Controlled light-mediated preparation of gold nanoparticles by a Norrish type i reaction of photoactive polymers

Article abstract of DOI:10.1002/anie.201505133

Gold nanoparticles (AuNPs) are subjects of broad interest in scientific community due to their promising physicochemical properties. Herein we report the facile and controlled light-mediated preparation of gold nanoparticles through a Norrish type I reaction of photoactive polymers. These carefully designed polymers act as reagents for the photochemical reduction of gold ions, as well as stabilizers for the in situ generated AuNPs. Manipulating the length and composition of the photoactive polymers allows for control of AuNP size. Nanoparticle diameter can be controlled from 1.5 nm to 9.6 nm. Instant preparation of Au nanoparticles! Mixing a photoactive polymer with HAuCl₄ and NaOH in DMF/H₂O and irradiating with light for a few minutes provides stable, spherical, polymer-coated Au nanoparticles with defined diameter. The diameter can be adjusted from 1.5 to 9.6 nm by varying the length and composition of the photoactive polymer.

Full text of DOI:10.1002/anie.201505133

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Angewandte
Communications
International Edition: DOI: 10.1002/anie.201505133
German Edition: DOI: 10.1002/ange.201505133
Gold Nanoparticles
Controlled Light-Mediated Preparation of Gold Nanoparticles by
a Norrish Type I Reaction of Photoactive Polymers
Florian Mäsing, Artur Mardyukov, Carsten Doerenkamp, Hellmut Eckert, Ursula Malkus,
Harald Nüsse, Jürgen Klingauf, and Armido Studer*
Abstract: Gold nanoparticles (AuNPs) are subjects of broad
interest in scientific community due to their promising
physicochemical properties. Herein we report the facile and
controlled light-mediated preparation of gold nanoparticles
through a Norrish type I reaction of photoactive polymers.
These carefully designed polymers act as reagents for the
photochemical reduction of gold ions, as well as stabilizers for
the in situ generated AuNPs. Manipulating the length and
composition of the photoactive polymers allows for control of
AuNP size. Nanoparticle diameter can be controlled from
1.5 nm to 9.6 nm.
atures, and complicated as well as expensive purification steps
are other drawbacks.[16,19]
In recent years, synthetic chemists have paid increasing
attention to the use of light to drive organic reactions, due to
both its infinite availability and ease of application in
industrial processes.[20] The preparation of AuNPs within
a polymer matrix using a photochemical approach would
therefore be a valuable strategy. Ideally, the reaction setup
should be simple and the light-mediated process may
facilitate control of the rate of nanoparticle formation. Spatial
and temporal control should also be feasible offering addi-
tional synthetic flexibility in the design of nanoparticle/
polymer hybrids.[21] In 2006, Scaiano and co-workers reported
the synthesis of AuNPs by using the Norrish type I photo-
chemical reactions for the in situ generation of reducing
radicals (Scheme 1a).[22] Commercially available Irgacure-
2959 (1) was employed to generate the ketyl radical 3a, which
G
old nanostructures with controlled size and shape have
found countless applications in a wide range of areas such as
nanoelectronics,[1] optics,[2] nanomedicine,[3] and catalysis.[4]
Although various methods for their preparation have been
reported,[5,6] the development of processes which allow for the
tuning and tailoring of nanoparticle size, shape, and compo-
sition is still challenging and of importance.[7] AuNPs with
defined size and shape have been prepared by using chemical
reductants,[8] electrochemical,[9] and photochemical meth-
ods.[10]
AuNPs can be stabilized by low-molecular-weight ligands
or by polymers. In systems where inorganic colloids are
assembled into polymeric materials, the polymer serves as
a matrix to prevent their agglomeration and precipitation,
ensuring long-term stability of the AuNPs.[11] Functionalized
polymers can mediate nanoparticle growth by controlling
entropic and enthalpic parameters.[12] Various homo- and
copolymers such as poly(vinylpyrrolidone),[13] polyethylene-
glycols,[14] polystyrenes,[15,16] polyacrylamides,[17] and dendritic
polymers[18] have been used for this purpose. Unfortunately,
current protocols for the preparation of polymer/metal nano-
particle hybrids often require complex multistep procedures,
and necessitate careful control of the addition of external,
harsh reducing reagents. Long reaction times, high temper-
Scheme 1. a) Previous work of Scaiano et al. using commercially avail-
able 1 for photochemical preparation of AuNPs.[21,22] b) Photochemical
polymer modification.[23] c) Novel concept for the preparation of
polymer-stabilized AuNPs.
