Photo-/Baso-Chromisms and the Application of a Dual-Addressable Molecular Switch

Article abstract of DOI:10.1002/asia.201900600

Two typical molecular switches of spiropyran (SP) and benzoxazine (OX) were fused by sharing an indole to achieve a new dual-addressable molecular switch (SP-OX-NO₂). Through proper molecular modification with NO₂, the transformation

Full text of DOI:10.1002/asia.201900600

CHEMISTRY
AN ASIAN JOURNAL
www.chemasianj.org
Accepted Article
Title: Photo-/ baso- chromisms and the application of a dual-
addressable molecular switch
Authors: Danyang Liu, Binghong Yu, Xing Su, Xiaojun Wang, Yu-Mo
Zhang, Minjie Li, and Sean Xiao-An Zhang
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To be cited as: Chem. Asian J. 10.1002/asia.201900600
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10.1002/asia.201900600
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Photo-/ baso- chromisms and the application of a dual-
addressable molecular switch
Danyang Liu, Binhong Yu, Xing Su, Xiaojun Wang, Yu-Mo Zhang, Minjie Li* and Sean Xiao-An Zhang*
Abstract: Two typical molecular switches of spiropyran (SP) and
benzoxazine (OX) were fused by sharing an indole to achieve a new
dual-addressable molecular switch (SP-OX-NO2). Through proper
molecular modification with NO2, the transformation from
merocyanine (MC) to ring-closed SP or ring-closed OX can be
controlled separately with visible light or base stimuli in solution,
respectively, and these processes are proved by UV-vis, NMR
spectra and control experiments. The cis-merocyanine (cis-MC) form
is involved in basochromic process in solution. DFT calculation
suggests the bidirectional switching property of the fused SP-OX
molecular switch can be controlled separately, when the OX isomer
is more stable than the deprotonated SP isomer. Because of the
significant color variations in solution, the simple dual-addressable
switch has been further applied to construct a multicolor reversible
display on paper successfully.
1d) are versatile switches with photo-, pH-, force- and electro-
addressabilities.[37-40] In order to give out different outputs,
incorporating different color switching units into
molecule is an effective strategy[1,12]. Based on the above
considerations, dual-addressable molecule (SP-OX-NO2)
a single
a
containing SP and OX (different absorption peaks) was
designed and synthesized by sharing an indole group (Scheme
1e). Through proper molecular modification with nitro functional
groups, both SP and OX isomers could be achieved separately
upon exposure to different stimuli to give out different colors.
Besides, the stimulation of base caused the SP isomer of SP-
OX-NO2 to undergo a ring-switching (spiral ring to oxazine ring)
process to OX isomer.[41-43] Interestingly, a metastable cis-MC
isomer was involved in the isomerization of MC or SP to OX
necessarily. The new molecule SP-OX-NO2 not only preserved
the bidirectional switching property under visible light and base
stimuli in solution, but also showed high contrast in both visible
and fluorescent color. Furthermore, the application of SP-OX-
NO2 with photochromic and basochromic properties in multicolor
rewritable paper was achieved.
