Microcontact Printing Patterning of an HOPG Surface by an Inverse Electron Demand Diels–Alder Reaction

Article abstract of DOI:10.1002/chem.201801326

The chemical modification of an sp² hybridized carbon surface in a controllable manner is very challenging but also crucial for many applications. An inverse electron demand Diels–Alder (IEDDA) reaction using microcontact printing technique is introduced to spatially control the modification of a highly ordered pyrolytic graphite (HOPG) surface under ambient conditions. The covalent modification was characterized by Raman spectroscopy, XPS, and SECM. Tetrazine derivatives can effectively react with an HOPG surface and with microcontact printing methods resulting in spatially patterned surfaces being produced with micrometer-scale resolution.

Full text of DOI:10.1002/chem.201801326

DOI: 10.1002/chem.201801326
Full Paper
&
Printing Chemistry
Microcontact Printing Patterning of an HOPG Surface by an
Inverse Electron Demand Diels–Alder Reaction
[
a]
Jun Zhu, Jonathan Hiltz, Ushula M. Tefashe, Janine Mauzeroll, and R. Bruce Lennox*
2
Abstract: The chemical modification of an sp hybridized
carbon surface in a controllable manner is very challenging
but also crucial for many applications. An inverse electron
demand Diels–Alder (IEDDA) reaction using microcontact
printing technique is introduced to spatially control the
modification of a highly ordered pyrolytic graphite (HOPG)
surface under ambient conditions. The covalent modification
was characterized by Raman spectroscopy, XPS, and SECM.
Tetrazine derivatives can effectively react with an HOPG sur-
face and with microcontact printing methods resulting in
spatially patterned surfaces being produced with microme-
ter-scale resolution.
[9]
Introduction
Diels–Alder conditions. A patterned surface is subsequently
[9]
produced by dip-pen lithography using this process. More re-
cently, Simon and co-workers demonstrated the direct visuali-
zation of the covalent cycloaddition of maleimide derivatives
on the defect-free basal graphene plane by scanning tunneling
Graphene has a number of fascinating electric, thermal, and
[
1–4]
mechanical properties.
The chemical or physical modifica-
2
tion of the highly inert sp surface of graphene provides an
entry into the controlled modulation of these properties and/
or the ability to interface graphene to materials and devices.
Covalent modification strategies provide control over the
extent of the surface reactions, site specificity of modification,
precise product formation, and robustness to subsequent
chemical modification/degradation. The most commonly used
method for the covalent modification of graphene or graphite
requires harsh reaction conditions (e.g., concentrated nitric/sul-
furic acid) or highly reactive reagents, such as those involved
in prolonged heating/photo-irradiation associated with diazo-
[10]
microscopy.
Inverse electron demand Diels–Alder reactions (IEDDA) have
been the subject of considerable interest in biorthogonal con-
[11]
jugations.
The Fox and Weissleder research groups inde-
pendently introduced the IEDDA reactions between a 1,2,4,5-
tetrazine and strained dieneophiles as a highly efficient
[12,13]
method for biomolecules.
The application of IEDDA for bi-
oorthogonal coupling has expanded quickly due to its fast re-
À1 À1
action kinetics (k =2000–22000m s ) and catalysis-free cou-
2
[14]
pling conditions. Beckmann et al. have applied the IEDDA re-
action for surface modifications on tetrazine-derivatized glass
slides, which can react with dienophile tethered functional car-
[
5,6]
nium radical chemistry.
A mild, catalysis free, and rapid co-
valent modification method for graphene is thus much sought
after.
[15]
bonhydrates using an auto-array printer.
Only a limited number of studies involving Diels–Alder reac-
tions on graphite and graphene have been reported, even
Microcontact printing is a well-established means to prepare
patterned surfaces due to the facile fabrication of the requisite
2
though these sp hybridized carbon materials can serve as
master stamps and the compatibility of the ink and stamping
[
7–10]
[16,17]
either as a dienophile or a diene.