[*] F. Mäsing, Dr. A. Mardyukov, Prof. Dr. A. Studer
Westfälische Wilhelms-Universität, Organisch-Chemisches Institut
Corrensstrasse 40, 48149 Münster (Germany)
E-mail: studer@uni-muenster.de
C. Doerenkamp, Prof. Dr. H. Eckert
Westfälische Wilhelms-Universität, Physikalisch-Chemisches Institut
Corrensstrasse 28/30, 48149 Münster (Germany)
is known to reduce metal ions.[21,22] It was shown by mass
spectrometry that the concomitantly generated benzoyl
radical 2 is oxidized by O2 to the corresponding benzoic
acid, which then contributes to the stability of the formed
AuNPs.[21]
U. Malkus, H. Nüsse, Prof. Dr. J. Klingauf
Institute of Medical Physics and Biophysics
Robert-Koch-Strasse 31, 48149 Münster (Germany)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201505133.
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We recently disclosed an efficient method for the photo-
chemical postmodification of polymers bearing a-hydroxy-
alkyl ketone (HAK) substituents as photocleavable side
chains. These polymers undergo a clean Norrish type I
photoreaction to give the corresponding acyl and ketyl radical
pairs which in the presence of nitroxides are efficiently
trapped to provide alkoxyamines (Scheme 1b).[23]
Herein, we report the synthesis and application of homo-
and copolymers bearing a-hydroxyalkyl ketone (HAK) sub-
stituents for controlled photochemical generation of stable,
spherical gold nanoparticles with adjustable diameter
(Scheme 1c). The polymer plays a dual role: it first acts as
an electron source for the photoreduction of Au salts to give
AuNPs and the remainder of the photochemically modified
polymer then serves as an organic matrix for AuNP stabiliza-
tion.[21,24] Importantly, we will show that the length and
composition of the parent polymer allows for control of
nanoparticle size leading to programmed nanoparticle prep-
aration. The AuNP hybrids are analyzed by UV/Vis, 1H NMR
and solid-state 13C NMR spectroscopy, attenuated total
reflection (ATR) Fourier transform infrared (FTIR) spec-
troscopy, transmission electron microscopy (TEM), dynamic
light scattering (DLS), X-ray photoelectron spectroscopy
(XPS), and thermogravimetric analysis (TGA).
Figure 1. Homo- 4, statistical copolymers 5–7, and block copolymer 8
investigated.
For the preparation of polymers of defined molecular
weight we employed the nitroxide-mediated radical polymer-
ization (NMP)[25] and the reversible addition–fragmentation
chain-transfer polymerization (RAFT).[26] Poly[2-hydroxy-2-
methyl-1-(4-vinylphenyl)propan-1-one] (poly(HAK), 4) and
statistical poly[2-hydroxy-2-methyl-1-(4-vinylphenyl)propan-
Figure 2. TEM images of AuNPs prepared with polymer 4
(Mn =14200 gmolÀ1) and polymer 7 (Mn =10600 gmolÀ1): a) 4 with-
out NaOH: 16.5Æ4.8 nm, b) 4 with 6.0 equiv NaOH: 5.1Æ1.0 nm,
c) 7 with 6.0 equiv NaOH: 1.8Æ0.5 nm.
1-one-co-4-(N,N-dimethylamino)styrene]
(poly(HAK-co-
DMAS), 5) were prepared by NMP. Statistical poly[2-
hydroxy-2-methyl-1-(4-vinylphenyl)propan-1-one-co-1-
(methylsulfinyl)-4-vinylbenzene] (poly(HAK-co-MSVB), 6),
statistical poly[2-hydroxy-2-methyl-1-(4-vinylphenyl)propan-
Table 1: Light-mediated preparation of polymer-protected AuNPs in
DMF/H2O with polymers 4–8 (ratio of photoactive HAK (m) unit to
HAuCl4 =10 to 1).
1-one-co-methyl(4-vinylphenyl)sulfane]
(poly(HAK-co-
Entry
Polymer
Mn [gmolÀ1
]
m/n/o[b]
Equiv.
Diameter[d]
[nm]
MVPS), 7), and poly{[2-hydroxy-2-methyl-1-(4-vinylphenyl)-
propan-1-one-co-methyl(4-vinylphenyl)sulfane]-block-sty-
rene} (poly((HAK-co-MVPS)-b-St), 8) were obtained by
RAFT. All polymers were characterized by NMR, GPC, and
FTIR (see the Supporting Information). Besides the photo-
active HAK moieties, copolymers 5–8 contain monomers that
bear functionalized side chains able to interact with Au
nanoparticles (Figure 1).
(PDI)[a]
NaOH[c]
1[e]
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
4
4
4
4
4
4
4
4
5
6
7
7
7
7
7
7
8
14200 (1.2)
14200 (1.2)
14200 (1.2)
14200 (1.2)
8000 (1.2)
12900 (1.2)
19500 (1.2)
26600 (1.2)
9400 (1.3)
–
–
–
–
–
–
–
–
0.0
1.0
3.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
16.5Æ4.8
9.6Æ1.8
7.0Æ1.3
5.1Æ1.0
ꢀ5[f]
ꢀ5[f]
ꢀ5[f]
ꢀ5[f]
We first investigated photochemical AuNP preparation
1:1.0
1:1.6
1:1.3
1:1.4
1:1.3
1:1.6
1:1.9
1:3.3
1:1.4:1.7
5.0Æ1.1
3.5Æ0.9
2.5Æ0.7
2.8Æ0.8
5.4Æ1.1
2.2Æ0.5
1.8Æ0.5
1.5Æ0.3
3.0Æ0.9
using homopolymer poly(HAK)
4
(Mn = 14200 gmolÀ1,
5800 (1.2)
PDI = 1.2). Initial studies were conducted in dimethylform-
amide (DMF) under argon atmosphere with poly(HAK) 4
and HAuCl4 in an estimated ratio of 10:1 (ratio of photoactive
HAK units (m)/HAuCl4 10:1). During irradiation (l =
254 nm), the solution of 4/HAuCl4 became pink/violet
within 10 min indicating successful formation of AuNPs.
These NPs showed a surface plasmon band (SPB) at l =
533 nm. Absorbance did not increase upon extended irradi-
ation time indicating full conversion to AuNPs. TEM analysis
revealed that the AuNPs formed are nonspherical with
a rather broad size distribution (16.5 Æ 4.8 nm; Figure 2a;
Table 1, entry 1). However, these NPs showed ripening effects
as observed by a shift of the SPB to l = 548 nm after several
12500 (1.1)
29300 (1.2)
83000 (1.5)
12800 (1.1)
10600 (1.1)
10500 (1.1)
19000 (1.2)
[a] Mn and PDI were determined by gel permeation chromatography
=
(GPC) in THF. [b] Ratio (m/n/o) of HAK to (functionalized) styrene CH2
CHC6H4X was determined by 1H NMR spectroscopy. [c] NaOH equiv-
alents with respect to HAuCl4. [d] Diameter and standard deviation of
AuNPs were determined by TEM, see the Supporting Information.
[e] Reaction performed in DMF. [f] Estimated by measurement of the
SPB.
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hours. To overcome the observed ripening we repeated the
experiment with a higher concentration of 4 (ratio of HAK
units/HAuCl4 20:1). Disappointingly, AuNPs with a broad
SPB at l = 564 nm were obtained indicating the formation of
polydisperse NPs with larger diameter.
sulfoxide-modified poly(HAK-co-MSVB) 6, however, pro-
vided AuNPs with a diameter of 3.5 Æ 0.9 nm (Table 1,
entry 10), indicating that the sulfoxide functionality has
a measurable influence on AuNP growth. Thioethers are
better ligands for Au and might be expected to show stronger
effects. Indeed, a further decrease in the NP diameter was
achieved in the presence of copolymer 7 (2.5 Æ 0.7 nm;
Table 1, entry 11). For 7 we noted that polymer length had
a marked effect on the size of the formed AuNPs. The
diameter increased from 2.5 to 5.4 nm when Mn was increased
from 12500 to 83000 gmolÀ1 (Table 1, entries 11–13). Similar
polymer size effects were previously reported by Saito et al.,
who investigated the growth process of silver nanoparticles in
organic media using poly(dihydroxystyrene-block-styrene)
poly(DHSt-b-St) as reductant,[29] and also by Wang et al.
using dodecanethiol (DDT) terminated poly(methacrylic
acid) for stabilization of AuNPs.[30] We also investigated
whether the relative ratio between stabilizing thioether
entities and HAK moieties shows any effect on the AuNP
formation and found that increasing the relative ratio of
thioether entities with respect to HAK from 1.3 to 3.3 leads to
a decrease of the AuNP diameter from 2.5 Æ 0.7 nm to 1.5 Æ
0.3 nm (Table 1, entries 11, 14–16). When the block copoly-
mer 8 was used, AuNPs (Au@8*) with a diameter of 3.0 Æ
0.9 nm were obtained showing that the styrene block has little
influence on NP growth (compared with Table 1, entry 11).
We also performed solubility and stability studies on our
gold polymer hybrids. Au@4* (5.1 nm) was found to be
soluble only in DMF. However, we expected good solubility
for AuNPs prepared from copolymer 7 (Au@7*) in various
organic solvents due to its hydrophobic solubilizing polymer
coat. To this end, Au@7* (2.5 nm) was first isolated by the
removal of DMF/H2O (simple evaporation under vacuum).
