Photolithographic Encoding of Metal Complexes

Article abstract of DOI:10.1002/chem.201502586

A platform technology for the creation of spatially resolved surfaces encoded with a monolayer consisting of different metal complexes was developed. The concept entails the light-triggered activation of a self- assembled monolayer (SAM) of UV-labile anchors, that is, phenacylsulfides, and the subsequent cycloaddition of selected diene-functionalized metal complexes at defined areas on the surface. The synthesis and characterization of the metal complexes for the UV-light assisted anchoring on the surface and a detailed study of a short-chain oligomer model system in solution confirm the high efficiency of the photoreaction. The hybrid materials obtained by this concept can potentially be utilized for the design of highly valuable catalytic or (opto-)electronic devices.

Full text of DOI:10.1002/chem.201502586

DOI: 10.1002/chem.201502586
Communication
&
Photolithography
Photolithographic Encoding of Metal Complexes
Christiane Lang,[a, b] Sebastian Bestgen,[c] Alexander Welle,[a, b] Rouven Müller,[a, b]
Peter W. Roesky,*[c] and Christopher Barner-Kowollik*[a, b]
the considerable catalytic activity of homogenously mono-
layered metal complexes.[4] Though examples for the direct
immobilization of any metal complexes as a monolayer are
scarce,[5] the complexes are predominantly assembled step-
wise.[6] Similarly, the growth of supramolecular metallopoly-
mers, molecular nanowires, or surface-attached metal–organic
frameworks (SURMOFs) from the surface is realized.[7] As al-
ready noted, however, these techniques most often lack spatial
control in the immobilization step. For the efficient encoding
of organic compounds on solid substrates, photolithographic
techniques have been established with photo labile precursors
immobilized as a homogenous SAM on the substrate. Employ-
ing a shadow mask, only the molecules in the irradiated area
react with the in situ-provided organic compounds to give pat-
terned functional materials with spatial and temporal control.
Commonly employed UV labile groups include photoenol de-
rivatives, phencyclones, or tetrazoles.[8] We utilize the transient
thioaldehydes formed from phenacylsulfides, which can either
be trapped by nucleophiles,[9] or act as dienophiles in subse-
quent cycloadditions.[10] To the best of our knowledge, none of
these techniques has to date been employed on metal–organ-
ic compounds enabling the spatially and temporally controlled
immobilization of monolayered metal complexes. Transferring
the knowledge of the photolithographic encoding from organ-
ic to metal–organic and inorganic compounds, we were able,
for the first time, to generate spatially defined monolayer pat-
terns composed of different metal complexes attached onto
a single surface. The approach features mild and fast ligation
conditions and can be employed for a variety of metal
complexes. The versatile concept paves the way to tailor
highly efficient and economic catalytic or electronic materials
in a spatially defined environment.
Abstract: A platform technology for the creation of
spatially resolved surfaces encoded with a monolayer con-
sisting of different metal complexes was developed. The
concept entails the light-triggered activation of a self-
assembled monolayer (SAM) of UV-labile anchors, that is,
phenacylsulfides, and the subsequent cycloaddition of
selected diene-functionalized metal complexes at defined
areas on the surface. The synthesis and characterization of
the metal complexes for the UV-light assisted anchoring
on the surface and a detailed study of a short-chain oligo-
mer model system in solution confirm the high efficiency
of the photoreaction. The hybrid materials obtained by
this concept can potentially be utilized for the design of
highly valuable catalytic or (opto-)electronic devices.
