Structure-Independent Conductance of Thiophene-Based Single-Stacking Junctions

Article abstract of DOI:10.1002/anie.201913344

The experimental investigation of intermolecular charge transport in π-conjugated materials is challenging. Herein, we describe the investigation of charge transport through intermolecular and intramolecular paths in single-molecule and single-stacking th

Full text of DOI:10.1002/anie.201913344

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
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Accepted Article
Title: Structure-Independent Conductance of Thiophene-Based Single-
Stacking Junctions
Authors: Wenjing Hong, Xiaohui Li, Qingqing Wu, Jie Bai, Songjun
Hou, Wenlin Jiang, Chun Tang, Hang Song, Xiaojuan Huang,
Jueting Zheng, Yang Yang, Junyang Liu, Yong Hu, Jia Shi,
Zitong Liu, Colin J. Lambert, and Deqing Zhang
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201913344
Angew. Chem. 10.1002/ange.201913344
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10.1002/anie.201913344
Angewandte Chemie International Edition
RESEARCH ARTICLE
Structure-Independent Conductance of Thiophene-Based Single-
Stacking Junctions
†
†
†
Xiaohui Li,[a] Qingqing Wu,[b] Jie Bai,[a] Songjun Hou,[b] Wenlin Jiang,[c] Chun Tang,[a] Hang Song,[a]
Xiaojuan Huang,[a] Jueting Zheng,[a] Yang Yang,[a] Junyang Liu,[a] Yong Hu,[a] Jia Shi,[a] Zitong Liu,[c]*
Colin J. Lambert,[b]* Deqing Zhang,[c]* Wenjing Hong[a]*
Abstract: Intermolecular charge transport is crucial in -conjugated
materials but the experimental investigation remained challenging.
Here, we show that charge transport through intermolecular and
intramolecular paths in single-molecule and single-stacking thiophene
junctions could be investigated using the mechanically controllable
break junction (MCBJ) technique. We found that intermolecular
charge transport ability through different single-stacking junctions is
approximately independent of molecular structures, which contrasts
with the strong length dependence of conductance in single-molecule
junctions with the same building blocks, and the dominant charge
transport path of molecules with two anchors transits from
intramolecular to intermolecular paths when the conjugation pattern
increased. The increase of conjugation further leads to higher binding
probabilities due to the variation in binding energies supported by
density functional theory (DFT) calculations. Our results demonstrate
that intermolecular charge transport is not only the limiting step but
also provides the efficient and dominate charge transport path at the
single-molecule scale.
strong electron-phonon interactions, as well as the disordered
microscopic structures. Despite substantial studies have been
3]
made to understand the intermolecular charge transport,[2d,
quantitative description of charge transport still remains
challenging. Until now the insights of the charge transport are
mostly from the theoretical calculations.[2a, 2c, 4] To investigate the
role of intermolecular interactions in charge transport, the
mechanically controllable break junction (MCBJ) studies have
demonstrated that charge transport through intermolecular paths
provides much lower conductance than that through
intramolecular paths in oligophenylene ethynylenes (OPEs),[5]
suggesting that the single-molecule break junction may offer new
insight to overcome the long-pending challenges.
Among the -conjugated materials, thiophene derivatives
attracted intensive attention in organic electronic devices and
molecular electronics owing to their outstanding electronic and
optical properties.[6] Understanding the intrinsic charge transport
through thiophene derivatives at the molecular level is essential
for designing high-performance functional organic materials and
devices. Until now, several groups have studied the
intramolecular charge transport through thiophene derivatives
based on its corresponding single-molecule junctions.[7] However,
the intermolecular charge transport through thiophene derivatives,
which plays a vital role in the ultimate charge-carrier mobility, has
never been studied yet.
In this work, we investigated the intermolecular charge transport
property in single-molecule and single-stacking thiophene
junctions using the MCBJ technique. It is found that the thiophene
molecules containing only one thiomethyl (-SMe) anchoring group
can form single-stacking junctions with measurable conductance.