The Au/polymer hybrid was then washed several times with
deionized water to remove NaCl, and these AuNPs (Au@7*)
were found to be soluble in DMF, DMSO, THF, CH2Cl2, and
CHCl3. Importantly, these NPs do not show any ripening for
weeks upon storage at 58C in these solvents. Block copolymer
stabilized Au@8* show the same solubility properties.
To prove that the polymer is acting as a stabilizer for the
AuNP, we performed TGA experiments with the isolated
Au@7* (2.5 Æ 0.7 nm). These experiments revealed a gold
loading of 21 wt% in the hybrid material. Furthermore, we
also deposited Au@7* by drop-casting on a carbon-coated
TEM grid.[31] After thermal annealing for 13 h under high
vacuum at 1508C no significant size change for the AuNPs
was observed (2.6 Æ 0.7 nm) indicating that the polymer acts
as a stabilizer for our nanoparticles (see the Supporting
Information).[32]
Organic solvents like DMF and some polymers are known
to be reducing reagents for Au salts in the absence of light.[33]
In our case, AuNP formation in the presence of 4 without UV
irradiation was not observed within 5 min. To exclude AuNP
generation by reduction with the solvent upon irradiation, we
ran an experiment in the absence of polymer 4 with light.
Upon UV irradiation of a HAuCl4/NaOH (ratio of 1:6)
solution in DMF/H2O, AuNP formation was observed to
begin after > 2 min. Note that complete photocleavage of the
HAK groups should occur in a few minutes, if one considers
We subsequently explored AuNP formation with polymer
4 in basic medium and found that NaOH has a distinct effect
on the size, stability, and dispersity of the generated AuNPs.
Irradiation of a mixture of 4/HAuCl4/NaOH (ratio of 10 HAK
units:1:1) in DMF for 5 min provided spherical gold NPs with
narrow size distribution (9.6 Æ 1.8 nm; Table 1, entry 2). Upon
varying the amount of NaOH we found the average diameter
of the AuNPs to decrease from 9.6 Æ 1.8 nm to 7.0 Æ 1.3 nm
and 5.1 Æ 1.0 nm (Figure 2b) as the concentration of NaOH
increased from 1 then 3 and finally 6 equivalents with respect
to HAuCl4 (Table 1, entries 2–4). All experiments delivered
spherical particles with narrow size distribution. TEM anal-
ysis agrees with the corresponding UV/Vis spectra where the
SPB shifted from l = 524 nm to l = 516 nm as the amount of
NaOH increased from 1 to 6 equivalents (see the Supporting
Information). Comparison of AuNP diameters determined by
TEM (5.1 Æ 1.0 nm) and DLS (8.2 Æ 2.4 nm) measurements
indicates the presence of a thin roughly 1.5 nm thick polymer
coating on the AuNP surface.
To study the effect of the polymer length on AuNP
formation, different poly(HAK) polymers 4 ranging from
Mn = 8000 gmolÀ1 to 26600 gmolÀ1 were tested (ratio of HAK
units/HAuCl4/NaOH 10:1:6; Table 1, entries 5–8). Photolysis
in the presence of the Au salt and base gave AuNPs with
a SPB at l = 516 Æ 1 nm for all systems indicating no
significant effects of polymer size on AuNP formation in the
tested Mn range. Notably, NMP- and RAFT-derived poly-
(HAK) provided the same result revealing that the end
groups in these polymers do not influence NP formation.
Importantly, no aggregation or precipitation of AuNPs was
observed when the NPs were stored in DMF/H2O for months
(58C).
We also studied the influence of the light source on AuNP
formation (ratio of HAK units/HAuCl4/NaOH 10:1:6) and
chose a 365 nm UV light source. Under these conditions
a significant decrease in the rate of AuNP formation was
observed. After two hours of irradiation very polydisperse
AuNPs with a range of diameters between 5 and 70 nm were
obtained, indicating that the wavelength and intensity of the
UV light source have a crucial influence on the AuNP
formation process.
We then investigated whether functional groups within
the polymer influence NP growth. It is known that com-
pounds containing nitrogen (amines, amides)[27] or sulfur
(thiols, thioethers, sulfoxides) stabilize NPs.[28] To this end,
statistical copolymers 5–7 and block copolymer 8 were tested
(see Figure 1 and the Supporting Information). Results
obtained for the photochemical synthesis of AuNPs with 5–
8 are included in Table 1.
When the amino-functionalized copolymer
5 was
employed, spherical AuNPs with a diameter of 5.0 Æ 1.1 nm
were generated, indicating that the tertiary amines in 5 have
no significant effect on NP growth, in comparison with results
obtained with parent 4 (Table 1, entries 4 and 9). The
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Chemie
acteristic signals of the HAK moiety (d =
204 ppm, d = 78 ppm, d = 29 ppm) after
irradiation indicated complete consumption
of the photoactive entities (Figure 3).
Importantly, a new signal at d = 172 ppm
appeared which was assigned to the car-
boxylate carbon atom and amide function,
supporting the formation of polymer 12
under the applied conditions (light, NaOH,
DMF).[39]
The oxidation state of gold nanoparti-
cles in the hybrid was determined by XPS,
unambiguously proving full photochemical
reduction of gold ions to Au0. The XPS
spectrum showed the two signals of the
characteristic binding energies for Au0
Scheme 2. Suggested mechanism for generation of Au nanoparticles using (co)polymers 4–
8, NaOH, and light.
a triplet lifetime in the range of 0.37–13 ns and a quantum
yield of 0.29–0.67 depending on the substituents at the para
position of aryl group.[34] In fact, AuNP formation upon UV
irradiation in the presence of 4 (ratio of HAK units/HAuCl4/
NaOH 10:1:6) was complete in ꢁ 2 min showing that 4 rather
than the solvent is the reducing reagent in our process.[35]
Our suggested mechanism for AuNP formation is
depicted in Scheme 2. As experimentally shown and discussed
above, NaOH plays an important role. We assume that NaOH
influences AuNP formation in three ways: Firstly, it is known
that the presence of hydroxide ions changes the redox
potential of Au3+ (HAuCl4 is transformed into M+AuCln-
(OH)4Àn) and influences NP growth.[36] Secondly, after photo-
cleavage the ketyl radical 3a is likely deprotonated by NaOH
to provide ketyl radical anion 3b which has a lower oxidation
potential than 3a.[37] Finally, hydroxide ions can probably trap
polybenzoyl radicals 9 to generate the reduced poly(carbox-
ylic acid) radical anions 10, which are in turn readily oxidized
by the Au salts to the corresponding poly(carboxylic acid)
salts 11.[38] We currently disregard formation of polyacids by
air oxidation of the acyl radicals to the corresponding peracids
Figure 3. Solid-state 13C–1H CP/MAS NMR spectra of a) poly(HAK) 4
(Mn =12900 gmolÀ1, PDI=1.2) and b) the corresponding polymer-
coated Au@4*. Signal intensities normalized based on the polystyrene
backbone (ꢀ44 ppm).
followed by reduction as suggested by Scaiano et al.,[21] since
AuNP formation has to be conducted under argon atmos-
phere (O2 is detrimental to this process).
To prove formation of the acid functionalities we etched
the gold nanoparticles with KCN (Au@4*) and characterized
the resulting polymer. NMR spectroscopy revealed formation
of the suggested carboxylic acid groups. However, along with
the acid functionality we also identified the N,N-dimethyl-
amide entity (around 50%) as polymer side chain probably
resulting from reaction of Au@4* with dimethylamine
derived from DMF. The structure of this copolymer was
further proved by independent synthesis (see the Supporting
Information). Moreover, upon increased irradiation time the
amide content in copolymer 12 also increased, indicating that
the poly(carboxylic acid) salt 11 is formed first (as suggested
in our mechanism) and is then likely further converted by
DMF to copolymer 12 (see Scheme 2).
(Au4f7/2, Au4f5/2; see the Supporting Information). Addi-
tional signals characteristic of gold ions were not detected.[5,40]
This was observed for both the larger (5.1 Æ 1.0 nm; Table 1,
entry 4) and smaller (2.5 Æ 0.7 nm; Table 1, entry 11) AuNPs.
Finally, we tested the catalytic activity of the AuNPs
prepared with the polymer 4 for the oxidation of 1-(4-
methoxyphenyl)ethan-1-ol to 1-(4-methoxyphenyl)ethan-1-
one using water as a solvent and H2O2 (2.5 equiv) as an
oxidant at 908C for 6 h (see the Supporting Information).[41]
Pleasingly, with Au@4* (1 mol%) the ketone was quantita-
tively formed under these conditions. Notably, since the
catalyst is dispersed in water, the product ketone can be
readily and cleanly isolated by simple extraction with
dichloromethane. The aqueous layer containing Au@4* was
successfully reused three times without significant loss in
Solid-state 13C NMR investigations were also performed
on poly(HAK) 4 (Mn = 12900 gmolÀ1, PDI = 1.2) and on the
corresponding polymer-coated AuNPs prepared from this
homopolymer (Au@4*). Quantitative disappearance of char-
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dridis, Langmuir 2004, 20, 8426 – 8430; c) T. K. Sau, C. J.
Murphy, J. Am. Chem. Soc. 2004, 126, 8648 – 8649.
[8] M. K. Corbierre, N. S. Cameron, R. B. Lennox, Langmuir 2004,
20, 2867 – 2873.
[9] a) S. Singh, D. V. S. Jain, M. L. Singla, Anal. Methods 2013, 5,
1024 – 1032; b) D. F. Yancey, E. V. Carino, R. M. Crooks, J. Am.
Chem. Soc. 2010, 132, 10988 – 10989.
[10] a) L. M. McGilvray, J. C. Scaiano, in CRC Handbook of Organic
Photochemistry and Photobiology, Vol. 2, 3 ed. (Eds.: A. Gries-
beck, M. Oelgemçller, F. Ghetti), CRC-Press, Boca Raton, FL,
2012, pp. 881 – 910; b) M. Grzelczak, L. M. Liz-Marzµn, Chem.
Soc. Rev. 2014, 43, 2089 – 2097; c) T. Itakura, K. Torigoe, K.
Esumi, Langmuir 1995, 11, 4129 – 4134.
[11] a) J. Shan, H. Tenhu, Chem. Commun. 2007, 4580 – 4598; b) P.
Xu, X. Han, B. Zhang, Y. Du, H.-L. Wang, Chem. Soc. Rev. 2014,
43, 1349 – 1360.
[12] a) M. Stamm, J.-U. Sommer, Nat. Mater. 2007, 6, 260 – 261;
b) A. C. Balazs, T. Emrick, T. P. Russell, Science 2006, 314, 1107 –
1110.
[13] a) C. Xiao, S. Chen, L. Zhang, S. Zhou, W. Wu, Chem. Commun.
2012, 48, 11751 – 11753; b) I. Pastoriza-Santos, L. M. Liz-
Marzµn, Langmuir 2002, 18, 2888 – 2894; see also Ref. [10c].
[14] a) T. Azzam, A. Eisenberg, Langmuir 2007, 23, 2126 – 2132; b) L.
Longenberger, G. Mills, J. Phys. Chem. 1995, 99, 475 – 478.
[15] C.-U. Lee, D. Roy, B. S. Sumerlin, M. D. Dadmun, Polymer 2010,
51, 1244 – 1251.
activity (cycles 1–3: 97%). However, in the fourth cycle
a slight decrease in reaction yield was observed (91%).
In summary, we have presented efficient light-mediated
formation of polymer-protected AuNPs by using readily
prepared photoactive homo- and copolymers as reducing
reagents. Upon photooxidation, polymers are converted to
poly(carboxylate-co-amide)-copolymers which in turn stabi-
lize the generated AuNPs. By simple variation of pH value
and composition and length of the polymer, the diameter of
the spherical AuNPs can be adjusted from 1.5 nm to 9.6 nm.
The AuNPs are soluble in a wide range of organic solvents
and show high stability over weeks. Moreover, they can be
used as recyclable catalysts for the oxidation of benzylic
alcohols. Our method for controlled and programmable
AuNP preparation is experimentally very easy to conduct. It
is an “instant” AuNP preparation process: just mix the
photoactive polymer, the Au3+ salt, and NaOH in DMF/H2O
and irradiate for a few minutes: ready! Isolation is conducted
by simple evaporation of the solvent. It is evident that this
process should be general for the preparation of polymer-
coated metal nanoparticles. Experiments on the application
of this methodology using other metal salts are currently
underway.
[16] A. Buonerba, C. Cuomo, S. Ortega Sµnchez, P. Canton, A.
Grassi, Chem. Eur. J. 2012, 18, 709 – 715.
[17] K. Kusolkamabot, P. Sae-ung, N. Niamnont, K. Wongravee, M.
Sukwattanasinitt, V. P. Hoven, Langmuir 2013, 29, 12317 – 12327.
[18] J. P. Hermes, F. Sander, U. Fluch, T. Peterle, D. Thompson, R.
Urbani, T. Pfohl, M. Mayor, J. Am. Chem. Soc. 2012, 134, 14674 –
14677.
[19] a) L. Gomez, V. Sebastian, S. Irusta, A. Ibarra, M. Arruebo, J.
Santamaria, Lab Chip 2014, 14, 325 – 332; b) J. Shan, M.
Nuopponen, H. Jiang, T. Viitala, E. Kauppinen, K. Kontturi,
H. Tenhu, Macromolecules 2005, 38, 2918 – 2926; c) H. Tsu-
noyama, H. Sakurai, Y. Negishi, T. Tsukuda, J. Am. Chem. Soc.
2005, 127, 9374 – 9375.
Acknowledgements
We thank the Deutsche Forschungsgemeinschaft (SFB 858)
for funding this work. Nanoanalytics GmbH, Münster is
acknowledged for performing XPS measurements. We thank
an anonymous referee for many helpful comments.
Keywords: controlled radical polymerization · gold ·
metal nanoparticles · photochemistry · radicals
[20] K. Dietliker, A. Braig, A. Ricci, Photochemistry, Vol. 38 (Ed.: A.
Albini), The Royal Society of Chemistry, Cambridge, 2011,
pp. 344 – 368.
How to cite: Angew. Chem. Int. Ed. 2015, 54, 12612–12617
Angew. Chem. 2015, 127, 12803–12808
[21] J. C. Scaiano, K. G. Stamplecoskie, G. L. Hallett-Tapley, Chem.
Commun. 2012, 48, 4798 – 4808.
[22] K. L. McGilvray, M. R. Decan, D. Wang, J. C. Scaiano, J. Am.
Chem. Soc. 2006, 128, 15980 – 15981.
[23] A. Mardyukov, A. Studer, Macromol. Rapid Commun. 2013, 34,
94 – 101.
[24] For polymers acting as reducing and stabilizing agent see
Ref. [7b] and [14b]. See also: a) C. E. Hoppe, M. Lazzari, I.
Pardinas-Blanco, M. A. López-Quintela, Langmuir 2006, 22,
7027 – 7034; b) S. Kracht, M. Messerer, M. Lang, S. Eckhardt, M.
Lauz, B. GrobØty, K. M. Fromm, B. Giese, Angew. Chem. Int. Ed.
2015, 54, 2912 – 2916; Angew. Chem. 2015, 127, 2954 – 2958; c) P.
Alexandridis, Chem. Eng. Technol. 2011, 34, 15 – 28.
[25] V. Sciannamea, R. JØrôme, C. Detrembleur, Chem. Rev. 2008,
108, 1104 – 1126.
[1] D. V. Talapin, J.-S. Lee, M. V. Kovalenko, E. V. Shevchenko,
Chem. Rev. 2010, 110, 389 – 458.
[2] a) H. S. Oh, S. Liu, H. S. Jee, A. Baev, M. T. Swihart, P. N.
Prasad, J. Am. Chem. Soc. 2010, 132, 17346 – 17348; b) S. Zeng,
X. Yu, W.-C. Law, Y. Zhang, R. Hu, X.-Q. Dinh, H.-P. Ho, K.-T.
Yong, Sens. Actuators B 2013, 176, 1128 – 1133.
[3] T. Sun, Y. S. Zhang, B. Pang, D. C. Hyun, M. Yang, Y. Xia,
Angew. Chem. Int. Ed. 2014, 53, 12320 – 12364; Angew. Chem.
2014, 126, 12520 – 12568.
[4] a) M. Stratakis, H. Garcia, Chem. Rev. 2012, 112, 4469 – 4506;
b) Y. Zhang, X. Cui, F. Shi, Y. Deng, Chem. Rev. 2012, 112, 2467 –
2505.
[5] M. Brust, M. Walker, D. Bethell, D. J. Schiffrin, R. Whyman, J.
Chem. Soc. Chem. Commun. 1994, 801 – 802.
[26] G. Moad, E. Rizzardo, S. H. Thang, Acc. Chem. Res. 2008, 41,
1133 – 1142.
[6] a) L. M. Liz-Marzµn, Chem. Commun. 2013, 49, 16 – 18; b) N. G.
Bastffls, J. Comenge, V. Puntes, Langmuir 2011, 27, 11098 –
11105; c) M.-C. Daniel, D. Astruc, Chem. Rev. 2004, 104, 293 –
346; d) I. Pastoriza-Santos, R. A. Alvarez-Puebla, L. M. Liz-
Marzµn, Eur. J. Inorg. Chem. 2010, 4288 – 4297; e) A. Jimenez-
Ruiz, P. Perez-Tejeda, E. Grueso, P. M. Castillo, R. Prado-Gotor,
Chem. Eur. J. 2015, 21, 9596 – 9609.
[27] a) Z. Shi, F. Guo, Y. Li, Z. Hou, J. Polym. Sci. Part A 2015, 53, 5 –
9; b) M. Aslam, L. Fu, M. Su, K. Vijayamohanan, V. P. Dravid, J.
Mater. Chem. 2004, 14, 1795 – 1797; c) Z. He, A. Zhong, H.
