Thiol-yne click reactions on alkynyl-dopamine-modified reduced graphene oxide

Article abstract of DOI:10.1002/chem.201300225

The large-scale preparation of graphene is of great importance due to its potential applications in various fields. We report herein a simple method for the simultaneous exfoliation and reduction of graphene oxide (GO) to reduced GO (rGO) by using alkynyl-terminated dopamine as the reducing agent. The reaction was performed under mild conditions to yield rGO functionalized with the dopamine derivative. The chemical reactivity of the alkynyl function was demonstrated by post-functionalization with two thiolated precursors, namely 6-(ferrocenyl)hexanethiol and 1H,1H,2H,2H-perfluorodecanethiol. X-ray photoelectron spectroscopy, UV/Vis spectrophotometry, Raman spectroscopy, conductivity measurements, and cyclic voltammetry were used to characterize the resulting surfaces. Modified graphene oxide: A simple method has been developed for the simultaneous exfoliation and reduction of graphene oxide (GO) to reduced GO (rGO) by using alkynyl-terminated dopamine as the reducing agent. The reaction was performed under mild conditions to yield rGO functionalized with the dopamine derivative (see figure). The chemical reactivity of the alkynyl function was demonstrated and the surfaces of the rGO characterized by a variety of techniques. Copyright

Full text of DOI:10.1002/chem.201300225

FULL PAPER
DOI: 10.1002/chem.201300225
Thiol–Yne Click Reactions on Alkynyl–Dopamine-Modified Reduced
Graphene Oxide
Izabela Kaminska,[a, b] Wang Qi,[a, c] Alexandre Barras,[a] Janusz Sobczak,[b]
Joanna Niedziolka-Jonsson,[b] Patrice Woisel,[d] Joel Lyskawa,[d] William Laure,[d]
Marcin Opallo,[b] Musen Li,[c] Rabah Boukherroub,*[a] and Sabine Szunerits*[a]
Abstract: The large-scale preparation
of graphene is of great importance due
to its potential applications in various
formed under mild conditions to yield
rGO functionalized with the dopamine
derivative. The chemical reactivity of
the alkynyl function was demonstrated
by post-functionalization with two thio-
lated precursors, namely 6-(ferrocenyl)-
hexanethiol and 1H,1H,2H,2H-per-
fluorodecanethiol. X-ray photoelectron
spectroscopy, UV/Vis spectrophotome-
try, Raman spectroscopy, conductivity
measurements, and cyclic voltammetry
were used to characterize the resulting
surfaces.
fields. We report herein
a simple
method for the simultaneous exfolia-
tion and reduction of graphene oxide
(GO) to reduced GO (rGO) by using
alkynyl-terminated dopamine as the re-
ducing agent. The reaction was per-
Keywords: alkynes · carbon · click
chemistry · reduction · thiols
Introduction
oxygen functionalities from the GO and re-establishing to a
certain extent the sp2 network. The product is thus referred
to as chemically converted graphene or reduced graphene
oxide (rGO). In addition to the restoration of the sp2 char-
acter of GO, considerable efforts are currently being direct-
ed towards the chemical modification of GO and rGO nano-
sheets, aiming at a better processability of graphene and
fine-tuning of its electronic, optical, and electrochemical
properties.[5,6] We[7–9] and others[10] have recently shown that
the direct reaction of GO with dopamine or tetrathiafulva-
lene (TTF) allows not only the reduction of GO to rGO in
an easy and environmentally friendly manner, but also re-
sults in the simultaneous modification of the rGO nano-
sheets with the dopamine or tetrathiafulvalene through p–p
stacking interactions. The interest in rGO functionalization
with dopamine derivatives has arisen from the ease with
which functional groups can be introduced through its
amine groups. For example, we have shown that rGO modi-
fied with dopamine bearing azide groups allows the post-
functionalization with ethynylferrocene by a CuI-catalyzed
1,3-dipolar cycloaddition reaction.
