Click and Patterned Functionalization of Graphene by Diels-Alder Reaction

Article abstract of DOI:10.1021/jacs.6b02209

Chemical functionalization is a promising approach to controllably manipulate the characteristics of graphene. Here, we designed cis-dienes, featuring two dihydronaphthalene backbones, to decorate a graphene surface via Diels-Alder (DA) click reaction. The installation of a diene moiety into a nonplanar molecular structure to form cis-conformation enables a rapid (-5 min) DA reaction between graphene and diene groups. Patterned graphene of sub-micrometer resolution can be obtained by easily soaking poly(methyl methacrylate)-masked graphene in solution of hydroxyl-substituted cis-diene at room temperature. The functionalization degree can be further controlled by carrying out the reaction at higher temperature. The present result gives important insight into the effect of molecular conformation on the graphene functionalization process, and provides an effective and facile method for graphene functionalization.

Full text of DOI:10.1021/jacs.6b02209

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Communication
Click and Patterned Functionalization of Graphene by Diels-Alder Reaction
Jing Li, Meng Li, Li-Li Zhou, Shuang-Yan Lang, Hai-Yan Lu, Dong Wang, Chuan-Feng Chen, and Li-Jun Wan
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.6b02209 • Publication Date (Web): 06 Jun 2016
Downloaded from http://pubs.acs.org on June 8, 2016
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† ‡
†
‡
† ‡
‡
†
,
,
,
Jing Li, Meng Li, LiꢀLi Zhou, ShuangꢀYan Lang, HaiꢀYan Lu, Dong Wang,* ChuanꢀFeng
†
†
,
,
Chen,* and LiꢀJun Wan*
†
Key Laboratory of Molecular Nanostructure and Nanotechnology and Beijing National Laboratory for Molecular
Sciences, Institute of Chemistry, Chinese Academy of Sciences (CAS), Beijing 100190, P. R. China.
‡
University of CAS, Beijing 100049, P. R. China.
Supporting Information Placeholder
dienoplile to react with representative dienophiles and
dienes under certain condition. Although the dienophile
ABSTRACT: Chemical Functionalization is one of the
promising approaches to controllably manipulate the charꢀ
acteristics of graphene. Here, we designed cisꢀdienes, feaꢀ
turing two dihydronaphthalene backbones, to decorate graꢀ
phene surface via DielsꢀAlder (DA) click reaction. The inꢀ
stallment of diene moiety into nonꢀplanar molecular strucꢀ
ture to form cisꢀconformation enables rapid (~ 5 min) DA
reaction between graphene and diene groups. Patterned
graphene of submicron resolution can be obtained by easily
soaking poly(methyl methacrylate) masked graphene in
solution of hydroxyl substituted cisꢀdiene at room temperaꢀ
ture. The functionalization degree can be further controlled
by carrying out the reaction at higher temperature. The preꢀ
sent result sheds important insight on the effect of molecuꢀ
lar conformation on the graphene functionalization process,
and provides an effective and facile graphene functionalizaꢀ
tion method.
character of graphene is proven to be slightly stronger than
9
the behavior as a diene, the asꢀreported dienes are of low
10
DA reactivity at room temperature. Bian et al., found the
DA reaction between cyclopentadiene and graphene can be
triggered by the mechanical force, which was utilized to
achieve patterned functionalization of graphene. Zhu et al.,11
reported the inverse electron demand DA reaction of graphꢀ
1
1
ite using tetrazine derivatives at room temperature.