For example, Haddon
method with many substrates.
Roling et al. applied the mi-
and co-workers showed that graphite/graphene can serve as a
diene by reacting with tetracyanoethylene (TCNE) at room
temperature. It can also serve as a dienophile, as in the reac-
crocontact printing method together with an IEDDA reaction
to introduce a tetrazine-terminated atom-transfer radical poly-
merization (ATRP) initiator onto an alkene terminated glass sur-
[
8]
[18]
tion with 2,3-dimethyl-1,3-butadiene (508C, 3 h). Wan and co-
face. Polymers containing a variety of functionalities can be
workers demonstrated that graphene can react with a sterically
introduced on to the patterned surface thereafter. However, to
the best of our knowledge, the IEDDA reaction has not been
applied to the preparation of patterned covalently modified
[7]
strained cis-diene leading to surface modifications. The
Braunschweig group showed that cyclopentadiene can cova-
lently react with a graphene surface under high pressure
2
sp hybridized carbon surfaces. We recently reported the use
of an IEDDA reaction to modify single-wall carbon nanotubes
and highly ordered pyrolytic graphite (HOPG) surfaces with tet-
[a] Dr. J. Zhu, Dr. J. Hiltz, Dr. U. M. Tefashe, Prof. J. Mauzeroll, Prof. R. B. Lennox
Department of Chemistry
McGill University
razine-derivatives and tetrazine-terminated gold nanoparticles
[19–21]
(
tetrazine-AuNP).
In these examples, the IEDDA reaction
8
01 Sherbrooke St. West, Montreal, QC H3A 2K6 (Canada)
was carried out under ambient conditions (room temperature,
atmosphere pressure) followed by a rapid retro-Diels–Alder re-
action to generate the final cycloaddition adducts. Here, we
E-mail: bruce.lennox@mcgill.ca
Supporting information and the ORCID number(s) for the author(s) of this
article can be found under https://doi.org/10.1002/chem.201801326.
Chem. Eur. J. 2018, 24, 1 – 7
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demonstrate the site-specific covalent modification of an
HOPG surface using microcontact printing delivery of IEDDA
reagents. A patterned PDMS stamp thus “inked” with tetrazine
derivatives generates a covalently modified HOPG surface
determine the spatial resolution of the microcontact printing
method as used here.
The outcome of the IEDDA reaction between HOPG and Fc-
O-Tz was assessed using Raman spectroscopy (Figure 1). Spec-
tra obtained (633 nm line of a HeNe laser, 4 mW power using a
(Scheme 1). The covalent modification of an HOPG surface was
100ꢁ microscope objective) at different areas on the unmodi-
fied surface are similar to that of the pristine HOPG; a charac-
À1
À1
teristic G band and 2D band at 1579 cm and 2680 cm , re-
spectively (Figure 1a). Spectra collected at different areas on
the modified surface are statistically consistent with there
being a uniform modification of the pattern area on the HOPG
surface (Figure 1b). The formation of the Fc-O-Tz adduct with
HOPG is readily established by comparing the Raman spectra
of (a) HOPG, (b) Raman spectra on (Fc-O-Tz-HOPG) and off
(
pristine HOPG) the modified HOPG surface, and (c) Fc-O-Tz. A
Scheme 1. Schematic of the process of microcontact printing of HOPG by
IEDDA covalent modification. (a) Microcontact print using ferrocene-tetrazine
(Fc-O-Tz). Scale bar 200 mm. (b) Synthesis of ferrocene-tetrazine (Fc-O-Tz) ink.
carried out at ambient conditions and characterized by Raman
spectroscopy and X-ray photoelectron spectroscopy (XPS). The
continuity and integrity of the conductivity of the resulting
patterned surface features were determined by scanning elec-
trochemical microscopy (SECM). The SECM technique provides
spatially resolved surface reactivity information with microme-
[
22,23]
ter level resolution.
