Dynamic Covalent Switches and Communicating Networks for Tunable Multicolor Luminescent Systems and Vapor-Responsive Materials

Article abstract of DOI:10.1021/jacs.9b07175

Molecular switches are an intensive area of research, and in particular, the control of multistate switching is challenging. Herein we introduce a general and versatile strategy of dynamic covalent switches and communicating networks, wherein distinct states of reversible covalent systems can induce addressable fluorescence switching. The regulation of intramolecular ring/chain equilibrium, intermolecular dynamic covalent reactions (DCRs) with amines, and both permitted the activation of optical switches. The variation in electron-withdrawing competition between the fluorophore and 2-formylbenzenesulfonyl unit afforded diverse signaling patterns. The combination of switches in situ further enabled the creation of communicating networks for multistate color switching, including white emission, through the delicate control of DCRs in complex mixtures. Finally, reversible and recyclable multiresponsive luminescent materials were achieved with molecular networks on the solid support, allowing visualization of different types of vapors and quantification of primary amine vapors with high sensitivity and wide detection range. The results reported herein should be appealing for future studies of dynamic assemblies, molecular sensing, intelligent materials, and biological labeling.

Full text of DOI:10.1021/jacs.9b07175

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Article
Dynamic Covalent Switches and Communicating Networks for Tunable
Multicolor Luminescent Systems and Vapor-Responsive Materials
Hanxun Zou, Yu Hai, Hebo Ye, and Lei You
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.9b07175 • Publication Date (Web): 23 Sep 2019
Downloaded from pubs.acs.org on September 24, 2019
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Dynamic Covalent Switches and Communicating Networks for
Tunable Multicolor Luminescent Systems and Vapor-
Responsive Materials
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Hanxun Zou,†,‡,§ Yu Hai,†,‡,§ Hebo Ye,† and Lei You*,†,‡
†State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese
Academy of Sciences, Fuzhou 350002, China.
‡University of Chinese Academy of Sciences, Beijing 100049, China.
ABSTRACT: Molecular switches are an intensive area of research, and in particular, the control of multistate switching is
challenging. Herein we introduce a general and versatile strategy of dynamic covalent switches and communicating
networks, wherein distinct states of reversible covalent systems can induce addressable fluorescence switching. The
regulation of intramolecular ring/chain equilibrium, intermolecular dynamic covalent reactions (DCRs) with amines, and
both permitted the activation of optical switches. The variation in electron-withdrawing competition between the
fluorophore and 2-formylbenzenesulfonyl unit afforded diverse signaling pattern. The combination of switches in situ
further enabled the creation of communicating networks for multistate color switching, including white emission, through
the delicate control of DCRs in complex mixtures. Finally, reversible and recyclable multi-responsive luminescent materials
were achieved with molecular networks on the solid support, allowing visualization of different types of vapors and
quantification of primary amine vapors with high sensitivity and wide detection range. The results reported herein should
be appealing to future studies of dynamic assemblies, molecular sensing, intelligent materials, and biological labeling.
Introduction
toward emissive systems in solution or solid state.8 The
assembly of building blocks to construct novel
fluorophores through reversible covalent linkages has also
been reported.9 Nevertheless, dynamic covalent multicolor
systems remains rare.
