Self-Assembly Behavior of Diacetylenic Acid Molecules upon Vapor Deposition: Odd–Even Effect on the Film Morphology

Article abstract of DOI:10.1002/chem.202002227

A series of linear carboxylic acids containing diacetylenic units at different positions along the chain (C₁₂H₂₅(C≡C)₂(CH₂)_nCOOH, n=7–11) were vacuum-deposited on clean silica substrates. The morphologies of the initial films after UV irradiation were studied. A clear odd–even effect on the morphology of the initial film was observed in that, depending on the spacer length between the diacetylenic unit and carboxyl head group, rings or dendrites of acid dimer layers were obtained. A molecular dynamic simulation of the aggregation process suggests that two competing intermolecular interactions and thus aggregation directions are involved and modulated by the odd or even carbon chain length. Further modulation of the interaction by substitution of a phenyl group at the terminus of the chain or by changing the carboxyl head group to an amidobenzoic acid head group led to a similar odd–even effect but with different dimensions or trends, which can be rationalized similarly. These results give the opportunity to create aligned conjugated polymer chains of different dimensions through self-assembly for applications in molecular/organic electronics.

Full text of DOI:10.1002/chem.202002227

Accepted Article
Accepted Article
Title: Self-Assembly Behavior of Diacetylenic Acid Molecules upon
Vapor Deposition: Odd-Even Effect on the Film Morphology
Authors: Chiao-Wei Tseng, Ding-Chi Huang, Han-Li Yang, Hsieh-
Cheng Lin, Fang-Cheng Li, Chun-Wei Pao, and Yu-Tai Tao
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: Chem. Eur. J. 10.1002/chem.202002227
Link to VoR: https://doi.org/10.1002/chem.202002227
0
1/2020

Chemistry - A European Journal
10.1002/chem.202002227
FULL PAPER
Self-Assembly Behavior of Diacetylenic Acid Molecules upon
Vapor Deposition: Odd-Even Effect on the Film Morphology
[
a]
[a]
[a]
[b]
[c]
Chiao-Wei Tseng, Ding-Chi Huang, Han-Li Yang, Hsieh-Cheng Lin, Fang-Cheng Li, Chun-Wei
[
c]
[a]
Pao,* and Yu-Tai Tao*
[a]
Dr. C.-W. Tseng, Dr. D.-C. Huang, H.-L. Yang, Prof. Y.-T. Tao
Institute of Chemistry
Academia Sinica
Taipei, Taiwan 11521
E-mail: ytt@gate.sinica.edu.tw
Dr. H.-C. Lin
Institute of Atomic and Molecular Sciences
Academia Sinica
Taipei, Taiwan
F.-C. Li, Dr. C.-W; Pao
[
[
b]
c]
Research Center for Applied Sciences
Academia Sinica,
Taipei, Taiwan 11521
Supporting information for this article is given via a link at the end of the document.
Abstract: A series of linear carboxylic acids containing diacetylenic
unit at different positions along the chain (C12 25(C≡C) (CH COOH,
7-11) were vacuum-deposited on clean silica substrate.
intra-chain charge conduction, a fully extended and aligned
polymer chain will be most promising and desirable. Pre-
organizing diacetylenic monomers directionally and then
subjecting them to topochemical polymerization to form aligned
conjugated polymers are highly interesting.17,18 Tremendous
efforts have been made towards aligning diacetylene molecules
into hierarchical nanostructures through various techniques
H
2
2 n
)
n
=
Morphologies of the initial films after UV-irradiation were studied. A
clear odd-even effect on the morphology of initial film was observed
in that, depending on the spacer length between the diacetylenic unit
and carboxyl head group, rings or dendrites of acid dimer layers were
obtained. A molecular dynamic simulation of the aggregation process
suggests that two competing intermolecular interactions and thus
aggregation directions are involved and modulated by the odd or even
carbon chain length. Further modulation of the interaction by
substitution of a phenyl group at the terminus of the chain or by
changing the carboxyl head group to amidobenzoic acid head group
led to similar odd-even effect but of different dimension or trend, which
can be rationalized similarly. These results would open the
opportunity to create aligned conjugated polymer chains of different
1
9-21
involving non-covalent forces.
Nevertheless, limited success
was achieved, presumably due to the strict packing requirements
of topochemical polymerization and the numerous defects that
may evolve during the preparation and polymerization
22
processes. A better understanding and even controlling of the
self-assembling behaviors for diacetylene molecules are needed.
Pentacosa-10,12-diynoic acid (PDA) is a highly crystalline
material which undergoes topochemical polymerization gradually
23,24
even in the room light.
Recently, in an effort to use
dimensions
through
self-assembly
for
applications
in
polymerized films of this compound for charge storage purpose in
memory device fabrication, we observed a unique ring formation
on silica surface upon vacuum deposition of PDA.25 This raises
the possibility of pre-organizing the molecules into specific
patterns for conjugated polymer formation. In this work, we
investigated a series of long chain carboxylic acids containing
diacetylene unit at different positions along the chain (i.e.
molecular/organic electronics.