A significant advantage of the tetra-
zine IEDDA chemistry used here is the accessible nature of the
mono- or di- derivatization of dichlorotetrazine with thiol- or
hydroxyl-containing molecules. Due to the higher strain and
greater steric hindrance of HOPG versus graphene, reactions
successfully performed on graphite/HOPG are likely to be ap-
[
24–27]
plicable to graphene as well.
Results and Discussion
The ferrocene-derivatized tetrazine (Fc-O-Tz) was synthesized
by reacting 3,6-dichlorotetrazine with ferrocenemethanol fol-
[18]
lowing a previously published procedure (Scheme 1).
The
microcontact printing stamps were prepared from a polydi-
methylsiloxane silicon elastomer (PDMS, Sylgard 184, Dow
Corning). The PDMS master stamp was prepared following the
[
28]
published standard thermal crosslinking method. Fc-O-Tz ink
À1
(
1 mgmL , in anhydrous DCM) was dropcast onto the PDMS
stamp. After evaporating the solvent for 1 min, the stamp was
applied to a fresh prepared HOPG surface (by exfoliation/peel-
À2
ing) and a force of 10 gcm applied to the stamp for 5 min.
The HOPG surface was then washed with copious amounts of
ethanol and dichloromethane until no unreacted tetrazine de-
rivatives were detected in the waste wash. As shown in
2
Scheme 1, square features with dimensions of 150ꢁ150 mm
Figure 1. Raman spectra of Fc-O-Tz on a microcontact-modified HOPG sur-
face. (a) Unmodified HOPG surface; (b) overlay of the Raman spectra on and
off the modified HOPG surface; (c) Fc-O-Tz;(d) Raman spectra were collected
at 3 mm intervals along the scan direction of a 10 mm wide stripe-pattern.
The sharp increase and drop of the Raman intensity along the scan direction
indicates a pattern resolution in micrometer dimension. The characteristic G
band, 2D band of HOPG, and D bands due to the IEDDA adducts are high-
lighted.
are formed on HOPG as revealed by optical microscopy imag-
ing. Control experiments using ferrocenemethanol, which is
not expected bind to HOPG, were also carried out using the
same printing and washing conditions. No residual ferrocene-
methanol was detected on the HOPG surface after washing.
Linear Raman spectroscopy measurements were performed to
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À1
D band observed at 1340 cm is attributed to the breathing
high-resolution XPS spectra of the non-modified HOPG. The
Diels–Alder adduct on the HOPG surface (Figure 2b) leads to a
new peak at 400.8 eV and is assigned to N1s. The doublet cen-
2
vibration mode of the sp carbon ring which becomes Raman-
active when the nearby lattice symmetry changes, as in the
2
3
conversion of sp carbon to sp carbon. As expected, the
Diels–Alder reaction of tetrazine derivatives with the HOPG sur-
3
face introduces sp carbons, leading to an increase of the D
À1
band intensity. Because the D band (at 1340 cm ) and G band
À1
(
at 1580 cm ) merge with the tetrazine adduct ring mode at
À1
1
385 and 1522 cm respectively, it was not possible to accu-
rately determine the ID/IG ratio. However, introducing the
Raman active cyclopentadiene groups (CP) from ferrocene im-
proves the ability to monitor the formation of the Diels–Alder
adducts. The large multiplets (associated with the cylclopenta-
À1
diene ring) observed between 550–600 cm are attributed to
the cyclopentadiene ring tilting and deformation modes. The
detailed Raman assignments are summarized in Table 1.
Table 1. Assignment of Raman bands of Fc-O-Tz on HOPG.