Zhang, L. Xiong, Y. Xu, T. Wang, M. Zhou, K. Huang, Chem.
Eur. J. 2015, 21, 10220 – 10225.
[28] a) M. Brust, J. Fink, D. Bethell, D. J. Schiffrin, C. Kiely, J. Chem.
Soc. Chem. Commun. 1995, 1655 – 1656; b) H. Häkkinen, Nat.
Chem. 2012, 4, 443 – 455; c) T. Peterle, A. Leifert, J. Timper, A.
[7] a) M. Grzelczak, J. PØrez-Juste, P. Mulvaney, L. M. Liz-Marzµn,
Chem. Soc. Rev. 2008, 37, 1783 – 1791; b) T. Sakai, P. Alexan-
12616 www.angewandte.org
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 12612 –12617

Angewandte
Chemie
Sologubenko, U. Simon, M. Mayor, Chem. Commun. 2008,
3438 – 3440; d) J. Liu, N. Ruffini, P. Pollet, V. Llopis-Mestre, C.
Dilek, C. A. Eckert, C. L. Liotta, C. B. Roberts, Ind. Eng. Chem.
Res. 2010, 49, 8174 – 8179.
[38] a) H. Zhang, R. Shi, A. Ding, L. Lu, B. Chen, A. Lei, Angew.
Chem. Int. Ed. 2012, 51, 12542 – 12545; Angew. Chem. 2012, 124,
12710 – 12713; b) H. Matsubara, C. T. Falzon, I. Ryu, C. H.
Schiesser, Org. Biomol. Chem. 2006, 4, 1920 – 1926.
[29] Y. Saito, H. Yabu, Chem. Commun. 2015, 51, 3743 – 3746.
[30] Z. Wang, B. Tan, I. Hussain, N. Schaeffer, M. F. Wyatt, M. Brust,
A. I. Cooper, Langmuir 2007, 23, 885 – 895.
[39] a) T. Ishizone, S. Wakabayashi, A. Hirao, S. Nakahama, Macro-
molecules 1991, 24, 5015 – 5022; b) T. Ishizone, A. Hirao, S.
Nakahama, Macromolecules 1989, 22, 2895 – 2901.
[31] S. Chen, J. M. Sommers, J. Phys. Chem. B 2001, 105, 8816 – 8820.
[32] M. Yoo, S. Kim, J. Lim, E. J. Kramer, C. J. Hawker, B. J. Kim, J.
Bang, Macromolecules 2010, 43, 3570 – 3575.
[40] X. Zhang, H. Shi, B.-Q. Xu, Angew. Chem. Int. Ed. 2005, 44,
7132 – 7135; Angew. Chem. 2005, 117, 7294 – 7297.
[41] a) J. Ni, W.-J. Yu, L. He, H. Sun, Y. Cao, H.-Y. He, K.-N. Fan,
Green Chem. 2009, 11, 756 – 759; b) G. L. Hallett-Tapley, M. J.
Silvero, M. Gonzµlez-BØjar, M. Grenier, J. C. Netto-Ferreira,
J. C. Scaiano, J. Phys. Chem. C 2011, 115, 10784 – 10790; c) G. L.
Hallett-Tapley, M. J. Silvero, C. J. Bueno-Alejo, M. Gonzµlez-
BØjar, C. D. McTiernan, M. Grenier, J. C. Netto-Ferreira, J. C.
Scaiano, J. Phys. Chem. C 2013, 117, 12279 – 12288.
[33] a) I. Pastoriza-Santos, L. M. Liz-Marzµn, Adv. Funct. Mater.
2009, 19, 679 – 688; b) T. Sakai, P. Alexandridis, J. Phys. Chem. B
2005, 109, 7766 – 7777; see also Ref. [7b], [14b], [24a] and [24c].
[34] a) S. Jockusch, M. S. Landis, B. Freiermuth, N. J. Turro, Macro-
molecules 2001, 34, 1619 – 1626; b) M. L. Marin, K. L. McGilv-
ray, J. C. Scaiano, J. Am. Chem. Soc. 2008, 130, 16572 – 16584.
[35] In the general procedure we always used 5 min irradiation time.
Control experiments revealed that the size of the AuNPs does
not change after 2 min.
[36] a) D. V. Goia, J. Mater. Chem. 2004, 14, 451 – 458; b) D. V. Goia,
Received: June 5, 2015
´
E. Matijevic, Colloids Surf. A 1999, 146, 139 – 152.
Revised: July 20, 2015
[37] P. S. Rao, E. Hayon, J. Am. Chem. Soc. 1974, 96, 1287 – 1294.
Published online: August 28, 2015
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