Unexpectedly, the conductance of single-stacking junctions is
approximately constant with the different conjugated pattern,
while the probability to form single-stacking junctions improves by
increasing the conjugation region, indicating the dynamic
formation process provides the driving forces for their charge
transport ability. Moreover, based on the detectable conductance
of thiophene-based single-stacking junctions, we explored the
intermolecular and intramolecular charge transport through
thiophene derivatives at the single-molecule level, demonstrating
the intermolecular and intramolecular charge transport can be
distinguished and investigated upon MCBJ technique. We found
that the intermolecular charge transport can be more efficient than
intramolecular charge transport in thiophene derivatives and that
the dominant charge transport path transitions from
intramolecular to intermolecular when the conjugation increased.
Our findings provide clear evidence that intermolecular, instead of
intramolecular charge transport, could be the dominant
conductance path for organic materials with large -conjugated
pattern.
Introduction
The unique electronic properties of organic -conjugated
materials lead to various applications in flexible and stretchable,
light-weight, ubiquitous devices for skin-like or wearable
electronics, the Internet of Things and flexible displays etc.[1]
Among the macroscopic -conjugated materials, intermolecular
charge transport is widely considered as the limiting step for the
electronic processes[2] due to their weak dielectric constants, and
[a]
X. H. Li, J. Bai, C. Tang, H. Song, X. J. Huang, J. T. Zheng, Y.
Yang, J. Y. Liu, Y. Hu, J. Shi and Prof. W. J. Hong
State Key Laboratory of Physical Chemistry of Solid Surfaces,
iChEM, College of Chemistry and Chemical Engineering
Xiamen University
Xiamen, Siming South Road (China)
E-mail: whong@xmu.edu.cn
[b]
[c]
Q. Q. Wu, S. J. Hou and Prof. C. J. Lambert
Department of Physics
Lancaster University
Lancaster LA1 4YB (UK)
E-mail: c.lambert@lancaster.ac.uk
W. L. Jiang, Z. T. Liu and D. Q. Zhang
Beijing National Laboratory for Molecular Sciences, CAS Key
Laboratory of Organic Solids, Institute of Chemistry
Chinese Academy of Sciences
Beijing, Zhongguancun North First Street 2 (China)
E-mail: zitong_@iccas.ac.cn, dqzhang@iccas.ac.cn
These authors contributed equally to this work.
[†]
Supporting information for this article is given via a link at the end of
the document.
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10.1002/anie.201913344
Angewandte Chemie International Edition
RESEARCH ARTICLE
molecular length calculated from theoretical simulations (see
Table S1). In comparison, the stretching distance of L state is
almost twice than that of H state (1.31±0.02 nm), which is in
Results and Discussion
Conductance measurement of the single-stacking junction.
The conductance of molecular junctions was characterized using
accordance with single-stacking junction of S-T1 dimer with
longer length. To further verify our hypothesis, the electronic
coupling types of two conductance states were confirmed by
flicker noise analysis[13] (details in Experimental Section). As
shown in Figure 1D, the noise power scales as G1.1 for H state
and as G1.8 for L state, corresponding to through-bond coupling in
the H state of single-molecule junctions and through-space
coupling in the L state of single-stacking junctions, which agrees
well with our hypothesis. The phenomenon is different to short
oligothiophene with iodide anchors at both ends, which tend to lie
flat on Au electrode and form single-molecule junctions through
metal- interactions, as reported by Xiang et al.[14] The possible
reason is that the thiophene molecules with -SMe at only one side
tend to stand on gold electrode rather than lie flat, thus facilitating
the formation of a gold-S donor-acceptor bond by the S atom of
the thiophene ring and the gold electrode during the stretching
process, which is supported by the stretching distance and flicker
noise analysis. These results indicate that the interactions
between thiophene rings are strong enough to form the single-
stacking junctions and the intermolecular charge transport ability
of single-stacking junctions base on S-T1 is much lower than that
of corresponding single-molecule, as reported before in an OPEs
sysem.[5a]
MCBJ
technique
in
solution
(tetrahydrofuran:1,3,5-
trimethylbenzene = 1:4, v/v) with/without 0.1 mM target molecules
at a bias voltage of 0.1 V (Figure 1A). Briefly, the breaking and
closing process between two electrodes was performed by the
controllable bending of notched gold-wire chips. In this way, the
molecular junctions were created by repeatedly breaking and
forming the gold-gold atomic contacts. To investigate the charge
transport through -stacked thiophene dimer, molecule S-T1 with
only one -SMe terminal was employed to form a single-stacking
junction via intermolecular interactions with each -SMe coupled to
a gold electrode (Figure 1A).