As a 2D atomic crystal composed of highly conjugated sp2
carbon atoms, graphene exhibits excellent electrical, therꢀ
1
mal and mechanical properties, and has inspired a great
2
application perspective. Chemical functionalization is one
3
of the promising approaches to controllably engineer the
4
5
a
energy band structure, create novel graphene derivatives,
Figure 1 The crystal structures of (a) D1 and (b) D2 as
characterized by XRD. (c) Raman spectra of graphene beꢀ
2
and manipulate the interfacial characteristics of graphene.3
One of the greatest challenges for graphene chemical funcꢀ
tionalization originates from its strong chemical inertness
and stability, thus highly reactive chemical radicals
harsh reaction conditions are generally needed. Cycloaddiꢀ
tion reaction, with the merits of no requirement of catalysts
and simultaneous formation of a pair of sp carbons, is a
class of reaction to decorate the graphene, taking advantage
of unsaturated and conjugated chemical structure of graꢀ
phene. However, the unique 2D and giant conjugated strucꢀ
ture of graphene make it have different and more chemically
inert reactivity than the small molecules. Thus, the reaction
with high reactivity and mild reaction condition for graꢀ
phene functionalization is highly desired.
fore and after soaking graphene/SiO sample into D1 and
D2 solution for 5 min at room temperature, respectively. (d)
Schematic representation of the DA reaction between D1
with graphene. The reaction site is highlighted by dashed
cyan circle. The hydrogen atoms are omitted for clarity in
each molecular structure.
3
a,6
or
3c
3
7
Herein, we find the cisꢀ and transꢀconformation dienes,
which are of nondetectable DA reactivation difference with
12
small dienophile molecules , have totally different DA reacꢀ
tivity on graphene film. The conformation of diene was fixed
by installing it into two cyclic aromatic hydrocarbon backꢀ
bones. The nonpolar structure of cisꢀdiene can both mainꢀ
tain the favorable conformation for DA reaction and greatly
decrease the strain effect during cycloaddition, thus results
in “clickꢀtype” DA reaction between cisꢀdiene with graphene
at room temperature. Furthermore, we demonstrate that
the DA reaction can achieve finely patterned functionality
DA reaction between conjugated diene and substituted
alkene (dienephile) is an important class of synthetic reacꢀ
tion and is ascribed to “clickꢀtype” reaction due to the high
efficiency, versatility, and selectivity. Haddon et al.,8
demonstrated that the graphene can act as both diene and
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Figure 2. (a) The schematic procedure for patterned functionalization of graphene by D3 (molecular structure as shown in
inset) in isopropanol solution at room temperature. (b) The optical image of PMMA pattern on graphene. The dark blue hexꢀ
agonal zones represent the exposure area of graphene. (c) The optical microscopy image of graphene surface after DA reaction
and dissolving PMMA mask. (d) The D peak Raman mapping image of the graphene zone as marked by yellow dashed rectanꢀ
gle in panel (c). (e) Raman spectra of the graphene spots as marked by triangles in panel (d). (f) The AFM topography and (g)
SKPM surface potential image of the graphene zone as marked by black dashed rectangle in panel (d). (h)The crossꢀsectional
height (red line) and surface potential (blue line) profiles alone the dashed line shown in panel (f) and (g), respectively. The
scale bars are all of 10 ꢁm in each panel.
with the assistance of polymethylꢀmethacrylate (PMMA)
mask. The functionalization degree can be further conꢀ
trolled by carrying out the reaction at higher temperature.
The DA reaction provides an effective, thermalꢀstable and
electrically conductivity improved functionalization method
to graphene. Fieldꢀeffect transistors (FETs) and Hallꢀeffect
measurements confirm that the DA reaction can result in pꢀ
type doping effect and improved conductivity to graphene.
