Wavelength-selective caged surfaces: How many functional levels are possible?

Article abstract of DOI:10.1021/ja110572j

The possibility of wavelength-selective cleavage of seven photolabile caging groups from different families has been studied. Amine-, thiol-, and carboxylic-terminated organosilanes were caged with o-nitrobenzyl (NVOC, NPPOC), benzoin (BNZ), (coumarin-4-yl)methyl (DEACM), 7-nitroindoline (DNI, BNI), and p-hydroxyphenacyl (pHP) derivatives. Caged surfaces modified with the different chromophores were prepared, and their photosensitivity at selected wavelengths was quantified. Different pairs, trios, and quartets of chromophore combinations with wavelength-selective photoresponse were identified. Our results show, for the first time, the possibility of generating surfaces with up to four different and independently addressable functional levels. In addition, this manuscript presents the first systematic comparison of the photolytic properties of different photolabile groups under different irradiation conditions.(Figure Presented)

Full text of DOI:10.1021/ja110572j

ARTICLE
pubs.acs.org/JACS
Wavelength-Selective Caged Surfaces: How Many Functional Levels
Are Possible?
Verꢀonica San Miguel,† Christian G. Bochet,‡ and Arꢀanzazu del Campo*,†
†Max-Planck-Institut f€ur Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany
‡Department of Chemistry, University of Fribourg, Chemin du Musꢀee 9, CH-1700 Fribourg, Switzerland
S Supporting Information
b
ABSTRACT: The possibility of wavelength-selective cleavage of seven photolabile caging
groups from different families has been studied. Amine-, thiol-, and carboxylic-terminated
organosilanes were caged with o-nitrobenzyl (NVOC, NPPOC), benzoin (BNZ),
(coumarin-4-yl)methyl (DEACM), 7-nitroindoline (DNI, BNI), and p-hydroxyphenacyl
(pHP) derivatives. Caged surfaces modified with the different chromophores were prepared,
and their photosensitivity at selected wavelengths was quantified. Different pairs, trios, and
quartets of chromophore combinations with wavelength-selective photoresponse were
identified. Our results show, for the first time, the possibility of generating surfaces with
up to four different and independently addressable functional levels. In addition, this
manuscript presents the first systematic comparison of the photolytic properties of different
photolabile groups under different irradiation conditions.
’ INTRODUCTION
similar approach to photoregulate cell adhesion and to obtain
micropatterns of cells on different substrates.4c Bifunctional
surfaces containing two types of chromophores have also been
developed in our group and tested for site-selective immobiliza-
tion of oligonucleotides and proteins.3h,i,4a,4f,13 This is a particu-
larly flexible approach, since a good number of photoremovable
groups are known that could be combined with the different
organic functional groups and applied to generate biosensors and
cell-responsive surfaces with a great number of biochemically
tunable states. However, this requires previous knowledge on the
photoreactivity of the different chromophores across the absorp-
tion spectrum.
In this manuscript we report the wavelength-selective photo-
lysis of seven surface-attached photoremovable groups that
belong to different families. Caged organosilanes have been
synthesized, and the resulting caged surfaces have been irradiated
with different wavelengths and doses. Our results evidence the
potential of this approach for generating photoactivatable sur-
faces with up to four independent functional levels that can be
tuned with accurate spatial, temporal, and compositional
resolution.
Photolabile caged compounds1 have been used over the last
30 years in cell biology to photoregulate the activity of different
bioactive agents.2 The biological activity of the caged com-
pound is blocked because of the presence of a (in most cases)
covalently bound chromophore. Light irradiation cleaves the
chromophore and restores function. Using this approach de-
fined concentration jumps of a bioeffector (i.e., Ca2þ, ATP,
glutamate) have been generated in the cell culture medium
within microseconds. More recently the activity of two different
molecular species could be photoregulated independently
based on the wavelength-selective response of two chromo-
phores.3 For this purpose, o-nitroveratryl esters have been used
in combination with pivaloylpropanediol,3e 3,5-dimethoxy-
benzoin,3c,h (coumarin-4-yl)methyl,3f,g,i and derivatives upon
single-3 or two-photon3g excitation.
