Tunable Visible and Near Infrared Photoswitches

Article abstract of DOI:10.1021/jacs.6b07434

A class of tunable visible and near-infrared donor-acceptor Stenhouse adduct (DASA) photoswitches were efficiently synthesized in two to four steps from commercially available starting materials with minimal purification. Using either Meldrum's or barbitu

Full text of DOI:10.1021/jacs.6b07434

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Article
Tunable Visible and Near Infrared Photoswitches
James R. Hemmer, Saemi O. Poelma, Nicolas Treat, Zachariah A. Page, Neil Dolinski, Yvonne J
Diaz, Warren Tomlinson, Kyle D Clark, Joseph P. Hooper, Craig J. Hawker, and Javier Read de Alaniz
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.6b07434 • Publication Date (Web): 04 Oct 2016
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Journal of the American Chemical Society
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Tunable Visible and Near Infrared Photoswitches
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James R. Hemmer, Saemi O. Poelma, Nicolas Treat, Zachariah A. Page, Neil D. Dolinski,
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Yvonne J. Diaz, Warren Tomlinson, Kyle D. Clark, Joseph P. Hooper, Craig Hawker, Javier
,†
Read de Alaniz*
†
Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States
‡
Materials Department, Materials Research Laboratory, University of California, Santa Barbara, California, 93106,
United States
§
Department of Physics, Naval Postgraduate School, 1 University Circle, Monterey, California 93943, United States
ABSTRACT: A class of tunable visible and near-infrared donor-acceptor Stenhouse adduct (DASA) photoswitches were
efficiently synthesized in 2 to 4 steps from commercially available starting materials with minimal purification. Using ei-
ther Meldrum’s or barbituric acid “acceptors” in combination with aniline-based “donors” an absorption range spanning
from 450 to 750 nm is obtained. Additionally, photoisomerization results in complete decoloration for all adducts, yield-
ing fully transparent, colorless solutions and films. Detailed investigations using density functional theory, nuclear mag-
netic resonance, and visible absorption spectroscopies provide valuable insight into the unique structure-property rela-
tionships for this novel class of photoswitches. As a final demonstration, selective photochromism is accomplished in a
variety of solvents and polymer matrices, a significant advantage for applications of this new generation of DASAs.
stable state, have the potential to overcome such limita-
tions, yet are far less common.
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Introduction:
Photoswitches have long held the interest of the scien-
tific community for their ability to alter molecular struc-
In the past decade, advances with azobenzene based
photoswitches demonstrated by Aprahamian,
24,25
26
Hecht,
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ture and thus properties using light as a stimulus. Upon
photoexcitation, the photoswitch transforms from a
thermodynamically stable state to a metastable photosta-
tionary state. In the photostationary state, molecules will
return to equilibrium by thermal relaxation, or upon pho-
toirradiation with a different wavelength. The resulting
change in structure can modify absorption, polarity,
and/or free volume. Not surprisingly, numerous applica-
tions have taken advantage of these property changes
including switching of surface polarity, membrane per-
meability, nanoparticle clustering, as well as control-
ling the properties of biologically active molecules.
Additionally, photoswitches have been used to create me-
chanical actuators and mechanical sensors (mechano-
phores).
Herges, and Woolley have allowed for visible light
isomerization across a broad range of wavelengths. How-
ever, in these photochromic systems switching occurs
between two colored states. This feature limits their use
in applications, such as sensing, that benefit from a more
notable color change. Although conversion from color-
less-to-colored is routine for spiropyran derivatives, they
have been shown to fatigue quickly upon repeated cycling
experiments. Exposure to high energy UV light and the
presence of singlet and triplet oxygen have been identi-
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fied as key factors leading to degradation.
To address
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–12
these challenges, we sought to design a robust and highly
tunable photoswitch platform using inexpensive reagents
and simple syntheses to provide a colored-to-colorless
transformation using visible light.
