Multistimuli responsive nanocomposite tectons for pathway dependent self-assembly and acceleration of covalent bond formation

Article abstract of DOI:10.1021/jacs.9b06695

Nanocomposite tectons (NCTs) are a recently developed building block for polymer-nanoparticle composite synthesis, consisting of nanoparticle cores functionalized with dense monolayers of polymer chains that terminate in supramolecular recognition groups

Full text of DOI:10.1021/jacs.9b06695

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Article
Multi-Stimuli Responsive Nanocomposite Tectons for Pathway
Dependent Self-Assembly and Acceleration of Covalent Bond Formation
Yuping Wang, Peter J Santos, Joshua Moses Kubiak,
Xinheng Guo, Margaret S. Lee, and Robert J. Macfarlane
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.9b06695 • Publication Date (Web): 29 Jul 2019
Downloaded from pubs.acs.org on August 1, 2019
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Multi-Stimuli Responsive Nanocomposite Tectons for Pathway
Dependent Self-Assembly and Acceleration of Covalent Bond
Formation
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Yuping Wang, Peter J. Santos, Joshua M. Kubiak, Xinheng Guo, Margaret S. Lee, and Robert J.
Macfarlane*
Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue,
Cambridge, Massachusetts 02139, United States
ABSTRACT: Nanocomposite tectons (NCTs) are a recently developed building block for polymer-nanoparticle composite
synthesis, consisting of nanoparticle cores functionalized with dense monolayers of polymer chains that terminate in
supramolecular recognition groups capable of linking NCTs into hierarchical structures. In principle, the use of molecular binding
to guide particle assembly allows NCTs to be highly modular in design, with independent control over the composition of the
particle core and polymer brush. However, a major challenge to realize an array of compositionally and structurally varied NCT-
based materials is the development of different supramolecular bonding interactions to control NCT assembly, as well as an
understanding of how the organization of multiple supramolecular groups around a nanoparticle scaffold affects their collective
binding interactions. Here, we present a suite of rationally designed NCT systems, where multiple types of supramolecular
interactions (hydrogen bonding, metal complexation, and dynamic covalent bond formation) are used to tune NCT assembly as a
function of multiple external stimuli including temperature, small molecules, pH, and light. Furthermore, the incorporation of
multiple orthogonal supramolecular chemistries in a single NCT system makes it possible to dictate the morphologies of the
assembled NCTs in a pathway-dependent fashion. Finally, multi-stimuli responsive NCTs enable the modification of composite
properties by post-assembly functionalization, where NCTs linked by covalent bonds with significantly enhanced stability are
obtained in a fast and efficient manner. The designs presented here therefore provide major advancement for the field of composite
synthesis by establishing a framework for synthesizing hierarchically ordered composites capable of complicated assembly
behaviors.
Introduction
structure19 or pathway-dependent organization of particles
within the polymer matrix.
Nanoparticle-polymer composites are an important class of
materials composed of disparate inorganic and polymeric
components, combined in a manner that allows the resulting
materials to exhibit physical characteristics not observed in
either of the single phases. By mixing nanoparticles and
polymers of different sizes, shapes, molecular structures, and
elemental compositions in varying stoichiometric amounts,
the bulk make-up of the resulting material can be tuned across
a diverse range of overall compositions.
The “Nanocomposite tecton” (NCT) is a recently developed
2
0
nanoparticle-based construct capable of programmed self-
assembly that is ideal for synthesizing these types of complex
composites. Each NCT is inherently a composite material in
itself, and contains multiple independently addressable design
elements that can be used to program interactions between
NCTs and their surrounding environment. NCTs consist of an
inorganic nanoparticle (NP) core functionalized with a dense
polymer brush, where each polymer chain that comprises the
brush terminates in a supramolecular recognition group;
interactions between these groups drive the assembly of NCTs
into hierarchically ordered structures. Importantly, the fact that
these supramolecular interactions can be tuned separately from
the composition of the NPs or polymer brushes potentially
enables independent control over the chemical make-up of the
particle and polymer components of the composite, the spatial
organization of the assembled structure, and the types of
interactions governing the assembly process. However, while
NCTs have significant potential in the development of unique
polymer nanocomposite materials, only a single type of
supramolecular interaction (hydrogen bonding) has so far been
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In order to fully
dictate the properties of these composites, however, it is
necessary to control the arrangement of individual polymer
and particle building blocks within the composite, as the
spatial positioning of different components affects how these
different phases interact with one another.1
6-17
The
development of methods to achieve this level of control
represents a major challenge for future materials syntheses. It
is therefore critical to establish new types of chemical
interactions and stimuli that can programmably dictate how
1
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the constituent components interact with one another.
Moreover, significant benefit could be obtained from the
ability to dynamically manipulate each of these types of
interactions after the composite has been prepared, as this
would enable post-synthetic modification of material
20
used to control particle assembly,
which limits the
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processing conditions and compositional diversity of NCT
assemblies. The development of wider variety of
that can be used to direct NCT
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a
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supramolecular groups
assembly would therefore be a major step towards addressing
the design criteria outline above that are needed to fully
manipulate composite structure and properties. In addition, the
ability to use multiple orthogonal supramolecular interactions
simultaneously would make it possible to develop
sophisticated NCT architectures capable of more complex
behaviors, such as composites that respond to multiple stimuli,
or the formation of different particle arrangements in a
processing-path dependent manner. Here, we introduce three
unique supramolecular bonding motifs in order to establish
new processing and assembly pathways capable of
manipulating nanocomposite structure. We subsequently
explore how the organization of these supramolecular groups
around a nanoscale scaffold affects the thermodynamics of
NCT assembly, and demonstrate how different stimuli (e.g.
heat, light, pH, small molecules) can be used to regulate their
collective binding interactions. Finally, we use the control
afforded by the incorporation of many different
supramolecular recognition chemistries into the NCT concept
to expand the capabilities of this modular materials synthon.
Specifically, we develop multi-stimuli responsive nanoparticle
arrays, enhance reaction kinetics for covalent bond formation,
and synthesize permanently crosslinked particle lattices that
are significantly more robust to heat and solvent changes than
prior systems. The designs presented here therefore provide
major advancement for the field of composite synthesis by
establishing a framework for synthesizing hierarchically
ordered composites that are capable of complicated assembly
behaviors.
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Figure 1. a) General synthetic route for the preparation of the
functionalized polystyrene (PS) used in this study. b) Chemical
structures of the different functional groups used to drive particle
assembly. c) Schematic illustration of the assembly of polymer-
functionalized NCTs via supramolecular interactions between end
groups.
supramolecular complexes in the presence of metal ions, and
the strength of these interactions can be controlled as a
2
7-28
function of which metal ion species are used.
Finally,
dynamic covalent chemistry (DCC) represents an interesting
potential means of assembling NCTs, as DCC bonds are only
reversible under specific environmental conditions. For
instance, hydrazide (Hdz) and aldehyde (CHO) functionalities
undergo irreversible covalent bond formation at moderate pH,
but these bonds can be made reversible by adding a strong
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Results and Discussion
acid.
System Design
By synthesizing NCTs with either HW/CA pairs, Tpy
complexes, or DCC bonds as their chemical recognition
motifs, the stability and stimuli responsiveness of the NCT
system should be readily expanded beyond what can be
achieved with DAP/Thy driven NCT assembly alone. In order
to incorporate each of these functional groups into an NCT
Previously, hydrogen bonding interactions between
diaminopyridine (DAP) and thymine (Thy) units have been
used to assemble NCT superlattices.20 However, the labile
nature of these interactions limits the ability of NCTs to
incorporate a diverse range of polymer compositions or
different stimuli to control material synthesis. These
limitations stem from the fact that the nanoparticle-tethered
DAP/Thy complexes are only stable in non-polar solvents
such as toluene, as solvents that contain more polar functional
groups potentially disrupt DAP/Thy hydrogen bonding
interactions. Therefore, directing NCT-NCT interactions with
stronger recognition motifs would be a major step towards
expanding the types of polymer and particle compositions that
can be used in NCTs.
Hamilton wedge (HW)/cyanuric acid (CA) complexes24
represent a simple alteration to the previously established NCT
system (Figure 1b), as they represent a stronger hydrogen-
bonding pair than DAP/Thy that should still follow similar
assembly behaviors. Compared with DAP/Thy complexes
which possess three H-bonds per complex, HW/CA pairs
construct, individual systems were prepared using a previously
20
established protocol,
modified to include these new
chemistries. Briefly, polystyrene (PS) chains were synthesized
using atom transfer radical polymerization (ATRP) from a
disulfide-containing initiator, and the binding groups were
attached to the ends of these chains through copper catalyzed
azide-alkyne cycloaddition (CuAAC, Figure 1a). Once the
polymer chains had been functionalized with these binding
groups, the disulfide was cleaved and the polymers were
attached to gold nanoparticles using gold-thiol chemistry. A
complete description of all synthesis protocols and full
characterization of all molecular, macromolecular, and
nanoparticle materials can be found in the SI.
NCT Assemblies Induced by Different Recognition Motifs
a
possess six H-bonds per complex, and the K of a single
Due to the similar nature of the supramolecular interactions
between the previously established DAP/Thy complexes and
the HW/CA system, these stronger hydrogen bonding
complexes were first investigated to confirm that more robust
chemical interactions could still result in NCT assembly
without any undesirable side reactions. Pre-assembled HW
coated NCTs were permanently dispersible in nonpolar
HW/CA pair is two orders of magnitude higher than a
25
DAP/Thy pair under the same conditions. Beyond hydrogen-
bonding, metal coordination bonds represent an even stronger
type of interaction, and are typically responsive to different
2
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stimuli, making them another ideal choice for robust NCT
assembly. As an example, terpyridine (Tpy) units can form
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While the HW/CA and Tpy systems were capable of
solvents like toluene, while some CA NCT systems exhibited
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a small amount of self-aggregation in these same solvents; this
aggregation was easily reversed by adding trace amounts of a
more polar solvent such as anisole. However, when HW- and
CA- NCTs were mixed, the complementary hydrogen bonding
interactions resulted in rapid assembly as monitored both
visually and via UV-Vis spectroscopy, as the assembly of gold
nanoparticles (AuNPs) results in a redshift and reduction of
the gold nanoparticles’ plasmon resonance, diminishing the
solution’s absorption intensity at 520 nm. While previous
DAP/Thy linked NCTs of comparable size and polymer length
assembling NCTs in a rapid manner, the initial attempts of
using DCC to assemble NCTs were unsuccessful, and no
aggregates were observed after mixing the Hdz- and CHO-
functionalized NCTs under weak acidic conditions, even after
a week at room temperature. This observation indicates that
the covalent hydrazone bond formation between Hdz- and
CHO-NCTs is negligible under these conditions. The inability
of DCC to induce particle assembly is ascribed to the
relatively low concentration (< 1 M) of the reacting groups
on the surface of NCTs. Unlike the supramolecular
interactions in the cases of hydrogen-bonding and Tpy ligands,
the chemical reaction-based DCC requires high concentrations
in order to facilitate effective collision between the Hdz and
CHO groups to drive the formation of the hydrazone bond.
These observations are consistent with prior attempts to induce
covalent bond formation between nanoparticles, where
particle-bound molecules only formed covalent bonds after
approximately a month, even when the reacting groups were at
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exhibited a melting temperature (T , the temperature at which
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NCT dissociate from one another) of 40 °C, HW/CA linked
NCTs were irreversibly linked in toluene even at the boiling
point of the solvent. This aggregation was also observed to
occur in both pure toluene as well as in toluene-anisole
mixtures up to 75 % anisole (an example with 28 AuNPs and
1
1 kDa polymers in 50 % anisole is shown in Figure 2a). The
assembly of the HW/CA-NCTs was also observed in mixtures
of toluene and more polar solvents, including CHCl , CH Cl
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a concentration 10 times higher than those on the NCTs in
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and o-dichlorobenzene (See SI, Figure S2). The ability of
HW/CA pairs to assemble NCTs both at elevated temperatures
and in the presence of polar solvents capable of disrupting
hydrogen bonding demonstrates that increasing the binding
strength of NCT supramolecular bonding groups increases the
compatibility of the system with more challenging assembly
environments.
this study. Therefore, while the NCTs examined here were
unable to form aggregates via dynamic covalent bond
formation, in principle it should be theoretically possible to
induce covalent bond formation if the local concentration of
reactive groups could be increased (vide infra).
External Stimuli-Driven Reversible NCT Assembly /
Disassembly
When investigating the assembly behavior of the Tpy ligand
functionalized NCTs, it is important to note that the strength
of a Tpy-metal ion complex depends on the identity of the
metal ion being coordinated. Therefore, three sets of identical
Tpy ligand functionalized NCT solutions were prepared (See
SI, Section 3 for experimental details), to which three different
While it is not surprising that the supramolecular
interactions above (which are stronger than the previously
examined DAP-Thy complexes) are able to induce particle
assembly, it is not necessarily obvious that these stronger
interactions also allow for particle disassembly,
reorganization, or stimuli response. Given that these factors
are critical for tackling the design criteria outlined at the
beginning of this work, it is important to determine what
external stimuli are capable of dynamically regulating the
assembly of these HW/CA and Tpy-complex driven particle
assemblies.