Introduction
Multi-addressable molecular switches have attracted a lot of
attention recently because of their multi-stimuli responsive
properties.[1-7] By integration of the typical molecular switches,
such as spiropyrans,[8-9] diarylethenes,[10-14] azobenzenes,[15-16]
oxazolidines[17-18], etc.[19-20] into one molecule, a series of multi-
addressable molecular switches have been achieved, which not
only expands the stimuli species, but also enriches the output
signals. Despite these efforts, there are still some challenges,
e.g., the difficulty in synthesis and the independent control of the
different switching units in single molecule.[16] In general, most of
the multi-addressable molecular switches are achieved by
linking two individual switches with non-covalent[21-27] or
covalent[28-32] bonds (Scheme 1a). However, switching motifs
with fewer and simpler units are more beneficial from the point of
atomic efficiency.[8] Therefore, dual-addressable systems by
fusing two switches through
a shared central unit are
designed.[12,33-35] These molecular systems can also achieve the
independent control of each unit (Scheme 1b).[32]
The typical photochromic spiropyrans (SPs) are well known to
undergo light-stimulated reversible isomerization between the
colored merocyanines (MCs) and the colorless SPs. And the
transition requires the changing of the C=C bond from trans to
cis configuration first and reforming the C–O bond subsequently
(Scheme 1c).[36-37] In addition, the benzoxazines (OXs) (Scheme
D. Liu, B. Yu, X. Su, Y. Zhang, X. Wang, Prof. M. Li, Prof. S. X. A. Zhang
State Key Lab of Supramolecular Structure and Materials, College of
Chemistry
Jilin University
2699 Qianjin street, Changchun, 130012, P. R. China.
E-mail: liminjie@jlu.edu.cn, seanzhang@jlu.edu.cn
Scheme 1. Illustration of the design of the (a) linked dual-switchable system
and the (b) fused dual-switchable molecule. (c) Photo-/ baso- chromisms of a
typical (c) nitrospiropyran and (d) oxazine. (e) Design and control of the
transformation of SP-OX-NO2 among its multiple states.
Supporting information for this article can be found via a link at the end of
the document.
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Results and Discussion
Investigation of the photochromic and basochromic
properties of SP-OX-NO2 in solution
The synthesis of SP-OX-NO2 was shown in Scheme 2. First, the
[1,3]oxazine part of the molecular switch was prepared by
reaction of 3H-indole with 4-nitro-2-chloromethylphenol.[44] Then
ortho-para-dinitrophenol was introduced to the protonated
[1,3]oxazine to synthesize SP-OX-NO2. And two control
molecules, SP-OX-CH3 and SP-OX-H as shown in Figure 1a
were also synthesized.
Because SP-OX-NO2 combined both
a
light responsive
spiropyran and a base responsive oxazine, we investigated the
photophysical properties of SP-OX-NO2 to explore whether it
had the bidirectional switching property in solution. Firstly, the
state of SP-OX-NO2 in solution was studied by NMR and UV-vis
spectra. In the 1H NMR spectrum of SP-OX-NO2 in DMSO-d6
(Figure 2a), the single peak of dimethyl and methylene on indole
and a coupling constant (J10-11 = 15.5 Hz) indicated that the SP-
OX-NO2 existed in its ring-open trans MC form (Figure 1a).
Besides, the DMSO solution of SP-OX-NO2 was magenta with
the absorption peak at 539 nm (Figure 1b, 1c), consistent with
the control molecule of dinitrospiropyran in its MC form (Figure
S5, S26).[45] Additionally, there was only one single peak for OH
(chemical shift above 11 ppm) in SP-OX-NO2 (Figure 2a, S23a)
while there were two single peaks in SP-OX-CH3 and SP-OX-H
(Figure S24, S25) for both phenol groups, which meant one of
the two hydroxyls lost a proton in SP-OX-NO2. Because the
phenolic hydroxyl on conjugated dinitrophenol was more acidic
than that on non-conjugated nitrophenol, the hydroxyl on the
conjugated dinitrophenol was inclined to dissociate and became
phenolate (Figure 1a). The above results were all in accordance
with the proposed structure of SP-OX-NO2 in Figure 1a.
Scheme 2. Synthetic routes for SP-OX-H, SP-OX-CH3 and SP-OX-NO2.
After exploring the initial state of SP-OX-NO2 in solution, we
investigated the tautomerization property with the stimuli of
visible light and base. A yellow LED lamp (20W), which emitted
light with a wide overlap with the absorption of SP-OX-NO2, was
chosen as the irradiation source. After irradiation for 5 min, the
magenta solution turned colorless and its absorption peak
shifted to 327 nm (Figure 1b, 1c). The color fading was caused
by the formation of ring-closed SP form of SP-OX-NO2, which
1
was confirmed with NMR spectra. In the H NMR spectrum of
SP-OX-NO2 after irradiation (Figure 2b), the single peaks for
dimethyl and methylene split into double and double-double
peaks respectively because of the formation of spiral ring.