The spatially defined immobilization of metal complexes
through printing or lithographic methods provides patterned
substrates partially coated with a thin layer of the compound.[1]
For applications in heterogeneous catalysis the minimization of
the layer thickness without a loss in reactivity is critical to save
precious material. Processes such as microcontact printing or
sputtering have been developed to make advances towards
this requirement while retaining the spatial control over the
immobilization step.[2] Ideally, the applied layer features a thick-
ness of only one molecule, which is realized with disregard to
spatial control in so-called self-assembled monolayers (SAMs),
that is, homogenous single layers from thiols on noble metal
substrates, carboxylic acids on indium tin oxide (ITO), or silanes
on silicon substrates.[3] Sawamura and co-workers have shown
In order to establish the novel metal complex encoding pro-
cess, diene functionalized metal complexes were synthesized
and tested in solution based model reactions prior to the sur-
face encoding (Scheme 1). Versatile access for the synthesis of
the metal–organic complexes was realized utilizing two well-
established and commonly used ligand systems, that is, phos-
phines and 2,2’-bipyridines. Those ligands allow the complexa-
tion and fixation of numerous metal ions, for example, PdII, PtII,
IrI, RuII, RhI, or AuI and the corresponding complexes are widely
used in industrial and pharmaceutical processes due to their
well-established catalytic and photophysical properties. The in-
troduction of a diene unit to the P/N-donor systems for the
subsequent Diels–Alder reaction was conducted employing
2E,4E-hexadienol in a Steglich esterification with 4-(diphenyl-
phosphino)benzoic acid providing ligand L1, or by Williamson
etherification with 4-(4-bromobutyl)-4’-methyl-2,2’-bipyridine
[a] Dr. C. Lang, Dr. A. Welle, R. Müller, Prof. C. Barner-Kowollik
Preparative Macromolecular Chemistry
Institut für Technische Chemie und Polymerchemie
Karlsruhe Institute of Technology (KIT)
Engesserstrasse 18, 76131 Karlsruhe (Germany)
E-mail: christopher.barner-kowollik@kit.edu
[b] Dr. C. Lang, Dr. A. Welle, R. Müller, Prof. C. Barner-Kowollik
Institut für Biologische Grenzflächen
Karlsruhe Institute of Technology (KIT)
Hermann-von-Helmholtz-Platz 1
76344 Eggenstein-Leopoldshafen (Germany)
[c] S. Bestgen, Prof. P. W. Roesky
Institute of Inorganic Chemistry
Karlsruhe Institute of Technology (KIT)
Engesserstrasse 15, 76131 Karlsruhe (Germany)
E-mail: roesky@kit.edu
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201502586.
Chem. Eur. J. 2015, 21, 14728 – 14731
14728
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
Scheme 1. Establishment of the photo-induced ligation of AuI (a, b) and PdII (c) complexes including complex synthesis, test reactions, and surface encoding.
yielding ligand L2. The functionalized phosphine ligand L1 was
reacted with [AuCl(tht)] and [AuBr(tht)] (tht=tetrahydrothio-
phene) to afford the two gold complexes [L1AuCl] (a) and
[L1AuBr] (b) in excellent yields. The bipyridine ligand L2 was
reacted with [PdCl2(COD)] (COD=1,5-cyclooctadiene) to give
[L2PdCl2] (c) in good yields. Sufficient photo stability of the
gold complexes was verified by recording 31P{1H} NMR spectra
of a and b before and after exposing the samples to UV light
(lmax =355 nm) for 4 h (Figure S8 in the Supporting Informa-
tion). Next, we attached the metal complexes a, b, and c in
a photo-induced Diels–Alder reaction to phenacylsulfide-deriv-
atized triethylene glycol (TEG, 1). The photoreactions were car-
ried out in methylene chloride employing a 36 W compact flu-
orescent lamp with an emission maximum at lmax =355 nm in
a custom built photoreactor (Figure S1 in the Supporting Infor-
mation). The corresponding metal complex-functionalized
oligomers 1a, 1b, and 1c were analyzed without further pur-
ification using electron spray ionization MS (ESI-MS) showing
quantitative conversion (Figure 1).
The observed changes in the m/z ratios, as well as the char-
acteristic isotopic patterns of the products, are in excellent
agreement with the theoretically expected values. In the spec-
tra of 1a and 1b a small amount of the oxidized cycloadduct
is visible, however, because the addition of the metal complex
was still successful, the side reaction will have no effects on
the efficiency of the encoding process.
The diene-functionalized metal complex a was also reacted
with phenacyl sulfide derivatized poly(ethylene glycol) mono-
methyl ether (PEG, 2) to give 2a. Due to the dispersity of the
polymer, the ESI-MS spectra of 2 and 2a (Figure S5 in the Sup-
porting Information) exhibit a distribution that is shifted com-
pletely to higher masses upon the ligation reaction. According
to these results, the applied method is not only suitable for
surface encoding but also for the efficient metal complex func-
tionalization of polymers featuring a UV-labile phenacylsulfide
endgroup. As an outlook, the incorporation of a polymeric
spacer between the surface and the metal complex could
increase the complex accessibility, for example, in catalytic
processes.
