Site-selective metal-coordination-based patterning of silane monolayers

Article abstract of DOI:10.1039/c0cc05318j

Herein, we report a method to pattern a derivatized nifedipine silane monolayer that aromatizes under UV irradiation. Using a functionalized SCS-Pd(ii) pincer complex, we demonstrate that a strong metal-coordination complex between the aromatized nifedipine derivative and the pincer complex is formed. This methodology integrates SAM photolithography (top-down) and molecular recognition directed self-assembly (bottom-up) strategies to create simple and rapid synthesizable functional patterned surfaces. The Royal Society of Chemistry.

Full text of DOI:10.1039/c0cc05318j

View Article Online / Journal Homepage / Table of Contents for this issue
This article is part of the
Supramolecular Chemistry web-
based thematic issue
celebrating the International Year of Chemistry 2011
Guest editors: Professors Philip Gale,
Jonathan Sessler and Jonathan Steed
All articles in this issue will be gathered together online at
www.rsc.org/chemcomm/supra.

Dynamic Article Links
ChemComm
Cite this: Chem. Commun., 2011, 47, 2802–2804
www.rsc.org/chemcomm
COMMUNICATION
Site-selective metal-coordination-based patterning of silane monolayerswz
˜
Minfeng Li,y Yu Wang, Victor Pinon III and Marcus Weck*
Received 1st December 2010, Accepted 6th January 2011
DOI: 10.1039/c0cc05318j
Herein, we report a method to pattern a derivatized nifedipine
silane monolayer that aromatizes under UV irradiation. Using a
functionalized SCS–Pd(II) pincer complex, we demonstrate that
a strong metal-coordination complex between the aromatized
nifedipine derivative and the pincer complex is formed. This
methodology integrates SAM photolithography (top-down) and
molecular recognition directed self-assembly (bottom-up)
strategies to create simple and rapid synthesizable functional
patterned surfaces.
but usually involve synthetic efforts that can be difficult on
surfaces, in particular when it comes to high yields. Physisorption
processes are straightforward but lack specificity and kinetic
stability. Supramolecular interactions such as metal–ligand
coordination combine the advantages of covalent chemistry
and physisorption, i.e. ease of formation while retaining
strength and specificity.19–21 Due to their dynamic nature,
supramolecular interactions have unique properties such as
self-checking and self-correction22 making self-assembly a very
attractive route for the fabrication of patterned functional
surfaces.23,24 We have introduced a surface functionalization
strategy that uses coordination chemistry between pyridine
and palladated pincer complexes thereby (i) providing for
uniform film deposition, (ii) having a high degree of control
of multilayer thickness, (iii) integrating a diverse set of polymer
components, and (iv) affording stable, yet responsive multi-
layers that can be manipulated by chemical means.25,26 In this
study, we demonstrate a versatile methodology based on our
metal-coordination surface functionalization strategy that
integrates SAM photolithography (top-down) and molecular
recognition directed self-assembly (bottom-up) strategies to
create simple and rapidly synthesizable functional patterned
surfaces.
Patterning functionalities on surfaces is essential for the
development of many technologies such as electronics,1
chemical sensor design,2 optics,3 microfluidics,4 biotechnology5
and bioanalytics.6 Many surface patterning techniques have
been developed including photolithography,7 as well as electron
and ion beam,8 scanning probe,9 and soft lithography.10 The
primary process of these patterning techniques is to chemically
or physically modify properties of designated regions of the
substrate of interest. Using light to modify surface properties
is a very attractive approach largely due to its simplicity and
compatibility with large-scale parallel processes. In recent
years, photo-patternable self-assembled monolayers (SAMs)
have attracted great interests.11–18 The SAM approach has the
advantage that it allows for the generation of well-defined
active groups on the surface during the photopatterning
process providing easy access to further functionalize
substrates via an additive approach. Several strategies have
been reported to photochemically generate well-defined
active sites on SAMs including the use of (i) photo-induced
degradation;12 (ii) photo-initiated polymerization;13,14 (iii)
photo-deprotection of ‘‘caged’’ functional groups15,16 and
(iv) photoisomerization.17,18
Our strategy is based on the photo-reactivity of nifedipine, a
derivative of 1,4-dihydropyridine, which is known as a generic
drug for the treatment of high blood pressure. Studies showed
that, upon exposure to UV irradiation, nifedipine undergoes
rapid oxidization/aromatization to afford the corresponding
pyridine through an intra-molecular charge transfer pathway.27,28
After aromatization, the resulting pyridyl group is a versatile
and efficient metal-binding ligand,29 which is able to form
stable coordination complexes with
a variety of metal
precursors including SCS–PdII pincer complexes.30–32 The
high specificity and robustness of this metal complex reaction
makes it very attractive as a smart ‘‘molecular glue’’ in
microstructure fabrication on surfaces.33
Covalent bonds and/or physisorption are common to
immobilize functional groups on photo-activated surfaces.
Covalent bonds have the advantage of strength and specificity
The key to our strategy is the design and synthesis of the
bi-functionalized silane 1 (Scheme 1) which contains a
terminal nifedipine derivative as a photoactive group at one
end and a triethoxy silane group for surface anchoring at
the other end of the molecule. Photosensitive silane 1 is
Molecular Design Institute, Department of Chemistry,
New York University, New York, NY 10003, USA
w This article is part of a ChemComm ‘Supramolecular Chemistry’
web-based themed issue marking the International Year of Chemistry
2011.
z Electronic supplementary information (ESI) available: Details of the
preparation of the substrates and SAM, surface characterizations,
the single crystal structure for aromatized 3, and NMR studies of the
photo-transformation reactions and the metal–ligand coordination
processes. See DOI: 10.1039/c0cc05318j
synthesized by
a microwave-assisted one-pot Hantzsch
reaction, followed by catalytic hydrosilylation to install the
triethoxysilane anchor group (see ESIz for details).
We initially investigated the binding of an aromatized
nifedipine derivative to SCS–PdII pincer complexes. For these
y Current address: College of Chemistry, Beijing Normal University,
Beijing 100875, People’s Republic of China.
c
2802 Chem. Commun., 2011, 47, 2802–2804
This journal is The Royal Society of Chemistry 2011