Research on molecular switches is generating intensive
interest, as they can shift between distinct states under
stimuli and serve as key precursors for creating complex
functional systems.1 Recently, the regulation of switches
has been shown to be an effective manner to control color-
conversion processes.1,2 The construction of tunable
multicolor luminescent materials, including white
emission, is receiving considerable attention due to their
extensive application, such as lighting and display,
Molecular networks containing interrelating dynamic
reactions, such as orthogonal and communicating DCC, is
an intriguing area of research recently.10 The evolution of
constitutional dynamic networks would allow access to
structural diversity and emerging properties. Among
elegant examples, three orthogonal DCRs (disulfide
exchange, hydrazone exchange, and boronic ester
exchange) were employed for programmed assembly of
templated chromophores11 and surface architectures,12
respectively. In another case, with thiols as shared inputs
exchanges of disulfide, thioester, and dithioacetal were
able to selectively intercommunicate to achieve multilayer
networks.13 Redox control of acylhydrazone based
configurational switches was also reported through
manipulating thiol/disulfide equilibrium along with thiol
based nucleophilic catalysis.14 Very recently, adaptive
visualized
sensing,
biological
imaging,
and
anticounterfeiting.2,3 The field of dynamic covalent
chemistry (DCC)4 has been flourishing, and the
interconversion through dynamic covalent reactions
(DCRs) and in response to external stimuli would lead to
switchable states, which closely resemble those for
molecular
switches.5
The
incorporation
of
fluorophores/chromophores into DCC systems has
provided ample means for the modulation of signal
outputs. For example, guest-triggered transformation
within dynamic combinatorial libraries was targeted for
chemical sensing.6 A variety of arylboronic acid derived
fluorescence receptors were developed for reversible
covalent bonding and detection of saccharides.7 Moreover,
aggregation induced emission active tetraphenylethene
motifs were integrated into dynamic covalent assemblies
dynamic
covalent
networks
of
macrocylic
benzopolysulfanes were showcased as an efficient venue
for cell penetration and delivery.15 In addition, DCC of
imine,16 hydrazone,17 or enamine18 has been combined with
metal coordination for the creation of multistep switching
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systems and signaling networks. Moreover, the strategy of
conceived a strategy of regulating ring-fusion DCR
photodynamic covalent bond was proposed to shift the
network to out-of–equilibrium states by taking use of
photoswitches.19 Despite significant advances, the use of
DCC for controlling multistate switches is challenging. The
exploration of optical materials within the context of
switchable molecular networks could open up
opportunities for sophisticated color-conversion systems
and associated functions.
partners on the periphery of a fluorophore (1A, Figure 1a),
wherein varied states of dynamic covalent system could
afford tunable optical switching accordingly. The aldehyde
reactive site in conjunction with pH sensitive sulfonamide
unit could realize multistate switching through the
manipulation of intramolecular and intermolecular DCRs,
such as those with amines (2) to create equilibrating imine
and its cyclic aminal (1I). Moreover, we foreseen this
approach to be readily generalized with structurally
diverse amine fluorophores. The versatile switching
patterns and optical responses could further offer a
pathway for multicolor communicating networks through
the combination of switches and interplay between their
DCRs (Figure 1b). Herein, we developed dynamic covalent
switching systems through the convergence of ring/chain
equilibrium and intermolecular DCRs. Furthermore,
molecular networks were constructed toward controllable
multistate fluorescence modulator, including pure white
emission. Finally, the switchability of the platform enabled
the creation of recyclable responsive luminescent
materials for sensing of various vapors.
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a
intramolecular equilibrium
O
S
O
O
S
O
O
O
N
pH
S
N
N
H
CHO
CHO
OH
1AO
1AOCB
1AR
intermolecular
equilibrium
NH2
NH2
2
2
O
O
O
S
O
O
S
O
S
pH
N
N
N
H
NH
N
N
1IR
1IO
1IOCB
b
Results and Discussion
O
O
S
N
Design and synthesis. In a straightforward manner, an
amino-containing fluorophore would be directly
connected to 2-formylbenzenesulfonamide. We postulated
that the conversion between open aldehyde (1AO in Figure
1a) and its cyclic hemiaminal (1AR) could impact the extent
of conjugation between the fluorophore and sulfonamide
nitrogen as well as potential intramolecular charge transfer
(ICT),25 thereby resulting in signaling modulation. In
addition, the deprotonation of sulfonamide of 1AO and 1IO
could make nitrogen a better electron donor in the open
conjugate base (1AOCB and 1IOCB).26 The electron-
withdrawing competition between fluorophores and
benzenesulfonamide unit would influence the electron
density on sulfonamide nitrogen and thereby ICT. (Figure
1b). Moreover, DCRs with amines would offer another
handle for control due to varied electron-pulling capability
between aldehyde and its imine. The change in competing
effect could afford various responding patterns through
facile modification of fluorophores, paving the way for
multicolor systems via communicating DCC. In short, a
network of intramolecular and intermolecular equilibria
was sought to harness multistate optical switching.
X
X = O,
N
1
2
3
communicating networks
for multicolor systems
electron-pulling competition
for versatile signaling
diverse switching patterns
and differential responses
c
O
O
S
N
R
R
Et2N
O
O
O
O
5A
OH
3A
6A
4A
7A
R =
CN
O
N
O
NC
MeO
O
O
O
S
O
S
O
N
H
CHO
N
8A
Figure 1. (a) Multiple states within dynamic covalent
switching systems, with the star representing the fluorophore.