with D3 molecules while the PMMA protected regions reꢀ
main intact (Figure 2e). The AFM topography shows little
height (Figure 2f and 2h) variation between the functionalꢀ
ized and nonꢀfunctionalized regions, presumably due to
relatively low reaction degree for room temperature funcꢀ
tionalization. However, the pattern boundaries can be clearꢀ
ly distinguished by scanning kelvin probe microscopy
(SKPM) as shown in Figure 2gꢀh, and the functionalized
regions shows lower surface potential (~ 100 meV) comꢀ
pared with the pristine graphene region,18 which demonꢀ
strates the effective tune result of D3 on the surface characꢀ
teristics of graphene. The crossꢀsectional profile in Figure
The graphene used in this work is mainly of chemical vaꢀ
por deposition (CVD) grown graphene on Cu substrate or
transferred onto other supporting substrates.13 The preferꢀ
ential conformations of D1 and D2 are cisꢀ and transꢀ reꢀ
spectively after installing diene into two nonꢀplanar dihyꢀ
dronaphthalene (D1) or indene (D2) backbones, as shown
by the Xꢀray diffraction results in Figure 1a. As revealed in
2
h shows the sharp pattern edge, which suggests the high
resolution (subꢀmicrometer) pattern could be achieved by
DA functionalization.
Figure 1c, soaking the graphene/SiO
2
sample into D1 soluꢀ
To further increase the DA functionalization degree, the
DA reactions were conducted at different reaction temperaꢀ
tures, and the experiments were carried out by heating the
tion for 5 min at room temperature can result in the presꢀ
ꢀ
1
ence of D peak (~ 1350 cm ) in Raman spectrum, which is
3
14 15
related with the graphene defects and sp C formation,
and the significant decrease of the doubleꢀresonance 2D
graphene/SiO
ture after drop casting 10 ꢁL D1 solution onto the graphene
surface.(Figure S2) The time evolution of I /I of graphene
samples are shown in Figure 3a. Higher reaction temperaꢀ
ture results in higher I /I , indicating larger reaction deꢀ
gree. The I /I ratio keeps increasing to reach the plateaus
2
sample on hot plate at designated temperaꢀ
ꢀ
1
peak (~ 2680 cm ). In contrast, no discernible Raman specꢀ
tral changes were observed in control experiments of D2
solution or pure solvents without D1 molecules (Figure S1).
Figure 1d illustrates the reaction scheme between D1 and
graphene via DA reaction.
D
G
D
G
D
G
after 5 minutes and beyond. The kinetic analysis demonꢀ
strates that the DA reaction is of first order reaction (Figure
The rapid DA reaction between D1 and graphene even at
room temperature promises facile method to achieve patꢀ
terned functionalization of graphene. The wellꢀcontrolled
functionalization pattern was achieved on graphene with the
assistance of PMMA film as mask, which is widely used in
3
b and Figure S6), and the activation energy is about 13.57
ꢀ
1
kJ·mol as shown in Figure 3c, which demonstrates the DA
reaction to be a low energy barrier reaction.
To exclude the influence of the CVD grain boundaries and
16
17
19
CVD graphene transfer process and surface lithography.
defects on the graphene reactivity, the DA reaction was
The hydroxyl substituted diene (D3) was designed and disꢀ
solved in isopropanol, which is nonꢀsolvent for PMMA mask.
The DA functionalization was conducted by simply soaking
the patterned graphene/SiO sample into D3 solution for 10
2
min (Figure 2a). The graphene with the exposed pattern of
hexagon was obtained by photolithography on PMMA film
conducted on both singleꢀcrystal CVD graphene and meꢀ
chanical exfoliated graphene (MEG). The D peak of Raman
mapping intensity exhibits uniform distribution on the meꢀ
chanical exfoliated graphene surface (Figure 3d), which
further confirms the homogenous reactivity of the DA reacꢀ
tion. The DA functionalization on thicker graphene is also
feasible as shown in Figure S8, and the graphite can also be
functionalized with cisꢀdiene in 5 min at 200 ˚C. Additionꢀ
(
Figure 2b). Raman D peak intensity mapping (Figure 2d)
reveals that the exposed region is effectively functionalized
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ally, the substrates underneath graphene show no influence
ity degradation effect, resulting in the conductance imꢀ
provement of graphene layer.
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on the graphene DA reactivity. It is worthy mention that, the
D1 functionalized graphene demonstrates good thermal
stability after annealing at 500 ˚C for 1 h (Figure S10).