Compared to other external stimuli, light offers a precise
spatiotemporal control of the activation step. For this reason,
photolabile caged compounds have been used in the past few
years to prepare chemically micropatterned surfaces based on
surface layers containing caged chemical functionalities.3h,i,4
Using masks or arrays of micromirrors for site-selective irradia-
tion, reactive sites down to submicrometer size can be activated
and used for subsequent attachment of other species. This
strategy has been exploited to directly synthesize biomolecules
at surfaces in an array format (microarrays) by means of iterative
light-activation and monomer coupling cycles.4b,5 Microarrays of
peptides,4b,6 oligonucleotides,7 and peptoids8 have been re-
ported. Other species such as metallic nanoparticles,9 polymer
colloids,3h,10 fluorescent dyes,10,11 or biotinylated proteins4e,12
have also been patterned using caged surfaces. We have used a
’ EXPERIMENTAL SECTION
Synthetic Procedure. All protocols for the synthesis of the
photolabile derivatives (Scheme 1) and the preparation of the photo-
sensitive surface layers are included as Supporting Information.
Received: December 6, 2010
Published: March 17, 2011
r
2011 American Chemical Society
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|

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Scheme 1. Synthetic Route and Chemical Structure of Obtained Photosensitive Silanes
Characterization of Surface Layers. Chromophore concentra-
tion at the surface was followed by recording UV/vis spectra on quartz
substrates. The surface density of the chromophore, Γ (molecs cmꢀ2),
sources. The wavelengths and irradiances used with the Polychrome
lamp were as follows: 345 nm (0.78 mW cmꢀ2), 350 nm (0.80
mW cmꢀ2), 358 nm (0.95 mW cmꢀ2), 366 nm (1.08 mW cmꢀ2),
412 nm (1.47 mW cmꢀ2), 420 nm (1.53 mW cmꢀ2), and 435 nm
(1.60 mW cmꢀ2); and with LUMOS 43 were as follows: 255 nm (0.45
mW cmꢀ2), 275 nm (1.65 mW cmꢀ2), 300 nm (1.76 mW cmꢀ2),
360 nm (2.55 mW cmꢀ2), 420 nm (364 mW cmꢀ2), and 435 nm
(262 mW cmꢀ2). After irradiation, substrates were sonicated in THF
and rinsed with Milli-Q water before recording UVꢀvis spectra.
Figure A in Supporting Information shows the UV spectra of the
different lamps.
Calculation of the Photolytic Efficiency at Different Wa-
velengths (conversion and ελO product). The conversion of the
photolytic reaction was calculated from the absorbance decay at λmax
measured by UV spectroscopy on modified quartz substrates after
exposure with increasing dose and washing. The ratio of the
can be estimated from the UV absorbance using Γ = /2[Aλελꢀ1NA],
1
where Aλ is the absorbance of the surface layer at a given wavelength, ελ
is the molar extinction coefficient of the chromophore in solution at λ,
and NA is Avogadro’s number.14ꢀ17 The factor 1/2 refers to the fact that
the quartz slides are modified on both sides. Note that this calculation
assumes that the molar extinction coefficients of the chromophores in
solution and at the surface are the same. This is true only if anchored
chromophoreꢀchromophore or chromophoreꢀsurface interactions are
disregarded.14
Photolysis Experiments at the Surface. Irradiation of the
substrates was carried out using a Polychrome V system (TILL
Photonics GmbH, Gr€afelting, Germany) and a LUMOS 43 (Atlas
Photonics Inc., Fribourg, Switzerland) as monochromatic light
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Figure 1. Comparative UV spectra of caged silanes in solution (a) and modified quartz surfaces (b).
Figure 2. Photolysis conversion (%) versus irradiation dose of each chromophore at different wavelengths.
absorbance at λmax after irradiation to the amount of initial absor-
bance multiplied by 100 gave the percent of chromophore remaining
after exposure for a given time. From this, the conversion (%) upon
exposure was found by subtraction for the different doses. The
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Scheme 2. Schematic Mechanism of Photocleavage and Photolytic Products of Modified Surfaces with Caged Silanes
Table 1. Spectroscopic Data of Different Caging Groups and
Caged Compounds in THF
absorption coefficient
chromophores
λmax [nm]
(ελmax) [Mꢀ1 cmꢀ1
]
nitroveratrol
346
350
340
340
350
245
247
365
385
363
357
358
434
366
366
268
267
267
7159
2499
457
NVOC-APTS (1)
NPPOC
2
471
NPPOC-APTS (3)
331
4
9979
6388
17429
7805
15710
13743
7478
7068
3594
2231
15993
9834
5988
BNZ-CPTS (5)
7
DEACM-TPTS (8)
DNI
11
Figure 3. Conversion (%) of the photocleavage at the surface of the
chromophore pHP-CPTS upon irradiation at different wavelengths and
the UV spectrum of the corresponding silane (inset).
DNI-APTS (13)
BNI
12
BNI-APTS (14)
pHP
dx
¼ ꢀ I0 lnð10Þελφx
dt
16
pHP-CPTS (17)
which was specially developed for photolysis experiments at
surfaces.18 In this equation x represents the relative surface coverage
of the photoreactive group, and I0 is the illumination intensity in
Einstein per units of time and area.
product ελφ for each exposure wavelength and chromophore was
calculated by fitting the conversion curves to the photokinetic
equation
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’ RESULTS
extent to the surface layer. We hypothesized that the photo-
products may strongly interact with the surface and that their
diffusion out of the dense surface layer may be hindered. In
addition, side reactions may reattach reactive photolysis products
to the surface (i.e., reaction of the aldehyde photoproduct with
the free amines in NVOC).3h In fact, we soaked the substrates in
different solvents for long periods of time prior to and after
photolysis for facilitating diffusion of precursors out of the layer,
and we used scavengers for capturing reactive byproduct, but
none of these measurements reduced the residual absorbance. In
summary, the measured spectra entailed two overlapping con-
tributions: a major contribution from the remaining caged
compound, and a minor contribution from photolytic products
that remain attached to the surface layer. This is especially the
case for the chromophores with a UV-absorbing byproduct such
as nitroveratryl and nitroindoline derivatives.
From the recorded UV spectra, we calculated the amount of
photocleaved chromophore upon exposure (conversion) from
the ratio between the absorbance at λmax before and after
irradiation. Note that these values are subjected to two error
sources. First, thin surface layers give low values of absorbance
(typically <0.01) and the error in these measurements, especially
at high conversions (i.e., low chromophore concentration at the
surface) is ca. 15%. Second, we cannot subtract the contribution
of the residual absorbance from the spectra, and therefore
conversion values are underestimated (i.e., they represent the
“worst” case).
Figure 2 shows the photolytic conversion of each chromo-
phore upon exposure to different wavelengths and irradiation
doses. The differences in the photosensitivity reflect the intensity
of the absorption bands at the UV spectrum of the chromophore
and, as expected, the photosensitivity of the chromophores is
maximized when irradiating close to λmax. Figure 3 shows the
results for pHP cage together with its absorption spectrum to
illustrate this point.
Figure 4 compares the photosensitivity of the different chro-
mophores at a selected wavelength. This representation allows us
to assess the potential and limitations of the chromophores for a
wavelength-selective response. At 255 nm BNZ was fully photo-
cleaved with low irradiation dose (1.1 ꢁ 102 mJ cmꢀ2) while all
other cages remained stable under these conditions (but could be
cleaved at higher doses). The comparative high efficiency of BNZ
at this wavelength can be explained by its remarkably high φ (see
Table B in Supporting Information for reported values of φ for
the different chromophores). At 275 nm, BNZ was cleaved
completely and pHP was cleaved up to 70% with doses up to 5
ꢁ 102 mJ cmꢀ2 while the other cages were not affected
significantly. The notable increase in efficiency of pHP from
255 to 275 nm correlates with the higher ε275. pHP could be
selectively cleaved at 275 nm against coumarin, nitroindoline, or
dimethoxynitroveratryl families.
Amine, thiol, and carboxylic groups were caged with seven
different chromophores belonging to five families: o-nitrobenzyl
(NVOC, NPPOC), benzoin (BNZ), (coumarin-4-yl)methyl
(DEACM), 7-nitroindoline (DNI, BNI), and p-hydroxyphenacyl
(pHP). The photosensitive silanes 1, 3, 5, 8, 13, 14, and 17 were
obtained and isolated in good yields following the synthetic route
specified in Scheme 1. The detailed synthetic protocols are
included as Supporting Information.
Figure 1a shows the UVꢀvis spectra of the photosensitive
silanes in solution, and Table 1 compares the values of λmax and
the absorption coefficient of the silanes and their precursors. The
caging reaction involves formation of a carbamate, carbonate, or
ester bond. This modification does not significantly change the
shape of the UV spectra of the chromophore, and the position of
λmax remains almost unchanged. Only BNI shows a 70 nm blue
shift of the maximum, which is explained by the fact that the
functionalization occurs directly on a conjugated functional
group (aniline-type nitrogen). However, the caging step signifi-
cantly decreases the absorbance of the chromophores by a factor
of 2 to 3 times. It is important to note that a decrease in
absorbance has a negative effect in the overall photolytic effi-
ciency. The absorbance coefficient also decreases upon silaniza-
tion. We do not have an explanation of these observations.
Figure 1b shows the UV spectra of the photosensitive silanes
after reaction with the silica surface. The general profile of the UV
spectra of the chromophores after surface attachment is similar to
solution spectra. This suggests that the attached chromophores
do not interact with the surface or within themselves, and
therefore we do not expect surface-induced variations of the
photochemical properties. From the absorbance values, and
assuming the same absorbance coefficient of the chromophore
at the surface and in solution, the surface density of chromophore
can be estimated (see Experimental Section part for details).
Values between 1.5 and 8 ꢁ 1014 molecs cmꢀ2 were obtained,
indicating a submonolayer surface coverage (note that surface
density of a self-assembled monolayer of thiols on gold with
maximum coverage19 is 4.5 ꢁ 1014 molecs cmꢀ2, whereas DNA
coverages on DNA chips are typically smaller5b and in the range
between 1012 and 1013 molecs cmꢀ2). The spectra display
significant differences in absorbance between the chromophores
across the spectrum that can be exploited for chromatic selec-
tivity. The following irradiation experiments address this
question.
The modified substrates were exposed to light of selected
wavelengths between 255 and 435 nm using two different light
sources: a Xe-lamp coupled to a monochromator and a LED-
based source (see Experimental Section for details). The photo-
lytic reaction cleaved the chromophore from the surface (see
Scheme 2), and the kinetics of the photolysis could be followed
by the decay in the UV absorbance of the substrates after
irradiation and a washing step (Figure B in Supporting Informa-
tion shows the UV spectra of the substrates before and after full
exposure at 255 nm). After full exposure (i.e., when longer
irradiation did not further change the UV spectrum), almost
no UV absorbance could be detected in pHP and BNZ sub-
strates. However, a residual absorbance was visible for the other
chromophores. The residual spectra show a profile different from
that of the original one, indicating a change in the chemical
structure of the surface-attached chromophore. This suggests
that photolysis products remained attached (or trapped) to some
Irradiation at 300 nm cleaved all chromophores at comparable
doses, and no selectivity could be detected. However, at
∼350 nm it was possible to cleave NVOC, DEACM, BNZ,
and DNI up to 70% while pHP and BNI remained stable. It is
important to note that NVOC, DEACM, BNZ, and DNI have
their absorption maxima in this region while pHP does not
absorb at λ > 300 nm and, therefore, remained stable against
irradiation at longer wavelengths. Reported studies have found a
low quantum yield of the photocleavage of BNI15 (see Table B in
Supporting Information), and this could be the reason for the low
conversion in comparison to the other chromophores under
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Figure 4. Conversion (%) of the photocleavage at the surface upon irradiation at different wavelengths.