Introduction
It has long been known that certain types of diacetylenic
molecules in their crystalline state can undergo “topochemical
polymerization” reactions, from which a conjugated poly(ene-yne)
chain system is produced with little perturbation of the original
crystal packing arrangement in the system.1-3 A specific packing
distance and relative tilt angle between the neighboring
diacetylene units are necessary for this 1,4-addition reaction to
proceed upon UV-irradiation or heat treatment.4 Owing to their
unique electronic and optical properties, the resultant
polydiacetylenes have been much explored for their applications
in a wide range of areas.7-12 One potential application is in the
area of organic electronics, where the conjugated polydiacetylene
chains are used as the semiconducting channel materials,1
since the intra-chain charge conduction is expected to be more
12 2 2 n
C H25(C≡C) (CH ) COOH, n = 7-11) and demonstrated that
unique film morphologies (dendrite- or ring-type form) were
observed depending on the spacer length between the
diacetylene unit and the carboxyl head group to be odd carbon
number or even carbon number (odd-even effect). Furthermore,
a modulation of intermolecular interactions by introducing a
phenyl group at the end of the linear acid or an amidobenzoic acid
group as the head group gave similar odd-even pattern dichotomy,
albeit with opposite trend or different ring dimensions. Molecular
Dynamics (MD/Monte Carlo) simulation was used to simulate the
molecular aggregation process. The results suggest that the
orientation of the cyclic H-bonded dimer of the carboxyl head
groups plays an important role in determining the growth direction
of the diacetylenic acid crystals, which in turn determines the
ultimate morphology and polymerization direction. While an odd-
even effect in the reactivity of diacetylenic molecules has been
-6
3,14
facile than the charge-hopping process commonly involved in
organic semiconductors.1
5,16
However, to take advantage of the
1
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.202002227
FULL PAPER
well-documented,26~28 due to the stringent orientation requirement
for neighboring diacetylene units, the odd-even effect in molecular
assembling process of these acids on a surface and thus their
morphologies have not been reported as far as we are aware of.
The insight obtained here opens the oppourunity to modulate the
morphology of polydiacetylene film (with more linear or more
curved conjugated chains) through changes in carboxyl head
groups. The type of surface on which the acid is deposited (flat or
rough, hydrophilic or hydrophobic...) also constitutes further
parameters to influence the morphology. With these parameters
understood, designing various conjugated polydiacetylenes
systems for applications in electronic materials are possible.
nominal thickness of 1 nm. The morphologies of the films as a
function of n are shown in Fig. 2 (a-e) (first row and second row
of different scales). There appeared to have two kinds of
morphologies: with n = 7, 9, and 11, a dendrite-like morphology
was obtained, with longer fibers spreading over the surface, from
which shorter branches were grown at an angle of ~60. Even
smaller branches then grew further from those shorter branches.
rd
The AFM micrographs (Fig. 2f, h, j, 3 row) show that numerous
cracks oriented in similar direction, which is nearly perpendicular
to the axis of the long fibers. This direction is extended into the
smaller branches. The line profiles of the AFM micrographs show
that the film is of rather uniform thickness, at ~5.6 nm for n = 7,
~
6.4 nm for n = 9, and ~7.2 nm for n = 11. These thicknesses are
about twice the thickness of corresponding molecules. In contrast,
when n = 8, and 10, a distinctly different morphology was obtained
for the deposited films, with rings or half-formed rings of similar
diameters dispersed on the substrate. The AFM micrographs also
show numerous cracks, nevertheless oriented roughly along the
periphery of the rings. The films also had a uniform thickness of
Results and Discussion
Scheme
corresponding abbreviations of the molecules used in this study.
They include series of linear chain derivatives
25(C≡C) (CH COOH, with 7-11, and phenyl-
terminated linear acids, Ph(CH (CH COOH, n = 8 and
amidobenzoic acids,
COOH, with n = 7 -11. Details
1
shows the chemical structures and
a
~
5.1 nm for n = 8, and ~5.4 nm for n = 10. These thicknesses are
C
12
H
2
)
2 n
n
=
a
close but smaller than twice of the molecular thickness and
systematically thinner than those with odd chains. It was shown
previously25 by attenuated total reflectance (ATR) IR that these
)
2 9
(C≡C)
of
2
2 n
)
9
,
and
a
series
C
12
H
2
25(C≡C) (CH
2 n 6 4
) CONHC H
-
1
films gave an IR absorption at 1685 cm , same as the carbonyl
stretching frequency for H-bond dimer of carboxylic acid in their
solid state. This suggests the formation of dimer layer. A plot of
the thickness versus the chain length (Figure S1) shows that the
odd chain and even chain system systems fall on two linear
curves with different slopes. The steeper curve implies less tilt
angle of the chain. Furthermore, the Near Edge X-ray Absorption
Fine Structure (NEXAFS) spectra as a function of incidence angle
are shown in Fig. 3a for the film of 12-DA-8-COOH. At an
incidence angle of 90˚, a strong band at 288.7 eV, assignable to
the σ* (C-H) transition, appeared. Whereas at an incidence angle
of 20˚, another band at higher energy of 294.8 eV, assignable to
σ* (C-C) transition, appeared at the expense of the original σ* (C-
H) transition. In light of the near orthogonal orientation of the C-C
and C-H bonds, this intensity change is in agreement with an alkyl
chain standing near normal to the surface.29 But the even chain
systems tilted more and thus gave a smaller thickness as stated
above.
regarding the syntheses and structure characterization of the
studied molecules are presented in the Supporting Information.