1
Compared with H NMR spectrum of trans MC form (Figure 2a),
Figure 1. (a) The chemical structures of SP-OX-NO
molecules, SP-OX-CH3 and SP-OX-H. (b) The natural color and fluorescent
images of SP-OX-NO upon adding different stimuli. (c) The normalized
absorption spectra of SP-OX-NO upon exposure to different stimuli (blank,
2
and the control
the 1H NMR spectrum of SP form (Figure 2b) exhibited obviously
highfield shifts overall. Hereinto, H10 exhibited the largest shift
(about 2.38 ppm) owing to the transition of the electron-
withdrawing effect of the nitrogen (imine cation) to the electron-
donating effect. In addition, an absorption tail was detected and
it could be attributed to the small amount of transformation of
trans MC from ring-closed SP during the dark spectra measuring
condition (Figure 1c, 1e).
2
2
yellow light irradiation for 5 minutes, 1 equiv. Et3N after yellow light irradiation,
adding 1 equiv. Et3N directly and being kept at room temperature for 20 days
after adding 1 equiv. Et3N) (The blue and green curves are overlapped). (d)
The emission spectra of SP-OX-NO
2
upon exposure to different stimuli. (e)
upon exposure to different stimuli.
The structure speculation of SP-OX-NO
2
Solution: DMSO. Concentration: 50uM. Excitation wavelength: 577nm; slits: 3,
3.
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ring of SP structure was destroyed and the C-O bond broke
upon adding base (Figure 1e). In addition, the absorption
1
spectra (Figure 1c) and H NMR spectra (Figure 2d) of the SP-
OX-NO2 solution with base directly coincided well with the results
of SP-OX-NO2 with base after visible light irradiation (Figure 1c,
2c), which indicated the initial trans MC form of SP-OX-NO2
could also converted to cis-MC upon adding base.
It’s reported the cis-trans isomerization can be triggered by light
as reported in the literature[2, 46-47]. By irradiating the cis-MC with
blue light (20W, 441nm), the absorption peaks of cis-MC isomer
decreased and the absorption peak at 539nm increased (Figure
S3b), indicating the cis-MC could photo-isomerize into trans MC,
in agreement with the literature report on cis-trans
isomerization[46]. Because the trans MC form of SP-OX-NO2 can
convert to ring-closed form of SP quickly with blue light
irradiation (Figure S3c), the generated trans MC then
transformed to ring-closed form of SP. So the photoinduced
cis−trans isomerizations indicate the structure cis-MC is truly
existence after adding base to trans MC of SP-OX-NO2.
Figure 2. 1H NMR spectra of (a) trans MC form of SP-OX-NO
2
, (b) SP-OX-
with K2CO3 after
with K2CO3 directly and (e) SP-OX-NO
NO
2
with yellow light irradiation for 5 minutes, (c) SP-OX-NO
2
yellow light irradiation, (d) SP-OX-NO
2
2
being kept at room temperature for 20 days after adding K2CO3 in DMSO-d6
solution.
After keeping the SP-OX-NO2 solution with base for 20 days at
room temperature, the spectrum exhibited absorption changes
and the absorption peak shifted to 429 nm, which was most
likely due to the fact of isomerization from cis-MC to OX isomer.