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Figure 4. (a) IDS versus V and (b) IDS versus VDS characꢀ
teristics of the pristine graphene and the same graphene
device which was consecutively reacted with D1 at different
temperature. Inset in panel (b) is optical microscopy image
of the FET device with the scale bar of 50 ꢁm; the green
dashed lines mark the graphene edge. The line of black, red,
blue and magenta represents pristine graphene, 30 ˚C, 70
˚C and 150 ˚C DA functionalized graphene, respectively, in
panel (a) to (c). (c) The electrical conductance change of
pristine graphene sheet and the same graphene sample conꢀ
secutively reacted with D1 at different temperature. Inset in
panel (c) is optical microscopy image of the Hall bar device
with the scale bar of 5 mm. (d) Histogram of carrier density
and mobility in graphene and functionalized graphene as
measured from the Hall bar devices.
D G
Figure 3 (a) The plot of Raman intensity ratios I /I of graꢀ
phene as a function of time at different reaction temperaꢀ
tures. (b) Kinetic analysis of functionalization degree vs
reaction time based on Raman data (See detailed kinetic
derivation in SI). Solid lines are fitting curves on the basis of
1st order kinetics. (c) The relationship between ln(k) and 1/T.
The reaction rate constant k is derived from panel (b). D
peak Raman mapping of mechanical exfoliated graphene
before (c) and after (d) DA reacted with D1. The scale bar is
Although several covalent modification methods have
been reported to modify graphene surface, most of which
results in severely degradation of carrier mobility, thus limit
10 ꢁm. (e) The AFM topological images of graphene before
and after DA reaction. The scale bar is 2 ꢁm. (f) The crossꢀ
sectional height profile alone the dashed line in panel (e).
the further application of graphene in high sensitivity senꢀ
sor and electrical devices.3
b,4b,7
Diazonium salt is one of the
Electrical transport measurements were performed to inꢀ
vestigate the effect of DA functionalization on graphene
electric property. The graphene FETs were fabricated on
most widely used chemicals to functionalize carbon nanoꢀ
3a
tube and graphene. The similar phenomenon of graphene
3
00 nm SiO
2
/Si substrate with a topꢀcontact bottomꢀgate
conductivity increase can be observed at high functionalizaꢀ
2
1
architecture. The pristine graphene exhibits an ambipolar
character with a Dirac point around 0 V and the carrier moꢀ
bility between 1000 ~ 4000 cm V s . Figure 4a shows that
as the DA reaction degree increases, the Dirac point of graꢀ
phene moves towards positive direction, demonstrating pꢀ
type doping effect to graphene.20 After 150 ˚C DA functionꢀ
tion extent. However, the coverage of diene molecules in
this experiment is about 3 % (quantitative analysis from the
peak ratio of C1s and Br3d from the XPS measurement in
Figure S5), which is lower than typical result for diazonium
2
ꢀ1 ꢀ1
3
a
chemistry (the coverage of nitrophenyl groups ~ 12.5 % ).