Raman Shift
Vibration Mode
À1
[cm
]
1
1
2
4
5
6
8
1
1
1
1
340
580
685
85
54–594
35
00
010
075
300
HOPG D band
HOPG G band
HOPG 2D band
CP ring tilting
CP ring tilting, deformation
ring deformation (tetrazine adduct)
CÀCl stretch
CP out of plane CH vibration
CP ring stretch
CÀOÀC=asymmetric stretch
ring stretching (tetrazine adduct)
385, 1522
To determine the spatial resolution of the microcontact
printing/ink method used in this study, a striped surface pat-
tern (10 mm wide stripe features) on HOPG was generated fol-
lowing the microcontact printing and cleaning procedures de-
À1
scribed above. Raman spectra (500–700 cm ) with the charac-
teristic Raman active cyclopentadiene ring mode and the tetra-
zine adduct ring deformation mode were collected by moving
the laser spot linearly in 3 mm intervals (Figure 1d). The sharp
increase (from position 3 mm to 6 mm) and decrease (from posi-
tion 12 mm to 15 mm) of the adduct intensities indicates that
the IEDDA reaction occurs solely on the areas defined by the
microcontact printing stamp. It is noteworthy that the well-de-
fined change (>60% over 3 mm, Figure S3) in the Raman in-
tensity is indicative of the high fidelity of the transfer IEDDA-
based reagents onto the HOPG surface. This suggests that
these tetrazine derivatives may be amenable to inkjet printing
[
29]
methods.
The unmodified HOPG and Fc-O-Tz modified surfaces were
further characterized by XPS. XPS can be used to confirm the
presence of elements introduced to the HOPG through the
Diels–Alder and retro-Diels–Alder reactions. The survey scan
spectra collected at different areas of the modified and non-
modified surface are clearly different. Representative spectra
are shown in Figure 2. No other elements are detected in the
Figure 2. XPS survey spectrum and high-resolution spectra of Fc-O-Tz-pat-
terned functionalized HOPG. The high-resolution spectra for each element
on (modified) and off (not modified) the pattern was collected for compari-
son purposes. No Fe, N, or Cl were detected on the unmodified regions. The
new elements on the modified area are associated with the IEDDA adducts.
(
a) Survey scan of a clean HOPG surface; (b) survey scan of a modified HOPG
surface; (c) Fe2p; (d) C1s; (e) N1s, and (f) Cl 2p1/2 and Cl 2p3/2. The C1s
2
peak originating from the sp carbon of unmodified HOPG arises at 285.0 eV.
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tered at about 202 eV is assigned to Cl2p /Cl2p (202.3 eV/
1/2
3/2
Conclusions
2
7
00.6 eV). The characteristic peaks of Fe2p3/2/Fe2p1/2 (708.3 eV/
21.1 eV) were also detected. The ratio of Fe:Cl:N is 1.0:1.0:2.1
The combination of an IEDDA reaction and microcontact print-
ing yields a relatively simple, highly efficient covalent modifica-
(after correction for sensitivity factors), consistent with the ele-
2
mental ratio (1:1:2) expected for the Diels–Alder adduct. A con-
trol experiment was carried out in which the corresponding
ferrocenemethanol was applied to an HOPG surface, under the
same stamping and purification conditions. The resulting XPS
spectra were similar to the pristine HOPG and no new peaks
are observed. This is consistent with the tetrazine-derivative
compounds being covalently bonded to the HOPG surface
rather than that associated by physical adsorption.
tion methodology to generate a patterned-modified sp hy-
bridized carbon surface. This modification can be carried out
on HOPG surfaces under very mild conditions, for example,
room temperature, atmosphere pressure, and catalyst-free. The
resulting surface-associated Diels–Alder adducts are character-
ized by Raman spectroscopy, XPS, and SECM. The IEDDA reac-
2
tion of tetrazine derivatives with an sp hybrid carbon surface
is thus shown to be an effective tool for the covalent modifica-
tion of 2D carbon nanomaterials and promising for the prepa-
ration of carbon-based nano-devices.
Surface modification is an effective way to tune the electron-
[
6,7]
ic properties of an HOPG surface.
After the IEDDA reaction
of tetrazine with HOPG, its surface conductivity can be evaluat-
[16,30]
ed using scanning electrochemical microscopy (SECM).