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While photoswitches have been extensively studied for
over a century the most widely used classes, including
azobenzene, diarylethene, dihydroazulene, and spiro-
Donor acceptor Stenhouse adducts (DASAs) are a new
class of negative photoswitches that can be synthesized
easily in two steps from commercially available starting
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pyran, often reside in a colorless thermodynamically
stable state that requires high-energy ultraviolet (UV)
light for activation. The use of UV light comes with inher-
ent limitations for a range of applications that arise from
irreversible chemical damage and limited penetration
depth in many materials. Alternatively, low-energy visible
light activated photoswitches, described as negative pho-
tochromes owing to their colored thermodynamically
materials. The colored DASA becomes colorless upon
irradiation with visible light.. This process initiates with a
light controlled alkene isomerization followed by a ther-
mal 4π electrocyclization to the colorless state. In initial
work, we described DASAs containing alkyl-based amine
“donors” (electron-rich) and Meldrum’s or barbituric acid
“acceptors” (electron-deficient) that display visible light
absorption, high fatigue resistance, and a significant po-
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larity and color change upon switching. However, with
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these first-generation DASAs, wavelength tunability was
limited to 545 and 570 nm for the Meldrum’s and barbitu-
tion is accomplished by trituration with hexanes, diethyl
ether, or THF, yielding the desired DASA products as
dark lustrous solids.
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ric acid derivatives respectively. Additionally, reversible
photoswitching was only possible in non-polar solvents
such as toluene and reversible switching could not be
With efficient access to a range of aniline-based DASAs,
it was evident immediately that subtle differences in the
aniline donor results in dramatic changes in color and the
ability to switch reversibly in a number of solvents. Prob-
ing aniline-based DASAs bearing N-methylaniline, tetra-
hydroquinoline, and indoline donors in detail revealed a
number of property trends that could be correlated back
to the structure, including peak absorption (λmax), calcu-
lated dihedral angle between the donor and acceptor (фD-
A), negative log of the acid dissociation constant (pKa) of
the donor amine, open/close equilibrium percentage, and
molar absorptivity (ε), (Figure 2b; characterization data
for all DASAs provided in Table S1).
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observed in solid-supported matrices.
To improve the
performance of DASA-based photoswitches, we have de-
signed a new system that overcomes these limitations,
while retaining the facile two-step synthetic approach
from commercially available materials. Specifically, we
report a study using secondary aniline-derivatives as do-
nors to provide wavelength tunable DASA photochromes
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(Figure 1) that absorb visible and near-IR light (ranging
from 450 to 750 nm) in solvents of varying polarity as well
as in polymer matrices. Detailed characterization to elu-
cidate structure-property relationships for these second
generation aniline-based donors is also provided. We
show that wavelength tunability can be exploited in sys-
tems where two different DASAs can be independently
switched in both solution and polymer films.
Figure 1. General structure for second generation donor
acceptor Stenhouse adducts containing aniline-based donors
and a Meldrum’s acid acceptor. The thermodynamically
stable colored “open” isomer (left) can be converted into the
photostationary colorless “closed” isomer (right) with visible
light irradiation.
Figure 2. Synthesis and characterization of aniline-based
donor acceptor Stenhouse adducts. a) Top: Meldrum’s acid
acceptor; Bottom: Barbituric acid acceptor. Reagents and
Results and Discussion
conditions: (i) H O; (ii) aniline-derivative, neat, DCM,
2
Synthesis. We have developed a two-step procedure
from commercially available starting materials for the
synthesis of aniline-based DASAs (Figure 2a). First, an
activated furan-carbon acid is generated by condensing
furfural, an inexpensive (~$2/kg) byproduct from non-
edible biomass, with either Meldrum’s or barbituric acid.
The synthesis is performed in water either at room tem-
perature (barbituric acid) or 70 °C (Meldrum’s acid),
where the pure product precipitates out of solution as a
MeOH or THF. b) Select properties of three representative
secondary aniline-based DASAs, highlighting stark differ-
ences for subtle changes in chemical structure; N-
methyaniline, tetrahydroquinoline, and indoline from left to
right.
Property Studies. The bathochromic shift in absorp-
tion of the aniline-based DASAs relative to the alkyl-
based DASAs was the first property we sought to evaluate.