This conclusion was further confirmed by 1H NMR spectra
(Figure 2e, S7). It was worth mentioning that the single peaks of
dimethyl and methylene split into double and double-double
peaks respectively because of the formation of oxazine ring; the
coupling constant of H10 and H11 converted to 16Hz, meaning
the C=C bond underwent a cis-trans isomerization; the spectrum
of OX exhibited obvious highfield shifts comparing with the initial
MC form of SP-OX-NO2 (Figure 2a) because the electron-
withdrawing effect of the nitrogen (imine cation) transformed to
the electron-donating effect. All of these phenomena declared
that the cis-MC isomer transformed to the OX isomer,
accompanying with a cis-trans isomerization of C=C bond.
Hence, cis-MC isomer of SP-OX-NO2 was the key intermediate
for the transformation process of SP or trans MC to OX after
adding base in solution. The transformation of cis-MC to OX
isomer could be promoted by increasing the temperature but
below 40oC, because heating SP-OX-NO2 at higher temperature
with base resulted the irreversible cleavage of the oxazine
heterocycle (Figure S8). Besides, the UV light (365nm, 20W)
can also be beneficial for the transformation of cis-MC to OX,
Following, the colorless solution of ring-closed form of SP-OX-
NO2 changed to yellow immediately upon adding 1 equiv. Et3N
with new absorption peaks at 403 nm and 436 nm (Figure 1b,
1c). Referring to the absorption peak at 439 nm of control
molecules (SP-OX-CH3, SP-OX-H) (Figure S4) and the
absorption peak at 434 nm for nitrophenol (Figure S6a) upon
adding base, the new long-wavelength peak (436 nm) might
come from the formation of non-conjugated nitrophenoxy anion
and the new short-wavelength peak (403 nm) could be assigned
to the adjustable structure of ring-closed SP form of SP-OX-NO2.
Moreover, in contrast to SP or OX segments of SP-OX-NO2
(Figure S5), the absorption peak at 403 nm and 436 nm might
be relevant to both the phenoxy anions after adding base.
Therefore, we had a bold speculation that the new isomer of SP-
OX-NO2 with absorption peaks at 403 nm and 436 nm could be
the cis form of merocyanine with two phenolate anions. The
structure of this metastable cis merocyanine was denoted as cis-
MC (Figure 1e) and confirmed by NMR measurement (Figure
2c). Specially, the peaks of dimethyl and methylene groups
changed from double and double-double to both singlets; the
coupling constant of the olefinic protons was 7.5 Hz; the peaks
of hydrogen in aromatic region was between the trans MC form
(Figure 2a) and ring-closed SP of SP-OX-NO2 (Figure 2b),
meaning that the indole part and dinitrophenol part of the new
molecule did not conjugate each other as well as in the planar
trans MC structure. All of the above results proved that the
twisted cis-MC form was produced from SP form of SP-OX-NO2
upon adding base. Compared with 1H NMR spectrum of SP
isomer, H10 and methylene of cis-MC isomer (Figure 2c)
exhibited downfield shift due to the electron-withdrawing effect of
imine cation, while H11 exhibited a highfield shift owing to the
electron-donating effect of oxygen anion on the conjugated
structure; the H1, H2 and H3 exhibited nearly no shift thanks to
the dual effects of nitrophenolate anion and the imine cation.
These results also demonstrated the cis-MC isomer with two
phenolate anions were generated, which indicated that the spiral
1
which is proved by UV-vis spectra and H NMR spectra (Figure
S9). In brief, with visible light irradiation or base addition, the
control molecules (SP-OX-CH3, SP-OX-H) transformed to the
ring-closed SP isomer (Figure S10, S11), while SP-OX-NO2
showed bidirectional switching property via structural
transformation among the initial trans MC, SP, cis-MC, and OX
isomers (Figure 1e, 2). What's more, the strong red fluorescence
of SP-OX-NO2 was quenched by either yellow light or base in
solution (Figure 1d, S13).