(b) The electron-withdrawing competition for the regulation
of fluorophores (using conjugate base as an example) and the
creation of communicating networks. (c) Structures of 3A-8A.
Fluorophores of spirolactone, spirothiolactone, and
spirolactam family, including fluorescein and rhodamine,
adopt a signaling mode of intramolecular cyclization/ring
opening and have been widely used as reaction based
sensors.20 The ring/chain isomerization also plays a critical
role in harnessing photoswitches, such as diarylethenes21
and spiropyrans.22 There is thus continued interest in
developing novel structures and mechanisms of ring/chain
switches and sensors.23 However, little attention has been
paid to intermolecular dynamic processes of these
ring/chain platforms. Recently, we introduced a concept of
switchable orthogonal DCC through the regulation of dual
reactivity of equilibrating ring/chain tautomers, and
further demonstrated the application in chirality sensing
and reaction networks.24 Inspired by the common
mechanism of ring/chain switches and our DCC system, we
To test our hypothesis, a suite of amine fluorophores
with different electronic and steric features as well as a
broad spectral range was chosen (Figure 1c), including 2-
aminoanthracene
(3A),27
3-amino-7-
diethylaminocoumarin (4A),28 4-methyl-7-aminocoumarin
(5A),29
4-amino-1,8-naphthalimide
(6A),305-
and
aminonaphthalene-1-sulfonamide
dicyanomethylenebenzopyran
(7A),31
(DCMB)-based
probe
(8A),32 which emits in the near-infrared region. The
corresponding 2-formylbenzenesulfonamide derivatives
were prepared in a modular fashion (Scheme S1) and
characterized (Figures S1-S12).
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e. 6A + 1-BuNH2
A
B
CH/6IOCB
O
N
O
S
N
O
O
+ DBU
O
O
N
O
S
N
H
H
MeO
OH
MeO
NHBu
d. 6A + 1-BuNH2
(3.0 equiv.)
O
6IR
6AR
NH2
c. 6A + 1-BuNH2
(1.2 equiv.)
O
O
CH/6IR
O
O
S
S
O
O
N
O
NH
H
NH
H
N
O
MeO
MeO
CH/6AOCB
O
NBu
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b. 6A + DBU
6AO
6IO
CH/6AR
DBU
CH/6AO
1-BuNH2 or DBU
6AR
a. 6A
O
S
O
O
S
N
O
O
N
O
O
N
O
N
H
NH2
H
11.0 10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5
MeO
MeO
O
NBu
f1 (ppm)
6AOCB
6IOCB
6A +
DBU +
amine
C
D
6A +
DBU
λ
ex = 454 nm
6A
70000
60000
50000
40000
30000
20000
10000
0
λ
ex = 344 nm
50000
1-BuNH2
1200
DBU
λ
ex = 454 nm
45000
40000
35000
30000
25000
20000
15000
10000
5000
DBU
1000
800
600
400
200
0
λ
ex = 344 nm
1-BuNH2
State State State
1
2
3
500
550
600
650
700
Wavelength (nm)
0
400
450
500
550
600
650
700
400
450
500
550
600
650
700
750
Wavelength (nm)
Wavelength (nm)
Figure 2. (A) The conversion of 6A triggered by DBU and 1-BuNH2, with the crystal structure of 6A listed. (B) 1H NMR spectra of
6A in CD3CN (a), with the addition of DBU (1.2 equiv.) (b), its reaction with 1-BuNH2 (1.2 equiv., c; 3.0 equiv., d), and the addition
of DBU (1.2 equiv.) into d (e). The methine (highlighted in red in Figure 2A) peak is labelled. (C) Fluorescence titration of 6A (50
μM) with DBU (0–1.4 equiv.) in CH3CN (λex = 344 nm; Inset: λex = 454 nm). (D) Fluorescence titration of 6A (50 μM) with 1-BuNH2
(0-50 equiv.) in CH3CN (Blue: λex = 344 nm; Green: λex = 454 nm; Inset: photograph of blue (state 1: 6A), quenched (state 2: 6A
with DBU), and green emission (state 3: 6A with DBU and 1-BuNH2) under a 365 nm UV lamp.
