Light-driven reversible surface functionalization with anthracenes: visible light writing and mild UV erasing

Article abstract of DOI:10.1039/c6cc09897e

We introduce a methodology to reversibly pattern planar surfaces via the light-induced dimerization of anthracenes, particularly involving a 9-triazolylanthracene motif. Specifically, we demonstrate that the visible light-induced forward reaction can be employed to pattern small molecule species as well as polymers in a spatially resolved fashion. Under UV irradiation, the generated patterns can be erased to regenerate reactive areas, which are then available for a new functionalization step. The dynamic change in surface chemistry is evidenced by ToF-SIMS.

Full text of DOI:10.1039/c6cc09897e

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Telitel, A. Welle, M. Bastmeyer, A. Vogt, G. Delaittre and C. Barner-Kowollik, Chem. Commun., 2017, DOI:
10.1039/C6CC09897E.
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Light-driven reversible surface functionalization with anthracenes:
visible light writing and mild UV erasing
Tanja K. Claus,ab Siham Telitel,ab Alexander Welle,ab Martin Bastmeyer,de Andrew P. Vogt,ab
Received 00th January 20xx,
Accepted 00th January 20xx
Guillaume Delaittre,ac* Christopher Barner-Kowollikabf
*
DOI: 10.1039/x0xx00000x
www.rsc.org/
We introduce a methodology to reversibly pattern planar surfaces Norrish-type mechanism occurs around 300 nm.12 In the last
via the light-induced dimerization of anthracenes, particularly years, significant efforts were therefore undertaken to shift the
involving
a
9-triazolylanthracene motif. Specifically, we activation wavelength of photoligations to a milder regime
demonstrate that the visible light-induced forward reaction can be (above 350 nm), or even in the visible light range (above 400
employed to pattern small molecules species as well as polymers in nm). The most widely employed visible light-induced reactions
a spatially resolved fashion. Under UV irradiation, the generated employ photoredox catalysis13 and are well established.14
patterns can be erased to regenerate reactive areas, which are then However, next to the molecules to be linked, an additional
available for a new functionalization step. The dynamic change in molecule is required, e.g., a metal complex. Recently, our team
surface chemistry is evidenced by ToF-SIMS.
introduced two visible light-triggered, catalyst-free 1,3-dipolar
cycloadditions.15 Both are based on the modification of well-
known reactive motifs (azirine and tetrazole) with an electron
rich, expanded aromatic pyrene system, leading to a red shift of
the absorption spectrum. Although these reactions allow fast,
extremely mild and versatile conjugations with small molecules,
polymers, and surfaces, they lack one specific feature, i.e.,
Starting with the first experiments of Trommsdorf in 1834 on
the characteristics of santonin and its light-triggered color
change,1 researchers soon realized the importance and
attractiveness of light-induced reactions synthesis.2 Since then,
a vast variety of UV-light induced reactions such as the Paterno-
Büchi [2+2] cycloaddition,3 Norrish Type I and II reactions,4 1,3-
dipolar cycloadditions based on tetrazoles5 or azirines,6 and
[4+4] cycloadditions with anthracenes7 have been established.