Scheme 1. Molecular structures and corresponding abbreviations for the
diacetylenic and the reference molecules used in this study and schematic
diagram of the molecular aggregation process upon vacuum deposition.
When freshly deposited films of 12-DA-8-COOH were taken
out of the vacuum chamber and examined by optical microscope,
the morphology changed with time, from the ring-type morphology
to scattered clusters (Fig. 1). Immediate irradiation by UV-light
Polarization-dependent Raman Spectroscopy (PDRS) was
used to examine the films after UV irradiation. As shown in Fig.
(wavelength 254 nm) upon removing out of the chamber resulted
3b for the 12-DA-8-COOH acid, which formed ring patterns, when
in a film whose morphology remained constant with time. There
seems that a metastable state was obtained when formed under
vacuum and a new equilibrium state will be reached when the
system was exposed to air and interact with air molecules. Thus,
all samples were UV-irradiated immediately and then examined.
the polarization of the electric field aligned along the tangential
direction of the ring, i.e., along the direction of cracks, three peaks,
at 1135, 1520, and 2120 cm-1 respectively, were observed clearly,
which are assignable to the stretching modes of the C-C bond,
the C=C bond, and the C ≡ C bond respectively. When the
polarization was oriented along the radial direction (perpendicular
to the direction of the cracks), no peaks were observed. This
suggested the formation of the poly(ene-yne) backbones of the
polydiacetylenes from the deposited films and the poly-
30
conjugated chains are along the ring periphery. In contrast, for
2-DA-9-COOH (Fig. 3c), which gave dendrite-like film structure,
1
Figure 1. Morphologies of 3 nm film of 12-DA-8-COOH as a function of time
after left in ambient air for (a) 5 min, (b) 4 hrs. (c) 24 hrs. The insets are enlarged
images.
when the polarization was oriented along the long axis of the
dendrite, no peaks were observed. With polarization oriented
perpendicular to the long axis (i.e. parallel to the direction of
cracks), the three peaks associated with the conjugated
backbone appeared. Thus the polymer chain is oriented
perpendicular to the long axis of the dendrites.
Thin films of the linear diacetylenic acids, 12-DA-n-COOH with
n = 7-11, were vacuum-deposited on clean silica substrates at a
2
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.202002227
FULL PAPER
Figure 2. (a-e) Optical micrographs, (f-j) AFM topographic images, and corresponding line profiles of the UV-irradiated films of diacetylenic acids, 12-DA-n-COOH
with n = 7-11, deposited on the silica substrate up to a nominal thickness of 1 nm, by vacuum evaporation.
Figure 3. (a) NEXAFS spectra of the carbon K-edge of the deposited film of 12-DA-8-COOH on silica substrate. (Theta is the angle between the incidence X-ray
and the substrate surface.) (b, c) Polarization-dependent Raman spectra (PDRS) of the ring- and dendrite-shaped films for 12-DA-8-COOH and 12-DA-9-COOH,
respectively, with E-field either in the tangential or radial direction of the rings or parallel or perpendicular to the long axis. The inset shows the focused point of
measurement in the patterns.
Summarizing the experimental observations, an overall picture
is suggested to be the following: deposition of these diacetylenic
acids results in self-assembling (aggregation) of the acid
molecules on the silica substrate. An odd-even effect of the
morphology was obtained: with even chain length between the
diacetylene group and the carboxyl group (n = 8 and 10), the acid
molecules form dimeric layers and mainly aggregate in one
direction but with a slight turn to give the ring patterns eventually.
3
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.202002227
FULL PAPER
The molecular chains stand near normal to the substrate but tilted
in the direction of aggregation.of growth. The diacetylenic groups
layer is formed, with the terminal CH
3
group in contact with the
oxide surface. One possible cause is the specific interaction
between the DA groups results in a conformation that weakens
the anchoring interaction of carboxyl group with the surface and
thus leading to dimer formation. The 14-DA-14, on the other hand,
tended to pile up and give rod-shaped islands, with the conjugated
backbones oriented along the long axes of the rods, according to
the PDRS analysis. Thus incorporating DA unit into the linear alkyl
chain enables the molecules to assemble more along one
direction to form long rod-like packing, as shown in Fig. 4c. This
direction is suggested to be the direction of the plane containing
the trans-zigzag carbon chains, along which there are more
favourable van der Waal interactions.31 Unlike the 2-dimensinal
sheets with the height close to the length of a molecule, the rods
of 14-DA-14 had very steep height of around 50-100 nm, although
the nominal thickness of the film was 1 nm. This may indicate a
strong intermolecular interactions and then 3-dimensional
aggregation. At a thicker film of 3 nm or 7 nm, the diacetylenic
acids maintain the ring-type or dendrite-type growth to fill up the
empty spaces on the substrate, whereas without carboxyl group,
the 14-DA-14 gave scattered but thicker rods (Fig. 4d, e, f). Thus
in the presence of the carboxyl group, an even coverage of the
surface was observed, presumably due to the stronger interaction
oriented in such
a way that UV irradiation results in
polydiacetylene backbones. Cracks are formed between the
chains due to the changing distance from aggregation of polymer
chains. With odd chain length between the diacetylenic group and
carboxyl group (n = 7, 9, and 11), the dimers of the acid molecules
aggregate in two competing directions at different speeds to give
dendrite-like patterns. The diacetylenic groups tilted less and
along the direction perpendicular to the long axis and polymerize
in this direction.
between the carboxyl groups and the hydroxylated SiO
2
surface
during the deposition.