NMR and fluorescence studies. 1H NMR spectra showed
the domination of the ring form for all probes (Table S2).
Taking 6A as an example (Figure 2A), the cyclic
hemiaminal accounted for 88% of the population for 6A in
CD3CN (a of Figure 2B), with a small amount of open
aldehyde (12%). X-ray analysis of 6A revealed the lack of
conjugation between sulfonamide nitrogen and
fluorophore plane as well as slight pyramidalization of
amide nitrogen in the ring form (Figures 2A and S13). Base
DBU was next titrated into 6A to shift the equilibrium
toward open aldehyde. The formation of the conjugate
base of aldehyde (6AOCB) was supported by the emergence
of the formyl proton around 11.2 ppm in 1H NMR spectrum
(b of Figures 2B). The DCR of 6A with 1.2 equiv. of 1-
butylamine afforded mainly 6IR, accompanied by the
disappearance of original hemiaminal methine peak at 6.4
ppm (c of Figures 2B). With an excess amount of amine (3.0
equiv.) serving as a base, the CH peak was found around
9.3 ppm, indicating the generation of the conjugate base of
imine (6IOCB, d of Figures 2B). This phenomenon was
validated by almost the same chemical shift with
subsequent addition of DBU into 6I (e of Figures 2B). In
essence, components within dynamic covalent systems can
be interconnected through amine nucleophile and base
(Figure 2A).
In order to transduce molecular network into optical
switching, fluorescence titration was conducted. The
maximum emission of 6A was observed at 450 nm while
excited at 344 nm, and a blue shift of 67 nm compared to
its parent amine (Figure S17) is in accordance with the lost
of p(nitrogen)-π(fluorophore) conjugation in the crystal
structure. Upon the titration with DBU, the blue emission
at 450 nm was quenched, with a concomitant emergence
of a tiny peak near 550 nm (Figures 2C and S40). DCR of
6A with 1-BuNH2 also enabled the decrease of the
fluorescence at 450 nm while affording a strong yellow-
green emission at 550 nm (Figures 2D and S41). We
rationalized these results as follows: when the base
converts the cyclic form into the conjugate base of open
aldehyde/imine,
electron-withdrawing
2-
formylbenzenesulfonyl unit can serve as an electron sink
and pull electrons away from the fluorophore, thus
resulting in the quenching of the original emission;33
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meanwhile, the deprotonation of sulfonamide can render
electron-withdrawing ability of the corresponding
nitrogen a better electron donor,26 and with a strong
naphthalimide acceptor pulling the electron towards the
fluorophore motif, the bidirectional electron-withdrawing
competition leads to a red shift. The striking difference
(~60 fold) in the intensity of the ICT band between the
conjugates base of open aldehyde and imine is likely due
to the former’s stronger electron-withdrawing ability (i.e.,
a more effective quencher).34 Moreover, the unique feature
of 6A allowed the construction of a three-state ON-OFF-
ON switching system (the inset of Figure 2D and Figure
S42): the blue emission of 6A (state 1) was turned off with
DBU (state 2), and the subsequent amine addition turned
on the yellow-green emission (state 3). Such a triple-mode
switching was verified by the significantly different
quantum yields of the solutions of 6A (0.178), 6AOCB
(0.002), and 6IOCB (0.708). The higher negative charge
distribution on the fluorophore portion of 6IOCB over 6AOCB
was further supported through DFT calculation (Figure
S43).
fluorophore acceptor and thereby echoes the design. For
simplicity, the emission at the original peak (386 nm) of 5A
was included in Figure 3.
100000
a
Aldehyde
+ DBU
90000
+ BuNH2
80000
+ BuNH2 + DBU
9
70000
60000
50000
40000
30000
20000
10000
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m
m
m
n
m
m
m
n
m
m
n
n
n
n
n
n
0
3
6
8
0
9
4
0
1
7
5
6
5
1
5
2
4
/
4
3
/
5
4
5
7
/
4
/
/
/
/
/
A
A
A
A
A
7
A
A
8
A
6
4
5
6
7
3
b
c
6000
5000
4000
3000
2000
1000
0
100000
80000
60000
40000
20000
0
pH and amine controlled switching. To demonstrate
the generality and versatility of our strategy, a series of
probes (Figure 1c) were next studied. NMR analysis
revealed the formation of imine 1I in all cases, but the
extent of ring/chain equilibrium of 1I was case dependent
(Figures S21-S53). In addition, DBU facilitated ring opening
of aldehyde 1A and imine 1I to afford their respective
MA
DBU
600
650
700
750
800
850
600
650
700
750
800
Wavelength (nm)
Wavelength (nm)
conjugate base 1AOCB and 1IOCB
. To illustrate the
differential optical responses of those probes toward base
and nucleophiles, the corresponding maximum emission
was compared (Figure 3a), with full spectra in SI (Figures
S21-S53). The quenching was found for 3A (427 nm, Figure
S23) and 4A (463 nm, Figure S29) with the addition of DBU
(red bar). However, the amine adduct of 3A and 4A turned
down and up the emission, respectively (green bar). DBU
also suppressed the fluorescence of 3I and 4I, as reflected
by the signal change triggered by the combination of 1-
butylamine and DBU (pink bar). Different from 6A, no
bathochromic peak was apparent during the titration of
base/nucleophile into 3A and 4A, respectively (Figures S24
and S30). Without an appropriate electron acceptor for
amide nitrogen, an ICT band would be unlikely for 3A and
Figure 3. (a) Fluorescence intensity of 3A-8A (50 μM, Blue)
and the response to the addition of DBU (1.2 equiv., Red), 1-
BuNH2 (50 equiv., Green), as well as both DBU (1.2 equiv.) and
1-BuNH2 (50 equiv., Pink). Each intensity was shown at
maximum emission while excited at corresponding maximum
excitation wavelength. The original and red shift ICT peaks of
6A and 7A are shown. Changes in emission spectra upon the
titration with DBU (0-1.2 equiv., b) and MA (0-1.2 equiv., c)
into a solution of 8A (50 μM) in CH3CN (λex = 526 nm).
In the case of 8A, the emission peak was revealed at 704
nm, in the near-infrared region (Figure 3a and 3b).
Interestingly, there was a sharp increase (~16 fold) in the
magnitude at 704 nm with 1.2 equiv. of DBU. Fluorescence
titration further verified the changes (Figures 3b and S50).
These findings can be interpreted from the perspective of
4A,
and
the
electron-pulling
effect
of
2-
formylbenzenesulfonyl unit would be dominant and thus
result in based induced quenching.
electron-withdrawing
competition:
base
induced
deprotonation of NH benefits the ICT, and with electron-
pulling ability of the fluorephore rivalling that of 2-
formylbenznesulfonyl unit the emission is turned up. This
explanation falls in line with the largest distribution of
aldehyde form for 8A (22%, Table S2) and is also supported
by an increase in the emission of 8A upon water addition,
which enhanced NH acidity (Figure S20). Furthermore, the
titration of methanesulfonic acid (MA) into 8A resulted in
a blue shift to around 660 nm, indicative of the emission of
the ring form 8AR (Figures 3c and S51). The reaction of 1-
butylamine with 8A to give imine 8I also increased the
fluorescence around 704 nm, and a modest enhancement
was further detected with DBU present (Figures 3a, S52 and
To further back our explanation, another two donor-
acceptor type probes (5A and 7A) were subjected to
analysis. Gratifyingly, base induced quenching of
fluorescence of 7A at 411 nm was detected, and a weak red-
shift peak emerged at 559 nm (Figures 3a and S46). Again,
the reaction of 7A with 1-BuNH2 allowed the amplification
of the red-shift signal (559 nm, Figure S47), as the case of
6A. The addition of DBU into 7I led to the conversion to
7IOCB, with a further increase of intensity. A similar ICT
band was revealed for 5A, albeit with only a modest red
shift (~25 nm, Figures S33 and S34). The difference between
5A, 6A, and 7A (Figure 3a) can be attributed to varying
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S53). These results demonstrate the diverse signaling
suppressed with MA and DBU, respectively (Figure S62).
2
3
4
5
pattern of pH/amine activated switching as well as the
feasibility of a combination of these stimuli, thereby
setting the stage for complexity studies.
These results are consistent with titration data in Figure 2
and highlight the reversibility for both pH and amine
induced switch. Moreover, the dynamic nature of DCRs
was corroborated with NMR spectra of component
exchange with amines or aldehydes (Figure S63 and S64).
6
7
8
9
a
MA
MA
Communicating networks for tunable multicolor
emitters. Due to varying reactivity and response of
aldehydes the interplay of multiple DCRs was harnessed to
create reaction networks as a means of modulating colors.
As a proof-of-concept, a multicolor system was designed to
create the white emission through the manipulation of
components within the network (Figure 5a). Probes 3A, 6A,
and 8A were chosen as their DCRs with amine can generate
blue, green and red color, respectively, which are the three
primary colors (Figure 5a). The CIE coordinate of 3A, 6A,
and 8A in acetonitrile was (0.15, 0.04), (0.15, 0.11), and
(0.69, 0.31), respectively (Table S3), and their
corresponding amine adducts 3I, 6I, and 8I had a CIE
coordinate of (0.15, 0.05), (0.41, 0.57), and (0.70, 0.29),
respectively, as plotted in CIE 1931 chromaticity diagram
(Figure 5b). A solution of 3A, 6A, and 8A (3:1:2) was mixed,
and a blue emission (0.16, 0.07) was found. The color was
gradually shifted from the blue to white emission region
with the addition of 1-buthylamine because DCRs of 6A
and 8A with amine turned on green and red emission,
respectively (Figure 5b). Almost pure white light emission
(0.32, 0.33) was obtained with 20 equiv. of 1-butylamine
(Figures 5b and S65).
6A
40000
30000
20000
10000
0
MA
MA
MA
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DBU
DBU
DBU
DBU
DBU
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b
MA
MA
MA
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6A +
BuNH2
DBU
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DBU
DBU
500
DBU
600
To take advantage of diverse switching behaviors of
these probes toward pH and amine stimuli, multistate
signal communication was further realized (Figures 5c, 5d,
and S66). With the goal of multicolor fluorescence
switching the interconversion between colors was
showcased in Figure 5c, and the corresponding structures
within the network are listed in Figure S67. The white color
(state 2), generated from state 1 (0.16, 0.07) in step a, was
reversed to original blue by MA (step b), as imines 3I, 6I,
and 8I decomposed into their respective aldehydes 3A, 6A,
and 8A. Moreover, in the presence of DBU the white color
was switched to yellow (0.44, 0.50) (state 3, step c), since
the blue emission from 3I was turned off. A red color (0.52,
0.28) (state 4) was detected when DBU was titrated into a
mixture of 3A, 6A, and 8A (state 1) due to the quench of
blue emission of 3A and 6A companied by turning up of
red emission of 8A (step e). Subsequent DCRs with amine
afforded the yellow color of state 3 (step g), which was
followed by the addition of MA, again leading to white
emission (state 2, step d). MA was also able to restore
original state 1 from state 4 (step f). Furthermore, the
yellow color (state 3) was converted into red (state 4, step
h) through aldehyde exchange with pyridine-2-
carboxaldehyde (2-PA). As a result, a switchable multicolor
system, including white emission, can be accomplished
through the delicate control of DCRs and pH in complex
mixtures. Moreover, we expect no hurdle to modulate
colors with other combination of switches.
0
100
300
400
Time (min)
Figure 4. (a) Fluorescence response of 6A (50 μM) at 450 nm
upon consecutive addition of DBU (1.2 equiv.) and MA (1.2
equiv.) in CH3CN (λex = 344 nm). (b) Fluorescence response of
6I (created from 6A (50 μM) and 1-BuNH2 (50 equiv.)) at 550
nm versus time upon consecutive addition of MA (50 equiv.)
and DBU (50 equiv.) in CH3CN (λex = 454 nm).
Reversibility. To ensure the utility of switching systems,
their reversibility was further checked. Taking 6A as an
example, the quenched emission at 450 nm upon the
addition of DBU was recovered with MA, and such a pH
regulated switch was further validated through several
cycles of base/acid (Figure 4a). The conversion between
cyclic hemiaminal form (6AR) and its open conjugate base
(6AOCB) in response to base/acid was also supported by
NMR (Figure S60). Furthermore, MA enabled the
decomposition of preformed imine 6I (created from 6A
and 1-BuNH2) into 6A, and the use of DBU then restored
imine (Figure 4b and Figure S61). The fluorescence was
tracked versus time, and the turning off and on of the
emission at 550 nm was observed upon repeated addition
of MA and DBU, with marginal loss of the magnitude
(Figure 4b). Opposite change was apparent for the
fluorescence at 450 nm, which was recovered and
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a
b
O
O
S
N
HO
3A
O
e
n
i
MeO
m
A
A
N
O
S
O
O
N
Base
HO
6A
8A
m
i
CN
n
NC
e
,
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B
a
s
e
O
S
O
O
N
HO
c
d
State 2
(0.32, 0.33)
(0.16, 0.07)
State 1
a. 1-BuNH2
b. MA
f. MA e. DBU
d. MA
c. DBU
g. 1-BuNH2
h. 2-PA
State 4
(0.52, 0.28)
(0.44, 0.50)
State 3
Figure 5. The creation and transformation of multicolor emissive systems with dynamic networks in solution. (a) The illustration
of a multicolor system with a mixture of 3A, 6A, and 8A triggered by amine and base. (b) CIE coordinates of the aldehyde mixture
of 3A (75 μM), 6A (25 μM), and 8A (50 μM) upon the addition of 1-BuNH2 (0, 0.5, 1.0, 2.0, 3.0, and 20.0 equiv.) on CIE 1931
chromaticity diagram. (c) The interconversion between four states (blue, white, yellow, and red) and associated fluorescence
photographs under a 365 nm UV lamp, with CIE coordinates listed. (d) CIE coordinates of the multicolor switch on CIE 1931
chromaticity diagram. 2-PA: pyridine-2-carboxaldehyde.
Vapor-responsive luminescent materials. Having
attained multicolor molecular networks in solution, we
next set out to construct a dynamic platform on the solid
support for the visualization of vapors. Vapor-responsive
luminescent materials have captured attention because of
their potential application in chemical sensing, invisible
ink, and others.35 Toward this end, a probe in acetonitrile
solution was written onto a Whatman filter paper followed
by evaporation to dry, and the filter paper was then
exposed to various volatile vapors. Taking 8A as an
example, the 8A written “DCC” letters showed a pale
yellow emission on the filter paper under a 365 nm UV
lamp (Figure 6A). After exposure to Et3N vapor, the red
color was clearly observed within a minute due to the
formation of open conjugate base of 8A (Scheme S2). The
yellow emissive letters were rapidly regenerated by HCl
vapor. The placement of 8A written letters into 1-BuNH2
vapor allowed the creation of imine and accordingly the
emergence of red emission, which was reversed to yellow
through exchange with formaldehyde vapor (Figure 6B).
Amine/aldehyde vapors triggered response of 8A required
slightly longer time (10 min, Figures S68 and S69) than
acid/base vapors. Vapor-sensitive fluorescence switching
was also accomplished with 6A (Figure S70). For example,
the blue emission of 6A turned to yellow upon exposure to
1-BuNH2 vapor, due to the formation of imine 6I (Figure
S70). With 1-BuNH2 also functioning as a base, the
conjugate base of imine can be afforded. The pH and DCR
induced color switching on the solid support falls in line
with solution studies. The reversibility was corroborated
through multiple cycles of vapor exposure.
Furthermore, the quantitative measurement of 1-BuNH2
vapor was performed with filter papers loaded with 6A. The
blue emission at 430 nm (a of Figure 6C) and yellow
emission at 546 nm (c of Figure 6C) were turned off and on
with a rapid response within three minutes, respectively.
Two linear response curves were afforded by analyzing the
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C
B
B
+ Et3N
+ HCl
8A
+ 1-BuNH2
+ HCHO
8A
a
b
1.0
D
1.0
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0.8
0.6
0.4
0.2
0.0
y = −9.23x + 0.932
State 1
State 2
1-BuNH2
0.8
0.6
0.4
0.2
0.0
R2 = 0.995
a. 1-BuNH2
b. HCHO
2
h.
1-BuNH
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700
750
0.00
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0.04
0.06
0.08
0.10
Et
3 N
e.
Wavelength (nm)
1-BuNH (ppm)
2
c
i. 1-BuNH2
j. HCl
d. HCHO c. t-BuNH2
d
1.0
0.8
0.6
0.4
0.2
0.0
g.