2
+
2+
2+
metal ions (Mn , Zn and Fe ) were added. Previous work
has shown that the association strength of Tpy ligands with
2+
2+
2+ 30
these metal ions follows the trend of Mn < Zn < Fe . In
the NCT system, all three metal ions were able to readily
induce the assembly of NCTs in toluene at nearly identical
rates (Figure 2b). The slow kinetics of this assembly process
compared with the hydrogen bond driven assemblies
presumably results from the Coulombic repulsion between the
In order to disassemble the NCTs using external stimuli,
both the enthalpic and entropic effects involved in the
assembly process need to be taken into account. The enthalpy
(H) is determined by both the binding affinity of each
individual supramolecular recognition moiety, as well as the
number of supramolecular groups that comprise an NCT-NCT
bond. Alterations to particle size and polymer length in the
NCT system can affect the local concentration of the
supramolecular recognition groups, thereby significantly
varying the multivalency of the NCT interactions, and thus the
2
+
positively charged M(Tpy)
2
complexes when forming large
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NCT aggregates. It is noteworthy that in all three cases the
metal ion-Tpy coordination-induced NCT assembly remained
assembled in toluene up to the boiling point of the solvent.
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collective H of the interparticle bonds. The entropy of these
interactions (S) is dictated by the reduced conformational
freedom of the supramolecular recognition groups and the
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polymer chains they tether upon assembling. While the
entropic effects of supramolecular complexation can generally
be overlooked in the case of small molecule functionalized
NPs, the polymer chains in the NCT system provide unique
handles to mediate the thermodynamics of the particle
assembly. This added design flexibility arises because the
entropy change associated with interparticle bonding is
significantly larger for the NCT system compared with the
small molecule functionalized NPs, as the number of
conformations an NCT polymer chain can adopt is severely
Figure 2. UV/Vis Spectroscopy investigation of a) the self-
assembly of the complementary 28 nm HW and CA-NCTs (11
kDa PS) in a 1:1 mixture of anisole and toluene at room
temperature, and b) kinetic study of the self-assembly process of
the 28 nm Tpy-NCTs (11 kDa PS) induced by different metal ions
in toluene.
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restricted upon the formation of NCT-NCT bonds. As a result,
the entropic effects have more pronounced influence on the
thermodynamics of the NCT systems (larger TS), making the
free energy change associated with NCT bonding more
thermally sensitive. Changes in both particle
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Figure 3. Thermal study of complementary 28 nm HW- and CA-NCT mixtures with a) the same polymer molecular weight (11 kDa) and
varying solvent composition, or b) different polymer weights (11 and 26 kDa), which demonstrates that the stronger HW/CA binding
groups allow for the NCTs to reversibly assemble in various solvent compositions with significantly broader range of polymer lengths. c)
and d) UV/Vis Spectroscopy investigation of the responsiveness of the different metal ion-induced 28 nm Tpy-NCT aggregates upon
titration of TFA, and the reversible acid-base induced disassembly-assembly of the 28 nm Zn -Tpy-NCTs upon adding TFA and TEA in
an alternating sequence. The percentage of the disassembled NCTs in c) is determined by comparing the absorbance of the TFA-treated
assemblies with that of the original free NCTs.
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+
size and polymer length should therefore shift the strength of
each NCT-NCT bond via changes to the chain dynamics of
individual polymers comprising the brush. In order to make
valid comparisons across the diverse range of design handles
that could potentially be used to regulate the thermodynamics
of the NCT supramolecular-driven assembly behavior (e.g.
particle size, polymer length, supramolecular binding group
identity, solvent conditions, etc.), comparisons will primarily
be made for NCTs of a standard particle size and polymer
length (28 nm particles and 11 kDa polymer chains);
additional NCT designs and thermodynamic analyses can be
found in the SI.
HW/CA recognition motif exhibits the same thermally-
reversible assembly behavior as the prior DAP-Thy NCT
constructs, but its significantly enhanced stability compared
with the previous hydrogen-bonded systems allows for much
greater flexibility in NCT design, making it a useful expansion
of the NCT toolbox.
While hydrogen-bonded ligands are typically easily
modified via changes to solution temperature, coordination
bonds are often not as labile. Indeed, the general high binding
affinity between the metal ions and the Tpy ligands has been
shown to prohibit the disassembly process in response to
common external stimuli such as temperature or solvent
35-36
The HW/CA-NCT assemblies were first treated with heat as
a simple means to study the reversibility of the assembly
process. Compared with the DAP/Thy NCTs that dissociated
changes in prior molecular or nanoparticle systems.
Strong
chelating reagents such as EDTA that have higher binding
enthalpy with the metal ions than Tpy are therefore typically
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36-37
at temperatures of ~25–60 °C when assembled in toluene, the
stronger HW/CA recognition motif actually prevented particle
dissociation in this non-polar solvent for most of the NCT
systems that were assembled, excluding the NCTs with the
longest polymer chains (See SI, Section 3). As a result, more
polar solvents than toluene needed to be added in order to
weaken the hydrogen bonds and enable particle disassembly.
By altering the solvent composition to contain different
amounts of anisole (a polar solvent that is highly miscible with
needed to reverse the assembly process.
However, the poor
solubility of EDTA in common organic solvents limits its use
in disassembling NP aggregates that exist in the organic phase.
As mentioned earlier, though, the polymer chains in the
NCT system make it possible in principle to reverse the
assembly process using the significant entropy penalty
associated with polymer tethering as a driving force. In other
words, chemical stimuli that have been shown to be ineffective
at dissociating small molecule Tpy-based NP assemblies could
potentially be used to force NCT disassembly. For example,
while trifluoroacetic acid (TFA) can be used to protonate the
pyridine groups on the Tpy complex (thereby reducing the
toluene), the T
tuned by tailoring the ratio of the two solvents. Indeed, it was
found that by increasing the polarity of the solvent, the T of
m
of the HW/CA linked NCTs could be easily
m
the NCT assemblies could be gradually decreased (Figure 3a)
from a permanent interaction that did not break even at the
boiling point of pure toluene, down to 40 °C in a mixture of
enthalpy of complex formation and shifting equilibrium
38-40
towards the unbound state),
the addition of acid was not a
strong enough driving force to dissociate previous Tpy-based
3
:1 toluene:anisole. In pure anisole, the hydrogen bonding
36, 41
NP assemblies.