The photochemical “click” reaction between alkynes or
alkenes and thiolated molecules has attracted increasing in-
terest in recent years because of its versatility and specifici-
ty.[11–15] It is believed that this reaction can overcome obsta-
cles relating to the high-density deposition of ligands, the
processing of large and bulky head-groups, and the direct
placement of ligands possessing multiple reactive functional-
ities. These reactions have “click” chemistry characteristics
such as high yield, regiospecificity, mild reaction conditions,
and tolerance to a variety of functional groups.[13,16,17] How-
ever, in contrast to CuI “click” chemistry,[16] no catalyst is re-
quired as the reaction is initiated thermally or photochemi-
cally. The main difference between the thiol–ene and thiol–
Graphene has attracted significant research interest as a
result of its remarkable electrical, thermal, and mechanical
properties, which are a consequence of its two-dimensional
hexagonal carbon lattice structure.[1] The top-down prepara-
tion of graphene by using graphite as a starting material is
currently considered one of the most cost-effective methods
for the synthesis of this two-dimensional sp2-bonded carbon
material.[2] In the first step, exfoliated graphene oxide (GO)
is obtained from graphite by the use of strong acids and ul-
trasonication. The graphitic nature of the resulting GO
nanosheets is, however, highly compromised by the presence
of a large number of surface oxygen functionalities, which
lead to a loss of conductivity. Reductive treatment by chemi-
cal[3] or thermal[4] methods resulted in the partial recovery
of the graphitic character by removing the majority of
[a] I. Kaminska, W. Qi, A. Barras, R. Boukherroub, S. Szunerits
Institut de Recherche Interdisciplinaire (IRI), CNRS USR 3078
Universitꢀ Lille 1, Parc de la Haute Borne, 50 avenue de Halley
BP 70478, 59658 Villeneuve dꢁAscq (France)
E-mail: rabah.boukherroub@iri.univ-lille1.fr
sabine.szunerits@iri.univ-lille1.fr
[b] I. Kaminska, J. Sobczak, J. Niedziolka-Jonsson, M. Opallo
Institute of Physical Chemistry, Polish Academy of Sciences
Kasprzaka 44/52, 01-224 Warszawa (Poland)
[c] W. Qi, M. Li
Key Laboratory for Liquid-Solid Structural Evolution
and Processing of Materials, (Ministry of Education)
Shandong University, Jinan 250061 (P.R. China)
[d] P. Woisel, J. Lyskawa, W. Laure
Universitꢀ Lille 1, Universitꢀ Lille Nord de France Unitꢀ
des Matꢀriaux et Transformations (UMET, UMR 8207)
Equipe Ingꢀnierie des Systꢂmes Polymꢂres (ISP) et ENSCL
59655 Villeneuve dꢁAscq (France)
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and heated at 708C to ensure solvent evaporation. rGO/alkynyl–dopa-
mine-modified ITO surfaces were immersed in a solution of 6-ferrocenyl-
hexanethiol (10 mm) or 1H,1H,2H,2H-perfluorodecanethiol (10 mm) or a
mixture (5 mm each) in absolute ethanol under nitrogen. The interface
was exposed to UV light irradiation at l=365 nm (P=100% or
100 mWcmÀ2) for 30 min at room temperature. The resulting surface was
thoroughly washed with ethanol then with water and dried under nitro-
gen stream.
yne reactions is the possibility of anchoring two thiol mole-
cules on to the alkyne to form a double addition product by
a radical process.[11,18,19]
In this article we demonstrate that a rGO/alkynyl–dopa-
mine nanocomposite material can be prepared by the simple
reaction of GO with alkynyl–dopamine under sonication for
two hours at room temperature. The interaction between
the alkynyl–dopamine and rGO takes advantage of strong
p–p interactions between the graphene sheets and the aro-
matic ring of dopamine, as shown previously.[8,10] We also de-
velop the concept of the reaction between a thiol and the
alkyne on the rGO nanocomposite. In a proof of concept
X-ray photoelectron spectroscopy (XPS): XPS experiments were per-
formed with
a PHl 5000 VersaProbe Scanning ESCA Microprobe
(ULVAC-PHI, Japan/USA) instrument at a base pressure below 5ꢄ
10À9 mbar. Monochromatic AlKa radiation was used and the X-ray beam,
focused to a diameter of 100 mm, was scanned over a 250ꢄ250 mm surface
at an operating power of 25 W (15 kV). Photoelectron survey spectra
were acquired by using a hemispherical analyzer with a pass energy of
117.4 eV and an energy step of 0.4 eV. Core-level spectra were acquired
with a pass energy of 23.5 eV and an energy step of 0.1 eV. All spectra
were acquired with 908 between the X-ray source and analyzer, and with
the use of low-energy electrons and low-energy argon ions for charge
neutralization. After subtraction of the Shirley-type background, the
core-level spectra were deconvoluted into their components with mixed
Gaussian–Lorentzian (30:70) shape lines by using the CasaXPS software.
