Tertiary Amines Differentiated from Primary and Secondary Amines by Active Ester-Functionalized Hexabenzoperylene in Field Effect Transistors

Article abstract of DOI:10.1002/asia.201801787

Herein, we report two novel derivatives of hexabenzoperylene (HBP) that are functionalized with ester groups. Methyl acetate functionalized HBP (1) in single crystals self-assembles into a supramolecular nanosheet, which has a two-dimensional π-stack of H

Full text of DOI:10.1002/asia.201801787

CHEMISTRY
AN ASIAN JOURNAL
www.chemasianj.org
Accepted Article
Title: Tertiary Amines Differentiated from Primary and Secondary
Amines by Active Ester-Functionalized Hexabenzoperylene in
Field Effect Transistors
Authors: Changqing Li, Yujing Wang, Tiankai Zhang, Bo Zheng,
Jianbin Xu, and Qian Miao
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To be cited as: Chem. Asian J. 10.1002/asia.201801787
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COMMUNICATION
Tertiary Amines Differentiated from Primary and Secondary
Amines by Active Ester-Functionalized Hexabenzoperylene in
Field Effect Transistors
1
1
2
1
2
1
Changqing Li, Yujing Wang, Tiankai Zhang, Bo Zheng, Jianbin Xu, Qian Miao *
Abstract: Herein, we report two novel derivatives of
hexabenzoperylene (HBP) that are functionalized with ester groups.
Methyl acetate functionalized HBP (1) in single crystals self-
assembles into a supramolecular nanosheet, which has a two-
dimensional π-stack of HBP sandwiched between two layers of ester
groups. With the same self-assembly motif, active ester-
functionalized HBP (2) in field effect transistors has enabled
differentiation of tertiary amines from primary and secondary amines,
in agreement with the fact that active ester reacts with primary and
secondary amines but not with tertiary amines to form amides.
reported by us earlier, the self-assembly of functionalized HBPs
presents an unusual type of two-dimensional π-stacking,[
12 ]
which can accommodate a variety of functional groups without
sacrificing π-π interactions in the solid state. As a result,
functionalized HBPs provide a general sensing platform, which,
in a device integrating an OFET channel and a microfluidic
channel, has enabled highly sensitive and selective detection of
fluoride ions and streptavidin in water.[13] Herein, we report two
novel functionalized HBPs, 1 and 2 (Figure 1a). Methyl acetate
functionalized HBP 1 with a short linker was found to exhibit the
same two-dimensional π-stacking in the crystals as other
functionalized HBPs. This crystal structure led us to hypothesize
that p-nitrophenyl ester functionalized HBP could self-assemble
into a π-stacked nanosheet. To test this hypothesis, thin films of
The capability of detecting amines with high sensitivity and
selectivity is of key importance to environmental monitoring,
medical diagnosis, food quality control and many other
applications because amines are ubiquitous in biology,
pharmaceuticals, and industry. A variety of techniques have
been developed to detect ammonia and amines. [1] Among these
techniques, organic field effect transistors (OFETs) offer unique
advantages because OFET-based sensors not only circumvent
the need for bulky and expensive equipment by combining the
sensory electrical output with easy device fabrication, but also
promise soft and biocompatible electronics for wearable and
implantable devices. [2, 3, 4] The sensing mechanism of the OFET-
based sensors for ammonia and amines [5] includes dedoping
effect, dipole-charge interaction [6] and chemical gating effect.[7]
As a result, these OFET-based sensors generally are not able to
achieve high selectivity for different amines. One strategy to
enhance selectivity is to introduce binding sites to the surface of
organic semiconductors in OFETs. For example, a layer of
cucurbit[7]uril on the top of organic semiconductors enabled
selective detection of amphetamine-type stimulants in water. [8]
Another strategy to enhance the selectivity of OFET-based
sensors is to equip organic semiconductors with reactive groups
that can react with the analytes. [9, 10] However, this strategy was
not reported for OFET-based sensors of amines to the best of
our knowledge. Herein, we demonstrate that attachment of
active ester to organic semiconductors enables differentiation of
tertiary amines from primary and secondary amines.