In the NCT system, however, addition of
interactions were sufficiently weakened such that no assembly
was observed for any of the NCT systems. More interestingly,
9
0 mM TFA at 22 °C resulted in complete dissociation of the
2+
2+
Mn - and Zn -Tpy-NCT assemblies (Figure 3c). However,
the Fe -Tpy assembled NCTs only exhibited ~15%
the change in the T
relationship with the anisole/toluene ratio (See SI, Figure S2),
which allows the T of the system to be precisely tailored by
m
of the assemblies exhibited a linear
2+
dissociation even when ~1 M TFA was added due to the
m
2+
21
stronger binding affinity between Tpy and Fe (K
a
> 10 ,
changing the solvent composition. Furthermore, the high
stability of the HW/CA pairs enables a wider range of polymer
designs to form reversible assemblies than can be achieved
when using the DAP/Thy system. HW/CA based NCTs with
PS brushes of molecular weight up to 26 kDa were still
observed to form stable assemblies in pure toluene at room
12
9
2+
2+
42
compared with 10 and 10 for Zn and Mn respectively).
Further increasing the entropic penalty associated with
forming Tpy complexes between adjacent particles does
2+
facilitate the disassembly process, though, as Fe -Tpy-linked
NCTs functionalized with 26 kDa PS polymer readily
disassembled upon the addition of 260 mM TFA at 22 °C
temperature (T
m
= 36 °C, Figure 3b, black trace). In all, the
2+
(
Figure S4a). The ability to disassemble these Fe -Tpy-linked
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absorption intensity of these NCT samples increased upon
NCTs with longer polymer chains is consistent with the fact
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that alterations to polymer configuration in the NCT system
provide a unique design handle to tune the assembly properties
of NPs.
exposure to UV light, an observation consistent with the more
polar MC species weakening the hydrogen bonding
interactions between NCTs, leading to disassembly. The
In order to demonstrate complete reversibility of this pH-
driven particle assembly process, acid (TFA) and base
(triethylamine, (TEA)) were added in an alternating sequence
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to the Zn -Tpy-NCT samples (Figure 3d); the assembly and
disassembly processes were easily repeated for multiple cycles
without deterioration of the NCT complexes. It is also
2
+
2+
noteworthy that the more weakly bound Zn /Mn -Tpy-NCT
aggregates can also disassemble upon the addition of free Tpy
compound (Figure S4b), which offers an alternative approach
to tune the assembly state of the Tpy-NCTs. Together, the use
of acid-base and small molecule stimuli to reverse the
assembly of Tpy-based NCTs in organic solvents is not only
an important step towards broadening the application scope of
coordination chemistry in the field of colloidal assembly, but
also serves as an example to demonstrate how the introduction
of polymer chains in the NCT system leads to unique
alterations to the thermodynamics of supramolecular
complexation.
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Because these HW/CA and Tpy NCTs can be reversibly
disassembled using the stimuli of solvent polarity and pH,
respectively, this opens up the possibility to use other design
handles that indirectly alter these solvent properties to control
the NCT assembly process. In principle, a small molecule
Figure 4. a) and b) Two possible approaches through which
spiropyran can induce the self-assembly/disassembly processes of
NCTs upon the application of photo-stimuli, including a) the
generation of the polar zwitterion species MC which can disrupt
the hydrogen bonding interactions of HW/CA complexes and b)
the generation of protons which can disrupt the coordination
+
additive that either changes its dipole or releases H in
response to an external stimulus could therefore be used to
control NCT aggregation. While multiple possible stimuli can
be used to alter the structures of small molecules in such a
manner, light is a desirable candidate because it can be easily
delivered to the system with a high degree of spatial and
temporal control. Photoresponsive NP systems have been
developed for prior NCT assembly systems, but many of the
state-of-the-art NP assembly methods that are responsive to
light rely on NPs functionalized directly with monolayers of
2+
interactions of Zn -Tpy complexes. c) and d) Absorption at 540
2
+
nm for the 16 nm HW/CA-NCT and Zn -Tpy-NCT systems
undergoing multiple disassembly-assembly cycles upon the
application of external photo-stimuli.
dispersed NCT sample remained in this state until exposed to
visible light, upon which the less polar SP form was
regenerated and the hydrogen bonds between NCTs reformed,
resulting in particle reassembly (Figure 4c). Upon addition of
4
3-45
light-responsive molecular switches.
These NP-bound
molecules can often be difficult to synthesize and difficult to
stimulate uniformly (e.g., the light has to penetrate the
aggregated NPs to trigger the switching process, which may
result in low efficiency). The use of solvent-borne
photoswitches that alter NP aggregation indirectly therefore
enable more facile development of light-responsive particle
+
4
48
4
mM MCH (ca. 2×10 equiv. to the Tpy groups, See SI,
2
+
Section 6 for experimental details) to the Zn -Tpy-NCT
assemblies, the resulting solution showed a strong absorption
band attributed to MCH at 460 nm and low absorption
intensity at 540 nm attributed to assembled NCTs (Figure S5).
+
When this mixture was irradiated with visible light, MCH
4
6
assemblies. .
was converted to SP, releasing a proton which subsequently
interacted with the Tpy groups. This change in solution acidity
Based on the results above, it was hypothesized that
spiropyran (SP), a molecule known for its rapid and reversible
bond-cleavage when stimulated with light,47 could potentially
introduce photoresponsive properties to the NCT assemblies
through two different mechanisms without the need to directly
couple it to the nanoparticles. Ring opening of SP upon
exposure to UV light generates the merocyanine (MC)
zwitterion (Figure 4a), which is significantly more polar than
the starting SP form, a change which would be expected to
weaken the hydrogen bond formation between the HW/CA
NCTs. Furthermore, the MC species can be protonated
2+
resulted in dissociation of the Zn -Tpy complex and
disassembly of the NCTs, as confirmed by the decrease in the
absorption band at 460 nm and the concomitant increase of the
absorption band at 540 nm. Upon removal of the visible light
source, the protons bound to the SP molecules (See SI, Section
+
6
), leading to regeneration of MCH and NCT reassembly
(Figure S7).
These
light-reversible
assembly
processes
were
subsequently repeated (Figure 4c and d) for multiple cycles for
both the HW/CA- and the Tpy-NCTs, demonstrating complete
reversibility of the assembly process.
+
yielding MCH , a photoacid capable of releasing and
+
47
capturing H reversibly in solution (Figure 4b) and this
process could therefore be coupled to the assembly and
disassembly of Tpy-NCTs
Multi-stimuli Responsive NCT system
The successful establishment of different stimuli, including
heat, pH, small molecules and light to tune the
assembly/disassembly state of the NCTs functionalized by
When a solution of 10 M SP (ca. 50 equiv. to the HW/CA
groups) was added to NCTs linked via HW/CA pairs, the
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different recognition groups makes it possible to construct responsive NCTs capable of assembling into different states
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more complicated NCT architectures with increased
functionality. Specifically, the functionalization of multiple
binding groups to a single nanoparticle scaffold would
introduce the possibility of developing multi-stimuli
under different conditions, or NCTs capable of pathway-
dependent assembly where the resulting morphologies
depended on the order in which different stimuli
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Figure 5. a) A schematic illustration of the NCTs that were used to examine the multi-stimuli responsive NCT self-assembly system. b-e)
UV/Vis Spectroscopic characterization of the NCT samples upon applying different external stimuli.
were introduced. In order to explore this possibility, two types
of NCT samples were prepared (Figure 5a): 16 nm AuNPs
functionalized with CA groups, and 28 nm AuNPs
functionalized with HW and Tpy groups using a 9:1 feed ratio
The multi-stimuli responsive behavior of the NCTs was also
confirmed by transmission electron microscopy (TEM) and
small angle X-ray scattering (SAXS), providing information
on the structure of the assembled NCTs. Specifically, when
the assembly behavior was driven exclusively by coordination
interactions, only 16 nm NCTs were observed in electron
microscopy images of the supernatant (Figure S8a) and only
28 nm NCTs were observed in the aggregate (Figure 6b, left),
and a single peak in low q region in the SAXS data confirms
the presence of a single average interparticle distance (d,
determined as d = 2/q , where q is the maximum of the
scattering peak), consistent with solely 28 nm NCTs being
part of the precipitate (Figure 6c, red solid trace). In
comparison, when the assembly was driven by hydrogen
bonding or both hydrogen bonding and coordination
interactions, the aggregate was comprised of a mixture of 28
and 16 nm NCTs (Figure 6b, right and Figure S8c-e).
(see SI Section 3). Encouragingly, the NCTs readily
assembled at room temperature upon mixing in a 3:1
toluene/anisole solution despite the introduction of the Tpy
groups (Figure 5b, purple trace), and the assemblies could be
melted upon heating the solution to ~60 °C (Figure 5c, red
2+
trace). In contrast, when Zn was present, the NCTs again
formed stable assemblies at 22 °C (Figure 5d, purple trace),
but the original absorption was only partially recovered when
the system was heated (Figure 5d, red trace). The fact that
only some of the NCT dissociated upon heating is ascribed to
fact that the 16 nm CA-NCTs could melt into solution, while
the 28 nm HW-Tpy-NCTs were locked into the assembled
0
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49
2
+
form by the Zn -Tpy coordination complex. This observation
confirms that (i) the formation of the hydrogen bonding
Importantly, however, the ability to orthogonally address
these two different assembly mechanisms potentially also
enables pathway-dependent assembly, allowing the positions
of the particles within a macroscopic aggregate to be
controlled as a function of the order in which different stimuli
are introduced. For example, when the 28 and 16 nm NCTs
were assembled (Figure S8d) via steps (i) and (v) as shown in
2
+
interactions is not compromised by the addition of Zn and
ii) both hydrogen bonding and coordination interactions can
(
be used simultaneously to govern the assembly process.
Finally, the coordination interactions between the NCTs can
be out-competed by the addition of free Tpy compound (3) as
demonstrated above, leaving only hydrogen bonding
interactions to mediate the assembly process. When excess
free Tpy was added to these assemblies, the thermal response
of the system matched the previous assembly and disassembly
2+
Figure 6a (first hydrogen bonding, then Zn complexation),
NCTs formed homogeneous aggregates with both sizes of
NCTs interspersed throughout the aggregate. This
homogeneity was noted by the presence of a single
interparticle distance of 38 nm observed in the SAXS data, as
indicated by only a single peak in the low q region. In
comparison, when the two sets of NCTs were assembled in the
2
+
behavior in the absence of Zn (Figure 5e). Taken together,
these data allow for the NCTs to exist in four unique states
depending on whether the Tpy complexes are formed, the
HW/CA complexes are formed, or both or neither are formed
(Figure 6a).
2+
opposite pathway (steps (iii) and (i), Zn -Tpy-complex
formation followed by hydrogen bonding), the 28 and 16 nm
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control the organization of particles within a macroscopic
NCTs were segregated into distinct regions within the
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composite in a more sophisticated manner.
assembliesthe 28 nm NCTs formed aggregates which were
surrounded by 16 nm NCTs (Figure S8e). Although TEM
images can potentially make full structure determination
challenging, the SAXS data unequivocally show this particle
segregation behavior, as two distinct peaks were observed in
the low q region, corresponding to the two different
interparticle distances that would be expected: a larger
distance of 52 nm for 28nm-28nm particle bonds linked with
Accelerating covalent bond formation via enhanced local
concentration
In addition to selectively controlling assembly, post-
assembly functionalization of NP-based materials is another
key challenge in the field of nano-chemistry and
2
+
nanocomposite
development.
For
example,
while
Zn -Tpy complexes, and a shorter distance of 37 nm for the
supramolecular interactions are often employed to direct NP
aggregation, using covalent bonds to link particles together
once assembled would potentially result in significantly more
stable NP assemblies. Such enhanced stability would open the
possibility to process NCT composites under different
conditions than are currently accessible. Despite these
potential benefits, forming covalent bonds between NPs is
challenging because nanoparticle solutions such as those used
in this work are typically several orders of magnitude more
dilute than typical organic synthesis schemes used to make
covalent bonds between molecules (nM particle solutions vs
mM solutions of molecules). While covalently linked NP
aggregates have been prepared using a large excess of reactive
2
6
8nm-16nm particle bonds consisting of HW/CA pairs (Figure
c, Table S1).
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These results show that the differences in interparticle
distance are a direct result of the differences in the assembly
pathway. In step (i), the 28 and 16 nm NCTs interact with each
other via hydrogen bonding and form aggregates consisting of
both particle types homogeneously dispersed throughout the
2
+
sample. The addition of Zn (step (v)) induces additional
interactions between adjacent 28 nm NCTs, but the initial
assembled structure with interspersed particle types is
retained. In comparison, when Zn2+ is added to the NCTs first,
the initial aggregates are composed exclusively of 28 nm
NCTs associated via coordination interactions (step (iii)).
Figure 6. a) A schematic illustration of the various responses of
the multi-stimuli responsive system in figure 5, demonstrating that
the pathway of stimulus addition controls the morphology of the
resulting composites. Conditions: (i) Cool; (ii) Heat; (iii) addition
2+
2+
of Zn , heat; (iv) addition of Tpy, heat; (v) addition of Zn ; (vi)
addition of Tpy. b) TEM images of the assembly induced by
coordination interactions only (left) and hydrogen bonding
interactions only (right). c) SAXS traces for the HW-Tpy and CA-
based multi-stimuli responsive NCT assemblies under different
conditions, where the difference in interparticle spacings
demonstrates the pathway-dependent nature of the assembly
process.
When the solution is subsequently cooled, 16 nm CA-NCTs
aggregate (step (i)) around the exterior of the 28 nm HW-Tpy-
NCT clusters through hydrogen bonding interactions, giving
rise to two distinct interparticle spacings.