DFT calculation to speculate the basochromism mechanism
As we designed, there would be two competitive nucleophilic
reactions of the fused SP-OX molecular switches when two
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phenolate anions of phenols were generated. One the one hand,
the conjugated phenol oxygen anion took a nucleophilic reaction
to generate deprotonated SP form with a negative charge (SP-
N). On the other hand, the nitrophenol attacked the carbon
positive on indole to switch to OX. However, only one kind of
ring-closed switch existed under the specific occasion and the
thermodynamic reaction was inclined to generate the more
stable isomer.
In order to investigate which isomer of OX and SP-N is more
stable, the DFT calculation was carried out. A comparison
between the calculated energies of the cis-MC, SP-N and OX
isomers revealed that OX was energetically the most favoured
conformer (Figure 3b, S15). The DFT calculation showed the
reaction of cis-MC to SP-N released 12.27 kcal/mol energy while
the reaction of cis-MC to OX released 20.93 kcal/mol energy
(Figure 3b), so the tautomerization of cis-MC to OX was
expected thermodynamically. We got the conclusion that when
the energy of OX isomer was lower than the deprotonated SP
isomer, the final product of the alkalization reaction was OX
isomer. And the ring-closed SP was generated from the fused
SP-OX molecule with visible light irradition, so the fused SP-OX
molecule could behave as SP or OX depending on conditions.
Besides, owing to the strong electron-withdrawing property of
nitro, the electron density of oxygen anion in dinitrophenol was
lower than that in nitrophenol. Thus, the nucleophilic reaction of
imine cation and nitrophenolate anion of cis-MC isomer was
much easier to take place and then to form OX, which was
consistent with the results of the NMR and UV-vis spectra.
For control molecules, SP-OX-CH3, SP-OX-H, the energy
difference of OX to SP-N yielded a value of 19.87 kcal/mol,
19.80 kcal/mol respectively (Table 1), indicating that the reaction
to generate SP-N released more energy than the reaction to
generate OX upon adding base, thus the SP-N was expexted
thermodynamically, which also fitted well with the experimental
data (Figure S3, S10-S11). According to the above results, the
control molecules (SP-OX-CH3, SP-OX-H) could only transform
to the ring-closed SP form with the stimuli of either visible light or
base, while the trans MC form of SP-OX-NO2 could transform to
the ring-closed form of SP and OX respectively thanks to the
more stable OX isomer.
Figure 3. (a) The structural transformation of SP-OX-NO2 upon adding base.
(b) The optimal structure and comparison of the relative energies (kcal/mol) of
the ground states of cis-MC, OX and SP-N isomers based on B3LYP/6-31G(d)
level by Gaussian 09.
Table 1. The energy differences (kcal/mol) between the different isomers of
SP-OX-NO2, SP-OX-CH3 and SP-OX-H.
ΔE(RB3LYP)/
kcal/mol
ΔE(RB3LYP)/
kcal/mol
ΔE(RB3LYP)/
kcal/mol
Molecules
(Cis-MC to OX)
(Cis-MC to SP-N)
(OX to SP-N)
SP-OX-NO2
20.93
12.27
-8.66
----a
---- a
---- a
---- a
19.87
19.80
SP-OX-CH3
SP-OX-H
(a) The cis-MC isomer of SP-OX-CH3 and SP-OX-H is not obtained by
B3LYP/6-31G (d, p) calculations.
Investigation of the multichromic property of SP-OX-NO2 on
the solid substrate
The observation of bidirectional switching property and obvious
color changes of SP-OX-NO2 in solution encouraged us to
further investigate the multi-color switching property on solid
matrix. Filter paper was chosen as a substrate, upon which
polyethylene glycol (PEG) was loaded to passivate the multi-
hydroxyl of paper (Figure 4a).[48-49] To examine the photochromic
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and basochromic properties of the SP-OX-NO2 based paper,
reflective UV–vis spectra were measured with an integrating
sphere upon exposure to the visible light or base. Before any
stimulation, the magenta paper exhibited a broad reflectance
peak at 539 nm, which was assigned to the trans MC form of
SP-OX-NO2 (Figure 4b). Besides, the SP-OX-NO2 based paper
showed highly red fluorescence with a 643 nm emission peak
(Figure 4d). With yellow light irradiation, a safe and convenient
stimulating method, the paper displayed a light yellow color
owing to the presence of the proton accepter PEG (Figure S22).