Next, we applied our method for the spatially resolved sur-
face encoding. Figure 2 summarizes the synthetic strategies for
the single and dual encoding process of the silicon substrates,
which were homogeneously prefunctionalized with a SAM of
phenacylsulfide silane (3).[10] Prior to the irradiation the sub-
strates were covered with the photomask and fixed into mask
holders (Figure 3h). The photoreactions of 3 with a, b, or
c were conducted under the same reaction conditions as used
for the test reactions. Subsequently, the surfaces were washed
thoroughly to remove any physisorbed residuals.
The patterned surfaces with the metal complexes immobi-
lized on the irradiated area of the surface were analyzed by
time-of-flight secondary ion mass spectrometry (ToF-SIMS)
imaging the spatially resolved composition of the substrate
surface with high sensitivity (Figure 3). The single encoded
surfaces were analyzed both for the fragment of the metal
counter ion, for example, ClÀ or BrÀ, as well as for fragments
Figure 1. ESI-MS spectra of 1 and the Diels–Alder-adducts 1a, 1b, and 1c.
Main peaks are enlarged on the left.
Chem. Eur. J. 2015, 21, 14728 – 14731
www.chemeurj.org
14729
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
ments assigned to the phenacyl-
sulfide moiety on substrate 3a
that are exclusively located on
the nonirradiated area. These
viable UV-activatable groups can
be addressed in another photo-
reaction to obtain dual-function-
alized substrates by two subse-
quent photoreactions. The ToF-
SIMS images of the dual-en-
coded surfaces are depicted in
Figure 3i–k. All combinations of
the employed metal complexes
(a, b, and c) were obtained,
Figure 2. Preparation of single- (top) and dual-encoded (bottom) substrates.
highlighting the versatility of our
photolithographic concept.
In summary, a highly versatile
and effective procedure for the preparation of patterned surfa-
ces with a monolayer of multiple metal complexes was devel-
oped. Solution-based reactions evidence the targeted conjuga-
tion on a molecular scale. Arbitrary structures can be produced
on the surface by simple variation of the employed photo-
mask. At the same time, other metal centers can readily be
integrated to create an entire library of encoded metal com-
plexes. ToF-SIMS imaging enabled the spatially resolved analy-
sis of the surface composition. Utilizing polymeric spacers with
variable chain lengths could additionally increase the metal
complex accessibility. As a perspective, the presented platform
technology could, for example, be employed to design highly
valuable flow-through cascade reactors where the catalytically
active metal complexes need to be arranged in a spatially
defined way.
Acknowledgements
C.B.-K. and P.W.R. acknowledge the Karlsruhe Institute of Tech-
nology (KIT) for financial support as well as the Deutsche For-
schungsgemeinschaft (DFG) through their Large Equipment
granting scheme. C.B.-K. acknowledges support for this project
from the STN program of the Helmholtz association. S.B. grate-
fully acknowledges the Fonds der Chemischen Industrie (FCI)
for a generous fellowship.
Keywords: hybrid materials
· metal-complex encoding ·
photochemistry · photolithography · surface chemistry
[1] a) D. Qin, Y. Xia, G. M. Whitesides, Nat. Protoc. 2010, 5, 491–502; b) B.
Radha, S. Kiruthika, G. U. Kulkarni, J. Am. Chem. Soc. 2011, 133, 12706–
12713.
[2] a) S. J. Adams, D. J. Lewis, J. A. Preece, Z. Pikramenou, ACS Appl. Mater.
Interfaces 2014, 6, 11598–11608; b) E. Smecca, C. Tudisco, A. E. Giuffri-
da, M. R. Catalano, A. Speghini, G. Malandrino, G. G. Condorelli, Eur. J.
Inorg. Chem. 2015, 1261–1268.
Figure 3. ToF-SIMS images of the single- (a–g) and dual-encoded (i–k) silicon
surfaces (fragment ions specified below each image). Middle: Encoded metal
complexes, the photomasks (h), and sample holder (h).
[3] a) A. Ulman, Chem. Rev. 1996, 96, 1533–1554; b) J. C. Love, L. A. Estroff,
J. K. Kriebel, R. G. Nuzzo, G. M. Whitesides, Chem. Rev. 2005, 105, 1103–
1170.
[4] a) K. Hara, R. Akiyama, S. Takakusagi, K. Uosaki, T. Yoshino, H. Kagi, M.