Quantification calculations were conducted by using sensitivity factors
supplied by PHI.
experiment,
6-ferrocenylhexanethiol
(HS-Fc)
or
1H,1H,2H,2H-perfluorodecanethiol (HS-PF) was photo-
chemically “clicked” onto the rGO/alkynyl–dopamine deriv-
ative.
Experimental Section
Cyclic voltammetry (CV): CV experiments were performed by using an
Autolab 20 potentiostat (Eco Chimie, Utrecht, The Netherlands). The
electrochemical cell consisted of a working electrode (ITO or modified
ITO), Ag/AgCl (Bioanalytical Systems, Inc.) as the reference electrode,
and platinum wire as the counter electrode. Cyclic voltammetry measure-
Materials: Graphite powder (<20 m), 6-ferrocenylhexanethiol (HS-Fc),
1H,1H,2H,2H-perfluorodecanethiol (HS-PF), tetrahydrofuran (THF),
ethanol, phosphate buffered saline (PBS), and tin-doped indium oxide
coated glass (ITO; sheet resistivity 15–25 Wcm2) were purchased from
Aldrich and used as received. NMR spectra were recorded at 258C, with
a Bruker Avance 300 spectrometer.
ments were performed in 0.1m PBS at a scan rate of 0.05 VsÀ1
.
rGO/alkynyl–dopamine-modified ITO electrodes were prepared by cast-
ing a solution of rGO/alkynyl–dopamine in THF (50 mL) onto the ITO
substrate followed by heating at 708C until complete evaporation of
THF.
Synthesis of prop-2-ynyl 5-(3,4-dihydroxyphenethylamino)-5-oxopenta-
noate (alkynyl-terminated dopamine): Dopamine hydrochloride (1.453 g,
9.49 mmol) was dissolved in MeOH (50 mL). Triethylamine (0.959 g,
9.49 mmol) and 2,5-dioxopyrrolidinyl prop-2-ynyl glutarate (2.31 g,
8.63 mmol, formed from 5-oxo-5-(prop-2-ynyloxy)pentanoic acid by reac-
tion with N-hydroxysuccinimide) dissolved in MeOH (20 mL) were
added slowly. The solution was stirred overnight at room temperature
under N2. Then the solvent was evaporated and the product dissolved in
CH2Cl2 (100 mL). The organic layer was washed with HCl (0.5m, 50 mL)
and water (2ꢄ50 mL), and dried over Na2SO4. After filtration, the sol-
vent was removed under reduced pressure and the crude product was pu-
rified by column chromatography (SiO2/CH2Cl2:MeOH, 10:1) to afford
the alkynyl-terminated dopamine in a yield of 80% as a white solid.
1H NMR (300 MHz, [D6]DMSO): d=1.73 (quint, J=7.09 Hz, 2H), 2.08
(t, J=7.45 Hz, 4H), 2.32 (t, J=7.45 Hz, 2H), 3.15 (q, J=7.45 Hz, 2H),
3.55 (t, J=2.49 Hz, 1H), 4.68 (d, J=2.49 Hz, 2H), 6.42 (dd, J=7.97 Hz,
1H), 6.56 (d, J=2.05 Hz, 1H), 6.62 (d, J=7.97 Hz, 1H), 7.86 (t, J=
5.48 Hz, 1H), 8.66 (brs, 1H), 8.76 ppm (brs, 1H); 13C NMR (75 MHz,
CDCl3): d=171.9, 171.14 (C=O), 145.0, 143.4, 130.2, 119.1, 115.9, 115.4
UV/Vis spectrophotometry: Absorption spectra were recorded by using a
Perkin–Elmer Lambda UV/Vis 950 spectrophotometer in plastic cuvettes
with an optical path of 10 mm. The wavelength range was 400–800 nm.