Figure 7. a) No covalent bond formation is observed upon mixing
NCTs functionalized with hydrazine and the aldehyde terminated
PS. b) A schematic illustration of the covalent bond formation
process assisted by supramolecular interactions between HW and
CA groups, where hydrogen-bond driven assembly results in
significant concentration of the reactive hydrazine and aldehyde
groups, increasing the rate of covalent bond formation. c) UV/Vis
spectra of the NCT samples shown in b) initial state (red dash), 48
h after mixing (black), followed by the treatment of the NCT
samples with DMF (blue), heat (green) and TFA (red),
demonstrating that all NCTs are covalently linked within 48 h of
mixing. d) Kinetic study of the covalent bond formation process
between the NCTs shown in b).
Taken together, the UV/Vis spectra, TEM images and
SAXS
measurements
demonstrate
that
the
assembly/disassembly of the multi-stimuli responsive NCT
system can be controlled by (i) hydrogen bonding interactions,
(ii) coordination chemistry, or (iii) both interactions in an
orthogonal and reversible manner. This pathway dependent
assembly process enables the selective self-assembly of a
particular NCT type from a mixture of NCTs, as well as the
potential for more complex assembly behaviors that can
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small molecules as a crosslinking agent, the need of removing More importantly, this strategy of enhancing the local
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the excess reagent after covalent bond formation and the
extremely slow (~ month) rates of covalent bond formation
limit their use, and strategies for directly forming covalent
bonds between NPs on more rapid time scales have not yet
been established.
concentration of binding groups to accelerate reaction kinetics
should be readily applicable to NP systems in a general
manner, meaning that it should be possible to form many
different types of covalent bonds between NPs.
3
2
Conclusions
In principle, the NCT system offers a distinct advantage in
developing methods to form covalent bonds between particles
using post-assembly functionalization strategy, specifically the
fact that NCTs are decorated with a large number of polymer
chains that result in a high local concentration of chain ends,
as well as conformation flexibility that allows these chain ends
to adopt different positions relative to the particle surface.
While initial efforts to link Hdz and CHO containing NCTs
discussed resulted in no observable particle assembly (Figure
7a), it should in principle be possible to increase the local
concentration of the reacting groups in a supramolecular-
In this work, we have demonstrated the ability of a single
NCT system to express finely-tuned assembly behaviors in
response to multiple external stimuli, and the feasibility of
using
a
supramolecular-assisted
post-assembly
functionalization approach to perform chemical reactions
between NPs. The unique role of the polymer tethers in the
NCT system sheds light on how to take advantage of the
entropic effects associated with polymer chain dynamics to
tune the assembly process. Moreover, the example of directly
linking NPs through covalent bonds provided here has
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important implications in the field of catalysis, as NP
assisted
post-assembly
functionalization
approach.
scaffolds can potentially be used to enhance the kinetics of
different chemical reactions via a local concentration effect.
Future work will focus on both the construction of hierarchical
self-assembled NCT architectures using the various
Specifically, by co-loading HW and CA group-functionalized
NCTs with Hdz and CHO terminated polymers, respectively
(Figure 7b, (i)), the use of hydrogen bonding to assemble
particles should result in a significant local concentration
increase of the reacting Hdz and CHO groups. Moreover,
because the polymer chains afford some degree of
conformational freedom to these binding groups, the Hdz and
CHO terminated polymer chains would be expected to be
much more likely to physically contact one another and form
covalent bonds than Hdz and CHO groups tethered to a
particle surface via small molecule linkers. As a result, the
DCC coupling reaction between NCTs should be able to occur
in a much shorter time frame than prior DCC-driven
nanoparticle assemblies (Figure 7b, (iii)).
recognition motifs established here and potentially many
52-53
others such as host-guest chemistry,
and using covalent
bonds to enhance the stability and mechanical properties of
long-range ordered NCT superstructures for their applications
in the solid phase.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website.
Synthesis and characterization of the new compounds, preparation
protocol of the NCT samples for different studies, UV/Vis
spectroscopic investigations and TEM, SAXS measurements of
NCT assemblies.
To test this hypothesis, HW-Hdz and CA-CHO
functionalized 16 nm NCTs were combined (See SI for
experimental protocols), and their assembly was monitored
using UV-Vis spectroscopy. Upon mixing, the NCTs
immediately self-assembled due to the hydrogen bonding
interactions, indicating that the presence of the Hdz and CHO
groups did not significantly affect HW-CA complex formation
AUTHOR INFORMATION
(Figure S10). After 48 hours, aliquots of the NCT aggregates
Corresponding Author
(Figure 7c, black trace) were either treated with DMF or
heated to 80 °C; both of these conditions have been shown to
disrupt hydrogen bonding interactions between NCTs (vide
supra). Notably, the UV/Vis spectra (Figure 7c, blue and
green traces) show no evidence for the dissolution of the HW-
Hdz/CA-CHO NCT aggregates. These observations are
consistent with the NCTs in this system being connected by
covalent hydrazone bonds formed between the Hdz and CHO
groups. The covalent bonding is further confirmed by the
addition of TFA, a strong acid known to cleave the hydrazone
bond, which causes the aggregates to readily re-disperse
* rmacfarl@mit.edu
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
This work was primarily supported by an NSF CAREER Grant,
award number CHE-1653289 and made use of the MRSEC
Shared Experimental Facilities at MIT, supported by the NSF
under Award DMR 14-19807. P.J.S. acknowledges support by the
NSF Graduate Research Fellowship Program under Grant
(Figure 7c, red trace). The kinetics of this covalent bond
1
122374. J.M.K. acknowledges support by the Department of
formation process between the NCTs were also investigated
(See SI, Section 3 for experimental details) by UV/Vis
spectroscopy. It was found (Figure 7d) that the hydrazone
bond formation between the NCTs was initiated within 10 min
of mixing and that over 90% of the NCTs were covalently
linked within 6 h of mixing, suggesting that compared with
other reported examples, the strategy described here using
Defense (DoD) through the National Defense Science &
Engineering Graduate Fellowship (NDSEG) Program.
REFERENCES
(1)
Mark, J. E. Some novel polymeric nanocomposites. Acc.
Chem. Res. 2006, 39, 881–888.
(2)
Sambhy, V.; MacBride, M. M.; Peterson, B. R.; Sen, A.
supramolecular complexation to form
a
high local
Silver bromide nanoparticle/polymer composites: Dual action tunable
antimicrobial materials. J. Am. Chem. Soc. 2006, 128, 9798–9808.
concentration of the reacting Hdz and CHO groups provides
an effective approach for covalently linking NPs with
(3)
Zou, H.; Wu, S.; Shen, J. Polymer/silica nanocomposites:
50
significantly shortened reaction time and elevated efficiency.