Figure 4. Optical micrographs and AFM topographic images of (a) C26, (b)
C
25COOH, and (c) 14-DA-14 film deposited on the silica surface with a nominal
thickness of 1 nm. Optical micrographs of diacetylenic films of (d) 14-DA-14, (e)
2-DA-8-COOH, and (f) 12-DA-9-COOH, deposited by vacuum evaporation to
1
a nominal thickness of 1nm, 3nm, and 7nm, and polymerized by UV irradiation.
To understand the effect of functional groups on the
formation of these unique patterns, reference molecules with
either DA unit only or acid group only, or neither of them, i.e., n-
15,17-dotricontadiyne (14-DA-14), n-cerotic acid (C25COOH), and
hexacosane (C26), were deposited under similar condition as that
for the DA-acids for comparison. Based on the optical
micrographs and step height analysis of the AFM micrographs
(Fig. S1, SI), these three molecules all tended to stand nearly
vertical on the silica surface, with C26 and C25COOH forming
sheet-like morphology, as shown in Fig. 4a, b. The C25COOH
gave patches of “monolayer” films compared to more continuous
film from C26. It is interesting to note that for simple saturated
carboxylic acid monolayer, the carboxyl group is in direct contact
with the oxide surface. While in the presence of DA unit, the dimer
Figure 5. (a) Schematic diagram showing an array of 16 DA-acid molecules
placed on top of silica substrate. The green pillars represent DA-acids tilting in
the direction of the plane containing the trans-zigzag carbon chains and the DA
units (purple plane). The red arrows show the pre-polymerization direction and
the orthogonal direction respectively. (b) Lowest energy conformation for 12-
DA-7-COOH and (d) for 12-DA-8-COOH in the array. The colored squares show
array views from different angles: white (from the side view 1) and yellow (from
the side view 2). (c) The top view of the 2-dimensional imaging of the array
4
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.202002227
FULL PAPER
consisting of 12-DA-8-COOH. The red line indicates a straight growth. (e)
Potential energy curve for the model array interacting with an extra molecule
approaching either in the pre-polymerization direction or the orthogonal
direction for 12-DA-7-COOH and (f) that for 12-DA-8-COOH. (g) Optical
micrographs and AFM topographic images of the dendrite- and ring-shaped
films of DA-acid molecules. (h) Lowest energy conformations of poly(ene-yne)
together with the side chains with the odd- and even-carbon spacers. The red
arrows show the direction of the conjugated backbone of the polymers.
Combining the experimental observations and simulation
results, the self-assembly of DA-acid molecules can be
rationalized as follows. Upon vapor deposition, the acid molecules
land and migrate on the silica substrate and nucleate to form H-
bonded dimers. Due to the van der Waal interaction, the
molecules tend to aggregate along the direction of the trans-
zigzag plane of the alkyl chain, with the DA units located at the
center of the molecules in the all-trans chain conformations, so
that the neighbouring DA units are tilted relative to each other in
a disposition suitable for topochemical polymerization. With more
molecules arriving at the surface and migrating around to the
nucleation sites, they can aggregate from different directions. For
odd chain-spacer acid, the growth from orthogonal direction is
somewhat favoured over the trans-zigzag (pre-polymerization)
direction. Thus, a dendritic morphology is obtained. Upon UV-
To gain more insight into the mechanism of the film formation,
molecular dynamics (MD) simulation was performed to simulate
the self-assembling process of the DA-acid molecules on the
substrate. An array of 16 DA-acid molecules were placed on top
of the silica surface and were allowed to equilibrate at 300 K for
about 100 ps; then, the system was quenched to 0 K by structural
relaxation (Fig. 5a). The resulted structures were then analyzed.
As shown in Fig. 5b and d, for both DA-acids with odd (n = 7) and
even (n = 8) carbon spacer, well-ordered crystalline array of acid
dimers was formed, with molecular chains tilted toward the
neighboring molecules within the plane containing the trans-
zigzag alkyl chain and the DA units. It is noted that similar
disposition of the diacetylenic groups are obtained for both acids
and this alignment allows for topochemical polymerization to
occur.32 Namely, the trans-zigzag plane direction is the pre-
polymerization direction and the plane contains the trans-zigzag
carbon chain and the DA unit is the pre-polymerization plane. It is
further noticed that with odd chain spacer (n = 7), the carboxyl
head groups form a cyclic dimeric ring structure with the ring plane
nearly parallel to the trans-zigzag plane (Fig. 5b). With even chain
spacer (n = 8), the head group dimer ring twisted away from the
trans-zigzag plane (Fig. 5d). This difference may affect the
packing of neighbouring molecules and ultimately the
morphologies of the films formed. Fig. 5h shows the polymer
structure for the DA-acids viewed from different directions. For
odd chain spacer acid (n = 7), the cyclic dimer groups, which is
parallel to the trans-zigzag plane, can be accommodated along
the plane containing the polymer backbone and a near linear
polymer chain can be maintained. Whereas for even chain spacer
acid (n = 8), the dimer groups have to twist at an angle to be
accommodated along the polymer backbone so that a slight
curving of the polymer backbone is obtained. A large-scale image
from extended system of atomistic simulation of the even chain
spacer acid also shows the curved growth of the assembly (Fig.
irradiation, the poly(ene-yne) is formed along
a direction
perpendicular to the long axis of the dendritic film. For even chain
spacer acid, the twist in the carboxyl dimer groups disfavour the
growth in the orthogonal direction so that the molecules aggregate
mainly along the trans-zigzag plane. To accommodate the dimer
head group, a slight distortion takes place so that a curved growth
and eventually a ring is formed. Polymerization by UV irradiation
takes place along this growth direction.