Raman spectroscopy: Micro-Raman spectroscopy measurements were
performed on a Horiba Jobin Yvon LabRam HR Micro-Raman system
combined with a 473 nm laser diode as excitation source. Visible light
was focused by a 100ꢄ objective. The scattered light was collected by the
same objective in backscattering configuration dispersed by a 1800 mm
focal length monochromator and detected by CCD.
Conductivity measurements: Electrical conductivity was determined by
the Hall effect using a HL 5500 PC system in a standard four-probe
setup. The graphene sample was prepared by filtration of the dispersion
through a PVDF membrane filter and then deposited in a p-doped silica
wafer.
ꢀ
À
À
À
(C=C), 78.5, 77.6 (C C), 51.5 (C O), 34.7, 34.1, 32.5 (C N and C C=O),
À
20.5 ppm (C C).
Preparation of graphene oxide (GO): Graphene oxide (GO) was synthe-
sized from graphite powder by a modification of Hummerꢁs method.[20]
The synthesized GO (5 mg) was dispersed in water (1 mL) and exfoliated
by ultrasonication for 3 h. This aqueous suspension of GO was used as a
stock suspension in subsequent experiments.
Results and Discussion
Formation of the rGO/alkynyl–dopamine nanocomposite
material: Our interest in the fabrication of rGO/alkynyl–
dopamine nanohybrid materials is motivated by the fact that
alkynyl functional groups can be further employed for the
covalent linking of thiolated molecules in a thiol–yne reac-
tion mechanism. We have recently shown that azide-termi-
nated dopamine can be used in a one-step reaction for the
reduction of graphene and the simultaneous incorporation
of azide moieties onto the graphene skeleton. The chemical
reactivity of the azide function was demonstrated by post-
functionalization with ethynylferrocene by the CuI-catalyzed
1,3-dipolar cycloaddition reaction. Although less investigat-
Preparation of graphene/alkynyl-terminated dopamine (rGO/alkynyl–
dopamine): The stock GO suspension (5 mgmLÀ1) was diluted in water
to obtain a 0.5 mgmLÀ1 solution (1:10). Alkynyl-terminated dopamine
(1 mL, 10 mm) was added to the GO solution (1 mL) and the mixture
was treated with ultrasound for 2 h at room temperature. The resulting
black precipitate was separated from the aqueous supernatant by centri-
fugation at 14000 rpm for 20 min. After washing with water (three
times), the resulting precipitate was dried in an oven (808C) and then
dispersed in water by ultrasonication for 30 min.
Thiol–yne reaction on rGO/alkynyl–dopamine: rGO/alkynyl–dopamine-
modified ITO electrodes were prepared by casting a solution of rGO/al-
kynyl–dopamine in THF (50 mL) onto previously cleaned ITO substrate
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Click Reactions on Modified Graphene Oxide
FULL PAPER
Figure 1. Top: Schematic illustration of the formation of rGO/alkynyl–dopamine nanosheets. Bottom: Reaction of the alkynyl–dopamine with thiols by
the thiol–yne radical-addition mechanism.
ed than the thiol–ene reaction, thiol–yne chemistry has the
advantage that the alkynyl group can react with two thiol
molecules to form a double addition product.[21] Alkynyl-ter-
minated dopamine was thus investigated for its ability to
reduce GO and at the same time be incorporated into the
graphene sheet. As was the case with azide-terminated dop-
amine, the rGO/alkynyl–dopamine nanocomposite material
was readily formed by the addition of alkynyl–dopamine to
GO under sonication at room temperature at neutral pH
(Figure 1, top). The precipitate formed was poorly dispersed
in polar solvents such as water, methanol, and ethanol, but
forms stable suspensions in solvents such as DMF, DMSO,
and THF with rGO/alkynyl–dopamine concentrations of up
to around 0.5 mgmLÀ1. The interactions between the alkyn-
yl-terminated dopamine and graphene are most likely domi-
nated by p-stacking between the hexagonal cells of the gra-
phene and the aromatic ring of dopamine. However, be-
cause the alkynyl-terminated dopamine acts as reducing
agent, the graphene oxide is likely to oxidize the ortho-
quinol structure of the dopamine ligand to radical or qui-
none intermediates, which are likely to covalently bind to
graphene or to each other.