Figure 1B shows several typical conductance-displacement
traces of S-T1 (red) and the solvent without molecules (black).
Unlike in direct tunneling traces obtained for the solvent, the
conductance indicated by the red traces decreases to two well-
defined molecular plateaus after the rupture of the last gold-gold
atomic contact at 1G0 (G0 = 2e2/h),[8] suggesting the formation of
two distinct molecular junctions for S-T1. The high conductance
(H) and low conductance (L) plateaus can appear individually or
together. To explore the correlation of the H and L states
statistically, 2D cross-correlation analysis[9] is constructed (Figure
S5A). A negatively correlated region centered at [10−2.2 G0, 10−4.0
G0] and [10−4.0 G0, 10−2.2 G0] is found for S-T1, indicating the two
conductance states appear competitively in most cases (details in
Supporting Information section 2). Then, one-dimensional (1D)
conductance histogram was generated to determine the most
likely conductance. As shown in Figure 1B, two evident
conductance peaks are obtained. The H peak centered at
10−2.18±0.04 G0 (517.1±44.0 nS) displays a narrow distribution and
was 68 times higher than that of the L peak (10−4.02±0.11 G0, 7.5±2.0
nS) with a broad distribution. So, We speculated that the H peak
corresponds to the single-molecule junctions bridged by -SMe[10]
and thienyl[11] (upper panel in Figure 1A) and the L peak
corresponds to the single-stacking junction through -stacked
dimers (bottom panel in Figure 1A). The broader peak width of the
L peak is related to more degrees of freedom during the stretching
process introduced by -stacked dimers.
To reveal more information from the stretching process
statistically, two-dimensional (2D) conductance histograms were
constructed from collecting thousands of individual traces without
data selection (Figure 1C). We note that the H intensity cloud
maintains almost flat during the stretching process, while the
slope of the L intensity cloud decreases significantly, suggesting
that the conductance of single-stacking junction highly depends
on the stacking configurations.[12] Besides, the stretching distance
of H state is much shorter than L state (inset of Figure 1C).
Considering the snap-back distance 0.5 nm[12] (details in
Supporting Information section 2.1), the stretching distance of H
state is 0.68 ± 0.03 nm, which is comparable with the S-T1
Figure 1. Conductance measurement of molecular junctions. (A) Schematic of
the MCBJ technique and the illustration of single-molecule S-T1 junction
(upper) and single- stacking S-T1 junction (bottom). (B) 1D conductance
histograms and typical conductance-displacement traces (inset) of S-T1 (red)
and solvent (black). (C) 2D conductance histogram and the relative stretching
displacement histograms from 10−0.3 G0 to 10−2.8 G0 of H state (0.18±0.03 nm,
left inset) and 10−0.3 G0 to 10−5.0 G0 of L state (0.81±0.02 nm, right inset). The
error bars are determined from the variations of the relative stretching
displacement values in three independent conductance measurements. (D) 2D
histogram of normalized flicker noise power versus average conductance of S-
T1.