Sawamura, Angew. Chem. Int. Ed. 2008, 47, 5627–5630; Angew. Chem.
containing the metal ion itself (Figure 3a–f). The metal
complexes are only immobilized on the irradiated area of the
surface. Exemplarily, Figure 3g depicts the imaging of frag-
Chem. Eur. J. 2015, 21, 14728 – 14731
www.chemeurj.org
14730
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
2008, 120, 5709–5712; b) K. Hara, S. Tayama, H. Kano, T. Masuda, S. Ta-
kakusagi, T. Kondo, K. Uosaki, M. Sawamura, Chem. Commun. 2007,
4280–4282.
laittre, C. Barner-Kowollik, Angew. Chem. Int. Ed. 2013, 52, 9714–9718;
c) C. Rodriguez-Emmenegger, C. M. Preuss, B. Yameen, O. Pop-Georgiev-
ski, M. Bachmann, J. O. Mueller, M. Bruns, A. S. Goldmann, M. Bastmeyer,
C. Barner-Kowollik, Adv. Mater. 2013, 25, 6123–6127.
[5] a) C. R. Glasson, W. Song, D. L. Ashford, A. Vannucci, Z. Chen, J. J. Con-
cepcion, P. L. Holland, T. J. Meyer, Inorg. Chem. 2012, 51, 8637–8639;
b) K. S. Joya, N. K. Subbaiyan, F. D’Souza, H. J. de Groot, Angew. Chem.
Int. Ed. 2012, 51, 9601–9605; Angew. Chem. 2012, 124, 9739–9743.
[6] a) C. H. Traulsen, E. Darlatt, S. Richter, J. Poppenberg, S. Hoof, W. E.
Unger, C. A. Schalley, Langmuir 2012, 28, 10755–10763; b) A. Fernandes,
P. Hensenne, B. Mathy, W. Guo, B. Nysten, A. M. Jonas, O. Riant, Chem.
Eur. J. 2012, 18, 788–792.
[7] a) R. Sakamoto, S. Katagiri, H. Maeda, H. Nishihara, Coord. Chem. Rev.
2013, 257, 1493–1506; b) H. Maeda, R. Sakamoto, H. Nishihara, Polymer
2013, 54, 4383–4403; c) A. BØtard, R. A. Fischer, Chem. Rev. 2012, 112,
1055–1083; d) O. Shekhah, J. Liu, R. A. Fischer, C. Wçll, Chem. Soc. Rev.
2011, 40, 1081–1106.
[9] a) T. Pauloehrl, A. Welle, K. K. Oehlenschlaeger, C. Barner-Kowollik,
Chem. Sci. 2013, 4, 3503–3507; b) K. Fuchise, P. Lindemann, S. Heissler,
H. Gliemann, V. Trouillet, A. Welle, J. Berson, S. Walheim, T. Schimmel,
M. A. Meier, C. Barner-Kowollik, Langmuir 2015, 31, 3242–3253.
[10] a) M. Glassner, K. K. Oehlenschlaeger, A. Welle, M. Bruns, C. Barner-Ko-
wollik, Chem. Commun. 2013, 49, 633–635; b) O. Altintas, M. Glassner,
C. Rodriguez-Emmenegger, A. Welle, V. Trouillet, C. Barner-Kowollik,
Angew. Chem. Int. Ed. 2015, 54, 5777–5783; Angew. Chem. 2015, 127,
5869–5875; c) T. Tischer, T. K. Claus, K. K. Oehlenschlaeger, V. Trouillet,
M. Bruns, A. Welle, K. Linkert, A. S. Goldmann, H. G. Bçrner, C. Barner-Ko-
wollik, Macromol. Rapid Commun. 2014, 35, 1121–1127.
[8] a) T. Pauloehrl, G. Delaittre, V. Winkler, A. Welle, M. Bruns, H. G. Bçrner,
A. M. Greiner, M. Bastmeyer, C. Barner-Kowollik, Angew. Chem. Int. Ed.
2012, 51, 1071–1074; Angew. Chem. 2012, 124, 1096–1099; b) T. Pau-
loehrl, A. Welle, M. Bruns, K. Linkert, H. G. Bçrner, M. Bastmeyer, G. De-
Received: July 2, 2015
Published online on August 28, 2015
Chem. Eur. J. 2015, 21, 14728 – 14731
www.chemeurj.org
14731
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim