Light-Switchable and Self-Healable Polymer Electrolytes Based on Dynamic Diarylethene and Metal-Ion Coordination

Article abstract of DOI:10.1021/jacs.0c11894

Self-healing polymer electrolytes are reported with light-switchable conductivity based on dynamic N-donor ligand-containing diarylethene (DAE) and multivalent Ni2+ metal-ion coordination. Specifically, a polystyrene polymer grafted with poly(ethylene glycol-r-DAE)acrylate copolymer side chains was effectively cross-linked with nickel(II) bis(trifluoromethanesulfonimide) (Ni(TFSI)2) salts to form a dynamic network capable of self-healing with fast exchange kinetics under mild conditions. Furthermore, as a photoswitching compound, the DAE undergoes a reversible structural and electronic rearrangement that changes the binding strength of the DAE-Ni2+ complex under irradiation. This can be observed in the DAE-containing polymer electrolyte where irradiation with UV light triggers an increase in the resistance of solid films, which can be recovered with subsequent visible light irradiation. The increase in resistance under UV light irradiation indicates a decrease in ion mobility after photoswitching, which is consistent with the stronger binding strength of ring-closed DAE isomers with Ni2+. 1H-15N heteronuclear multiple-bond correlation nuclear magnetic resonance (HMBC NMR) spectroscopy, continuous wave electron paramagnetic resonance (cw EPR) spectroscopy, and density functional theory (DFT) calculations confirm the increase in binding strength between ring-closed DAE with metals. Rheological and in situ ion conductivity measurements show that these polymer electrolytes efficiently heal to recover their mechanical properties and ion conductivity after damage, illustrating potential applications in smart electronics.

Full text of DOI:10.1021/jacs.0c11894

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Light-Switchable and Self-Healable Polymer Electrolytes Based on
Dynamic Diarylethene and Metal-Ion Coordination
Hui Nie,§ Nicole S. Schauser,§ Jeffrey L. Self, Tarnuma Tabassum, Saejin Oh, Zhishuai Geng,
Seamus D. Jones, Manuel S. Zayas, Veronica G. Reynolds, Michael L. Chabinyc, Craig J. Hawker,
Songi Han, Christopher M. Bates, Rachel A. Segalman,* and Javier Read de Alaniz*
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ABSTRACT: Self-healing polymer electrolytes are reported with
light-switchable conductivity based on dynamic N-donor ligand-
containing diarylethene (DAE) and multivalent Ni2+ metal-ion
coordination. Specifically, a polystyrene polymer grafted with
poly(ethylene glycol-r-DAE)acrylate copolymer side chains was
e ff e c t i v e l y c r o s s - l i n k e d w i t h n i c k e l ( I I ) b i s -
(trifluoromethanesulfonimide) (Ni(TFSI)2) salts to form a
dynamic network capable of self-healing with fast exchange
kinetics under mild conditions. Furthermore, as a photoswitching compound, the DAE undergoes a reversible structural and
electronic rearrangement that changes the binding strength of the DAE−Ni2+ complex under irradiation. This can be observed in the
DAE-containing polymer electrolyte where irradiation with UV light triggers an increase in the resistance of solid films, which can be
recovered with subsequent visible light irradiation. The increase in resistance under UV light irradiation indicates a decrease in ion
mobility after photoswitching, which is consistent with the stronger binding strength of ring-closed DAE isomers with Ni2+. 1H−15N
heteronuclear multiple-bond correlation nuclear magnetic resonance (HMBC NMR) spectroscopy, continuous wave electron
paramagnetic resonance (cw EPR) spectroscopy, and density functional theory (DFT) calculations confirm the increase in binding
strength between ring-closed DAE with metals. Rheological and in situ ion conductivity measurements show that these polymer
electrolytes efficiently heal to recover their mechanical properties and ion conductivity after damage, illustrating potential
applications in smart electronics.
azobenzene to mediate reversible changes in conductivity by
competitive guest−host interactions.3,17,18 We recently devel-
oped a photoswitchable polymeric ionic liquid based on
imidazolium-containing diarylethene (DAE) cations and
observed that ionic conductivity can be reversibly modulated
by tuning the positive charge distribution and cation−anion
interaction upon light irradiation.19 However, current light-
responsive ion-conducting polymer electrolytes have relatively
poor solid-like mechanical properties, because they are either
viscous liquids with a low glass-transition temperature (Tg ≪
20 °C) or solvent-containing hydrogels.3,19 Consequently, the
materials are difficult to integrate into devices.20−23 The
development of light-responsive, ion-conducting polymers that
are mechanically robust, capable of self-healing, and inherently
tunable remains a major challenge.