strategy. Due to its wide applications in many areas, Si wafers
were chosen as substrates. For silane SAM formation, it
is essential to obtain clean and fully hydroxylated silicon
surfaces. Several surface cleaning processes were screened
using an advancing water contact angle as the criterion. It
was found that silica wafers sequentially treated with a RCA
(HCl:H2O2) and piranha (H2SO4:H2O2) gave the best
results (see ESIz for details). The native silicon wafer had an
advancing water contact angle of 20–251. After the cleaning/
oxidizing treatment, the angle was reduced to o31 suggesting
that very hydrophilic surfaces with high hydroxyl group
coverage were obtained. The pre-treated substrates were then
immersed in a solution of 1 (10% v/v) in dry toluene at room
temperature for one hour, rinsed with toluene and sonicated in
toluene for three minutes. The wafers were then annealed
overnight at 65 1C in B80% relative humidity. The value of
the advancing water contact angle of the resulting substrate
increased to >851 demonstrating the presence of a silane 1
SAM on the silicon wafer. After blanket UV exposure at
356 nm for 15 minutes, the contact angles decreased slightly
to 70–751. The formation of the silane 1 SAM and the
sequential photo activated aromatization were further
confirmed by Fourier-transform infrared reflection absorption
spectroscopy (FT-IRRAS) (Fig. 2a). The bands at 3331 cmꢂ1
and 1647 cmꢂ1 are assigned to the N–H stretch of the
dihydropyridine and the CQC stretches of the non-aromatic
double band, respectively.34,35 After UV exposure, the N–H
stretch fully disappears. Furthermore, the non-aromatic CQC
stretch either disappears completely too or at least diminishes
significantly (there is a chance that the signal overlaps with
other signals next to it). Both of these observations strongly
suggest that the 1 SAM on the surface aromatized under UV
irradiation.
Scheme 1 Schematic illustration of direct photo-patterning and site
selective deposition of the fluorescence dye (coumarin) on the surface
via SCS–PdII pincer self-assembly as well as the structure of the model
compound 3.
studies, we prepared the model compound 3 and exposed it
(in an ethanol solution) for 2 h to UV irradiation at 356 nm.
The resulting aromatized 3 was characterized by NMR
spectroscopy. Furthermore, the single crystal structure of
aromatized 3 has been obtained and confirms the oxidation
step (ESIz). 1H NMR spectroscopic binding studies proved
that aromatized 3 formed a stable 1 : 1 complex with the PdII
pincer complex 4 (see ESIz for details).30 The equilibrium
constant (Keq) for the self-assembly between the aromatized
nifedipine 3 and an acetonitrile coordinated PdII pincer complex
(a hexyl group derivative of 4 was employed for solubility
reasons) was determined by ITC using a single-site binding
model. The Keq was measured to be 3.2 ꢀ 103 ꢁ 10% Mꢂ1 in
CHCl3 (Fig. 1).
For the fabrication of the patterned surfaces, the 1 SAM
was irradiated with collimated UV light (356 nm) through a
photomask for 10 minutes. The photo-patterned substrate was
then immersed in a chloroform solution (5 mM) of dye
functionalized acetonitrile–PdII pincer (2) for 20 minutes.
After thorough washing with fresh chloroform and drying
by a stream of air, the resulting substrate was characterized by
fluorescence microscopy and atomic force microscopy (AFM).
Fig. 2b–d shows the images of a square pattern (for other
pattern, see ESIz). A transparency with a 20 ꢀ 20 mm square
After demonstrating that aromatized nifedipine derivatives
form strong coordination bonds with palladium pincer complexes,
we investigated our surface patterning and functionalization
Fig. 2 (a) FT-IRRAS spectra of 1 SAM before (black) and after (red)
UV-vis (356 nm) exposure. 1320 scans were accumulated for each
spectrum at
a resolution of 4 . (b) Microscopy image,
cmꢂ1
Fig. 1 ITC binding isotherm for the model compound 3 and a
hexyl-substituted pincer complex in CHCl3 at 30 1C.
(c) fluorescence microscopy image and (d) contact-model AFM height
image of a 20 ꢀ 20 mm square patterned surface.
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 2802–2804 2803

pattern was used as photomask. Fig. 2b and c show that the
photomask pattern was precisely registered on the Si substrate.
The dye-functionalized PdII–pincer complexes (2) were able to
recognize and selectively bind to the UV-exposed area. No
fluorescence was observed immediately adjacent to the
squares. The AFM image in Fig. 2d confirmed that the pincer
complexes specifically bind to the designated area on the
patterned Si surface as evidenced by the height difference.
The use of high-resolution photo masks, for instance
chromium-based photomasks, as well as other illumination
optics should allow for higher resolution images.
10 Y. Xia and G. M. Whitesides, Angew. Chem., Int. Ed., 1998, 37,
550–575.
11 S. P. A. Fodor, J. L. Read, M. C. Pirrung, L. Stryer, A. T. Lu and
D. Solas, Science, 1991, 251, 767–773.
12 M. E. Anderson, C. Srinivasan, J. N. Hohman, E. M. Carter,
M. W. Horn and P. S. Weiss, Adv. Mater., 2006, 18, 3258–3260.
13 S. Monsathaporn and F. Effenberger, Langmuir, 2004, 20,
10375–10378.
14 N. Kanoh, S. Kumashiro, S. Simizu, Y. Kondoh, S. Hatakeyama,
H. Tashiro and H. Osada, Angew. Chem., Int. Ed., 2003, 42,
5584–5587.
15 A. D. Campo, D. Boos, H. W. Spiess and U. Jonas, Angew. Chem.,
Int. Ed., 2005, 44, 4707–4712.
16 J. Nakanishi, Y. Kikuchi, S. Inoue, K. Yamaguchi, T. Takarada
and M. Maeda, J. Am. Chem. Soc., 2007, 129, 6694–6695.
17 T. Griesser, J. Adams, J. Wappel, W. Kern, G. J. Leggett and
G. Trimmel, Langmuir, 2008, 24, 12420–12425.
18 A. Lex, P. Pacher, O. Werzer, A. Track, Q. Shen, R. Schennach,
G. Koller, G. Hlawacek, E. Zojer, R. Resel, M. Ramsey,
C. Teichert, W. Kern and G. Trimmel, Chem. Mater., 2008, 20,
2009–2015.
19 H. Hofmeier and U. S. Schubert, Chem. Soc. Rev., 2004, 33,
373–399.
20 T. F. A. De Greef, M. M. J. Smulders, M. Wolffs, A. P. H.
J. Schenning, R. P. Sijbesma and E. W. Meijer, Chem. Rev., 2009,
109, 5687–5754.
21 C. R. South, C. Burd and M. Weck, Acc. Chem. Res., 2007, 40,
63–74.
22 J. M. Lehn, Rep. Prog. Phys., 2004, 67, 249–265.
23 H. Xu, R. Hong, T. X. Lu, O. Uzun and V. M. Rotello, J. Am.
Chem. Soc., 2006, 128, 3162–3163.
24 L. Motiei, M. Altman, T. Gupta, F. Lupo, A. Gulino,
G. Evmenenko, P. Dutta and M. E. van der Boom, J. Am. Chem.
Soc., 2008, 130, 8913–8915.
25 C. R. South, V. Pinon and M. Weck, Angew. Chem., Int. Ed., 2008,
47, 1425–1428.
In summary,
a
triethoxysilane bearing photoactive
derivatized nifedipine was designed and synthesized. A SAM
of this photo-sensitive silane was prepared on a Si surface and
photo-patterned through a photomask. We found that SCS
PdII–pincer complexes are able to recognize and selectively
coordinate to the pyridyl group in the UV exposed areas.