The light yellow paper returned to its initial magenta state
o
reversibly by heating at 80 C within 30 seconds (Figure S21a).
These results indicated that the photochromic property of SP-
OX-NO2 was retained in solid substrate. Treating the magenta
paper with a methanol solution containing 5mM Et3N resulted in
a bright yellow color on the paper. And about 20% of reflectance
at 442 nm was observed, meaning that the color was quite
obvious in naked eyes (Figure 4c). The yellow paper could be
repetitively wrote with base and erased by heating at 80 oC
(Figure S21b). What’s more, the fluorescence of the SP-OX-NO2
could be quenched with the stimuli of either visible light or base
(Figure 4d, 4e). Additionally, both the natural-color and
fluorescent microscopy images of different states of SP-OX-NO2
revealed that there was no aggregation on the paper substrates
before and after treatment with light and base (Figure 4f).
Figure 5. (a) Schematic illustration of the rewritable paper based on SP-OX-
NO2 upon exposure to visible light and base. (b) The natural-color and
fluorescent images of the SP-OX-NO2 based rewritable paper.
The pictures in ambient light or under UV light all gave naked-
eye legibility and good resolution (Figure 5b). Placing the
drawing paper with yellow painting and purple background upon
exposure to sunlight for a week, the background of the paper
gradually faded to light yellow, which was agreed with the
advocated reduction of light pollution to human’s eyes and the
characters kept bright as initial color stably (Figure S20). In brief,
the paper material based on SP-OX-NO2 displayed multi-color
using yellow light, base and heat with stability and reversibility.
The visible light, base and heat stimuli could be applied
independent of each other, which was beneficial for drawing
more colorful patterns (Figure S19) and practical usage. In
Figure 5, various patterns were drawing on the SP-OX-NO2
based paper by yellow light with photomasks and a base-ink pen.
Conclusions
A dual-addressable molecular switch SP-OX-NO2 by fusing
the switches of SP and OX through a sharing central indole
has been synthesized. The trans MC form of SP-OX-NO2
transformed to ring-closed form of SP or OX upon visible
light irradiation or base addition in solution respectively. An
unexpected formation of cis-MC was also observed in
untreated or visible light irradiated SP-OX-NO2 solution
upon adding base and could be regarded as the
intermediate during the OX switching process. The
interconversions of the four different states were proved by
UV-vis, NMR spectra and DFT calculation. The calculated
results also suggested that the fused SP-OX molecular
switches showed the bidirectional switching property highly
dependent on more stable isomer of OX than SP-N. Moreover,
this attractive multistate photo- and basochromic molecule
SP-OX-NO2 was used for rewritable paper with high
contrast in both visible and fluorescent color, repeatability
and good resolution. The strategy adopted in this work
simplifies the molecular design for multi-addressable
systems, and encourage us to further explore the multi-
function in multicolor reversible display, sensing, logic gates
and so on.
Figure 4. (a) Illustration of the three-layer structure of rewritable paper based
on the SP-OX-NO2. Reflective UV− Vis spectra of the SP-OX-NO2 based
rewritable paper, (b) before and after yellow light irradiation, (c) before and
after adding 5mM Et3N. The emission spectra of the SP-OX-NO2 rewritable
paper, (d) before and after yellow light irradiation, (e) before and after adding
5mM Et3N. (f) The natural-color and fluorescent microscopy images of the
initial state, with the stimuli of vis-light and 5mM Et3N (scale bar = 200μm).