convoluted into four components with binding energies of
around 283.8, 284.7, 286.7, and 287.9 eV assigned to sp2-hy-
À
À
À
bridized carbon atoms, C H/C C, C O, and C=O species,
respectively. The C/O ratio of GO is 1.73, comparable to
values reported in the literature.[22,23] After reaction of GO
with alkynyl-terminated dopamine, XPS analysis of the re-
sulting product indicated significant changes in the C1s
core-level spectrum (Figure 2; top, curves b). The band at
283.8 eV arising from sp2-hybridized carbon atoms became
predominant, which suggests the reconstitution of the graph-
itic network. The bands at 285.2, 286.7, 287.9, and 289.2 can
À
À
À
À
be attributed to C H/C C, C O, C=O, and N C=O/OC=O
species of the dopamine derivative and of some remaining
oxygen functionalities on the rGO. The C/O ratio increased
to 3.6, comparable to the C/O ratio of 3.4 obtained for GO
reduced with azide-functionalized dopamine.[8] The success
of the incorporation of the dopamine derivative was also
confirmed by the presence of 2.4 at.% nitrogen (Table 1).
The formation of rGO was also validated by UV/Vis spec-
trophotometry. The UV/Vis absorption spectra of GO and
rGO/alkynyl–dopamine in THF are presented in Figure 2
(middle). GO dispersed in water exhibits a maximum ab-
sorption at 228 nm, attributed to the p–p* transition in the
X-ray photoelectron spectroscopy (XPS) analysis was per-
formed on GO before and after
its reaction with alkynyl-termi-
nated dopamine to gain further
Table 1. Atomic percentages of rGO/alkynyl–dopamine before and after reaction with thiolated ferrocene.
À
À
information on its chemical Interface investigated
composition. The C1s core-level
C 1s
[at.%]
O 1s
[at.%]
N 1s
[at.%]
Fe 2p
[at.%]
S 2p (C S)
[at.%]
S2 p (S O)
[at.%]
G
G
E
G
G
ACHTUNGTRENNUG
rGO/alkynyl–dopamine
+10 mm HS-Fc
+10 mm HS-Fc upon photoirradiation
74.30
73.18
72.50
23.30
23.60
22.20
2.40
2.20
2.10
0.00
0.50
1.60
0.00
0.37
1.10
0.00
0.15
0.50
XPS spectrum of GO nano-
sheets is displayed in Figure 2
(top, curves a) and can be de-
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R. Boukherroub, S. Szunerits et al.
Raman scattering is a useful tool for characterizing the
structural properties of graphene-based materials. Figure 2
(bottom) shows the Raman spectra for GO and rGO/alky-
AHCTUNGTREGnNNNU yl–dopamine; the main features of the graphene-based ma-
terials are a D band at 1351 cmÀ1, a G band at 1570 cmÀ1,
and a 2D band at around 2700 cmÀ1.[24] The ratios of the in-
tensities of the D and G bands (ID/IG) are 0.71 for GO and
0.67 for rGO/alkynyl–dopamine, comparable to the ID/IG
value of 0.63 for hydrazine-reduced graphene oxide.[25]
In addition, the room-temperature conductivity of rGO/
alkynyl–dopamine was measured by a standard four-probe
method. The nanocomposite showed a conductivity of
0.89 SmÀ1, which is lower than that measured for hydrazine-
reduced graphene (145 SmÀ1) by using the same technique.
However, the value is comparable to that reported recently
with azido-terminated tetrathiafulvalene.[7]
The amount of alkynyl–dopamine incorporated into the
rGO matrix was estimated on the basis of cyclic voltamme-
try (CV) experiments. The rGO/alkynyl–dopamine compo-
site material was drop-cast onto bare ITO. The drop-casting
process is very reproducible and leads to homogeneous
rGO/alkynyl–dopamine films of around 280 nm, comparable
to rGO/azide-dopamine films (Figure 3, top).[8] Figure 3
(bottom) shows the electrochemical signature of the rGO/al-
kynyl–dopamine-modified ITO interface. A redox wave
with E1ox =0.19 V versus Ag/AgCl is observed, characteristic
of dopamine oxidation in a two-electron process. The load-
ing of alkynyl–dopamine on to the rGO surface was calcu-
Figure 2. Top: C 1s core-level XPS spectra of GO a) before and b) after
reaction with alkynyl–dopamine. Middle: UV/Vis spectra of a) GO in
water and b) rGO/alkynyl–dopamine in THF. Bottom: Raman spectra of
a) GO and b) rGO/alkynyl–dopamine.