Meldrum’s acid and barbituric acid acceptors were both
synthesized and characterized, with representative ab-
sorption spectra given for the barbituric acid derivatives
in Figure 3 (the full barbituric acid and Meldrum’s acid
derivatives described in Figure S1 and S2). The same ab-
sorption trends are observed for both barbituric and Mel-
drum’s acid-based DASAs, but all wavelengths are batho-
chromically shifted by approximately 25 nm for the barbi-
turic structures. The peak absorptions for N-
methylaniline (8), tetrahydroquinoline (9), and indoline
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yellow solid in near quantitative yield. Isolation and pu-
rification are accomplished by filtration and subsequent
washing with water. Second, the activated furan adduct is
mixed with a secondary aniline-derivative, either neat
using 3-5 equivalents of the amine or in solution using 1
equivalent. Less nucleophilic aniline-derivatives, such as
N-methylaniline, require neat conditions for optimal
yields, while more electron rich/nucleophilic anilines,
such as indoline or 5-methoxyindole, can be run in tetra-
hydrofuarn (THF) or dichloromethane (DCM). Purifica-
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(
10) are 582, 599 and 615 nm respectively (Figure 2b and
out of plane, a donating group, such as p-methoxy, has
little impact on the wavelength and only results in a 2 nm
bathochromic shift compared to its unsubstituted coun-
terpart. However, in the indoline case, the addition of a p-
methoxy group causes a 13 nm redshift. Planarity of the
aryl ring in the aniline donor is therefore critical for in-
creasing conjugation and extending the absorption max-
ima wavelength. Of note, these trends can be predicted
using DFT calculations (Figure S6).
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Figure 3). The wavelength could be extended further by
incorporating electron donating groups at the para-
position of the cyclic anilines, such as methoxy (11) and
N,N-dialkyl (12) which led to red-shifts in absorption (λmax
=
629 and 669 nm respectively), compared to native indo-
line (λmax = 615 nm). The most notable structural differ-
ence between these derivatives and the alkyl-based DA-
SAs is the presence of an aromatic ring, where homocon-
jugation may result in a bathochromic absorption shift
due to enhanced hybridization of molecular orbitals be-
tween the electron rich donors and acceptor groups, an
effect commonly observed with “push-pull” systems in
organic semiconductors.
line-based donors the absorbance maxima of barbituric-
based DASAs were tuned from 582 to 669 nm.
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Using readily available ani-
Figure 4. Computational density functional theory modeling
of representative aniline DASAs, determining HOMO orbital
overlap, energy gap (represented by λmax), and dihedral angle
between donor and acceptor (фD-A).
The molar absorptivities (ε) for N-methylaniline (8),
tetrahydroquinoline (9) and indoline (10) barbituric acid
derivatives were determined through a combination of
NMR and absorption spectroscopies at equilibrium (Fig-
ure S7). The ε values for these derivatives are uniformly
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high at ~10 M cm . The strong dye character for DASAs
highlights their potential for colorimetric sensing applica-
tions because the naked eye can identify even minute
amounts.
Figure 3. Representative absorption spectra for aniline-based
DASAs highlighting the wavelength tunability with barbitu-
ric acid derivatives. Measured as 10 uM solutions in DCM.
During the molar absorptivity investigations it was ob-
served that an equimolar solution of p-methoxy-N-
methylaniline derivative (14) in dichloromethane (DCM)
appeared darker and required more time to switch with
visible light than the corresponding N-methylaniline de-
rivative (13). Because intensity of color and rate of switch-
ing is a critical property for numerous applications of
negative photochromes, we sought to better understand
this observation. All aniline-based DASAs are isolated in a
nearly all open triene (colored) form via precipitation, as
In contrast to the cyclic indoline derivatives, acyclic de-
rivatives such as p-methoxy-N-methylaniline does not
lead to a significant change in λmax compared to unsubsti-
tuted N-methylaniline (Figures 4 and S3). To address the
difference between acyclic and cyclic substituted N-
methylaniline derivatives, density functional theory
(
DFT) calculations at the B3LYP/6-31G(d) level were per-
formed to identify the dihedral angle between the donor
and acceptor groups (фD-A) and character of the highest
occupied molecular orbitals (HOMOs) overlap (Figures
1
seen with H NMR spectroscopy (see SI), however given
2
b, 4, and S4-S5). N-Methylaniline (8 and 15) derivatives
time to thermally equilibrate in solution the aniline de-
rivatives partially cyclize to the closed cyclopentenone
(transparent) form. This process could be monitored by
were found to have a substantial out-of-plane twist (фD-A
≈
40º), while indoline (10 and 16) derivatives were planar
фD-A ≈ 0º). As a consequence, indoline derivatives have
more HOMO overlap/conjugation, resulting in a narrow-
1
(
H NMR and it was determined that the equilibrium posi-
tion can be approximately correlated to the pKa of the
aniline derivatives (Figure S9–S13). For example, the per-
cent of open colored form in CD Cl goes from 2% to 12%
ing of the energy gap (E )/bathochromic shift of ~30 nm
g
relative to the corresponding N-methylaniline derivatives.