these exposure conditions, even at a wavelength close to λmax. In
fact, irradiation at 360 nm with higher doses also cleaved BNI.
Irradiation at 412 nm cleaved DEACM and DNI up to 60%
while NVOC and BNZ remained stable. At 420 nm NVOC,
DEACM, and DNI cages reached their maximum photocon-
version at a similar dose (4.2 ꢁ 105 mJ cmꢀ2), even though
they presented a wide difference in ε420. Obviously the change
in the molar absorption coefficient is compensated by a change
in the quantum yield. BNZ does not absorb in that region, and
therefore it remained at the surface upon irradiation at
wavelengths longer than 420 nm. Irradiation at 420 nm with
a lower dose (4.8 ꢁ 103 mJ cmꢀ2) allowed the cleavage of
DEACM up to 50% without affecting DNI and NVOC
significantly. At 435 nm, DEACM could be differentiated
and was cleaved up to 70%, while the other chromophores
remained stable.
The photosensitivity is determined by the product of the
absorption coefficient (ελ) and the quantum yield (φ) of the
photolytic reaction at the given wavelength. We obtained the
experimental value of the product ελφ from the conversion curves
by fitting them to a photokinetic equation modeling the special case
of photolysis at surfaces (see ref 18 and Experimental Section part
for more details). Table 2 presents the obtained values of ελ φfor the
different caged compounds. It is important to highlight that these
values are affected by the underestimated conversion values due to
residual absorbance in the UV spectra (as stated before). This
means that they should be regarded as orientative but not accurate,
as it is typically assumed from solution experiments where the
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Table 2. Calculated Values of the Product ελO for the Caged
Organosilanes Obtained by Fitting the Experimental Con-
version Data in Figure 4 Following the Photokinetic Equation
from Ref 18a
Table 3. Final Conversion Data (%) of the Photocleavage at
the Surface for Silanesa
caged silanes
λ [nm]
(E [mJ cmꢀ2])
NVOC NPPOC BNZ DEACM DNI BNI pHP
cages
λirradiation (nm)
ελφ (Mꢀ1cmꢀ1
)
(1)
(3)
(5)
(8)
(13) (14) (17)
NVOC (1)
255
275
300
345
360
412
420
435
255
255
275
300
350
360
255
275
300
345
360
412
420
435
255
275
300
358
360
412
420
435
255
366
360
255
275
300
310
504
370
380
97
255 (1.1 ꢁ 102)
255 (2.2 ꢁ 103)
275 (3.0 ꢁ 102)
275 (5.0 ꢁ 102)
300 (6.3 ꢁ 102)
300 (2.1 ꢁ 103)
X
50
55
--
100
100
100
100
72
X
X
X
30
--
57
98
60
92
81
81
X
57
37
55
60
89
70
68
X
32
X
--
27
X
24
50
65
52
--
--
--
43
--
72
21
62
--
0.61
0.30
1167
8239
4001
1206
263
65
∼350 (2.9
ꢁ
--
82
25
103)
NPPOC (3)
BNZ (5)
360 (6.1 ꢁ 103)
412 (4.5 ꢁ 103)
420 (4.2 ꢁ 105)
435 (6.3 ꢁ 105)
81
X
--
--
--
--
100
X
75
58
88
70
64
34
65
30
71
--
X
--
--
--
81
30
X
--
X
--
a Data reflect possible chromophore combinations for a wavelength-
selective response. The symbol X indicates that the chromophore
cannot be cleaved under the corresponding conditions. The symbol --
indicates that the photolysis experiment was not performed at that
wavelength because, according to the results at neighboring wavelengths
and the expected photosensitivity from the UV spectrum, no relevant
wavelength sensitive response was expected.