INTRODUCTION
■
The ability to remotely modulate ion and/or charge transport
using light not only is essential for neurological activity in
nature1 but also enables the fabrication of multifunctional
smart materials including photoswitchable organic light-
emitting transistors,2 supramolecular hydrogels,3 metal organic
frameworks,4 and semiconductors.5 By introducing light-
responsive functional groups into these materials, the optical
and/or electrical properties can be noninvasively tuned with
excellent spatial and temporal resolution, making them pivotal
components for emerging optoelectronics applications such as
smart displays, photodetectors, and logic circuits.3,6−8 Among
these materials, polymer electrolytes are an attractive platform
due to their high ionic conductivity, tunable polymeric scaffold,
and robust mechanical properties.9,10 Importantly, ion mobility
and conductivity in these materials are highly dependent on
different types of weak interactions, such as cation−anion,11
polymer−ion,12 and Lewis acid−base interactions.13,14 The
rational and noninvasive modulation of these weak interactions
by integrating light-responsive moieties into the structure of
polymer electrolytes provides an elegant way to tune the ion
mobility and conductivity in situ.15,16 Huang and co-workers
reported supramolecular ion-conducting hydrogels using
Received: November 12, 2020
Published: January 13, 2021
https://dx.doi.org/10.1021/jacs.0c11894
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Figure 1. (a) Synthesis of DAE−acrylate monomer and copolymer brushes of DAE−acrylate and PEG−acrylate using RAFT controlled radical
polymerization from a PS macro-CTA. (b) Molecular structure and schematic of the polymer network before and after metal salt addition,
illustrating salt solvation and formation of DAE−Ni2+complexes. Isomerization of DAE from the ring-open to ring-closed form with UV light
irradiation leads to stronger M−L interactions. Reversion back to the ring-open form occurs with visible light irradiation. This reversibly tunable
M−L coordination and photostationary state impacts the mobility of metal ions (ionic conductivity).
Here, we demonstrate that cross-linked polymer electrolytes
with covalently bonded imidazole-containing DAE ligands and
t h e m u l t i v a l e n t m e t a l s a l t n i c k e l ( I I ) b i s -
(trifluoromethanesulfonimide) (Ni(TFSI)2) leads to robust
networks that self-heal and reversibly change ionic conductivity
in response to light irradiation (Figure 1). Through the
stronger binding strength of the metal−ligand (M−L)
complex, decreased mobility of Ni2+ and thus ionic
conductivity are observed in the solid state. This design
strategy demonstrates that reversible light-switching and self-
healing polymer electrolytes can be engineered with a useful
balance of different properties.
light-responsive cross-linking sites. For the synthesis of DAE−
PS, the DAE-containing acrylate monomer (DAE−acrylate)
was initially prepared via Michael addition of DAE to 1,4-
butanediol diacrylate (Figure 1a). The grafted copolymer was
then obtained by reversible addition−fragmentation chain
transfer polymerization (RAFT) of DAE−acrylate and PEG−
acrylate (Mn = 480 g/mol) using a previously reported PS
macro-chain transfer agent (macro-CTA).24 The macro-CTA
used here contains ∼140 repeating units of PS with ∼10 mol %
of the RAFT chain transfer groups along the backbone. After
polymerization in DMF, the average degree of polymerization
of the randomly grafted copolymer side chains was ∼36
1
repeating units with about 30 mol % DAE as measured by H
RESULTS AND DISCUSSION
NMR (Figure S1). According to the literature, a high
incorporation of imidazole-containing monomer is essential
■
Polymer Electrolytes Design and Synthesis. To
achieve cross-linked polymer electrolytes with light-control-
lable ionic conductivity and self-healing properties, a
polystyrene (PS) polymer grafted with poly(ethylene glycol-
r-DAE)acrylate copolymer side chains (DAE−PS) was
employed. Inclusion of the PS component enhances the
mechanical properties24 of the material, whereas the poly-
ethylene glycol (PEG) monomers are beneficial for ion
solvation, and the DAE-containing monomers are used as
for efficient cross-linking with metal ions in the materials.24
A
linear copolymer of DAE−acrylate (30 mol %) and PEG−
acrylate (L-DP) was also synthesized for comparison (Figure
S2).
