 2013, 52, 8828-8878.
13] W. Pisula, M. Zorn, J. Y. Chang, K. Mullen, R. Zentel, Macromol. Rapid
Commun. 2009, 30, 1179-1202.
Differential scanning calorimetry (DSC) was performed on a PerkinElmer
−
1
DSC 7 with a heating rate of 10 K min . Three heating and two cooling
curves were measured and the thermal data were extracted from the
second heating curves.
[14] S. Chen, B. Sun, W. Hong, H. Aziz, Y. Meng, Y. Li, J. Mater. Chem. C
2014, 2, 2183-2190.
[15] G. Schweicher, V. Lemaur, C. Niebel, C. Ruzie, Y. Diao, O. Goto, W. Y.
Lee, Y. Kim, J. B. Arlin, J. Karpinska, A. R. Kennedy, S. R. Parkin, Y.
Olivier, S. C. Mannsfeld, J. Cornil, Y. H. Geerts, Z. Bao, Adv. Mater.
Polarizing Optical Microscopy (POM) images were taken between two
glass slides on a Zeiss Axioskop equipped with a Mettler FP 90 hot
stage. For the shearing experiments the glass slides in the hot stage with
the samples in between were sheared manually and observed in the
microscope. The images are the original data without further treatment.
2
015, 27, 3066-3072.
[
[
[
16] S. A. Ponomarenko, S. Kirchmeyer, in Silicon Polymers (Ed.: A. M.
Muzafarov), Springer Berlin Heidelberg, Berlin, Heidelberg, 2011, pp.
3
3-110.
17] S. A. Ponomarenko, N. N. Rasulova, Y. N. Luponosov, N. M. Surin, M. I.
Buzin, I. Leshchiner, S. M. Peregudova, A. M. Muzafarov,
Macromolecules 2012, 45, 2014-2024.
Wide-angle x-ray scattering (WAXS) was done using an Empyrean setup
2
from PANalytical. A copper x-ray tube (line source of 12×0.04 mm )
18] D. V. Anokhin, M. Defaux, A. Mourran, M. Moeller, Y. N. Luponosov, O.
V. Borshchev, A. V. Bakirov, M. A. Shcherbina, S. N. Chvalun, T.
Meyer-Friedrichsen, A. Elschner, S. Kirchmeyer, S. A. Ponomarenko, D.
A. Ivanov, J. Phys. Chem. C 2012, 116, 22727-22736.
provided CuK radiation with λ = 0.1542 nm. In the Bragg-Brentano
α
o
geometry used, the divergent beam (divergence slit of 1/8 ) was
refocused at a pixel detector and recorded as a function of the scattering
angle 2θ. The perpendicular divergence was restricted by soller slits to
o
[19] W. H. de Jeu, K. Rahimi, U. Ziener, R. Vill, E. M. Herzig, P. Muller-
angles ≤ 2.3 . Subsequently, the peak positions were calculated from q =
Buschbaum, M. Moller, A. Mourran, Langmuir 2016, 32, 1533-1541.
2
π/d = (4π/λ) sinθ, in which q is the scattering vector.
[
[
20] A. Kreyes, PhD thesis, University of Ulm (Ulm), 2010.
21] A. Kreyes, S. Ellinger, K. Landfester, M. Defaux, D. A. Ivanov, A.
Elschner, T. Meyer-Friedrichsen, U. Ziener, Chem. Mater. 2010, 22,
Scanning force microscopy: The surface morphology of a thick film (the
sample was a molten powder which was used to measure the x-ray
diffraction data) was imaged with a scanning force microscope (Bruker
Dimension ICON) in tapping mode. The tapping mode imaging was
2
079-2092.
This article is protected by copyright. All rights reserved.

European Journal of Organic Chemistry
10.1002/ejoc.201700046
FULL PAPER
[
22] A. Kreyes, A. Mourran, Z. Hong, J. Wang, M. Möller, F. Gholamrezaie,
[32] Z. Chen, V. Stepanenko, V. Dehm, P. Prins, L. D. A. Siebbeles, J. Seibt,
P. Marquetand, V. Engel, F. Würthner, Chem.-Eur. J. 2006, 13, 436-
449.