C=C bonds of the aromatic skeleton, and a broad shoulder
at around 297 nm due to the n–p* transition arising from
the C=O bonds in the carboxylic acid functions. The spec-
trum of the rGO/alkynyl–dopamine nanocomposite shows a
broad absorption band at 269 nm. The redshift of the band
at 228 nm (GO) to 269 nm for rGO/alkynyl–dopamine is
consistent with the restoration of the sp2 structure in rGO.
Figure 3. Top: SEM image of an ITO/graphene/alkynyl–dopamine elec-
trode formed by drop-casting (thickness=280 nm). Bottom: Cyclic vol-
tammogram of an ITO electrode modified by drop-casting with rGO/al-
kynyl–dopamine in 0.1m PBS (scan rate=0.05 VsÀ1).
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Click Reactions on Modified Graphene Oxide
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À
lated by integrating the anodic peak area according to G=
QA/nFA, in which F is the Faraday constant, n is the number
of electrons exchanged (n=2), A is the surface area (A=
0.12 cm2), and QA is the anodic charge transferred. A value
of G=(2.07Æ0.73)ꢄ1014 moleculescmÀ2 was obtained. This
value is lower than that determined for rGO modified with
TTF by a similar approach (G=8.9ꢄ1014 moleculescmÀ2),[9]
but comparable to that obtained for unmodified dopamine
(G=(3.05Æ0.73)ꢄ1014 moleculescmÀ2).
(S2p3/2) and 165.3 eV (S2p1/2) due to S C bonds and contri-
butions at higher energies, 166.9 (S2p3/2) and 168.1 eV (S2p1/
2), due to oxidized S4+ in the form of S O with a ratio of S
À
À
À
C/S O of 2.2. The presence of oxidized thiols was also ob-
served in the initial 6-ferrocenylhexanethiol solution with a
À
À
S C/S O ratio of 2.4. This indicates that only a small frac-
tion of 6-ferrocenylhexanethiol molecules are oxidized
during the photochemical reaction and interact nonspecifi-
cally with the rGO/alkynyl-terminated dopamine nanomate-
rial. The atomic ratio of N/S is 1.3 (Table 1). Taking into
consideration the fact that about 0.65 at% of SH-Fc is oxi-
dized rather than reacting in the thiol–yne reaction, a ratio
À
Thiol–yne reactions on rGO/alkynyl–dopamine-modified
ITO interfaces: Because the thiol–yne reaction allows the
addition of two thiolated molecules to an alkyne, it appears
to be perfectly suited to obtaining high surface densities of
the functional group of interest on the interface. 6-Ferroce-
nylhexanethiol (SH-Fc) and 1H,1H,2H,2H-perfluorodecane-
thiol have been studied as model systems to investigate the
reactivity of the reduced GO modified with alkynyl-termi-
nated dopamine (Figure 1; bottom). The photochemical
thiol–yne reactions were performed at 365 nm for 30 min
under nitrogen with a light power of 100 mWcmÀ2 and the
reactions were monitored by XPS. Figure 4 (top) shows the
S2p core-level high-resolution XPS spectrum of rGO/alky-
of N/ACTHNUTRGENU(GN S C) of 1.9 was determined, which is close to the the-
oretically expected ratio of N/S of 2.0 for a double addition
rather than a monoaddition. The nonspecific adsorption of
6-ferrocenylhexanethiol or its oxidized counterpart onto the
rGO surface was verified in a control experiment in which
ITO interfaces modified with rGO/alkynyl–dopamine films
were immersed in a 10 mm ethanolic solution of 6-ferroce-
nylhexanethiol as before for 30 min but without light irradi-
ation. As seen from Table 1, the presence of bands due to
S2s and Fe2p indicates some nonspecific adsorption onto
rGO/alkynyl–dopamine interfaces most likely due to p–p
stacking interactions.