2
were prepared by dip-coating and studied with different
techniques. Containing a p-nitrophenyl ester group, 2 was
designed to differentiate primary and secondary amines from
tertiary amines because p-nitrophenyl ester reacts with primary
or secondary amines (Figure 1b) but does not react with tertiary
amines to give amides. By combing an OFET channel with a
microfluidic channel, the thin films of
differentiation of primary and secondary amines from tertiary
amines as detailed below.
2 have enabled
Figure 1. a) Structures of ester functionalized HBPs 1 and 2; b) reaction of 2
The organic semiconductor used in this study is
hexabenzoperylene (HBP), which is a double [5]helicene.[11] As
with an amine yielding the corresponding amide.
Ester-functionalized HBPs 1 and 2 were synthesized by
modifying the reported synthesis of other functionalized HBPs
as shown in Scheme 1. The HBP moiety in 1 and 2 was formed
by the Scholl reaction of 5a and 5b, respectively, which were
synthesized by the Diels-Alder reaction of alkyne 3a and 3b,
respectively, with cyclopentadienone 4 [14] and the subsequent
in-situ decarbonylation. Single crystals of 1 qualified for X-ray
[
[
a]
b]
Dr. C. Li, Y. Wang, Prof. Dr. B. Zheng, Prof. Dr. Q. Miao
Department of Chemistry
The Chinese University of Hong Kong
Shatin, New Territories, Hong Kong, China
E-mail: miaoqian@cuhk.edu.hk
[13]
T. Zhang, Prof. Dr. J. Xu
Department of Electronic Engineering
The Chinese University of Hong Kong
Shatin, New Territories, Hong Kong, China
Supporting information for this article is given via a link at the end of
the document.
crystallography were grown from
a
solution of
1
in
dichloromethane and ethyl acetate by slow evaporation of
solvents. As found from the crystal structure, [15] 1 adopts a chiral
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arrangement, which is essentially the same as those of other
functionalized HBPs in crystals. [13] Since the HBP backbone of 1
can be regarded as two roughly planar benzotetracene subunits
jointed by the twisted central benzene ring, the face-to-face π-
stacking of 1 is along two directions with the same π-to-π
distance of 3.6 Å. This packing motif leads to a 1.70 nm-thick
supramolecular nanosheet, which has a two-dimensional stack
of π-faces sandwiched between two layers of ester groups as
shown in Figure 2b. In addition, the crystal of 1 contains co-
crystallized water molecules (not shown in Figure 2) between
two adjacent nanosheets.
In order to prepare electrical sensors that integrate an OFET
channel and a microfluidic channel, thin films of 2 were
fabricated by dip coating films of 2 a silicon substrate, which had
successive layers of titanium oxide, alumina and 12-
methoxylphosphonic acid (MODPA) as a composite dielectric
material. Here, MODPA formed a self-assembled monolayer
(
SAM) on alumina to provide an ordered dielectric surface
wettable by common organic solvents.[ It is worth noting that
each step in the dip coating processes in this study, including
removal of solvent residues in a vacuum, was conducted at
room temperature to avoid thermal isomerization of HBP.[ 14 ] The
dip-coated films of 2 consisted of well aligned crystalline fibers
as found from the reflection polarized light micrograph shown in
Figure 3a. In contrast, dip-coating solution of 1 onto the same
substrate resulted in isolated thick crystals that were not suitable
for fabrication of field effect transistors likely because of the
lower solubility of 1. The fabrication of transistors was completed
by vacuum-deposition of gold onto the dip-coated films of 2
through a shadow mask to form top-contact source and drain
electrodes. As measured from 16 channels of these devices in
air, the film of 2 behaved as a p-type semiconductor with field
effect hole mobility in the range of (3.4 ± 0.6)×10−2 cm /Vs.