Even more striking than the difference between the acy-
clic and cyclic anilines is the effect of a donating group
para to the aniline nitrogen. Since the N-methylaniline is
2
2
to 41% for the p-chloro-N-methyaniline (S1), N-
methylaniline (13), and p-methoxy-N-methylaniline (14)
1
derivatives, respectively (determined with H NMR). As
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expected, substitution of aniline derivatives will affect zene in the absence of light and allowed to thermally re-
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basicity and the pKa of the conjugate acid of p-chloro-N-
methyaniline, N-methylaniline, and p-methoxy-N-
methylaniline increasing from 4.0 to 4.9 to 5.9. This rela-
tionship between pKa and percent of open form in DCM
also exists for the cyclic aniline derivatives. The respective
conjugate acid pKa values for N-methylaniline, tetrahy-
droquinoline, and indoline are 4.9, 5.1 and 5.5 and the
open percent of DASA of these derivatives at equilibrium
in DCM goes from 11% to 19% to 31% (Figures 2b and
S10). Notably, by using electron rich 5-diheptylamino
indolines (S3 and 13) as the donor shifts the equilibrium
to nearly 100% in the open form in DCM. This demon-
strates that the equilibrium of these systems can be con-
trolled by the basicity of the donor amine, which can also
be used to tune the depth of color. Finally, the equilibri-
um ratio plays a role in observed rate of switching with
electron deficient anilines switching from colored-to-
colorless the fastest.
lax to equilibrium (from triene to triene-cyclopentenone
mixtures) at four different temperatures inside the NMR.
Integration of protons unique to the open triene and
closed cyclopentenone forms were utilized to monitor the
rate of closing over time. The data obtained from the
NMR experiments was fit to an isomer equilibrium model
assuming first order rates of opening and closing. The
model used was of the form:
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ꢅꢆꢇꢈꢉ ꢊ kꢋꢌꢆꢍꢈꢎꢏꢐꢑꢒꢓꢔꢕꢖꢗꢑꢔꢘꢖꢙꢚꢃ
ꢀꢁꢂ ꢄ
ꢀꢁꢂꢛ
ꢃ
ꢅꢋꢌꢆꢍꢈ ꢊ ꢅꢆꢇꢈꢉ
Where ꢅꢜꢝꢎꢞ, ꢅꢟꢠꢜꢡꢎ, ꢢꢞꢣ ꢁ represent the rate of opening,
0
the rate of closing, and the initial concentration, respec-
tively. Interestingly, the rates of equilibration were found
to increase from tetrahydroquinoline (9)
<
N-
methylaniline (8) < indoline (10), with indoline being ~3.5
times faster than aniline. In addition, by plotting the rate
constants vs 1/T we could use the Arrhenius expression to
extract activation energies (Eopen and Eclose ) (Figure 5b,
Table S1). The Eopen and Eclose values were similar for the
three derivative, ranging from 60 to 71 kJ/mol (Table S1).
This is comparable to both experimental and computa-
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tional results obtained by Feringa and Jacquemin for
dialkyl DASAs, and lower than the ~90 kJ/mol measured
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for reported spiropyran-based photoswitches.
Fatigue Resistance. Reversibility and stability are fur-
ther crucial performance parameters in photochromic
systems, in particular for applications that rely on recy-
clability of the photoswitch (e.g., actuators, sensors,
mechanophores, etc.) To test the robustness of these ani-
line-based DASA derivatives, we performed extensive cy-
cling tests with the p-methoxy indoline barbituric acid
derivative 11 given its fast reversible kinetics (Figure 6).
Pump-probe absorption spectroscopy with a broadband
white light emitting diode (LED) for excitation and a
heated stage for equilibration (50 ºC in chlorobenzene,
1
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7% open by H NMR) were used for the cycling experi-
ments under ambient atmospheric conditions (i.e., in the
presence of oxygen). Figure 6a shows a detailed plot of
absorption at λmax (629 nm) during the first cycle, where a
snap-shot (100 ms exposure time) of the absorption trace
was taken every 5 seconds over the course of 20 minutes,
with irradiation for the first 30 seconds, then off for the
remaining time. The following cycles were recorded by
taking individual measurements immediately following
photoswitching and thermal equilibration (Figure 6b).
Similar to the previously reported dialkyl DASAs, minimal
Figure 5. Open to close equilibration kinetics for select N-
methylaniline based barbituric acid DASA (8) determined
using H NMR spectroscopy in chlorobenzene-d5 at the spec-
ified temperatures. Inset provides the corresponding Arrhe-
nius plot for activation energy determination.
1
32
degradation was observed after 10 cycles. Extending to
Kinetics. For aniline-based DASA compounds it was
also observed that the rate of thermal relaxation varied
depending on the derivative and as such we sought to
investigate the fundamental kinetic properties of this new
photochromic system. The opening and closing rates and
1
8
00 cycles then 200 cycles showed slow degradation with
0% and 60% absorbance recovery respectively with no
observable change to the absorption profile. These in-
depth cycling experiments highlight the stability of DA-
SAs in the presence of oxygen and at elevated tempera-
tures, making them good candidates for applications re-
quiring a recyclable color-to-transparent photoswitch
that operates under ambient conditions.
activation energies (E ) of the aniline DASAs were deter-
A
1
mined by H NMR spectroscopy. N-Methylaniline (8),
tetrahydroquinoline (9), and indoline (10) barbituric acid
derived DASAs were dissolved in deuterated chloroben-
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Figure 6. Pump-probe absorption spectroscopy of p-methoxy indoline barbituric acid DASA 11 in chlorobenzene at 50 ºC, excit-
ing with a broadband white light emitting diode. (a) Detailed first cycle showing the rapid photoresponse (<30 seconds), fol-
lowed by thermal equilibration over 20 mins. (b) Cycling study showing approximately 20% decrease in absorption every 100
cycles.
Figure 7: Representative photoswitchability in solvents of
Switching Properties. A significant advantage of these
second generation aniline-based DASAs is photoswitcha-
bility in a variety of solvents. While the previously report-
ed dialkyl DASAs were limited to photoswitching in non-
polar solvents (e.g., toluene, xylenes, etc.) the aniline DA-
SAs are capable of photoswitching in polar solvents such
as THF, DCM, ethyl acetate and acetonitrile as highlight-
ed in Figure 7 for N-methylaniline barbituric acid DASA
8. In all cases, quantitative photoconversion, evident by
the generation of colorless solutions and UV/Vis absorp-
tion spectroscopy, was observed in a range of solvents
with the exception of 12. In this case photoswitching was
largely limited to less polar solvents such as a tolu-
ene/hexanes mixture, presumably due to the increased
basicity of the aniline. It is worth noting that one unique
aspect of DASA based photoswitches, compared to, for
example, azobenzene or acylhydroazones, is that photo-
mediated reaction (E–Z alkene isomerization) is coupled
with a thermal 4π electrocyclization. As a consequence,
this cascade process provides a pathway to leverage a po-
tentially incomplete E–Z alkene isomerization into an
efficient photoswitch. However, this also makes the eval-
uation of photostationary states (PSS) difficult because
the Z-isomer can convert to the colorless cyclopentenone
adduct.
varying polarity for alkyl-based DASAs (top) and aniline-
based DASAs (bottom). Diethyl- and N-methylaniline-
barbituric acid DASA was dissolved in the denoted solvent,
followed by shining a broadband white light source on the
sample, taking pictures before and after exposure to light.
The ability to efficiently activate the new aniline-
derivatives in a variety of solvents is a critical break-
through that provides the potential for DASA-based pho-
toswitches to be used in numerous applications that re-
4
1
quire polar matrices (e.g., sensors, mechanophores, etc.).