ACHTUNGTRENNUNGnyl–dopamine after photochemical reaction with 6-ferroce-
nylhexanethiol. It can be deconvoluted into bands at 164.2
The bonded ferrocene moiety shows a redox potential at
around 0.6 V versus Ag/AgCl and integration of the anodic
peak area revealed
a surface coverage of G=5.04ꢄ
1014 moleculescmÀ2. This value is approximately 2.4-fold
higher than that obtained for the dopamine ligand incorpo-
rated on to the rGO and suggests preferential double addi-
tion together with some nonspecific adsorption. In addition,
it is much higher than that determined for rGO/dopamine-
N3 nanomatrices produced by using CuI click chemistry.[8]
Given the high cross-section of fluorine in XPS analysis,
1H,1H,2H,2H-perfluorodecanethiol was used as a second
model compound to investigate the thiol–yne reaction.
Figure 5 (top) displays the XPS survey spectrum of the
rGO/alkynyl–dopamine interface after photochemical reac-
tion for 30 min. The success of the reaction is evidenced by
the presence of F1s (688 eV) and S2p (164 eV) bands in ad-
dition to C1s (284.5 eV), O1s (513 eV), and N1s (400 eV)
bands. The high-resolution C1s XPS spectrum of the per-
fluorodecanethiol-modified rGO matrix is shown in Figure 5
(bottom). The presence of CF3 and CF2 groups is clearly
seen by the contributions at 293.1 and 290.7 eV, respectively.
The other bands arise from sp2-hybridized carbon atoms
À
À
À
À
À
(283.9 eV),
C C/C H
(284.5 eV),
C S/C N/C O
(285.8 eV), and C=O (287.8 eV). The atomic ratio of N/S is
1.3, lower than the N/S=2 expected for the double addition
product, which indicates the preferential formation of the
monoaddition product in this case. The formation of only
the monoproduct might be due to the increase in hydropho-
bicity of the rGO/alkynyl–dopamine after the first addition
with the water contact angle of 448 changing to 978 upon re-
action with perfluorodecanethiol.
Figure 4. Top: S2p high-resolution XPS spectrum of rGO/alkynyl–dopa-
mine after photochemical reaction (l=365 nm) with 10 mm 6-ferrocenyl-
hexanethiol for 30 min at room temperature (P=100 mWcmÀ2). Bottom:
CV of the ITO interface modified with rGO/alkynyl–dopamine after pho-
tochemical reaction with 10 mm 6-ferrocenylhexanethiol in 0.1m PBS
(scan rate=0.05 VsÀ1).
Chem. Eur. J. 2013, 00, 0 – 0
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Conclusion
This study has demonstrated that alkynyl-terminated dopa-
mine reacts in a similar way to dopamine inducing simulta-
neous reduction of graphene oxide to graphene and func-
tionalization of the rGO at room temperature under sonica-
tion. The motivation for using dopamine is that such re-
duced graphene oxide nanocomposites allow the postfunc-
tionalization of rGO/alkynyl–dopamine with thiols by
photochemical “click” reactions between alkynes and thiols.
This approach opens up new perspectives for the covalent
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Acknowledgements
I.K. thanks the International Ph.D. Projects Programme of the Founda-
tion for Polish Science, co-financed by the European Regional Develop-
ment Fund within the Innovative Economy Operational Programme
“Grants for Innovation”. The Centre National de la Recherche Scientifi-
que (CNRS) and the Nord-Pas de Calais Rꢀgion are gratefully acknowl-
edged for financial support.
Received: January 21, 2013
Revised: March 25, 2013
Published online: && &&, 0000
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These are not the final page numbers!

Click Reactions on Modified Graphene Oxide
FULL PAPER
Click Chemistry
I. Kaminska, W. Qi, A. Barras,
J. Sobczak, J. Niedziolka-Jonsson,
P. Woisel, J. Lyskawa, W. Laure,
M. Opallo, M. Li, R. Boukherroub,*
S. Szunerits* ................... &&&& — &&&&
Thiol–Yne Click Reactions on
Alkynyl–Dopamine-Modified Reduced
Graphene Oxide
Modified graphene oxide: A simple
method has been developed for the
simultaneous exfoliation and reduction
of graphene oxide (GO) to reduced
GO (rGO) by using alkynyl-termi-
nated dopamine as the reducing agent.
The reaction was performed under
mild conditions to yield rGO function-
alized with the dopamine derivative
(see figure). The chemical reactivity of
the alkynyl function was demonstrated
and the surfaces of the rGO character-
ized by a variety of techniques.
Chem. Eur. J. 2013, 00, 0 – 0
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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These are not the final page numbers!