5c, with the red line indicating a straight growth).
Furthermore, to have energetic insights into the preferential
growth directions, the potential energy surfaces of one extra DA
acid molecule approaching the molecular array from both the pre-
polymerization direction and the orthogonal direction were
computed (Fig. 5e). For the odd chain spacer case (n = 7), the
potential energy decreased faster and reaching the minimum
earlier if the molecule is approaching from the orthogonal direction
than from the pre-polymerization direction (Fig. 5e). Growth in the
pre-polymerization also occurs (branching out from the main
growth direction). For even chain spacer case (n = 8), on the other
hand, the potential energy decreased faster and reaching its
minimum earlier if the molecule is approaching from the pre-
polymerization direction (Fig. 5f). This suggests the growth along
the trans-zigzag plane is preferred kinetically, even though the
growth in the orthogonal direction is of slightly lower potential
energy. Due to rotation of the carboxyl dimer groups, the growth
occurs with a slight deviation from linear growth to give eventually
a circle (Fig.5c).
Figure 6. (a, b) The lowest energy conformation of Ph-DA-acids in the array on
the silica surface: (a) the Ph-DA acid with the odd-carbon spacer, i.e., Ph-9-DA-
7-COOH, (c) the Ph-DA acid with even-carbon spacer, i.e., Ph-9-DA-8-COOH.
(
b, d) Potential energy curves for the model array interacting with an extra
molecule approaching either in the polymerization direction or the orthogonal
direction for the Ph-DA-acids with (b) the odd-carbon spacer and (d) the even-
carbon spacer. (e, f) Photomicrographs and corresponding AFM topographic
images of the UV irradiated films of DA-acids, i.e., Ph-9-DA-9-COOH and Ph-9-
DA-8-COOH, with a nominal thickness of 1 nm, deposited on the silica surface
by vacuum evaporation. The white arrows show the long axis direction of the
patterns.
5
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.202002227
FULL PAPER
To test the generality of the odd-even dichotomy in the film
morphology of diacetylenic acids, another series of diacetylenic
acid, linear diynoic acids with a phenyl group substituted at the
end of the chain, abbreviated as Ph-9-DA-n-COOH, with n = 8
and 9, were used to prepare thin films. From the analysis above,
we suggest that the direction of the cyclic carboxyl dimer in the
bilayer may dictate the film growth direction and the ultimate
morphology to be dendrites or rings. Here we carry out the MD
calculation to relax the system and examine the orientation of the
cyclic carboxyl dimer in this series. Again, an odd-even effect
appeared. However, this odd-even effect is the opposite to that
observed in the linear DA acid case, i.e., with odd chain spacer (n
Furthermore, the potential energy surface for an approaching
molecule from orthogonal direction or pre-polymerization direction
showed that for odd chain spacer acid, lower energy is reached
earlier from the pre-polymerizaton direction (Fig. 6b). This will
favor a ring formation. For even chain spacer case, the potential
energy surfaces are similar for both directions, with orthogonal
direction slightly favored (Fig. 6d). This would favor a two-
dimensional and thus dendrite-type growth. Indeed, the deposited
films exhibited morphology in agreement with the
analysis/expectation, as shown in Fig. 6 (e, f) and Fig. S2 in SI.
The odd chain spacer system gave a ring-type morphology and
the polymerization direction was along the periphery of the rings.
The even chain spacer system gave a dendrite-type morphology
and the polymerization direction is perpendicular to the long axis
of growing.
=
7), the carboxyl dimer ring twisted out of the trans-zigzag plane
Fig. 6a) whereas with even chain spacer (n = 8), the carboxyl
dimer rings align within the trans-zigzag plane (Fig. 6c).
(
2 2 n
Figure 7. Optical micrographs (a-e) and corresponding AFM micrograms (f-j) of the UV-irradiated films of C12H25(C≡C) (CH ) CONHPhCOOH, with n = 7-11,
vacuum-deposited on silica substrate at a nominal thickness of 1 nm, after UV-irradiation. The white arrows show the direction of long axis of the dendrites or the
periphery of the rings.
6
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.202002227
FULL PAPER
Figure 8. (a) Schematic diagram of field-effect transistor setup and the optical micrographs of the devices for dendrite- and ring-shaped patterns. (b) The output
characteristics of the device with the ring-shaped pattern of 12-DA-8-COOH. The curves for gate voltages between -30V and +20 V are overlapping with each other.
(
c) Transfer characteristics and corresponding average charge mobility of the devices with the dendrite- or ring-shaped patterns for the cases of linear DA-acids
and the amidobenzoic acid-based DA-acids (i.e., C12 25(C≡C) (CH COOH, n = 7 and 8 and C12 25(C≡C) (CH CONHPhCOOH, n = 7 and 8 respectively.