Many of these reactions have proven to be powerful tools
either in organic synthesis,8 polymer conjugation,9 or for
surface functionalization.10 However, these reactions usually
entail rather harsh wavelength regimes. The Paterno-Büchi
reaction, for example, requires UVB or even UVC irradiation
(250–300 nm),11 while typical photodegradation following a
reversibility. Ideally, a photochemical reaction should be
λ-
orthogonally gated16 by one specific wavelength for the forward
reaction and another one for the reverse process. Reversibility
in photoreactions can be categorized into two processes:
photoswitches17 and (retro)cycloadditions.18 From a synthetic
point of view, cycloadditions are the more interesting of the
two, allowing for a reversible covalent linkage between two
molecules at a specific wavelength. The most widely employed
reversible cycloadditions in polymer chemistry are [2+2] and
[4+4]-type
reactions.19
Examples
for
[2+2]-based
photoreversible reactions are dimerizations of cinnamates,20
coumarins,21 or maleimides,22 whereas the most common
example for the [4+4] cycloaddition is the dimerization of
anthracene.23 Anthracenes are widely employed in polymer and
surface chemistry to achieve a range of reversible linkages, e.g.,
for block copolymer formation/fission,24 single chain
a.Preparative Macromolecular Chemistry, Institut für Technische Chemie und
Polymerchemie, Karlsruhe Institute of Technology (KIT), Engesserstr. 18, 76131
Karlsruhe E-mail: christopher.barner-kowollik@kit.edu;
christopher.barnerkowollik@qut.edu.au; guillaume.delaittre@kit.edu
b.Institut für Biologische Grenzflächen (IBG), Karlsruhe Institute of Technology (KIT)
Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
c. Institute for Toxicology and Genetics (ITG), Karlsruhe Institute of Technology (KIT),
Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
d.Zoological Institute, Cell and Neurobiology, Karlsruhe Institute of Technology
(KIT), Fritz-Haber-Weg 4, 76131 Karlsruhe, Germany
e. Institut für funktionelle Grenzflächen (IFG), Karlsruhe Institute of Technology
(KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen,
Germany
f. School of Chemistry, Physics and Mechanical Engineering, Queensland University
of Technology (QUT), 2 George Street, QLD 4000, Brisbane, Australia
Electronic Supplementary Information (ESI) available: Materials, synthetic
protocols, and additional data. See DOI: 10.1039/x0xx00000x
nanoparticle
folding/unfolding,25
supramolecular
assembly/disassembly,26 and surface writing/erasing.26
However, the reverse reaction usually entails rather harsh
conditions, i.e., either UVA irradiation or elevated
temperatures.18
To combine the benefits of a mild, visible/near UV light trigger
and achieving light-induced reversibility, we designed an
This journal is © The Royal Society of Chemistry 20xx
Chem. Commun., 2013, 00, 1-3 | 1
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Br
R
+
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DOI: 10.1039/C6CC09897E
a
b
c
R
R
N
Visible light (410 nm)
mild UV light (360 nm)
N
N
N
N
N
N
N
N
N
N
N
N
O
N
N
N
O
O
N
O
NH
O
N
-
N
R
R = Br or polymer
1 mm
1 mm
1 mm
1 mm
360 nm
48 h
Scheme 1. Reversible surface functionalization via anthracene dimerization, involving
an anthracene derivative with electron-rich substitution at the 9-position to red-shift
the absorption spectrum and allow for entirely light-based reversible reactivity.
N
N
N
electron-rich anthracene derivative to produce rewritable
surfaces (Scheme 1). The red shift in absorption for the forward
as well as the backward reactions is enabled by tethering an
electron-rich triazole ring at the 9-position of anthracene.27 This
is obtained through an efficient synthetic route (see Scheme 2),
O
HN
410 nm
4 h
which includes a Sonogashira cross-coupling reaction,
deprotection, and copper-catalyzed azide–alkyne
cycloaddition to yield the acid derivative . The latter can then
be further modified by either esterification or amidation. To
achieve our aim of a recodable surface, was coupled to (3-
aminopropyl)triethoxysilane to generate the functional silane
a
a
Br
4
N
N
N
4
5
(Scheme 2), allowing for its anchoring onto silicon surfaces. For
synthetic procedures and characterization, refer to the
Supporting Information. Subsequently, silanization of activated
O
NH
wafers with 5 led to the visible light-reactive surface.
To initially assess the reactivity of the surface-tethered
triazolylanthracene, we first employed a commercially available
brominated anthracene derivative, as halogens typically
enables unambiguous characterization by time-of-flight
secondary-ion mass spectrometry (ToF-SIMS). Thus, a coated
silicon wafer was irradiated for 4 h through a dotted photomask
in the presence of 9-bromoanthracene (9-BA) with a custom
made LED setup at 410 nm (1 mg/mL in DCM). For the retro-
cycloaddition, the patterned silicon surfaces were simply placed
in solvent and irradiated at 360 nm (mild UVA light) with a low
intensity, commercially available UV lamp for 48 h to fully
remove the immobilized anthracenes. To follow the success of
the surface coding and erasing, ToF-SIMS allows for an in-depth
360 nm
d
48 h
N
N
N
O
HN
0.50
1.00
0.00
Sum of bromine fragments
Figure 1. ToF-SIMS ion maps of 79Br- plus 81Br- for the writing and erasing of 9-BA patterns
obtained after irradiation of a silicon wafer: a) visible light (410 nm) for 4 h in the
presence of 9-BA (1 mg/mL in DCM); b) mild UV light (360 nm, 48 h, DCM); c) same as
a); d) same as b).