Additionally, alkyl-based DASAs were not readily respon-
sive to visible light when dispersed in a solid polymer
matrix, irrespective of the polymer tested (e.g., polysty-
rene, poly(methyl methacrylate), etc.). In direct contrast,
N-methylaniline (8), tetrahydroquinoline (9), and indo-
line (10) barbituric acid DASAs were found to be photoac-
tive as physical blends in polymer matrices (Figure S17).
To illustrate this feature, three DASA derivatives were co-
dissolved with poly(methyl methacrylate), poly(ethyl
methacrylate) or poly(butyl methacrylate) in DCM (1
wt% DASA relative to polymer), drop-cast onto glass
slides, dried at 50 ºC and irradiated with broadband visi-
ble light. Significantly, this results in photoswitching in
all matrices with the initial color of the equilibrated films
having different shades. This is believed to indicate vary-
ing ratios of open:close forms in each matrix, an attribute
which we are actively exploring in more detail.
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a result, the initial violet solution was converted to tur-
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quoise (color of 11). Alternatively, by using a broad spec-
trum white LED light source, both DASAs switched to
their colorless cyclized form at the same time.
1
3
11
A+B
Encouraged by these results, the selective switching
methodology was also investigated for the same pair-wise
combination of DASA derivatives dispersed in a solid ma-
trix of poly(methyl methacrylate) (PMMA). The films
were prepared by drop-casting a DCM solution contain-
ing 100 mg/mL PMMA and ~1 mg/mL of 11 and 13 onto a
glass slide (Scheme 1). Irradiation of the DASA blend in
PMMA with a 650 nm LED again resulted in a distinct
color change from purple to pink due to the selective
photoswitching of 11. Alternatively, 13 could be selectively
switched by irradiating with a 450 nm LED to give a tur-
quoise film. Finally, broad-spectrum white light led to the
cyclization of both derivatives, leaving a transparent film,
while heating the sample at 50 ºC for 2 min reverted the
sample back to its original colored state. This clearly
demonstrates for the first time the ability to selectively
and reversibly switch mixtures of DASA derivatives in
both solution and the solid state.
6
50 nm
light
514 nm
light
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3’
1
1
11’
1
0.5
0
450
600
Wavelength (nm)
750
450
600
Wavelength (nm)
750
13 + 11’
Figure 8. Selective photoswitching of two mixed DASAs, N-
methylaniline Meldrum’s acid, 13, and indoline barbituric
acid, 11 using filtered broadband white LED. 11 and 13 were
mixed in toluene, followed by photoswitching through a 514
nm bandpass filter to cyclize 13 or a 650 nm longpass filter to
cyclize 11.
white light
650 nm
light
heat
1
3 + 11
13’ + 11’
An enabling aspect of the aniline-based DASAs is ad-
dressability (the difference in absorption wavelengths
between two different isomers or photoswitches), which
relies on the inherent tunabilty of the absorption wave-
length. This feature is critical for independently control-
ling two different photoswitches and holds great potential
for various applications. Accordingly, we sought to
demonstrate the selective switching of two different DA-
SAs in solution (Figure 8). DASA (13) bearing an N-
methylaniline donor and Meldrum’s acid acceptor group
λmax, 560 nm in PhMe) and DASA (11) bearing a p-
methoxy indoline donor and barbituric acid acceptor
group (λmax, 623 nm in PhMe) were chosen based on their
minimal absorption overlap (Figure 8). First, a longpass
50 nm filter (red light) was used to selectively switch 11
at room temperature, converting the initially violet solu-
tion to pink (color of 13). Of note, the minor decrease at
60 nm during the course of >650 nm irradiation corre-
white light
514 nm
light
white light
42
1
3’ + 11
43
Scheme 1. Selective photoswitching of two mixed DASAs,
N-methylaniline Meldrum’s acid, 13, and indoline barbitu-
ric acid, 11 suspended in drop-cast films containing ~1
wt% DASA in PMMA using filtered broadband white LED.