Considering that the pyridyl group is a very versatile ligand:
(i) in its neutral form it has a strong affinity towards a wide
variety of metals and the ability to form hydrogen bonds as the
H-bond acceptor, and (ii) in its protonated form, it can
electrostatically interact with other charged species, our
method provides easy and rapid access to patterned pyridyl
functionalities on surfaces and could be a very powerful tool
for technology and device development.
We thank the National Science Foundation (CHE-0911460)
for financial support of this research.
26 C. R. South and W. Weck, Langmuir, 2008, 24, 7506–7511.
27 J. A. Berson and E. Brown, J. Am. Chem. Soc., 1955, 77, 447–450.
28 E. Fasani, M. Fagnoni, D. Dondi and A. Albini, J. Org. Chem.,
2006, 71, 2037–2045.
29 P. J. Steel, Coord. Chem. Rev., 1990, 106, 227–265.
30 H.-J. van Manen, K. Nakashima, S. Shinkai, H. Kooijman,
A. L. Spek, F. C. J. M. van Veggel and D. N. Reinhoudt, Eur.
J. Inorg. Chem., 2000, 2533–2540.
31 M. Albrecht and G. van Koten, Angew. Chem., Int. Ed., 2001, 40,
3750–3781.
32 M. E. van der Boom and D. Milstein, Chem. Rev., 2003, 103,
1759–1792.
33 A. Friggeri, H. J. van Manen, T. Auletta, X. M. Li, S. Zapotoczny,
Notes and references
1 E. Menard, M. A. Meitl, Y. Sun, J.-U. Park, D. J. Shir, Y.-S. Nam,
S. Jeon and J. A. Rogers, Chem. Rev., 2007, 107, 1117–1160.
2 C. Zhang and K. S. Suslick, J. Am. Chem. Soc., 2005, 127,
11548–11549.
3 C. Koos, P. Vorreau, T. Vallaitis, P. Dumon, W. Bogaerts,
R. Baets, B. Esembeson, I. Biaggio, T. Michinobu, F. Diederich,
W. Freude and J. Leuthold, Nat. Photonics, 2009, 3, 216–219.
4 J. E. Kreutz, L. Li, L. S. Roach, T. Hatakeyama and
R. F. Ismagilov, J. Am. Chem. Soc., 2009, 131, 6042–6043.
5 D. B. Weibel, W. R. DiLuzio and G. M. Whitesides, Nat. Rev.
Microbiol., 2007, 5, 209–218.
6 G. MacBeath and S. L. Schreiber, Science, 2000, 289, 1760–1763.
7 M. J. Tarlov, D. R. F. Burgess and G. Gillen, J. Am. Chem. Soc.,
1993, 115, 5305–5306.
8 Q. Xu, R. M. Rioux, M. D. Dickey and G. M. Whitesides,
Acc. Chem. Res., 2008, 41, 1566–1577.
H. Schonherr, G. J. Vancso, J. Huskens, F. C. J. M. van Veggel
¨
and D. N. Reinhoudt, J. Am. Chem. Soc., 2001, 123, 6388–6395.
34 K. L. A. Chan, S. G. Kazarian, D. Vassou, V. Gionis and
G. D. Chryssikos, Vib. Spectrosc., 2007, 43, 221–226.
35 K. L. A. Chan, O. S. Fleming, S. G. Kazarian, D. Vassou,
G. D. Chryssikos and V. J. Gionis, J. Raman Spectrosc., 2004,
35, 353–359.
9 X. Yin, N. Fang, X. Zhang, I. B. Martini and B. J. Schwartz,
Appl. Phys. Lett., 2002, 81, 3663–3665.
c
2804 Chem. Commun., 2011, 47, 2802–2804
This journal is The Royal Society of Chemistry 2011