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To address how intermolecular charge transport through
thiophene-stacking junctions vary among conjugation pattern, we
synthesized another three kinds of thiophene-based derivatives i)
molecules with increased thiophene units (S-T2, S-T3), ii) fused
thiophene with more rigid structure (S-TTT) and iii) molecules with
substituent groups on thiophene rings (S-T1-Cl, S-T1-Br). Figure
2 shows the 1D conductance histograms of the six thiophene
derivatives. As shown in Figure 2A, S-T2 and S-T3 with two and
three thiophene units each have only one conductance peak, and
the conductance varies slightly from 10–4.05±0.04 G0 (7.0±0.6 nS) to
10–3.91±0.03 G0 (9.6±0.7 nS) compared with S-T1 (10–4.02±0.11 G0).
The stretching distances of these molecular junctions are
significantly longer than calculated molecular lengths (see
Figures S3A,B and Table S1). In addition, flicker noise analysis
shows that the noise power scales as G2.0 for S-T2 and as G1.6 for
S-T3 (Figures S3C,D), which are indicative of the through-space
coupling through S-T2 or S-T3 dimers. Accordingly, we attribute
the conductance peaks around 10–4.0 G0 to single-stacking
junctions of S-T2 and S-T3. The absence of single-molecule
junctions is possibly caused by the weak competitiveness
compared with single-stacking junctions as the molecular
conjugation length increase since the absence of single-molecule
junctions and single-stacking junctions are competitive as
discussed above. Then, the effects of substituent and different
conjugation pattern on intermolecular charge transport were
investigated. Interestingly, single-stacking junctions of S-T1
derivatives with substituent groups, i.e., chlorine S-T1-Cl
(10−4.01±0.09 G0, 7.7±1.6 nS) and bromine S-T1-Br (10−4.07±0.02 G0,
6.6±0.4 nS), and fused-ring thiophene S-TTT (10−3.97±0.05 G0,
8.3±0.9 nS) also show similar conductance values centered at 10–
4.0 G0 (Figure 2B), suggesting that charge transport ability through
the single-stacking junctions based on thiophene units is nearly
independent of the conjugation pattern. To explore the
universality of the above findings, we extended the studies to
benzene-based junctions with fused-ring from phenyl (S-P1) to
naphthyl (S-P2) and to anthryl (S-P3) as shown in Figure S6. The
conductance of S-P1 (10−4.34±0.01 G0, 3.5±0.05 nS) and S-P2
(10−4.42±0.10 G0, 3.0±0.7 nS) are similar but decrease apparently for
S-P3 (10−4.60±0.08 G0, 1.9±0.3 nS). Compared with thiophene
system, the intermolecular charge transport ability of single-
stacking junctions based on benzene units is generally lower.
These results indicate that the thiophene-based single-stacking
junctions exhibit excellent intermolecular charge transport ability,
which is also more tolerant to the variation of molecular
architecture.
Figure 2. Investigation of intermolecular charge transport of thiophene
derivatives. (A) Molecular structures and 1D conductance histograms of
molecules S-T1 (10–4.02±0.11 G0), S-T2 (10–4.05±0.04 G0) and S-T3 (10–3.91±0.03 G0)
at 0.1 mM. (B) Molecular structures and corresponding 1D conductance
histograms of S-T1-Cl (10−4.01±0.09 G0 and 10−2.01±0.03 G0), S-T1-Br (10−4.07±0.02 G0
and 10−2.09±0.02 G0) and S-TTT (10−3.97±0.05 G0). Detail analysis can be found in
Figure S6.