H
2
2
)
n
H
2
2 n
)
The orientation of the cyclic carboxyl dimer group seems to
dictate the interaction between neighbouring molecules in
different directions so as to influence the aggregation and thus the
final morphology. In an attempt to modulate this part of the
molecule, a very different acid group was then used, i.e., the
amidobenzoic acid group (Scheme 1). The introduction of amide
group and the benzene ring is expected to strengthen the dimeric
carboxyl through additional H-bonding and π-π stacking, as
devices of DA-acid and DA-ab-acid showed typical p-type
transistor characteristics, with a large on/off current ratio (Ion/Ioff
)
5
exceeding 10 in both cases. Besides, the average of charge
mobility is 1.2 (±0.75) × 10- cm /Vs for the DA-acid devices
2
2
whereas the DA-ab-acid devices had a larger drain current
-
7
-2
(around 10 A) and higher charge mobility, i.e., 7.9 (±4.3) × 10
2
cm /Vs. Since the stronger H-bonding interaction of DA-ab-acid
and a less strained and less curved ene-yne conjugated
backbone, thus a higher charge transport capability was achieved.
The best charge mobility obtained on the DA-ab-acid device is
more than 6 times higher than that of the DA-acid device.
illustrated by the reported crystal structure of a representative
alkyl amidobenzoic acid (Fig. S3 in SI).3
3-35
The effect of odd-even
spacer chain on the orientation of the cyclic dimer is interesting.
Thus the films of 12-DA-n-Ab-COOH (n=7-11) were deposited at
a nominal thickness of 1 nm and the morphologies are shown in
Fig. 7. Interestingly, a similar odd-even effect for the morphologies
was observed: with n = 7, 9, and 11, dendrite-type films were
obtained and the polymerization direction (reflected by the cracks)
was perpendicular to the long axis of the arms, whereas with n =
Conclusion
Although an odd-even effect has been observed in the reactivity
(
polymerizability) of diacetylenic molecules due to the stringent
8
and 10, ring-type films were observed and the polymerization
requirement of relative position of neighboring diacetylenic units
and the different packing/orientation of the odd-chain and even-
chain systems, we demonstrated here a new odd-even effect in
direction paralleled the periphery. For the ring-type films, however,
it is noted that larger rings were obtained compared to that for
linear DA-acid molecules, with a diameter of ~100 micrometer,
twice as large as the ring formed in the linear DA-acids (~50
micrometer). It is suggested the stronger H-bonding at the
carboxyl head groups results in less twist of the dimer ring plane
in the assembly and less curvature (or larger diameter) of the
rings formed.
Since the conjugated poly(ene-yne) backbones are formed in
these systems in specific directions, field-effect transistors with
these polymer chains as conduction channels were attempted.
The bottom-gate, top-contact transistors were prepared on bare
2 2 n
that linear diacetylenic acids, i.e., C12H25(C≡C) (CH ) COOH,
vacuum-deposited on clean silica surface exhibited an odd-even
effect in that the morphology of the thin films can be affected by
the chain length, so that a ring-type morphology was obtained for
acids having even carbon chain (n = 8 and 10) between the
diacetylene unit and the carboxyl head group, whereas dendrite-
type morphology was obtained for acids with odd carbon chain (n
=
7, 9, and 11) between diacetylene and the carboxyl head group.
The thermally evaporated acid molecules migrated on the surface
and nucleated into dimers and aggregated. Molecular dynamic
calculation showed that depending on the chain length (odd or
even carbon) between the diacetylene unit and the carboxyl group,
the cyclic H-bonded dimer of carboxyl head groups orients either
along the trans-zigzag plane or twisted out of the trans-zigzag
plane. This difference results in different aggregation speeds for
additional molecules along the trans-zigzag plane direction or
orthogonal to the plane. Unique ring-type or two-dimensional
SiO
2
(300 nm)/Si substrates, with Au deposited along the
backbones of the polymer patterns (either dendrites or circles) as
source and drain electrodes, as shown in Fig. 8a. The IDS-VDS
output curves of the representative system, i.e., 12-DA-8-COOH,
are shown in Fig. 8b. Fig. 8c shows the transfer characteristics of
the bilayer polymers formed by DA-acid film and DA-ab-acid film,
with odd chain spacer (n = 7) and even chain spacer (n = 8)
respectively. The dendrite-polymer devices of DA-acid and DA-
ab-acid gave a maximum current around 10-13 and 10-12 A under
dendrite-type
morphology
is
generated
consequently.
Topochemical polymerization upon UV-irradiation occurred in
both systems and results in polydiacetylene chains along the
periphery of the rings or perpendicular to the long arms of the
a
gate bias of -80 V, respectively, without field-effect
characteristics. On the other hand, the ring-polymer-based
7
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.202002227
FULL PAPER
dendrites. Introduction of a phenyl group at the end of the chain
resulted in opposite odd-even effect on morphology, in agreement
with that suggested by the molecular dynamic calculation.
Change of the simple carboxyl group to amidobenzoic acid leads
to different H-bond strength or steric requirement. Similar ring-
type or dendrite-type morphology was generated depending on
the even or odd chain length but the diameter of the rings was
twice as large. This implies a modulation of the acid group size
and their interaction with neighbouring molecules can affect their
film morphology. Field-effect transistors based on the
polydiacetylene chains in the ring-type film obtained from the
amidobenzoic acid derivative (which gave larger rings) yielded an
average mobility of 7.9 (±4.3) ×10-2 cm /Vs, which is ~6 times
higher than that of the simple carboxyl group derivative (which
gave smaller rings). This study offers some insights to the self-
assembly behaviors and film growth of diacetylenic acids at a
surface. Further systematic studies will be conducted to control
the morphology of polydiacetylene films for potential electronic
applications through modulating the size and orientation of the
carboxyl head group.