DEACM (8)
517
136
69
135
75
126
2.2
(see Figure C in Supporting Information for data with DNI-
APTS). It seems that adsorbed water on the surface layers as a
consequence of air humidity acts as a protic solvent component
for the photolysis.
0.91
589
221
170
128
84
DNI (13)
’ DISCUSSION
We have demonstrated that photoremovable caging groups
maintain their photochemical properties when attached to
surfaces. Table 3 summarizes the values of the final conversion
at full exposure for the different chromophores and wavelengths.
According to these data, the following combinations of pairs,
trios, and quartets have shown wavelength-selective responses
within different spectral regions. The following list specifies the
ones in which the cleavage of the chromophore is achieved at
conversion values >70% (according to Table 3). The energy
doses under which we have proofed the wavelength sensitivity
appear in parentheses. This list proves that caged surfaces with up
to four different functional levels can be obtained. Up to now
only bifunctionality had been demonstrated.3c,d,h,i
Pairs:
237
1.09
0.27
385
89
BNI (14)
pHP (17)
47
540
1379
1473
a See Experimental Section and Table A in Supporting Information for
more details.
contributions to absorbance from the photolysis products can be
accurately determined. Because a direct measurement of ελ of the
chromophore at the surface is not accessible, we cannot make an
accurate estimation of φ (a rough estimation could be made by
taking the value of ελ of the chromophore in solution included in
Table A in Supporting Information).
The collection of data presented above was recorded by
irradiating the modified (dry) substrate under ambient condi-
tions. However, according to reported data on the photolysis of
pHP, DEACM, DNI, and BNI in solution, the presence of protic
solvents alters the photolytic mechanism, products, and
kinetics.2b We performed the same experiments by irradiating
the substrate immersed in a water-containing solution. No
significant differences in the photolysis data could be observed
(1) BNZ (5) at 255 nm (1.1 ꢁ 102)/NVOC (1) at 420 nm
(4.2 ꢁ 105); orthogonal
(2) BNZ (5) at 255 nm (1.1 ꢁ 102)/DEACM (8) at 420 nm
(4.2 ꢁ 105); orthogonal
(3) BNZ (5) at 255 nm (1.1 ꢁ 102)/DNI (13) at 420 nm
(4.2 ꢁ 105); orthogonal
(4) DEACM (8) at 420 nm (4.2 ꢁ 105)/pHP (17) at 275 nm
(5.0 ꢁ 102)
(5) pHP (17) at 300 nm (6.3 ꢁ 102)/DEACM (8) at 420 nm
(4.2 ꢁ 105); orthogonal
(6) DNI (13) at 360 (6.1 ꢁ 103)/pHP (17) at 275 nm
(5.0 ꢁ 102); orthogonal
(7) NVOC (1) at 360 (6.1 ꢁ 103)/pHP (17) at 275 nm
(5.0 ꢁ 102)
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(8) BNZ (5) at 360 nm (6.1 ꢁ 103)/pHP (17) at 275 nm
(5.0 ꢁ 102)
’ ACKNOWLEDGMENT
The authors thank Josꢀe María Alonso and Gemma Rodríguez
for previous work in this field and support in the synthetic
protocols and also thank Michele Drechsler for support in the
synthetic work. A.d.C. and V.S.M. thank DFG (Project CA880/
3-1) for financial support.