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Experimental Section
1-(2-hydroxy-5-nitrobenzyl)-2,3,3-trimethyl-3H-indol-1-ium chloride
(1mmol, 0.35 g) and 2-hydroxy-5-methylbenzaldehyde (1.2mmol,
0.16 g) were heated and refluxed in 10 ml ethanol solution for 6 h
under argon atmosphere. The solvent was evaporated and added
with ether to extract precipitate. The product was filtered and
washed for several times with ethyl acetate and anhydrous ether to
obtain the orange solid product (338 mg, 73%).1H NMR (500 MHz,
Materials
DMSO (chromatographic grade), acetonitrile (chromatographic grade),
trifluoroacetic acid (TFA) and triethylamine (TEA) were purchased from
Aladdin Reagent Company (Shanghai, China), ethanol (EtOH) and
dichloromethane (CH2Cl2) were purchased from Beijing Chemical Works
(Beijing, China). 3,5-dinitrosalicylic aldehyde, 5-methylsalicylaldehyde,
salicylaldehyde, p-nitrophenol, dinitrophenol, 1,2,3,3-tetramethyl-3H-indol
were purchased from Energy Chemical Company (Shanghai, China).
PEG 20000 (molecular weight: 17,000-22,000) was purchased from
Guangfu Fine Chemical Research Institute (Tianjin, China). Cellulose
filter paper (Whatman-Xinhua, grade 91, Hangzhou, China) was used as
the paper substrate.
DMSO-d6), δ= 12.00 (s, 1H), 11. 00 (s, 1H), 8.60 (d, J = 16.5 Hz,
1H), 8.49 (s, 1H), 8.14 (dd, 1H), 7.90 (m, J = 16.5 Hz, 2H), 7.81 (d,
J = 7.5 Hz, 1H), 7.57 (m, 2H), 7. 31 (d, J = 7.5 Hz, 1H), 7.11 (d, J =
9.0 1H), 7. 01 (d, J = 9.0 Hz, 1H), 5.96 (s, 2H), 2.28 (s, 3H) ,1.80 (s,
6H). LC-HRMS: m/z calcd. [M+H]+ 429.1809, found 429.1804.
(E)-1-(2-hydroxy-5-nitrobenzyl)-2-(2-hydroxystyryl)-3,3-
dimethyl-3H-indol-1-ium:
Instruments
1-(2-hydroxy-5-nitrobenzyl)-2,3,3-trimethyl-3H-indol-1-ium
chloride
1H NMR spectra were recorded on a 500 MHz BrukerAvance at room
(1mmol, 0.35 g) and 2-hydroxybenzaldehyde (1.2mmol, 0.15 g) were
heated and refluxed in 10 ml ethanol solution for 6 h under argon
atmosphere. The solvent was evaporated and added with ether to extract
the precipitate. The product was filtered and washed for several times
with ethyl acetate and anhydrous ether to obtain red solid product (314
mg, 70%). 1H NMR (500 MHz, DMSO-d6) , δ= 12.05 (s, 1H), 11.24 (s,
1H), 8.64 (d, J = 16.0 Hz, 1H), 8.42 (s, 1H), 8.13 (dd, 1H), 7.96 (d, J =
16.0 Hz, 1H), 7.90 (d, J =7.0 Hz, 1H), 7.82 (d, J = 7.0 Hz, 1H), 7.58 (m,
2H), 7.49 (t, H), 7.12 (m, 2H), 6.98(t, 1H), 5.96 (s, 2H), 1.81 (s, 6H). LC-
HRMS: m/z calcd. [M+H]+ 415.1652, found 415.1645.
temperature. 13C NMR spectra were recorded on
a 126 MHz
BrukerAvance. The deuterated solvents of DMSO-d6 were used for 1H
NMR and 13C NMR. Tetramethylsilane (TMS, δ = 0.00 ppm) was used as
an internal standard for 1H NMR. DMSO-d6 (δ = 77.00 ppm) were used
as internal standards for 13C NMR. Absorption spectra were measured on
a Shimadzu UV-2550 PC double-beam spectrophotometer. Reflective
spectra were tested by integrating sphere on Analitik Jena Specord®210
plus UV-Vis spectrophotometer, using BaSO4 as background, slit was 2
cm. Fluorescence spectra were measured with
a
RF-5301PC
spectrofluorometer. LC-HRMS analysis was performed on an Agilent
1290-micro TOF-Q II mass spectrometer (electrospray ionization (ESI)
source). The LED light source and ultraviolet lamp was used for
irradiation experiments (yellow light and bule light, 20 W; 365nm, 8W).