Figure 3b shows transfer I–V curves for a representative
transistor of 2 as measured in air. The output curve of the same
transistor was displayed in Figure S4 (Supporting Information).
The supramolecular assemblies of 2 in the thin films were
studied with UV–vis absorption spectroscopy, X-ray diffraction
16]
Scheme 1 Synthesis of ester functionalized HBPs 1 and 2
2
(
XRD), and atomic force microscopy (AFM). The dip-coated film
of 2 on glass exhibited a broad absorption band in the visible
light region with the longest-wavelength maxima at 570 nm,
(1×10−5 M) exhibited the
2 2
whereas the solution of 2 in CH Cl
longest-wavelength absorption peak at 512 nm as shown in
Figure S3 (Supporting Information). The red shifted absorption
of 2 in films relative to that in solutions is 58 nm, which is similar
to those of functionalized HBPs as reported previously.[12, 13] It
can be attributed to electronic delocalization between π-stacked
molecules, suggesting strong π–π interactions between the
Figure 2. a) A nanosheet of 1 as viewed along the b axis of the crystal lattice;
b) a nanosheet of 1 as viewed along the c axis of the crystal lattice. (The P-
and M-enantiomers, except their ester groups, are shown in yellow and light
blue, respectively. Co-crystallized water molecules are removed for clarity.)
formed π-stacked nanosheets.[17, 18] XRD from the film of 2 on
x x
MOPDA/TiO /AlO /Si substrate exhibited one intense peak at 2θ
= 5.16° (d spacing of 1.71 nm) accompanied with two higher
order peaks at 2θ = 10.43° (d spacing of 0.85 nm) and 2θ =
15.78° (d spacing of 0.56 nm). These diffractions suggest that
twisted conformation having its fjord regions distorted with
torsion angles of 42.1° and 40.5°. The crystal of 1 is racemic
containing P- and M-enantiomers, which are shown in yellow
and light blue, respectively, in Figure 2a. Each P-enantiomer of
the dip-coated film of 2 have a layered nano-structure with each
layer of 1.7 nm thick. As found from AFM section analysis
(Figure 3c), the fibers of 2 in the dip-coated films were 30.5 to
41.8 nm thick and thus consisted of 18 to 24 of nanosheet layers.
Based on the above results, we conclude that molecules of 2
self-assemble into π-stacked nanosheets in the dip-coated films.
1
stacks with four adjacent M-enantiomers in a brickwork
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in order to exclude the response of the drain current toward
water. The compounds tested in this study included two primary
amines (i.e., n-hexylamine and phenethylamine), two secondary
amines (i.e., diethyl amine and piperidine), and two tertiary
amines (triethylamine and pyridine) as well as ammonia. Figure
5
a shows the transfer I-V curves of 2 as measured under
deionized water and under a solution of n-hexylamine for a
certain period of time. The drain current (VDS = −4 V and VGS
4 V) decreased by 19% after the transistor channel was
=
−
exposed to n-hexylamine for 1 minute, and decreased by 30%
after 5 minutes. Similarly, after the transistor channel was
exposed to diethylamine for 1 minute and 5 minutes, the drain
current (VDS = −4 V and VGS = −4 V) decreased by 30% and
49%, respectively, as shown in Figure 5b. In contrast, the drain
current did not decrease after exposure of the transistor channel
to triethylamine for 1 minute, while exposure to triethylamine for
5
minutes resulted in decrease of the drain current (VDS = −4 V
and VGS = −4 V) by 7% as shown in Figure 5c. Figure 5d
summarizes the responses of the OFETs of 2 toward different
amines as well as ammonia in aqueous solutions, clearly
indicating that this sensor can differentiate triethylamine and
pyridine from other amines with apparently smaller change of
Figure 3. a) Reflection polarized light micrograph for a dip-coated film of 2 on
MODPA-modified TiO
with an active channel of 150 μm long and 1 mm wide as tested in air; c)
AFM image and cross-section analysis for a dip-coated film of 2 on MODPA-
modified TiO /AlO /Si. (The film of 2 was prepared by immersing the substrate
into a solution of 2 in 1:1 (v/v) CH Cl -ethyl acetate and then pulling it up with
a constant speed of 0.15 mm min−1.)
x x
/AlO /Si; b) transfer curves for a representative OFET of
2
x
x
2
2
0
drain current (ΔI/I ). It was found that replacing the aqueous
solution of primary or secondary amines in the microfluidic
channel with deionized water did not lead to increase of the
drain current. This is in agreement with the irreversible reaction
of active ester with amines. In contrast to the device of 2, the
OFET of unfunctionalized HBP 7 [ was not able to differentiate
a tertiary amine from primary and secondary amines as shown
in Figure S9 in the Supporting Information. When the OFET
channel of 7 was exposed to n-hexylamine, diethylamine and
triethylamine for 5 minutes, the drain current decreased by 20%.
12]
13% and 16%, respectively, in a control experiment.
The observed decrease of drain current of 2 toward different
amines can be attributed to two mechanisms. First, amines that
diffuse into the active channel can quench mobile holes by
reacting with the cations of 2.[6] Second, the reaction of the
active ester with primary and secondary amines results in the
corresponding amide and thus changes the dipole and
hydrophilicity of the surface. The first mechanism is applicable to
all amines while the second mechanism is only applicable to
primary and secondary amines as well as ammonia. In
agreement with this, the contact angle of the film of 2 with water
decreased more than 10 degrees after exposure to ammonia,
hexylamine, phenethylamine, diethylamine and piperidine while
only decreased by less than 5 degrees after exposure to
triethylamine and pyridine (Figure S6 in the Supporting
Information).
Figure 4. Schematic drawing of the sensor combining a microchannel and a
transistor channel (150 μm long and 4 mm wide) of 2.
Electrical sensors were fabricated by carefully placing a
piece of polydimethylsiloxane (PDMS) with preformed
microfluidic channels onto the top-contact OFETs of 2 under a
microscope so that water in the microfluidic channel contacted
the organic semiconductor layer but did not touch the gold
electrodes. Figure 4 shows a schematic drawing of this sensor,
which is the same as that reported by us earlier except the
molecular structure of the organic semiconductor. In this device,
the transistor of 2 exhibited good stability when exposed to
deionized water for 30 minutes (Figure S5 in the Supporting
Information). To test the sensing ability of 2 toward different
amines as well as ammonia, a solution of amine or ammonia
In conclusion, methyl acetate functionalized HBP (1), similar
to other functionalized HBPs, in single crystals self-assembles
into
a π-stacked supramolecular nanosheet. Active ester
functionalized HBP (2) in dip-coated films exhibits the same self-
assembly motif as revealed by UV–vis absorption spectroscopy,
XRD and AFM. The electrical sensor integrating an OFET
(
0.2 mM) in deionized water was injected into the microchannel
channel of
2 and a microfluidic channel has enabled
using a syringe pump with a speed of 30 µL/min and the flow of
the solution was kept for 5 minutes. Before injection of the
solution of amine, the microchannel was filled with deionized
water for about 30 minutes until the drain current became stable
differentiation of tertiary amines from primary and secondary
amines in water because tertiary amines, unlike primary and
secondary amines, do not react with active ester to form amides.
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Chemistry - An Asian Journal
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COMMUNICATION
Entry for the Table of Contents
COMMUNICATION
Active ester-functionalized
Changqing Li, Yujing Wang, Tiankai
Zhang, Bo Zheng, Jianbin Xu, Qian
Miao*
hexabenzoperylene in field effect
transistors has enabled differentiation
of tertiary amines from primary and
secondary amines in water.
Page No. – Page No.
Tertiary Amines Differentiated from
Primary and Secondary Amines by
Active Ester-Functionalized
Hexabenzoperylene in Field Effect
Transistors
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