The Supporting Information is available free of charge on the website at
DOI:, including Synthetic procedures and characterization data (1H NMR
spectra, 13C NMR and Mass); Modelling the nucleation and growth of DA-
acids; AFM topographic images and corresponding line profiles of C26
,
C25COOH, and 14-DA-14 film deposited on the silica surface;
Photomicrographs, AFM topographic images and corresponding line
profiles of Ph-DA-acid films, i.e., Ph-9-DA-9-COOH and Ph-9-DA-8-COOH,
deposited on the silica sur-face; Crystal images of the alkyl amidobenzoic
acid (alkyl ab-acid).
Acknowledgements
2
Financial supports from Academia Sinica, Taiwan and Ministry of
Science and Technology, Taiwan (Grant No. 103-2120-M-009-
003-CC1) are gratefully acknowledged.
Keywords: Topochemical polymerization • self-assembly • odd-
even effect • polydiacetylenes • conjugated polymer
[
[
1]
2]
M. Hasegawa, Chem. Rev. 1983, 83, 507-518.
T. Itoh, E. Morita, R. Takakura, H. Nakajima, T. Uno, M. Kubo, N. Tohnai,
M. Miyata, Macromolecules 2016, 49, 4802-4816.
Experimental Section
[
3]
4]
K. Hema, K. M. Sureshan, Angew. Chem. Int. Ed. 2019, 58, 2754-2759.
H. Guo, J. Zhang, D. Porter, H. S. Peng, D. W. P. M. Lowik, Y. Wang, Z.
Zhang, X. Chen, Z. Shao, Chem. Sci., 2014, 5, 4189-4195.
J. J. Bang, K. K. Rupp, S. R. Russell, S. W. Choong, A. A. Claridge, J.
Am. Chem. Soc. 2016, 138, 4448-4457.
Pentacosa-10,12-diynoic acid (12-DA-8-COOH), n-hexacosane
[
(C
26), and n-cerotic acid (C25COOH) were obtained from
commercial sources. Dotriaconta-15,17-diyne (14-DA-14), and
the other diacetylenic acids, including C12 25(C≣C) (CH COOH
with n = 7, 9-11, C 22(C≣C) (CH COOH with n = 8, 9,
and C12 25(C≣C) (CH CONHPhCOOH with n = 7-11 (structures
[5]
H
)
2 n
2
2 n
)
[
[
6]
7]
K. S. Mali, N. Pearce, S. De Feyter, N. R. Champness, Chem. Soc. Rev.
6
H
5
-C11
H
2
2017, 46, 2520-2542.
H
2
2 n
)
Y. Li, L. Wang, Y. Wen, B. Ding, G. Sun, T. Ke, J. Chen, J. Yu, J. Mater.
Chem. A 2015, 3, 9722-9730.
and corresponding abbreviations shown in Scheme 1) were
1
synthesized in the laboratory and fully characterized by H NMR,
[8]
9]
T. L. Mako, J. M. Racicot, M. Levine, Chem. Rev. 2019, 119, 322-477.
N. M. Sangeetha, U. Maitra, Chem. Soc. Rev. 2005, 34, 821-836.
13
C
NMR, and Mass Spectrometry (see the Supporting
[
Information). n-Type silicon (100) wafers covered with 300 nm-
[10] X. Lu, Z. Zhang, X. Sun, P. Chen, J. Zhang, H. Guo, Z. Shao, H. Peng,
thick, thermally-grown oxide layer were used as the substrate.
Chem. Sci., 2016, 7, 5113-5117.
[
11] V. K. Rao, N. L. Teradal, R. Jelinek, ACS Appl. Mater. Interfaces 2019,
The substrate was cleaned by Piranha solution (70% H
), followed by rinsing with pure water and drying with a
stream of N . The diacetylenic films were prepared by thermally
2 4
SO /30%
11, 4470-4479.
2 2
H O
[
[
12] X. Qian, B. Stadler, Chem. Mater. 2019, 31, 1196-1222.
2
13] J. Nishide, T. Oyamada, S. Akiyama, H. Sasabe, C. Adachi, Adv. Mater.
depositing the monomers (in a vacuum of 2 × 10-6 Torr and at a
depositing rate of ~0.1 Å/s) on a substrate kept at ambient
temperature up to various nominal thicknesses. After the samples
were taken out of the vacuum chamber, they were irradiated
immediately by a UV-lamp (wavelength 254 nm, with an intensity
2006, 18, 3120-3124.
[14] B. P. Krishnan, S. Mukherjee, P. M. Aneesh, M. A. G. Namboothiry, K.
M. Sureshan, Angew. Chem. Int. Ed. 2016, 55, 2345-2349.
[15] Y. Okawa, S. K. Mandal, C. Hu, Y. Tateyama, S. Goedecker, S.
Tsukamoto, T. Hasegawa, J. K. Gimzewski, M. Aono, J. Am. Chem. Soc.