W. S. C. Roelofs, D. M. de Leeuw, U. Ziener, Chem. Mater. 2013, 25,
2
128-2136.
[
[
[
[
[
23] I. E. Marko, S. Sterin, O. Buisine, R. Mignani, P. Branlard, B. Tinant, J.
P. Declercq, Science 2002, 298, 204-206.
[33] T. Yasuda, H. Ooi, J. Morita, Y. Akama, K. Minoura, M. Funahashi, T.
Shimomura, T. Kato, Adv. Funct. Mater. 2009, 19, 411-419.
[34] C. Cuerva, J. A. Campo, P. Ovejero, M. R. Torres, M. Cano, Dalton
Trans. 2014, 43, 8849-8860.
24] I. Markó, S. Stérin, O. Buisine, G. Berthon, G. Michaud, B. Tinant, J.-P.
Declercq, Adv. Synth. Catal. 2004, 346, 1429–1434.
25] S. Ellinger, U. Ziener, U. Thewalt, K. Landfester, M. Möller, Chem.
Mater. 2007, 19, 1070-1075.
[35] W. H. de Jeu, Basic X-Ray Scattering for Soft Matter, Oxford University
Press, 2016.
26] A. Kreyes, M. Amirkhani, I. Lieberwirth, R. Mauer, F. Laquai, K.
Landfester, U. Ziener, Chem. Mater. 2010, 22, 6453-6458.
27] S. Ellinger, A. Kreyes, U. Ziener, C. Hoffmann-Richter, K. Landfester, M.
Möller, Eur. J. Org. Chem. 2007, 5686-5702.
[36] V. Percec, W.-D. Cho, G. Ungar, D. J. P. Yeardley, J. Am. Chem. Soc.
2001, 123, 1302-1315.
[37] K. Antczak, J. F. Kingston, S. J. Alward, A. G. Fallis, Can. J. Chem.
1984, 62, 829-837.
[
[
28] S. Ponomarenko, S. Kirchmeyer, J. Mater. Chem. 2003, 13, 197-202.
29] I. Dierking, in Textures of Liquid Crystals, Wiley-VCH Verlag GmbH &
Co. KGaA, 2003, pp. 141-144.
[38] Y. Zhang, C. Wang, L. Rothberg, M.-K. Ng, J. Mater. Chem. 2006, 16,
3721-3725.
[39] A. Carpita, R. Rossi, C. A. Veracini, Tetrahedron 1985, 41, 1919-1929.
[40] P. Bäuerle, F. Würthner, G. Götz, F. Effenberger, Synthesis 1993,
1099-1103.
[
[
30] I. Dierking, in Textures of Liquid Crystals, Wiley-VCH Verlag GmbH &
Co. KGaA, 2003, pp. 91-122.
31] T. Cardinaels, J. Ramaekers, P. Nockemann, K. Driesen, K. Van Hecke,
L. Van Meervelt, S. Lei, S. De Feyter, D. Guillon, B. Donnio, K.
Binnemans, Chem. Mater. 2008, 20, 1278-1291.
[41] V. Duchenet, C. G. Andreu, J. M. Catel, G. Coustumer, Phosphorus,
Sulfur Silicon Relat. Elem. 1996, 118, 117-128.
[42] W. A. Herrmann, V. P. W. Bohm, C. W. K. Gstottmayr, M. Grosche, C.
P. Reisinger, T. Weskamp, J. Organomet. Chem. 2001, 617, 616-628.
This article is protected by copyright. All rights reserved.

European Journal of Organic Chemistry
10.1002/ejoc.201700046
FULL PAPER
Entry for the Table of Contents
FULL PAPER
Highly systematic double branching of
substituents in α,ω-substituted
oligothiophene series leads to
surprisingly low transition enthalpies
and entropies.
Substituents engineering
Si
Si
Si
Si
Si
Si
S
7
Jochen Gülcher, Roman Vill, Khosrow
Rahimi, Wim H. de Jeu, Ahmed Mourran
and Ulrich Ziener*
Page No. – Page No.
Effect of Double Branching in α,ω-
Substituted Oligothiophenes on
Thermal Solid-State Properties
This article is protected by copyright. All rights reserved.