SECM images were thus obtained with the microelectrode Experimental Section
positioned over the modified HOPG surface in a 1.0 mm ferro-
Commercial solvents and reagents: HOPG (SPT-II) was purchased
cenemethanol/0.1m KCl solution; the microelectrode was
from SPI Supplies (USA) and fresh HOPG surfaces were generated
by tape peeling. The compounds guanidine hydrochloride, hydra-
zine monohydride, 2,4-pentanedione, sodium nitrite, trichloroiso-
cyanuric acid, 2,4,6-collidine, and ferrocenemethanol were pur-
chased from Aldrich and used as received. Potassium carbonate
poised at E =0.35 V versus Ag/AgCl. The Faradaic current re-
T
sulting from the oxidization of ferrocenemethanol depends on
[
31,32]
the electrochemical activity of the substrate.
SECM probe approaches an inert surface, a smaller current
negative feedback response), relative to that collected over a
When the
(Caledon), chloroform-d6 (Cambridge Isotope Laboratories) were
(
also used as received. Dichlorotetrazine was synthesized following
conductive surface is observed. The resulting shear-force con-
trolled SECM linear line scan of the patterned HOPG surface
[19]
reference 19. All solvents were purchased from Aldrich and were
used as received.
(Figure 3a) reports that the regions of the surface which have
1
13
General instrumentation: H NMR spectra and C NMR spectra
were recorded using a Varian Mercury 400 (400 MHz) in deuterated
chloroform solution and are reported in parts per million (ppm),
with the residual protonated solvent resonance used as a refer-
ence. HR-MS (ESI, APCI) analyses were recorded in the McGill Uni-
versity, Department of Chemistry Mass Spectrometer Facility. X-ray
photoelectron spectroscopy was collected using a ThermoFisher
Scientific K-alpha instrument employing a monochromatic AlKa X-
ray source (1486.6 eV) and a hemispherical electrostatic analyzer.
Raman scattering data were acquired from dried films using a JY
LabRamHR confocal Raman microscope (633 nm laser, 4 mW
power). The SECM experiments were carried out using a HEKA
scanning electrochemical microscope ELPro scan 1 integrated with
shear force unit (HEKA Electronik, Germany). The cell was made
from Teflon with a small opening in the middle into which the
HOPG sample was tightly fitted. A 25 mm diameter platinum micro-
electrode (ME) was utilized as the working electrode, a chloridized
silver wire as a quasi-reference electrode (Ag/AgCl QRE) and a
been covalently modified exhibit low SECM currents, whereas
the pristine HOPG surface remains highly conductive in SECM
feedback mode. The variation of the linear scan current with
distance is consistent with a modified surface, the feature sizes
of which are about 150 mm. The SECM map (Figure 3b) deter-
mines that the modified area is a square with dimensions of
150ꢁ150 mm, as per both the feature dimensions of the micro-
contact master stamp and the optical image thereof. The cova-
lently modified surface exhibits very good stability over the
course of the SECM experiment and the SECM images collect-
ed after a long immersion time (2 h) of the patterned surface.
The delivery of IEDDA reagents to an HOPG surface using mi-
crocontact printing methods thus produces a spatially differen-
tiated derivatized surface.
0
.5 mm diameter platinum wire as a counter electrode (Goodfellow
Cambridge Limited, Huntingdon, England). MEs were fabricated in-
house by sealing Pt wires (Delta Scientific Laboratory Products
Ltd., Canada) into borosilicate glass capillaries with outer diameter
of 1.5 mm, inner diameter of 0.7 mm (Sutter Instrument, USA) and
sharpening the probe end to a ratio RG=rglass/r ꢀ10, in which r
T
glass
is the radius of the insulating sheath and r is the radius of the
T
active ME.
Figure 3. SECM characterization of the microcontact printed HOPG surface.