2011, 133, 8227-8233.
-
2
of 4 mW cm ) for 5 min in air. For field-effect transistor fabrication,
source and drain electrodes were deposited through a shadow
mask to achieve a top-contact, bottom-gate FET device with a
channel length of 15 μm and a channel width of 35 μm.
[
[
[
16] Y. F. Yao, H. L. Dong, F. Liu, T. P. Russell, W. P. Hu, Adv. Mater. 2017,
9, 1701251.
2
17] B. P. Krishnan, S. Raghu, S. Mukherjee, K. M. Sureshan, Chem.
Commun. 2016, 52, 14089-14092.
Atomic force microscopy analyses were carried out with a
Multimode Atomic Force Microscope (Digital Instruments,
Nanoscope III) using tapping mode with a silicon tip. The NEXAFS
data were obtained at the wide-range beamline (BL24A) of the
Taiwan Light Source of NSRRC, using the total electron yield
detection mode. Raman spectra were collected from a micro-
Raman setup (Jobin-Yvon) with an argon-ion laser at 514.5 nm.
18] J. Huo, Q. Deng, T. Fan, G. He, X. Hu, X. Hong, H. Chen, S. Luo, Z.
Wang, D. Chen, Polym. Chem. 2017, 8, 7438-7445.
[19] S. R. Diegelmann, N. Hartman, N. Markovic, J. D. Tovar, J. Am. Chem.
Soc. 2012, 134, 2028-2031.
[
20] Y. Ishijima, M. Okaniwa, Y. Oaki, H. Imai, Chem. Sci., 2017, 8, 647-653.
21] G. Shin, M. I. Khazi, U. Kundapur, B. Kim, Y. Kim, C. W. Lee, J.-M. Kim,
ACS Macro Lett. 2019, 8, 610-615.
[
[22] W. Jeong, M. I. Khazi, D. G. Lee, J.-M. Kim, Macromolecules 2018, 51,
2
The dispersed spectra were recorded by a liquid-N -cooled
10312-10322.
charge-coupled device (CCD) camera. A low laser power density
was used for the measurement to prevent local heating and
decomposition of polydiacetylenes. The electrical characteristics
[
23] O. Yarimaga, B. Yoon, D. Y. Ham, J. Lee, M. Hara, Y. –K. Choi, J. –M.
Kim, J. Mater. Chem., 2011, 21, 18605-18612.
[24] S. Lee, J. –Y. Kim, X. Chen, J. Yoon, Chem. Commun., 2016, 52, 9178-
9196.
-
of the transistor devices were measured in vacuum (about 1 × 10
4
[25] C. W. Tseng, Y. T. Tao, ACS Appl. Mater. Interfaces 2010, 2, 3231-3240.
torr) with a HP4156 parameter analyzer.
[
26] H. Tachibana, R. Kumai, N. Hosaka, Y. Tokura, Chem. Mater., 2001, 13,
55-158.
1
8
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.202002227
FULL PAPER
[
[
[
[
27] N. Fujita, Y. Sakamoto, M. Shirakawa, M. Ojima, A. Fujii, M. Ozaki, S.
Shinkai, J. Am. Chem. Soc., 2007, 129, 4134-4135.
28] H. Menzel, S. Horstmann, M.D. Mowery, M. Cai, C. E. Evans, Polymer,
2000, 41, 8113-8119.
29] A. Fujimori, M. Ishitsuka, H. Nakahara, E. Ito, M. Hara, K. Kanai, H. Ishii,
Y. Ouchi, K. Seki, J. Poly. Sci. B 2004, 42, 2329-2336.
30] Y. Narita, T. Tadokoro, T. Ikeda, T. Saiki, S. Mononobe, M. Ohtsu, Appl.
Spectrosc. 1998, 52, 1141-1144.
[
31] A. Ulman, J. E. Eilers, N. Tillman, Langmuir 1989, 5, 1147-1152.
32] G. M. J. Schmidt, et al. In Solid State Photochemistry (Eds.: D. Ginsburg),
Verlag Chemie: Weinheim, 1976.
[
[
[
33] M. J. Shin, J.-D. Kim, Langmuir 2016, 32, 882-888.
34] N. Han, H. J. Woo, S. E. Kim, S. Jung, M. J. Shin, M. Kim, J. S. Shin, J.
Appl. Polym. Sci. 2017, 134, 45011.
[
35] J. P. Lee, H. Hwang, S. Chae, J.-M. Kim, Chem. Commun. 2019, 55,
9395-9398.
9
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.202002227
FULL PAPER
Entry for the Table of Contents
Vacuum-deposited thin films of three series of diacetylenic acids exhibited distinctly different morphologies, depending on the spacer
chain length to be odd or even number of carbons (odd-even effect). The carboxyl head groups form cyclic dimers, whose orientation
relative to the trans-zigzag plane of the hydrocarbon chain appears to be different when the spacer chain length is odd or even number.
This will determine the direction of aggregation during crystal growth. Unique ring-type or two-dimensional dendrite-type morphology
was obtained if the spacer length is even or odd number carbons respectively. Modulation of the intermolecular interaction through
change of substitution or head group structure may further change the dimension of the ring patterns. This would offer opportunity to
create aligned conjugated polymer chains as conducting channels in organic electronics application.
1
0
This article is protected by copyright. All rights reserved.