Pd(PPh3)2Cl2
CuI
TMS
Piperidine
TEA
K2CO3
Br
THF/MeOH
TMS
+
110 °C
98 %
RT
2
99 %
chemical and spatial characterization with high sensitivity. The
ToF-SIMS results for writing and erasing a dot pattern of 9-BA
onto an activated silicon wafer are shown in Figure 1. Note that
the same wafer is employed through all the steps and that the
ToF-SIMS images have all been referenced to the same intensity
to ensure comparability of the results. Figure 1a depicts the first
coding step: a clean dot pattern of bromine fragments,
characteristic of the attached 9-BA, is observed. Successful
removal of the pattern is evidenced in Figure 1b. In order to
prove the recovered reactivity of the previously written and
erased areas, this same wafer was subjected to the exact same
cycle again. After irradiating a second time with visible light in
1
Cu(I)Br
PMDETA
Toluene/DMF
1:1 (v:v)
RT
N3
HO
O
+
76 %
3
1) CDI
2) APTS
THF
O
N
N
HN
N
N
N
RT
68 %
N
Si
O
O
5
4
O
O
OH
Scheme 2. Four-step synthetic pathway to obtain the visible light-sensitive anthracene
derivative for surface modification.
2 | Chem. Commun., 2012, 00, 1-3
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P1
+
Figure 2a: C7H7 map). For the retro-cycloaddition, the
View Article Online
a
DOI: 10.1039/C6CC09897E
patterned silicon surface was placed in pure acetonitrile (MeCN)
N
N
and irradiated at 360 nm for 48 h. After the successful removal
+
N
of P1
(
Figure 2b: C7H7 map, identical analysis parameters and
scale as Figure 2a), the same silicon wafer was placed back
below the photomask and irradiated at 410 nm for 4 h in the
presence of P2 (2 mg/mL in MeCN) to rewrite the surface
O
NH
(
Figure 2c: sum of C3H3O2-, C2HO-, C4H9O-, C2H3O-, C4H3O-, CHO2-
1 mm
, C3H3O-, 79Br- and 81Br-). As a last step, the surface was again
360 nm
48 h
placed in pure MeCN and irradiated at 360 nm for 48 h to erase
b
c
the pattern once more
(Figure 2d: same fragments,
measurement parameters and comparable scale as 2c). Again,
the same wafer is employed through all the steps. In order to
ensure the comparability between written and erased surfaces,
ToF-SIMS images have been referenced two-by-two to the
adequate corresponding fragment intensity scales according to
the considered polymer (either P1 or P2): Figures 2a and 2b for
P1 fragments and Figures 2c and 2d for P2 fragments. Figure 2a
displays a clear dot pattern of the characteristic fragments of
the polystyrene repeating unit, proving the amenability of the
visible light-induced dimerization for polymer attachment. The
stability of the written pattern upon storage was assessed by
storage for 3 months under ambient conditions, yet away from
light, before removal of the pattern. This showed the absence
of oxidation or other possible side reaction occurring after a
long storage time. The removal of the pattern was carried out
afterwards and is shown in Figure 2b, where a clear drop of the
intensity is observed compared to Figure 2a. Re-irradiation of
the wafer with P2 under visible light yielded a dot pattern of
characteristic fragments for the backbone of P2 as well as for
the bromine end group, as depicted in Figure 2c, and proved the
reactivity of the erased patterns of P1. In a final step, the
pattern of P2 could be removed again, as indicated by the drop
in intensity of the measured fragments of P2 in Figure 2d.