The Microscale colors of the media were imaged in transmission mode
using Leica DM4000 M microscope. The melting point was measured by
using a SGW X-4B microscopy melting point apparatus (Shanghai,
China).
Acknowledgements
This work was financially supported by the National Science
Foundation of China (21572079 and 21574058).
Conflicts of interest
General Synthesis and characterizations of SP-OX-CH3, SP-OX-H
and SP-OX-NO2
The authors declare no conflict of interest.
SP-OX-CH3, SP-OX-H and SP-OX-NO2 were synthesized in the same
way according to the synthetic routes shown in Scheme S1[44]
.
Keywords: multi-addressable molecular switch • spiropyran•
benzoxazine • visible light and base• rewritable paper
(E)-2-(2-(1-(2-hydroxy-5-nitrobenzyl)-3,3-dimethyl-3H-indol-1-ium-2-
yl)vinyl)-4,6-dinitrophenolate:
1-(2-hydroxy-5-nitrobenzyl)-2,3,3-trimethyl-3H-indol-1-ium chloride
(1mmol, 0.35 g) and 2-hydroxy-3,5-dinitrobenzaldehyde (1.2mmol, 0.25 g)
were heated and refluxed in 10 ml ethanol solution for 8 h under argon
atmosphere. After cooling to ambient temperature, the solvent was
filtered to get the precipitate and washed with ethanol for several times to
obtain a red-black solid powder (338 mg, 67%). Melt point: 195.3 oC.1H
NMR (500 MHz, DMSO-d6), δ= 11.87 (s, 1H), 8.93 (d, J = 3.0 Hz, 1H),
8.62 (d, J = 15.5 Hz, 1H), 8.56 (d, J = 3.0 Hz, 1H), 8.54 (d, J = 15.5 Hz,
1H), 8.19 (d, J = 2.5 Hz, 1H), 8.14 – 8.11 (dd, 1H), 7.87 (d, J = 8.0 Hz,
1H), 7.72 (d, J =8.0 Hz, 1H), 7.52 (t, 2H), 7.02 (d, J = 9.0 Hz, 1H), 5.77 (s,
2H), 1.84 (s, 6H). 13C NMR (126 MHz, DMSO-d6) δ = 183.84, 169.52,
162.05, 152.92, 143.14, 141.07, 140.98, 139.57, 134.62, 128.89, 128.45,
128.40, 126.21, 126.18, 125.55,124.98,122.97, 120.35, 115.92, 114.77,
110.86, 51.70, 45.82, 26.47. LC-HRMS: m/z calcd. [M+H]+ 505.1359,
found 505.1355.
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Entry for the Table of Contents (Please choose one layout)
Layout 1:
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A
dual-addressable molecule (SP-
Danyang Liu, Binhong Yu, Xing Su,
OX-NO2) containing SP and OX was
designed by sharing indole in a single
molecular system. The bidirectional
switching property could be controlled
with the stimuli of visible light or base
in solution, respectively. Further, SP-
OX-NO2 was applied in rewritable
paper displaying multi-color with
different stimuli including vis-light,
base and heat.
Xiaojun Wang, Yu-Mo Zhang, Minjie Li*
and Sean Xiao-An Zhang*
Page No. – Page No.
Photo-/ baso- chromisms and the
application of a dual-addressable
molecular switch
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