With the DAE−PS brush copolymer architecture in hand,
Ni(TFSI)2 was chosen as a cross-linker (DAE−PS−Ni) based
on M−L coordination for the following reasons: (1) from our
previous work, the plateau modulus increases by an order of
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magnitude after adding Ni(TFSI)2,25 and (2) metal salts with a
0.6 mW/cm2, ∼1 min) resulted in a distinct color change from
near colorless to blue due to the photocyclization of DAE
units. In agreement with the behavior in solution,28 the UV−
vis spectra of DAE−PS−Ni films exhibited an absorption at
about 276 nm with rapid switching observed upon UV
irradiation, leading to the appearance of new band at 660 nm
with a shoulder at ∼370 nm. These absorption characteristics
of ring-open and ring-closed isomers are in accordance with
the UV−vis spectra derived from density functional theory
(DFT) calculation (Figures S5 and S6). Significantly,
subsequent irradiation with visible light (white light, 47
mW/cm2, ∼6 min) reversed these spectral changes, resulting
in color loss, clearly demonstrating the reversible photo-
switching nature of supported DAE units in these graft
copolymer thin films. In addition, the calculated energy
difference between the ring-open and the ring-closed isomers
of imidazole-containing DAE is 28.4 kcal/mol, which is similar
to reported dithienylbenzene as well as the charged
imidazolium-containing DAE from our previous work (Figure
S7).33 To estimate the photostationary state (PSS) of these
DAE units, a small molecule model system, butyl acrylate-
DAE, was synthesized for easy quantification of PSS in solution
by UV−vis spectroscopy and 1H NMR. The extinction
coefficients of ring-open and ring-closed isomers (εopen and
εclosed) were calculated to be ∼31 800 (276 nm) and ∼37 500
(660 nm) L mol−1 cm−1, respectively (Figures S8−S10). On
the basis of the assumption that the model molecule in
solution and polymer-supported DAE units in thin films have
similar εopen and εclosed, the PSS of DAE−PS and DAE−PS−Ni
thin films is estimated to contain 54 and 34 mol % of the ring-
closed isomer (Figures 2b and S10−S12). We also note that
the addition of Ni(TFSI)2 decreased the molar ratio of ring-
closed isomers at the PSS in the polymer, possibly due to
stabilization of the aromatic imidazole in the ring-open state by
the transition metal.34 The thermal relaxation process of this
T-type DAE in thin films is shown in Figure S13.
TFSI anion feature good solubility and thermal stability.26
A
molar ratio r = 0.1 ([Ni2+]:[DAE−acrylate monomer]) was
used to balance efficient cross-linking, efficient photoswitching,
and ionic conductivity. Incorporation of Ni salt resulted in a
change of mechanical properties from a viscous polymer melt
to a soft solid, suggesting the formation of Ni-mediated
crosslinks between polymer chains. Moreover, as shown in
Figure S3, after the addition of Ni(TFSI)2, the intense
absorption band at ca. 276 nm corresponding to π-to-π* and
n-to-π* transitions of the imidazole and thiophene moieties
present in DAE broadens and an absorption shoulder at ca.
290 nm appears. This red-shifted absorption agrees with other
metal−imidazole- or pyridine-containing ligand coordination
systems and suggests metal-ion binding to the DAE
ligands.27,28 The DSC traces of DAE−PS with and without
Ni(TFSI)2 show transitions at around −29 and 91 °C (Figure
S4), which are assigned as the Tg values of the poly(PEG−
DAE) and PS domain,29 respectively. While permanently
cross-linked polymer networks are difficult to postprocess,30,31
the DAE−PS−Ni network is readily dissolvable and can be
reshaped or spin coated on a variety of surfaces.