The comparable improvement of conductivity at low coverꢀ
age may be related with the simultaneous formation of a
2
ꢀ
alization for 5 min, the carrier mobility is 500 ~ 1000 cm V
1
ꢀ1
3
s . Figure 4b reveals the IꢀV characters of the pristine and
pair of sp carbons caused by the DA reaction of one diene
molecule.7
,22
modified graphene. The slope of IꢀV curve increases as the
DA functionalization degree on graphene surface increases,
In summary, we demonstrate a simple, highly effective
and controllable DA reaction to functionalize graphene by
using cisꢀdiene. The DA reaction can be finished in 5
minutes. The hydroxyl substituted cisꢀdiene molecules (D3)
is compatible with the PMMA lithography process to realize
the graphene pattern by covalent functionalization. The DA
functionalization can result in pꢀtype doping effect and imꢀ
provement of the conductivity of graphene film, which may
2
1
which implies an improvement of conductivity. To further
elucidate the DA functionalization effect on graphene elecꢀ
tric property, the Hall bar device was fabricated by shadow
mask as shown in Figure 4c. The resistivity of pristine graꢀ
phene decrease from ~ 800 ꢂ/□ to 450 ꢂ/□ after functionꢀ
alization, which is consistent with the FET results. As the
DA functionalization extent increases, the carrier mobility
2
ꢀ1 ꢀ1
2
ꢀ1 ꢀ1
decreases gradually from ~ 1600 cm V s to ~ 800 cm V s
23
be used as transparent electrodes . The possibility to install
(
×
Figure 4d). In contrast, the carrier density increases from 5
10 cm to 1.7× 10 cm . The covalent attached diene
other functional groups on diene molecule through opposite
benzene rings while maintaining the high DA reactivity
make cisꢀdiene based DA functionalization a promising way
to achieve customized graphene derivatives for sensor apꢀ
plications. This clickꢀfunctionalization of graphene via DA
12
ꢀ2
13
ꢀ2
molecules on graphene surface serve as electronꢀ
withdrawing groups to improve the hole density in graphene.
Additionally, the holeꢀdonating effect overweighs the mobilꢀ
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reaction sheds important insight on the effect of molecular
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conformation on the graphene functionalization process,
and provides an effective and facile graphene functionalizaꢀ
tion method.
ASSOCIATED CONTENT
Supporting Information
2
139.
(13) (a)Li, J.; Ji, H.; Zhang, X.; Wang, X.; Jin, Z.; Wang,
Experimental section, supplementary figures are included.
This material is available free of charge via the Internet at
http://pubs.acs.org.
D.; Wan, L.ꢀJ. Chem. Commun. 2014, 50, 11012; (b)Li, J.;
Wang, X.ꢀY.; Liu, X.ꢀR.; Jin, Z.; Wang, D.; Wan, L.ꢀJ. J.
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AUTHOR INFORMATION
Corresponding Author
Lazzeri, M.; Mauri, F.; Piscanec, S.; Jiang, D.; Novoselov, K.
S.; Roth, S.; Geim, A. K. Phys. Rev. Lett. 2006, 97, 187401.
(15) Kim, Y. A.; Fujisawa, K.; Muramatsu, H.; Hayashi, T.;
*
wangd@iccas.ac.cn;
Endo, M.; Fujimori, T.; Kaneko, K.; Terrones, M.; Behrends,
J.; Eckmann, A.; Casiraghi, C.; Novoselov, K. S.; Saito, R.;
Dresselhaus, M. S. ACS Nano. 2012, 6, 6293.
(16) (a)Reina, A.; Jia, X.; Ho, J.; Nezich, D.; Son, H.;
Bulovic, V.; Dresselhaus, M. S.; Kong, J. Nano Lett. 2009, 9,
30; (b)Li, X.; Cai, W.; An, J.; Kim, S.; Nah, J.; Yang, D.;
Piner, R.; Velamakanni, A.; Jung, I.; Tutuc, E.; Banerjee, S.
K.; Colombo, L.; Ruoff, R. S. Science. 2009, 324, 1312.
cchen@iccas.ac.cn;wanlijun@iccas.ac.cn.
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
This work was supported by National Natural Science
Foundation of China (21127901, 21233010, 21433011,
21373236), and the Strategic Priority Research Program of
the Chinese Academy of Sciences (Grant No.
XDB12020100).
(17) Xia, Y.; Rogers, J. A.; Paul, K. E.; Whitesides, G. M.
Chem. Rev. 1999, 99, 1823.
(18) Xu, W.; Wang, L.; Liu, Y.; Thomas, S.; Seo, H.ꢀK.;
Kim, K.ꢀI.; Kim, K. S.; Lee, T.ꢀW. Adv. Mater. 2015, 27,
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