ACS Paragon Plus Environment

Page 9 of 11
Journal of the American Chemical Society
Preparation, characterization, properties, and applications. Chem. Rev.
2008, 108, 3893–3957.
4) Kao, J.; Thorkelsson, K.; Bai, P.; Rancatore, B. J.; Xu, T.
Toward functional nanocomposites: taking the best of nanoparticles,
polymers, and small molecules. Chem. Soc. Rev. 2013, 42, 2654–
(22) Song, N.; Yang, Y.-W. Molecular and supramolecular
switches on mesoporous silica nanoparticles. Chem. Soc. Rev. 2015,
44, 3474–3504.
(23) Elacqua, E.; Zheng, X.; Shillingford, C.; Liu, M.; Weck, M.
Molecular Recognition in the Colloidal World. Acc. Chem. Res. 2017,
50, 2756–2766.
(24) Chang, S.; Hamilton, A. D. Molecular Recognition of
Biologically Interesting Substrates - Synthesis of an Artificial
Receptor for Barbiturates Employing 6 Hydrogen-Bonds. J. Am.
Chem. Soc. 1988, 110, 1318–1319.
(25) Chen, S. B.; Binder, W. H. Dynamic Ordering and Phase
Segregation in Hydrogen-Bonded Polymers. Acc. Chem. Res. 2016,
49, 1409–1420.
(26) Knight, A. S.; Larsson, J.; Ren, J. M.; Zerdan, R. B.;
Seguin, S.; Vrahas, R.; Liu, J.; Ren, G.; Hawker, C. J. Control of
amphiphile self-assembly via bioinspired metal ion coordination. J.
Am. Chem. Soc. 2018, 140, 1409–1414.
(27) Lohmeijer, B. G. G.; Schubert, U. S. Playing LEGO with
macromolecules: Design, synthesis, and self-organization with metal
complexes. J. Poly. Sci. Part a-Poly. Chem. 2003, 41, 1413–1427.
(28) Winter, A.; Hager, M. D.; Newkome, G. R.; Schubert, U. S.
The marriage of terpyridines and inorganic nanoparticles: synthetic
aspects, characterization techniques, and potential applications. Adv.
Mater. 2011, 23, 5728–5748.
(29) Deng, G.; Tang, C.; Li, F.; Jiang, H.; Chen, Y. Covalent
cross-linked polymer gels with reversible sol-gel transition and self-
healing properties. Macromolecules 2010, 43, 1191–1194.
(30) Rossow, T.; Habicht, A.; Seiffert, S. Relaxation and
Dynamics in Transient Polymer Model Networks. Macromolecules
2014, 47, 6473–6482.
1
2
3
4
5
6
7
8
9
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1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
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3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
2
678.
(5)
Li, K.; Liu, B. Polymer-encapsulated organic nanoparticles
for fluorescence and photoacoustic imaging. Chem. Soc. Rev. 2014,
3, 6570–6597.
6) Rahim, F. A.; Dong-Hwan, K. Nanoparticle polymer
4
(
composites on solid substrates for plasmonic sensing applications.
Nano Today 2016, 11, 415–434.
(7)
Chen, Y.; Thakar, R.; Snee, P. T. Imparting nanoparticle
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
function with size-controlled amphiphilic polymers. J. Am. Chem.
Soc. 2008, 130, 3744–3745.
(8)
Nakano, T.; Kawaguchi, D.; Matsushita, Y. Anisotropic
self-assembly of gold nanoparticle grafted with polyisoprene and
polystyrene having symmetric polymer composition. J. Am. Chem.
Soc. 2013, 135, 6798–6801.
(9)
Liu, Z.; Peng, W.; Zare, Y.; Hui, D.; Rhee, K. Y. Predicting
the electrical conductivity in polymer carbon nanotube
nanocomposites based on the volume fractions and resistances of the
nanoparticle, interphase, and tunneling regions in conductive
networks. RSC Advances 2018, 8, 19001–19010.
(10) Chen, H. Y.; Lo, M. K. F.; Yang, G. W.; Monbouquette, H.
G.; Yang, Y. Nanoparticle-assisted high photoconductive gain in
composites of polymer and fullerene. Nat. Nanotechnol. 2008, 3,
543–547.
(11) Sharma, N.; McKeown, S. J.; Ma, X.; Pochan, D. J.;
Cloutier, S. G. Structure-property correlations in hybrid polymer-
nanoparticle electrospun fibers and plasmonic control over their
dichroic behavior. ACS Nano 2010, 4, 5551–5558.
(31) Wu, W. J.; Wang, J.; Chen, M.; Qian, D. J.; Liu, M. H.
Terpyridine-functionalized
NanoSiO
2
multi-dentate
linkers:
(12) Jang, S. G.; Kramer, E. J.; Hawker, C. J. Controlled
preparation, characterization and luminescent properties of their
metal-organic hybrid materials. J. Phy. Chem. C 2017, 121, 2234–
2242.
(32) Kay, E. R. Dynamic covalent nanoparticle building blocks.
Chem.-a Eur. J. 2016, 22, 10706–10716.
(33) Barnard, A.; Smith, D. K. Self-assembled multivalency:
dynamic ligand arrays for high-affinity binding. Angew. Chem. Int.
Ed. 2012, 51, 6572–6581.
(34) Martinez-Veracoechea, F. J.; Leunissen, M. E. The entropic
impact of tethering, multivalency and dynamic recruitment in systems
with specific binding groups. Soft Matter 2013, 9, 3213–3219.
(35) Schubert, U. S.; Eschbaumer, C. Functionalized oligomers
and copolymers with metal complexing segments: A simple and high
yield entry towards 2,2':6',2''-terpyridine monofunctionalized
telechelics. Macromol. Symp. 2001, 163, 177–187.
(36) Norsten, T. B.; Frankamp, B. L.; Rotello, V. M. Metal
directed assembly of terpyridine-functionalized gold nanoparticles.
Nano Lett. 2002, 2, 1345–1348.
(37) Dewi, M. R.; Gschneidtner, T. A.; Elmas, S.; Ranford, M.;
Moth-Poulsen, K.; Nann, T. Monofunctionalization and Dimerization
of Nanoparticles Using Coordination Chemistry. ACS Nano 2015, 9,
1434–1439.
(38) Drew, M. G. B.; Hudson, M. J.; Iveson, P. B.; Russell, M.
L.; Liljenzin, J. O.; Skalberg, M.; Spjuth, L.; Madic, C. Theoretical
and experimental studies of the protonated terpyridine cation. Ab
initio quantum mechanics calculations, and crystal structures of two
different ion pairs formed between protonated terpyridine cations and
nitratolanthanate(III) anions. J. Chem. Soc. Dalton Trans. 1998,
2973–2980.