As further evidence for the powerful nature of our recoding
procedure, the ability to pattern more than one functional
anthracene onto one surface was investigated. To achieve a
N
N
N
O
HN
1 mm
410 nm
4 h
P2
N
N
N
O
NH
1 mm
360 nm
48 h
d
N
N
N
O
HN
1 mm
O
Br
n
O
S
0.50
1.00
0.00
n
O
Sum of characteristic
fragments of P1 or P2
O
S
dual functional pattern on the surface, a 5-coated wafer was
irradiated at 410 nm in the presence of 9-BA (1 mg/mL in DCM)
for 4 h, which resulted in a surface homogeneously grafted with
P1
P2
Figure 2. ToF-SIMS ion maps for the writing and erasing of two polymer patterns
obtained after irradiation of a silicon wafer: a) visible light (410 nm) for 4 h in the
presence of P1 (2 mg/mL in DCM); b) mild UV light (360 nm, 48 h, MeCN); c) visible light
the
bromine-functionalized
anthracene.
This
fully
functionalized wafer was subsequently placed in pure MeCN
(410 nm) for 4 h in the presence of P2 (2 mg/mL in MeCN); d) mild UV light (360 nm, and irradiated at 360 nm for 48 h through the dotted
48 h, MeCN).
photomask to achieve
a negative dot pattern of free
triazolylanthracene. This was followed by filling back the
reactive dots with polymer through masked irradiation of a
solution of P1 (2 mg/mL in MeCN) at 410 nm for 4 h. The
resulting dual pattern of 9-BA and P1 was analysed via ToF-
SIMS, see Figure 3. The first two ion maps (Figures 3a and 3b)
depict the individual ion maps corresponding to bromine and
P1-related fragments, respectively. Both exhibit a clear contrast
evidencing once more the efficiency of the erasing process
(Figure 3a) and the recovered reactivity towards dimerization of
the erased areas (Figure 3b). Figure 3c is an overlay of the two
individual ion maps and showcases the ability of our method to
produce multifunctional surfaces with the help of mild
photochemical activation.
the presence of 9-BA, a clear dotted pattern could be observed
again (Figure 1c). In a last irradiation step with mild UV light, the
pattern could finally be removed (Figure 1d). Potential
dimerization of two adjacent surface-bound triazolylanthracene
cannot be entirely discarded, yet seems clearly less efficient due
to unfavorable electronic considerations (see Figure S21). To
further investigate the scope of the process, we decide to
write/erase larger molecules, i.e., two polymers. Anthracene
end-functionalized polystyrene (P1) and poly(n-butyl acrylate)
(
P2
)
were synthesized by reversible-deactivation radical
-coated
polymerization (see Supporting Information). Again, a
5
silicon wafer was irradiated for 4 h through a photomask, this
time in the presence of P1 at 410 nm (2 mg/mL in DCM; see
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0.50
0.00
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5
1 mm
79
-
81
-
6
7
Br ,
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b
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-
81
Overlay of sum of Br , Br
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and sum of C H
,
CC H
7
7
6 7
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P. Lederhose, K. N. Wust, C. Barner-Kowollik and
Figure 3. ToF-SIMS ion maps obtained after dual functionalization of a silicon wafer with
9-BA (no mask, 410 nm, 4 h), erasing a dot pattern (360 nm, 48 h) and back-filling the
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In summary we report a synthetically readily accessible triazole-
substituted electron-rich anthracene derivative that is
amenable to fully light-driven reversible dimerization with
classic anthracene compounds. Importantly, the cycloaddition
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was directly investigated for surface patterning and proved
successful for writing and erasing patterns of low-molar-mass
anthracenes as well as anthracene-terminated polymers. In
depth ToF-SIMS analyses evidenced a successful recovery of the
surface reactivity after writing and erasing cycles, allowing to
fully re-pattern the surface or to access multifunctional
patterns. Owing to its mild operating irradiation conditions, we
envision that our methodology could be transferred to a
biopatterning context.
The authors thank V. Trouillet for one XPS analysis. C.B.-K., M.B.,
and G.D. acknowledge funding for this project from the German
Research Council (DFG). C.B.-K. additionally acknowledges long
term funding from the Karlsruhe Institute of Technology (KIT) in
the context of the BIFTM and STN program of the Helmholtz
association. G.D. thanks the German Federal Ministry of
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Notes and References
1
H. Trommsdorf, Annaler der Pharmacie, 1834, 11, 190-207.
4 | Chem. Commun., 2012, 00, 1-3
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