Synthesis of Fc-O-Tz
(
(
a) line scan; (b) SECM image after 2 h immersion. The working electrode
WE) was biased at E =0.35 V vs. Ag/AgCl. An overall scan time of 15 min
T
Dichloroteterazine (30.0 mg, 0.16 mmol), ferrocene-methanol
was required to acquire the SECM map. The line scan and image measure-
ments were acquired at shear-force controlled constant distance mode
SECM. The amplitude-controlled shear-force scan parameters were: stimula-
tion amplitude=120 mV, stimulation frequency=317 kHz, scan
(
(
29.0 mg, 0.13 mmol), and 17.2 mL of anhydrous 2,4,6-collidine
0.13 mmol) were dissolved in 10 mL of anhydrous CH Cl under Ar.
2
2
The solution turned from orange to dark red in 5 min. The reaction
continued for 35 min and the solvent was removed by rotary evap-
À1
speed=0.2 mms , and piezo step size=3 nm.
&
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oration. Fe-O-Tz was then purified by flash chromatography and
gave 42.4 mg of Fc-O-Tz as a dark red crystalline solid (93% yield).
Acknowledgements
1
H NMR (CDCl3, 400 MHz): d=4.75 (t, J=4.7 Hz, 2H), 4.70 (bs, 2H),
This work was supported by grants from NSERC (R.B.L.) and
FQRNT (R.B.L.). The authors thank Dr. Mohamed A. Mezour for
his assistance with the XPS analysis.
13
4
.27 (t, J=4.7 Hz, 2H), 4.27 ppm (bs, 5H); C NMR (CDCl 60 MHz):
3,
d=175.21, 163.66, 80.94, 74.27 (2C), 73.11, 70.26 (5C), 70.05 ppm
+
(
2C); HR-MS (APCI), exact mass ([M+H] , C H ClFeN O) calc.
13 12 4
3
31.0049; found: 331.0057.
Conflict of interest
The inverse electron demand Diels–Alder reaction between
Fc-O-Tz with HOPG
The authors declare no conflict of interest.
Fc-O-Tz and ferrocenemethnol solutions were prepared by dissolv-
ing 1 mg of Fc-O-Tz or ferrocenemethanol in 1 mL anhydrous
CH Cl . A fresh HOPG surface was generated by tape peeling im-
mediately before use. 50 mL of the Fc-O-Tz solution was applied to
the PDMS stamp surface. The tetrazine ink was allowed to dry for
Keywords: inverse electron demand · Diels–Alder reaction ·
microcontact printing · highly ordered pyrolytic graphite ·
tetrazine
2
2
1
min. The PDMS stamp was applied to the HOPG surface with a
À2
force of 10 gcm for 5 min. The HOPG surface was then rinsed
with copious quantities of EtOH and CH Cl to remove the unreact-
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1
laser power at the sample to approximately 4 mW. Spectra were
À1
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XPS spectra were referenced to the C1s binding energy (B.E.)
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p3/2/2p1/2 peak ratio of 2.0 and a peak separation of 1.6Æ0.1 eV.
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1
Electrochemical cleaning of microelectrode (ME) was performed in
[
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Manuscript received: March 16, 2018
Version of record online: && &&, 0000
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ÝÝ These are not the final page numbers!

Full Paper
FULL PAPER
Printing on small scale: An inverse
electron demand Diels–Alder reaction
combined with the microcontact print-
ing technique introduces, under ambi-
ent conditions, a spatially resolved
chemical patterning to highly ordered
pyrolytic graphite (HOPG) surfaces.
&
Printing Chemistry
J. Zhu, J. Hiltz, U. M. Tefashe, J. Mauzeroll,
R. B. Lennox*
&
& – &&
Microcontact Printing Patterning of an
HOPG Surface by an Inverse Electron
Demand Diels–Alder Reaction
Chem. Eur. J. 2018, 24, 1 – 7
www.chemeurj.org
7
ꢀ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