Structure dependence of the stacking probability. Even
though the conductance values of the single-stacking junctions
remained nearly structure-independent, the conductance peaks,
especially for benzene-based junctions (Figures S6D-F), become
more pronounced as the conjugation region increases. This trend
suggests that the structure of the conjugated core plays a role in
the dynamic formation of single-stacking junctions. To evaluate
the role of conjugation patterns in the intermolecular interactions
quantitatively, we constructed displacement distribution
histograms for S-T1, S-T2 and S-T3 at the conductance range
between 10–(Gm−1) G0 and 10–(Gm+1) G0 (details in Supporting
Information section 2.1). As illustrated in Figure 3A, the
displacement distributions centered at 0.36 nm represent the
direct tunneling feature without molecular junction (T), while the
longer displacement distributions are assigned to single-stacking
junctions (J). The area ratios of the relative stretching distance
histograms obtained by Gaussian fitting reveal the formation
percentage of single-stacking junctions. It was found that the
stacking probability of thiophene-based junctions started from
80±0.9% (S-T1), increasing slightly to 83±1.0% for S-T2 and
95±1.6% for S-T3 (Figure 3B), which is attributed to the effective
- stacking interactions arising from the increasing conjugated
patterns. By contrast, the stacking probability of molecule S-P1
was determined to be only 62±2.7%. When the -conjugated core
was expanded to yield the anthryl (S-P3), the stacking probability
increased to a value as high as 91±3.9% (Figure 3B). The
generally higher stacking probabilities of thiophene-based
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10.1002/anie.201913344
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junctions are enhanced by the introduction of sulfur atoms, which
introduce additional S-S[15] and S- interactions[16] and increase
the stability of the single-stacking junctions. Stacking probability
analysis, together with the constant conductance of single-
stacking junctions, provides essential insight into the charge
transport enhancement induced by aggregation in organic
semiconductors[3b] that aggregation increases the formation
probability of short-range -stacked units and subsequently leads
to the enhanced charge transport through-conjugated materials.
with the conductance increasing from 10−4.31±0.07 G0 (3.8±0.6 nS,
0.001 mM) to 10−3.89±0.05 G0 (9.9±1.2 nS, 0.1 mM), as shown in
Figure 4D. Figure 4E shows the 2D conductance-distance
histogram and electronic coupling through flicker noise analysis
of S-T3-S at 0.1 mM. The noise power scales as G1.6 for S-T3-S,
indicating that the charge transport through S-T3-S was through-
space-dominated at higher concentration. Furthermore, the
concentration-dependent fluorescence emission spectra of S-T3-
S reveal that monomer prevails below 0.01 mM and begins to
aggregate from 0.01 mM to 0.1 mM (Figure S8), indicating that
the conductance at low concentration of 0.001 mM and high
concentration of 0.1 mM could be assigned to single-molecule
junctions and single-stacking junctions, respectively. Therefore,
the S-T3-S will undergo the transition from single-molecule to
single-stacking at higher concentration. The concentration-
dependent behavior of S-T3-S found here is different from that of
oligothiophene reported by Capozzi et al.[7b] The discrepancy was
possibly attributed to the structural difference between
oligothiophene and the thiophene/phenylene co-oligomer which
forms intermolecular complexes with the increasing
concentrations.[17] However, no concentration dependence was
observed for short molecules like S-T2-S, and the corresponding
noise power scale as G1.2 for 0.1 mM. These results demonstrated
that the charge transport paths between intermolecular and
intramolecular could be controlled by rational molecular design.
Long conjugation structure is more favorable for the construction
of intermolecular charge transport, because of the strong
molecular interactions.
Figure 3. Structure dependence of the stacking probability. (A) The
displacement distribution histograms of single-stacking junctions with molecules
S-T1, S-T2 and S-T3 determined from 10–(Gm–1) G0 to 10–(Gm+1) G0. We refer to
the direct tunneling feature as “T” (dashed black lines) and the molecular
junction feature as “J”. (B) Stacking probability as a function of the number of
aromatic ring n without regard to p-phenylene connected with -SMe anchor
group. The error bars are determined from the variations of the stacking
probability in three independent conductance measurements.
Figure 4F summarised the conductance evolution of single-
stacking (dashed line) and single-molecule (solid line) junctions
varying with molecular length. The single-molecule conductance
of S-T1-S, S-T2-S and S-T3-S decrease exponentially with the
increasing thiophene units, which is consistent with the
conductance decay of single-molecule oligothiophene junctions[7a,
The
transition
from
intramolecular
transport
to
intermolecular transport. As discussed above, the charge
transport through thiophene-based single-stacking junctions can
be detected using MCBJ technique, providing the opportunity to
explore the intermolecular and intramolecular charge transport,
(as shown in Figure 4A), through thiophene derivatives at the
single-molecule level. To distinguish the intermolecular and
intramolecular charge transport, our approach was to investigate
charge transport through single-stacking and single-molecule
junctions with the same thiophene backbone. As shown in Figure
4B, the molecules in orange with only one -SMe terminal were
employed to form a single-stacking junction as we have discussed,
and the intramolecular charge transport through the thiophene
backbones was investigated using the molecule in purple with
both –SMe terminals bridged between two gold electrodes.