(
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In summary, a second generation aniline-based donor
acceptor Stenhouse adduct was developed and character-
ized. The new photochromic platform is highly tunable,
providing a wide photoresponsive region from 500 – 650
nm that is not restricted to solution-state or non-polar
matrices for reversible switchability. Through careful
choice of the donor moiety, the wavelength and solvent
switching properties can be precisely controlled. This
combined with computational modeling and equilibrium
kinetics provide valuable guidelines for the development
of future DASA systems. Finally, selective switching in
5
sponds to photoswitching of 11 (not 13) due to partial ab-
sorption overlap of a shoulder at 560 nm. This was con-
firmed by running control experiments where red light
irradiation of a solution containing only 13 did not lead to
photoswitching (Figure S18). For the alternative case a
5
14 nm bandpass filter (green light) was used to selective-
ly switch 13 with minimal switching 0f 11 (Figure S21). As
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both solutions and polymer-matrices highlights the sig-
nificant potential of inverse DASA photoswitches in ma-
terials applications.
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Irie, M.; Fukaminato, T.; Matsuda, K.; Kobatake, S. Chem.
Rev. 2014, 114, 12174.
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ASSOCIATED CONTENT
Supporting Information. The Supporting Information is
available free of charge on the ACS Publication website
http://pubs.acs.org. Experimental procedures and characteri-
zation data for all compounds (PDF).
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AUTHOR INFORMATION
Corresponding Author
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Yang, Y.; Hughes, R. P.; Aprahamian, I. J. Am. Chem. Soc.
2014, 136, 13190.
Yang, Y.; Hughes, R. P.; Aprahamian, I. J. Am. Chem. Soc.
*
javier@chem.ucsb.edu
2012, 134, 15221.
Notes
Bléger, D.; Schwarz, J.; Brouwer, A. M.; Hecht, S. J. Am.
Chem. Soc. 2012, 134, 20597.
Siewertsen, R.; Neumann, H.; Buchheim-Stehn, B.; Herges,
R.; Näther, C.; Renth, F.; Temps, F. J. Am. Chem. Soc. 2009,
The authors declare the following competing financial inter-
est. A patent has been filed on the photochromic materials.
ACKNOWLEDGMENT
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Mason, B. P.; Whittaker, M.; Hemmer, J.; Arora, S.; Harper,
A.; Alnemrat, S.; Mceachen, A.; Helmy, S.; Read de Alaniz,
J.; Hooper, J. P. Appl. Phys. Lett. 2016, 108, 041906.
Li, X.; Li, J.; Wang, Y.; Matsuura, T.; Meng, J. J. Photochem.
Photobiol., A 2004, 161, 201.
Radu, A.; Byrne, R.; Alhashimy, N.; Fusaro, M.;
Scarmagnani, S.; Diamond, D. J. Photochem. Photobiol., A
2009, 206, 109.
Helmy, S.; Oh, S.; Leibfarth, F. A.; Hawker, C. J.; Read de
Alaniz, J. J. Org. Chem. 2014, 79, 11316.
Helmy, S.; Leibfarth, F. A.; Oh, S.; Poelma, J. E.; Hawker, C.
J.; Read de Alaniz, J. J. Am. Chem. Soc. 2014, 136, 8169.
Singh, S.; Friedel, K.; Himmerlich, M.; Lei, Y.; Schlingloff,
G.; Schober, A. ACS Macro Lett. 2015, 4, 1273.
We thank the National Science Foundation (MRSEC pro-
gram, DMR 1121053) and California NanoSystems Institute
(
CNSI) Challenge Grant Program for support. Y.J.D. thanks
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National Science Foundation for a Graduate Research Fel-
lowship. Thanks to Dr. Alexander Mikhailovsky for his help
constructing the optical setup used for the cycling and selec-
tive switching experiments. Also thanks to Dr. Jerry Hu for
his help with cryoprobe and DOSY NMR experiment meas-
urements.
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Of note, the ability to photoswitch in a given solvent
depends on the basicity of the amine. The N-methyl aniline
DASAs readily switched in a variety of solvents, while the 5-
diheptylamino-indole derivatives photoswitched only in
non-polar solvents such as toluene or hexanes.
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Feringa, B. L. Chem. Soc. Rev. 2015, 44, 3358.
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Feringa, B. L.; Nature Commun. 2016,7, 12504.
The absorption for each DASA at equilibrium was
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