Trios:
(9) DEACM (8) at 435 nm (6.3 ꢁ 105)/NVOC (1) at
420 nm (4.2 ꢁ 105)/BNZ (5) at 255 nm (1.1 ꢁ 102)
(10) DEACM (8) at 435 nm (6.3 ꢁ 105)/NVOC (1) at
360 nm (6.1 ꢁ 103)/pHP (17) at 275 nm (5.0 ꢁ 102)
(11) DEACM (8) at 435 nm (6.3 ꢁ 105)/DNI (13) at
420 nm (4.2 ꢁ 105)/BNZ (5) at 255 nm (1.1 ꢁ 102)
(12) DEACM (8) at 435 nm (6.3 ꢁ 105)/DNI (13) at
420 nm (4.2 ꢁ 105)/pHP (17) at 275 nm (5.0 ꢁ 102
(13) DEACM (8) at 435 nm (6.3 ꢁ 105)/BNZ (5) at
360 nm (6.1 ꢁ 103)/pHP (17) at 275 nm (5.0 ꢁ 102)
(14) NVOC (1) at 420 nm (4.2 ꢁ 105)/BNZ (5) at 360 nm
(6.1 ꢁ 103)/pHP (17) at 275 nm (5.0 ꢁ 102)
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(15) DNI (13) at 420 nm (4.2 ꢁ 105)/BNZ (5) at 360 nm
(6.1 ꢁ 103)/pHP (17) at 275 nm (5.0 ꢁ 102)
Quartets:
(16) DEACM (8) at 435 nm (6.3 ꢁ 105)/NVOC (1) at
420 nm (4.2 ꢁ 105)/BNZ (5) at 360 nm (6.1 ꢁ 103)/
pHP (17) at 275 nm (5.0 ꢁ 102)
(17) DEACM (8) at 435 nm (6.3 ꢁ 105)/DNI (13) at
420 nm (4.2 ꢁ 105)/BNZ (5) at 360 nm (6.1 ꢁ 103)/
pHP (17) at 275 nm (5.0 ꢁ 102)
Not all combinations of cages are orthogonal, meaning that in
the irradiation sequence one chromophore should always be
cleaved before the other. Only the orthogonality between NVOC
and BNZ had been proofed already and exploited in solution3c
and surface experiments.3h Our results extend the number and
wavelength range of orthogonal deprotection to five different
combinations of cages (as indicated in the list).
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For DEACM and BNZ, selective photocleavage was obtained
by changing the energy dose using the same wavelength. Such
intensity-selective uncaging could be important for sensing
applications.
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’ SUMMARY
We have analyzed the photolysis of seven different surface-
attached photolabile groups at different wavelengths and identi-
fied spectral windows where the chromophores show different
photosensitivities. Our results demonstrate that caged surfaces
with up to four independently photoactivatable functional levels
can be obtained using DEACM/NVOC and DNI/BNZ/pHP as
chromophores and 435/420/360/275 nm as an irradiation
sequence. An extension of the number of functional levels by
using other caging families or two-photon excitation is a work in
progress in our groups.
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Natl. Acad. Sci. U.S.A. 2002, 99, 5034.
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Jonas, U.; Kreiter, M. Adv. Mater. 2008, 20, 4563.
’ ASSOCIATED CONTENT
S
Supporting Information. Synthetic protocols, UV spec-
b
tra of the irradiation sources, UV spectra of caged surfaces after
full exposure, conversion data of DNI-APTS in the presence/
absence of water, and the calculated ελφ product for the caged
organosilanes. This material is available free of charge via the
Internet at http://pubs.acs.org.
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ꢀ
(13) Alvarez, M.; Best, A.; Unger, A.; Alonso, J. M.; del Campo, A.;
Schmelzeisen, M.; Koynov, K.; Kreiter, M. Adv. Funct. Mater. 2010,
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’ AUTHOR INFORMATION
Corresponding Author
delcampo@mpip-mainz.mpg.de
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Journal of the American Chemical Society
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