7b]
and DFT calculations (Figure S11J). In contrast, the
conductance of single-stacking junctions is almost unchanged.
When the molecules are relatively short, the conductance of
single-stacking junctions is lower than those of corresponding
single-molecule junctions. However, there is a reversal when the
conjugation pattern increased to three thiophene rings that the
single-stacking conductance of S-T3 is ~200% higher than the
single-molecule conductance of S-T3-S, suggesting the
intermolecular charge transport is even more efficient than
intramolecular charge transport with large conjugation patterns.
The conductance transition originates from the significant
conductance decay with length of intramolecular charge transport
and the near length-independence of intermolecular charge
transport through single-stacking junctions. Such low length
decay of through-space charge transport is also found in single-
stacking junctions based on benzene (Figure S7P) and previous
report about -folded molecular junctions based on anthracene
Different from the structure-independent conductance of single-
staking junctions, the conductance of single-molecule junctions
decreased significantly from 10−3.43±0.10 G0 (29.5±6.9 nS, S-T1-S)
to 10−3.78±0.05 G0 (12.8±0.2 nS, S-T2-S), as shown in Figure 4C.
For S-T3-S, significant concentration-dependence is observed
moieties[18]
.
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10.1002/anie.201913344
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RESEARCH ARTICLE
stretching process. However, only the high conductance state
was obtained in our experiments due to the relatively high
stretching rate, which is in accordance with the previous report.[21]
Figure 5C show the room-temperature conductance evolutions
during stretching obtained from the transmission coefficients at
the Fermi level estimated by DFT. During junction stretching,
oscillations in conductance occur, as theoretically predicted[22]
and measured[21] in previous works, and the conductance
histograms (inset of Figure 5C) suggest that the calculated
conductance of dimers is approximately 10−5.0 G0. The similar
conductance regions among different derivatives and variation
tendency provide qualitative theoretical evidence for the
conductance consistency observed experimentally.
Figure 4. Investigation of intermolecular and intramolecular charge transport.
(A) Schematic illustration of intramolecular and intermolecular charge transport.
(B) Molecular structures used for comparison. (C) 1D conductance histograms
of S-T1-S and S-T2-S. (D) 1D conductance histograms of S-T3-S at different
concentrations. (E) 2D conductance histograms and 2D histogram of
normalized flicker noise power versus average conductance of S-T3-S at 0.1
mM. (F) The conductance as a function of the number of thiophene ring n in
single-molecule (solid line) and single-stacking (dotted line) junctions at 0.1 mM
except for S-T3-S at 0.001 mM. The error bars are determined from the
variations of the most probable conductance values in three independent
conductance measurements.
Figure 5. Transmission curves and stacking energies calculated between
single-stacking junctions. (A) Schematics of the stretching simulation from full-
stacking (1.52 nm) to zero-stacking (2.22 nm) of S-T1 junction. (B)
Representative transmission curves of single-stacking S-T1 junction at different
separation distance between two -stacked dimer, where “0” is the initial full-
stacking state, and increases in increments of 0.1 nm until to zero-stacking state
(“0.7”). (C) The corresponding conductance evolutions obtained from the
transmission coefficients at the Fermi level versus separation distance of S-T1,
S-T2 and S-T3 and the conductance histograms (inset) with a bin size of 0.4
log(G/G0). (D) Stacking energies calculated between dimers of molecule S-T1,
S-T2 and S-T3 versus the relative separation distance between two gold
electrodes.