(39) Dobrawa, R.; Ballester, P.; Saha-Möller, C. R.; Wü rthner,
F. Thermodynamics of 2,2':6',2''-terpyridine-metal ion complexation.
In metal-containing and metallosupramolecular polymers and
materials; ACS Symposium Series; American Chemical Society: 2006;
Vol. 928, pp 43−62.
supramolecular assembly of micelle-like gold nanoparticles in ps-b-
p2vp diblock copolymers via hydrogen bonding. J. Am. Chem. Soc.
2
011, 133, 16986–16996.
13) Kim, Y.; Kook, K.; Hwang, S. K.; Park, C.; Cho, J.
(
Polymer/perovskite-type nanoparticle multilayers with multielectric
properties prepared from ligand addition-induced layer-by-layer
assembly. ACS Nano 2014, 8, 2419–2430.
(14) Barrow, M.; Taylor, A.; Murray, P.; Rosseinsky, M. J.;
Adams, D. J. Design considerations for the synthesis of polymer
coated iron oxide nanoparticles for stem cell labelling and tracking
using MRI. Chem. Soc. Rev. 2015, 44, 6733–6748.
(15) Kim, C. R.; Uemura, T.; Kitagawa, S. Inorganic
nanoparticles in porous coordination polymers. Chem. Soc. Rev. 2016,
4
5, 3828–3845.
16) Zhang, H.; Liu, Y.; Yao, D.; Yang, B. Hybridization of
(
inorganic nanoparticles and polymers to create regular and reversible
self-assembly architectures. Chem. Soc. Rev. 2012, 41, 6066–6088.
(17) Feng, L. H.; Zhu, C. L.; Yuan, H. X.; Liu, L. B.; Lv, F. T.;
Wang, S. Conjugated polymer nanoparticles: preparation, properties,
functionalization and biological applications. Chem. Soc. Rev. 2013,
4
2, 6620–6633.
(18) Grzelczak, M.; Liz-Marzan, L. M.; Klajn, R. Stimuli-
responsive self-assembly of nanoparticles. Chem. Soc. Rev. 2019, 48,
342–1361.
19) Udayabhaskararao, T.; Altantzis, T.; Houben, L.;
1
(
Coronado-Puchau, M.; Langer, J.; Popovitz-Biro, R.; Liz-Marzan, L.
M.; Vukovic, L.; Kral, P.; Bals, S.; Klajn, R. Tunable porous
nanoallotropes prepared by post-assembly etching of binary
nanoparticle superlattices. Science 2017, 358, 514–518.
(20) Zhang, J.; Santos, P. J.; Gabrys, P. A.; Lee, S.; Liu, C.;
Macfarlane, R. J. Self-assembling nanocomposite tectons. J. Am.
Chem. Soc. 2016, 138, 16228–16231.
(21) Yang, H.; Yuan, B.; Zhang, X.; Scherman, O. A.
Supramolecular chemistry at interfaces: host-guest interactions for
fabricating multifunctional biointerfaces. Acc. Chem. Res. 2014, 47,
(40) Offenhartz, P.; George, P.; Haight, G. P. Ionization
constants for ligand 2,2',2''-tripyridine. J. Phys. Chem. 1963, 67, 116–
118.
2
106–2115.
(41) Zhao, Y.; Newton, J. N.; Liu, J.; Wei, A. Dithiocarbamate-
ACS Paragon Plus Environment

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Page 10 of 11
+
coated SERS substrates: sensitivity gain by partial surface
passivation. Langmuir 2009, 25, 13833–13839.
relatively high concentration of H is needed in order to disassociate
the coordination complex.
1
2
3
4
5
6
7
8
9
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4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
42) Rossow, T.; Seiffert, S. Supramolecular polymer gels with
potential model-network structure. Poly. Chem. 2014, 5, 3018–3029.
43) Piech, M.; George, M. C.; Bell, N. S.; Braun, P. V.
(49) Hyland, L. L.; Taraban, M. B.; Yu, Y. Using small-angle
scattering techniques to understand mechanical properties of
biopolymer-based biomaterials. Soft Matter 2013, 9, 10218–10228.
(50) The cyanuric acid groups functionalized on the NCTs,
which are in close proximity to the covalent bond reaction center,
may also serve as a catalyst due to its weak acidic nature, as the
HW/CA assisted covalent bond formation process is faster than the
Tpy assisted process. See SI, Section 9.
(51) Daniel, M. C.; Astruc, D. Gold nanoparticles: Assembly,
supramolecular chemistry, quantum-size-related properties, and
applications toward biology, catalysis, and nanotechnology. Chem.
Rev. 2004, 104, 293–346.
(52) Yang, Y.-W.; Sun, Y.-L.; Song, N. Switchable host-guest
systems on surfaces. Acc. Chem. Res. 2014, 47, 1950–1960.
(53) Wang, X.; Liu, Z.-J.; Hill, E. H.; Zheng, Y.; Guo, G.;
Wang, Y.; Weiss, P. S.; Yu, J.; Yang, Y.-W. Organic-inorganic
hybrid pillarene-based nanomaterial for label-free sensing and
catalysis. Matter 2019, 1, 1–14.
(
Patterned colloid assembly by grafted photochromic polymer layers.
Langmuir 2006, 22, 1379–1382.
(44) Shiraishi, Y.; Shirakawa, E.; Tanaka, K.; Sakamoto, H.;
Ichikawa, S.; Hirai, T. Spiropyran-modified gold nanoparticles:
reversible size control of aggregates by uv and visible light
irradiations. ACS Appl. Mater. & Interfaces 2014, 6, 7554–7562.
(45) Zhao, H.; Sen, S.; Udayabhaskararao, T.; Sawczyk, M.;
Kucanda, K.; Manna, D.; Kundu, P. K.; Lee, J. W.; Kral, P.; Klajn, R.
Reversible trapping and reaction acceleration within dynamically self-
assembling nanoflasks. Nat. Nanotechnol. 2016, 11, 82–88.
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(46) Kundu, P. K.; Samanta, D.; Leizrowice, R.; Margulis, B.;
Zhao, H.; Borner, M.; Udayabhaskararao, T.; Manna, D.; Klajn, R.
Light-controlled self-assembly of non-photoresponsive nanoparticles.
Nat. Chem. 2015, 7, 646–652.
(47) Klajn, R. Spiropyran-based dynamic materials. Chem. Soc.
Rev. 2014, 43, 148–184.
(48) Due to the large association constant of the Zn(Tpy)
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1
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complex (K
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~ 10 ) and weak basicity of Tpy groups (pK
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~ 9),
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