Photoswitching Properties. Encouraged by these initial
results, we next investigated the photochemical behavior of
DAE−PS−Ni thin films, which is a driver for many
applications of polymer electrolytes.32 Figure 2a depicts
representative UV−vis absorption spectra of spin-coated
DAE−PS−Ni thin films. Irradiation with UV light (300 nm,
Light-Responsive M−L Coordination. The binding
affinity of Ni2+ to DAE units in the polymer can be reversibly
modulated using different wavelengths of light. When the DAE
unit is present as the ring-open isomer, the imidazole ring is
aromatic with (4n + 2) p electrons (Figure S14) and the Ni2+
ions coordinate with the pyridine-like nitrogen in the ring.35,36
Irradiation with UV light triggers cyclization to give the ring-
closed isomer with associated electronic rearrangement,
leading to a nonaromatic Schiff base. The lone pair of
electrons on the Schiff base nitrogen also has the ability to
coordinate with a Ni2+ cation,37 and the higher electron density
of the nitrogen atom increases the σ-donor strength for M−L
coordination.35 As shown with 1H−15N heteronuclear multiple
bond correlation (HMBC) NMR spectra of a model DAE
molecule (methyl DAE), the pyridine-like nitrogen experiences
an upfield chemical shift from 260.9 to 235.8 ppm upon UV
light irradiation (300 nm, 1.3 mW/cm2, 20 min in an NMR
tube). This indicates that the nitrogen atoms in the ring-closed
isomer feature higher electron density than the ring-open
isomer (Figures 3a and S15). Here, an 15N NMR spectrum of
15N-labeled methyl DAE allowed the peaks of each nitrogen
atom in the structure to be fully assigned (Figure S16). On the
basis of these NMR results, the ring-closed isomer has stronger
σ bonding with the metal ions. Continuous wave electron
paramagnetic resonance spectroscopy (cw EPR) was then used
to further assess the strength of M−L coordination in these
polymer electrolytes before and after isomerization. Cu2+ was
Figure 2. (a) UV−vis absorption spectra of DAE−PS−Ni polymer
thin films on ITO before and after UV (300 nm) and broad-band
white light irradiation. (b) Kinetic traces of a DAE−PS−Ni polymer
(r = 0.1) thin film during initial exposure to 300 nm light followed by
broad-band white light.
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A|| and A⊥ values of DAE−PS−Cu(TFSI)2 before UV
irradiation are 530 10 and 50 5 MHz, and g|| and g⊥
values are 2.045 0.001 and 2.260 0.005, respectively, as
obtained from simulation (using the “pepper” function for
solid-state cw spectra in EasySpin, a MATLAB toolbox). These
values are similar to those reported for other Cu2+−imidazole
systems.41 In addition, a value of g|| < 2.3 implies covalent
character for the Cu2+−DAE coordination.42 After being
subjected to UV irradiation, the percentage of ring-closed
isomers in DAE−PS−Cu(TFSI)2 solution increased as
evidenced by pump−probe measurement (Figure S17) with
concomitant EPR spectral changes being observed. Compared
with the sample before UV light irradiation, the g value does
not change but A|| (475 5 MHz) and A⊥ (40 5 MHz)
decrease. The value of α, calculated from a model developed
by Kivelson and co-workers, is used to quantify the covalency
of DAE−Cu2+ coordination before and after UV light
irradiation43
A
i
y
3
7
2
j
j
z
z
α = −
+ (g − g ) + (g⊥ − ge) + 0.04
j
j
z
z
e
P
k
{
where P is the interaction dipolar term of the free Cu2+ ion
(0.036 cm−1) and ge is the g factor of a free electron (2.0023).
For a completely ionic bond α2 = 1, whereas for a completely
covalent bond α2 = 0.5. We find that the α2 values decrease
from 0.68 to 0.63 after UV irradiation, suggesting the Cu2+−
DAE coordination increases in covalency. Another noteworthy
observation is the broadening of spectra and superhyperfine
features arising from 14N coupling after UV irradiation. This is
consistent with an increased covalency of Cu2+−14N bonds
that can result in concurrently stronger hyperfine coupling
interactions with the hydrogen atoms in the DAE ring, yielding
an increase in the number of EPR lines and less well-resolved
features in the 14N region.44 In addition to the NMR and EPR
observations, DFT calculations corroborate the decreased N−
Ni2+ bond lengths of ring-open and ring-closed DAE isomers
(Table S1). The presence of Ni2+ lowers the DFT-calculated
difference in energy between the ring-open and the ring-closed
isomers to ∼13 kcal/mol. This difference can be attributed to
the higher binding energy of the ring-closed isomer to Ni2+
(Figure S18). In summary, the combination of 1H−15N
HMBC NMR, EPR spectral analysis, and DFT calculations
indicates that the ring-closed isomer has a stronger interaction
with metal ions than the ring-open isomer.
Figure 3. (a) 1H−15N HMBC NMR spectra of methyl DAE after UV
light (300 nm) irradiation. Fraction of the ring-open isomers was
switched to ring-closed isomers upon UV irradiation. (b) Continuous
wave EPR signals of DAE−PS Cu(TFSI)2 (r = 0.1) in DCM with
[Cu2+] = 5 mM before and after UV (300 nm) light irradiation.
selected as a local probe to detect the changing environment
around metal ions while photoswitching DAE for the following
reasons. First, Cu2+ has one unpaired electron in its d9 orbital
and two magnetically active and naturally occurring isotopes
(63Cu 69.13%; 65Cu 30.83%) with nuclear spin I = 3/2,
resulting in hyperfine interactions between the electron and the
nuclear spins to be studied. Second, the resulting strong spin−
orbit coupling and electron−ligand field interactions lead to
anisotropy of the g value and hyperfine (A) value, which are
especially sensitive to the local environment around Cu2+.38
Third, Cu2+−imidazole EPR spectra are well studied in the
literature, which provides a basis for analysis of the Cu2+−DAE
systems studied in this work.39 Fourth, the DAE units undergo
reversible photoswitching in the presence of Cu2+ (Figure
S17), which is similar to Ni2+. A solution sample of DAE−PS
polymer with Cu(TFSI)2 ([Cu2+] = 5 mM, molar ratio
Cu2+:DAE = 0.1) in DCM was used for EPR measurements,
and as shown in Figure 3b, the EPR spectra of polymer and
Cu(TFSI)2 resemble typical Cu2+−imidazole systems.40 The
Light-Switchable Ionic Conductivity. The exciting
ability to reversibly switch the M−L coordination strength
with light holds potential for tuning ionic conductivity with
external stimuli. The bulk ionic conductivity of DAE−PS−Ni
with r = 0.1 salt loading is around 3.9 × 10−7 S/cm at room
temperature (Figure 4a) with an activation energy of 0.61 eV
from the Arrhenius equation, which are within the typical
range of PEO-based polymer electrolytes.45 It is worth noting
that the ionic conductivity included both Ni2+ and TFSI− ions
transport, similar to our previous study.25,38,46 The light-
switchable DAE ligand modulates the mobility of Ni2+ and thus
the ionic conductivity. From X-ray scattering, no obvious
features of aggregation or crystallization of added ions were
observed, suggesting that ions are homogeneously dispersed in
the material (Figure S19). To monitor the change of ionic
conductivity with light irradiation, in situ through-plane
analysis of spin-coated DAE−PS−Ni thin films was carried
out on precleaned ITO with evaporated Au electrodes as top
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contacts (Figure S20).19 As shown in Figure 4b, the resistance
of the polymer thin film increased upon UV irradiation (313
nm, 0.8 mW/cm2, different time intervals) and subsequently
decreased upon exposure to visible light (white light, 0.4 mW/
cm2, different time intervals). These trends are consistent with
the NMR and EPR results, which indicate that polymers with
ring-closed DAE units have stronger M−L coordination and
thus decreased Ni2+ ion mobility (higher resistance) than the
corresponding ring-open isomers. To further support that
resistance changes of DAE−PS−Ni are induced by the
photoswitching of DAE, the absorption intensity of the ring-
closed isomer was monitored with the same light irradiation
conditions as during conductivity measurements. As shown in
Figure 4c, the kinetics and time scale of ring-open to ring-
closed isomerization are in quantitative agreement with the
resistance variation. Significantly, the ability to tune con-
ductivity with light irradiation was reproducible for at least 6
cycles (Figure S21), albeit with a slight variation of resistance
possibly due to minor degradation of the DAE units.47 The
spatial control of photochemical regulation further enables the
patterning of local conductivity in polymer thin films using UV
light (Figure S22).
Self-Healing Properties. In addition to light-induced
changes in conductivity, the DAE−PS−Ni polymer electrolytes
are soft solids that can self-heal under mild conditions. As
shown in Figure 5a, the storage modulus (G′) of DAE−PS−Ni
is higher than the loss modulus (G″) across 0.01−10 Hz as
measured by oscillatory rheology at room temperature. These
solid-like properties arise at fast and intermediate time scales
due to the transient M−L cross-links with a frequency
dependence that matches the molecular exchange dynam-
ics.24,48 In contrast, samples synthesized with no PS
component or without Ni(TFSI)2 are viscous liquids at all
frequencies (Figure S23). These results suggest that the
synergistic combination of a PS component and DAE−Ni2+
coordination is required to generate a soft solid as M−L bonds
are too labile at room temperature. Since dynamic DAE−Ni2+
complexes reside in the percolating PEG domain, DAE−PS−
Ni polymer electrolytes can self-heal. As demonstrated in
Figures 5a and S24, a DAE−PS−Ni sample that was damaged
subsequently recovered its original properties after heating on
the rheometer plate at 45 °C under nitrogen for 1.5 h. Figures
Figure 4. (a) Temperature dependence of the ionic conductivity for a
bulk DAE−PS−Ni with r = 0.1 before photoswitching. (b)
Normalized resistance of DAE−PS−Ni thin films under UV (300
nm) and white light irradiation. (c) Variation of the absorption
intensity of ring-closed isomers in DAE−PS−Ni thin films at 660 nm
with UV (300 nm) and white light irradiation.
Figure 5. (a) Room-temperature frequency sweeps of original and healed (45 °C, 1.5 h) polymer electrolyte. (b) Normalized ionic conductivity
before and after the polymer electrolyte was cut with a blade, showing 93% recovery of the initial conductivity after 35 min at 45 °C. (c)
Normalized ionic conductivity before and after the polymer electrolyte was cut with a blade (∼50% of the film thickness) and 96% of the initial
conductivity was recovered after 16 h at room temperature (31 °C).
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5b and 5c show that the ionic conductivity of DAE−PS−Ni is
significantly reduced after applying a deep cut (∼50% of the
film thickness). Notably, 94% and 96% of the ionic
conductivity is restored after 35 min at 45 °C and 16 h at
room temperature, respectively. Importantly, healed samples
also show similar ionic conductivity when drop cast (∼550 μm
thickness) on a quartz slide with Au electrodes deposited on
the top surface (Figures S25 and S26). The time required for
healing at 45 °C is shorter than that at room temperature,
which we believe originates from faster metal-ion exchange
kinetics and a decrease in the modulus (G′, G″) as the
temperature of the material increases (Figures S27 and S28).
The accelerated polymer dynamics at increased temperature
results in faster self-healing behavior which is consistent with
literature reports.49,50 The efficient recovery of not only the
mechanical properties but also the electronic properties
showcases the advantage of a self-healing M−L coordination
network.
Nicole S. Schauser − Materials Department and Materials
Research Laboratory, University of California−Santa
Barbara, Santa Barbara, California 93106, United States
Jeffrey L. Self − Department of Chemistry and Biochemistry,
University of California−Santa Barbara, Santa Barbara,
California 93106, United States
Tarnuma Tabassum − Department of Chemistry and
Biochemistry, University of California−Santa Barbara, Santa
Barbara, California 93106, United States
Saejin Oh − Department of Chemistry and Biochemistry,
University of California−Santa Barbara, Santa Barbara,
California 93106, United States
Zhishuai Geng − Materials Department and Materials
Research Laboratory, University of California−Santa
Barbara, Santa Barbara, California 93106, United States
Seamus D. Jones − Department of Chemical Engineering and
Materials Research Laboratory, University of
California−Santa Barbara, Santa Barbara, California
93106, United States
Manuel S. Zayas − Department of Chemistry and
Biochemistry, University of California−Santa Barbara, Santa
Barbara, California 93106, United States
Veronica G. Reynolds − Materials Department and Materials
Research Laboratory, University of California−Santa
Barbara, Santa Barbara, California 93106, United States
Michael L. Chabinyc − Materials Department and Materials
Research Laboratory, University of California−Santa
Barbara, Santa Barbara, California 93106, United States;
orcid.org/0000-0003-4641-3508
Craig J. Hawker − Department of Chemistry and
Biochemistry, University of California−Santa Barbara, Santa
Barbara, California 93106, United States; Materials
Department and Materials Research Laboratory, University
of California−Santa Barbara, Santa Barbara, California
93106, United States; orcid.org/0000-0001-9951-851X
Songi Han − Department of Chemistry and Biochemistry,
University of California−Santa Barbara, Santa Barbara,
California 93106, United States; Department of Chemical
Engineering, University of California−Santa Barbara, Santa
Barbara, California 93106, United States; orcid.org/
0000-0001-6489-6246
Christopher M. Bates − Department of Chemistry and
Biochemistry, University of California−Santa Barbara, Santa
Barbara, California 93106, United States; Materials
Department and Materials Research Laboratory, University
of California−Santa Barbara, Santa Barbara, California
93106, United States; orcid.org/0000-0002-1598-794X
CONCLUSION
■
Incorporation of photoswitchable units into polymer electro-
lytes constitutes a design strategy for functional materials with
remotely tunable conductivity. On the basis of DAE as a
photoresponsive building block, the reversible electronic
rearrangement between ring-open and ring-closed states
changes the binding strength of ligands to multivalent metal
ions. With the appropriate choice of polymeric building blocks,
these materials are soft solids at room temperature that can
self-heal under mild heating and change ionic conductivity in
response to light irradiation. Our results demonstrate that
light-responsive M−L coordination is a versatile design
concept to create novel polymer electrolytes with potential
applications ranging from photodetectors to smart circuits and
soft robotics.
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/jacs.0c11894.
General methods, synthesis and characterization of
materials, photoisomerization studies, DFT calculations,
ion conductivity measurements, self-healing studies
(PDF)
AUTHOR INFORMATION
■
Complete contact information is available at:
https://pubs.acs.org/10.1021/jacs.0c11894
Corresponding Authors
Rachel A. Segalman − Materials Department, Materials
Research Laboratory, and Department of Chemical
Engineering, University of California−Santa Barbara, Santa
Barbara, California 93106, United States; orcid.org/
0000-0002-4292-5103; Email: segalman@
Author Contributions
§H.N. and N.S.S.: These authors contributed equally.
Funding
engineering.ucsb.edu
This work was supported by the MRSEC Program of the
National Science Foundation under Award No. DMR 1720256
(IRG-2). The research reported here made use of shared
facilities of the National Science Foundation (NSF) Materials
Research Science and Engineering Center at UC Santa
Barbara, DMR-1720256. The UCSB MRSEC is a member of
the Materials Research Facilities Network (www.mrfn.org).
N.S.S gratefully acknowledges the Fannie and John Hertz
Foundation and the National Science Foundation Graduate
Javier Read de Alaniz − Department of Chemistry and
Biochemistry, University of California−Santa Barbara, Santa
Barbara, California 93106, United States; orcid.org/
0000-0003-2770-9477; Email: javier@chem.ucsb.edu
Authors
Hui Nie − Department of Chemistry and Biochemistry,
University of California−Santa Barbara, Santa Barbara,
California 93106, United States
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pubs.acs.org/JACS
Article
Super-Delocalized Polyanion. Angew. Chem., Int. Ed. 2016, 55 (7),
2521−2525.
Research Fellowship Program under Grant 1650114. V.G.R.
gratefully acknowledges the National Science Foundation
Graduate Research Fellowship Program under Grant
1650114. Use was made of computational facilities purchased
with funds from the National Science Foundation (CNS-
1725797) and administered by the Center for Scientific
Computing (CSC). The CSC is supported by the California
NanoSystems Institute and the Materials Research Science and
Engineering Center (MRSEC; NSF DMR 1720256) at UC
Santa Barbara. Any opinions, findings, and conclusions or
recommendations expressed in this material are those of the
authors and do not necessarily reflect the views of the National
Science Foundation. This work was supported in part by NSF
Major Research Instrumentation award, MRI-1920299, for
magnetic resonance instrumentation. X-ray scattering measure-
ments were performed at the National Synchrotron Light
Source II (NSLS-II, beamline 11-BM, Brookhaven National
Laboratory).
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Notes
The authors declare no competing financial interest.
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