Theoretical investigation of the transmission function and
stacking energy. To understand the intermolecular-dominated
charge transport, we further calculated the transmission function
T(E) describing electrons of energy E passing from one electrode
to the other using a combination of the software package
SIESTA[19] based on ab initio DFT and the quantum transport
code Gollum.[20] To model the evolution of the single-stacking
junction, two target molecules were initially attached to two gold
pyramidal-shaped electrodes, as shown in Figure 5A (upper) for
molecule S-T1. Then, the electrode spacing d was increased
gradually in increments of 0.05 nm, from d = 1.52 nm to the break-
off distance of the -stacked dimers, as shown in Figure 5A
(bottom). Figure 5B shows examples of the transmission
functions of a single-stacking S-T1 junction at various stages of
the stretching simulation (details in Figure S11A). The
transmission curves demonstrate that both constructive and
destructive quantum interference are observed during the
To investigate the effect of molecular structure on the stacking
probability, we also calculated the stacking energy of the dimers
in the junctions at each increment of the stretching process. As
shown in Figure 5D, the binding energies (see Supporting
Information) decrease almost monotonically as the separation
distance d increases. The initial binding energy for thiophene-
based S-T1 is lower than that of S-T2 and S-T3, because the area
of the initial - overlap area of S-T1 is smaller than the initial
overlap areas of S-T2 and S-T3. This feature supports our
experimental results indicating that the binging probability of S-T1
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is lower than that of S-T2 and S-T3. Since the measured stacking
probabilities follow the trends observed for the initial binding
energies, it is inferred that the structure dependence of the
stacking probability originates from variations in the binding
energies of the - stacking.
[4]
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Conclusion
In conclusion, we investigated the intermolecular and
intramolecular charge transport properties in single-molecule and
single-stacking thiophene junctions using MCBJ technique. We
demonstrated that the conductance of thiophene-based single-
stacking junctions is nearly independent of the conjugated pattern
and the dominant charge transport path transits from
intramolecular to intermolecular paths when the conjugation
pattern increased. We also found that the major effect from the
increased conjugated region is to improve the dynamic formation
process of single-stacking junction rather than its intrinsic
conductance at molecular level. The results were further
confirmed by the theoretical calculations, which predict similar
conductance tendencies and different binding energies of the
single-stacking junctions. Our results not only provides the
fundamental understanding of structure-property relationship but
also offer fundamental insight into how, from a single-molecule
perspective, microscopic charge transport in highly disordered
materials enables existing aggregation to increase the formation
probability of intermolecular charge transport channels. We
believe our findings will inspire various new design strategies for
the fabrication of high-performance organic devices via molecular
engineering of intermolecular interactions.
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Acknowledgments
This work was supported by the National Natural Science
Foundation of China (Nos. 21933012, 21722305, 21673195,
21703188), National Key R&D Program of China
(2017YFA0204902), FET Open project 767187–QuIET, the EU
project BAC-TO-FUEL, and the UK EPSRC grants EP/N017188/1,
EP/P027156/1 and EP/N03337X/1 for funding instrumentation
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Keywords: thiophene • single-stacking junction • mechanically
controllable break junction • structure-independent conductance•
intermolecular charge transport
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This article is protected by copyright. All rights reserved.

10.1002/anie.201913344
Angewandte Chemie International Edition
RESEARCH ARTICLE
RESEARCH ARTICLE
We demonstrated that the
Xiaohui Li, Qingqing Wu, Jie Bai,
conductance of thiophene-based
single-stacking junctions is nearly
independent of the conjugated pattern
that the dominant charge transport
path transits from intramolecular to
intermolecular paths when the
conjugation pattern increased.
Songjun Hou, Wenlin Jiang, Chun Tang,
Hang Song, Xiaojuan Huang, Jueting
Zheng, Yang Yang, Junyang Liu, Yong
Hu, Jia Shi, Zitong Liu,* Colin J.
Lambert,* Deqing Zhang,* Wenjing
Hong*
Page No. – Page No.
Structure-Independent Conductance
of Thiophene-Based Single-Stacking
Junctions
This article is protected by copyright. All rights reserved.