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
HCl
2
-BuNH
t
f.
State 3
State 4
1-BuNH2
k. t-BuNH2
y = 0.00845x + 0.170
R2 = 0.994
l. HCl
450
500
550
600
650
700
750
800
0
10 20 30 40 50 60 70 80 90 100
Wavelength (nm)
1-BuNH (ppm)
2
Figure 6. Multi-responsive luminescent materials for the visualization and quantification of vapors with dynamic networks on
solid support. The photographs of probes loaded on filter papers in response to various vapors under a 365 nm UV lamp: (A) 8A
with exposure to Et3N followed by HCl; (B) Reaction of 8A with 1-BuNH2 followed by HCHO. (C) 6A loaded filter papers were
exposed to various concentrations of gaseous 1-BuNH2. The emission spectra with excitation at 360 nm (a) and 432 nm (c), and
corresponding linear calibration lines at 430 nm (b) and 546 nm (d) are shown. (D) The switchable interconversion between four
states of “4”, “6”, and “8” written with 4A, 6A, and 8A on a filter paper triggered by various vapors.
data at 430 nm (0-0.10 ppm, b of Figure 6C) and 546 nm
(2.5-100 ppm, d of Figure 6C). The significantly higher
sensitivity of the former is due to the quenching of the blue
the color of “6” (yellow) and “8” (red) remained similar as
state 2 (state 3). The interconversion between states 2 and
3 was realized through amine exchange (step e, f), and
again HCHO reversed state 3 into state 1 (step d).
fluorescence by 1-BuNH2 as
a
base. With more
concentrated amine the creation of imine led to the yellow
emission. These observations are consistent with solution
results (Figure 2C). The limit of detection (LOD) based on
the data at 430 nm was found to be 0.026 ppm (Figure S73),
which is well below permissible exposure limit (5 ppm) and
is also lower than reported LOD values for gaseous 1-
BuNH2 in Table S7. Therefore, by taking use of the dual role
of the primary amine as a base and a nucleophile, both high
sensitivity and wide detection range were achieved.
The introduction of HCl (step g) quenched the blue
emission of “4” due to the protonation of diethylamine
group, which serves as a donor in 4A (Figure S71).
Meanwhile, the accumulation of ring form of 6A and 8A
under acidic condition resulted in the appearance of blue
and yellow emission of “6” and “8”, respectively (state 4).
Et3N (step h) was able to restore original state 1 from state
4. To achieve the transformation from state 4 to state 2
(step i), 1-BuNH2 was used for the neutralization of the acid
followed by DCRs with probes. The recovery of state 4 from
state 2 (step j) was carried out with HCl vapor for the
decomposition of imines into aldehydes. Similar switching
process between states 3 and 4 was accomplished by using
t-BuNH2 and HCl (steps k and l). It is notable that all twelve
conversions in the molecular network were conducted
with only a single filter paper, showcasing excellent
switchability and recyclability. Unique switching behaviors
of 1-BuNH2, t-BuNH2, and Et3N also allowed the
discrimination between them. To further show the utility,
real samples were tested. The visualization of amine vapors
from fish spoilage36 (Figure S75) as well as aldehyde
Encouraged by these findings, responses of vapors to a
set of probes in the network were performed by writing “4”,
“6”, and “8” on a filter paper with 4A, 6A, and 8A,
respectively (state 1, Figure 6D), with the corresponding
structures within the network listed in Figure S74. The
reaction of 1-BuNH2 (step a) gave cyclic hemiaminal for 4A
and open imine for 6A and 8A, affording blue, light yellow,
and red emission, respectively (state 2). The recovery of
state 1 (step b) was realized through aldehyde exchange
with formaldehyde vapor. Then t-BuNH2 vapor (step c)
converted blue emission of “4” into a faint color owning to
the formation of open imine (Figures S71 and S72), while
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odorants from a perfume37 (Figure S76) was also feasible.
In a word, facile multicolor luminescent materials that can
rapidly and reversibly respond to different types of volatile
vapors, including acid, base, nucleophile, and aldehyde,
have been developed. The multiple responsive mode also
afforded additional layers of complexity and thus enriched
the information, paving the way for further application in
multilevel logic gates and anticounterfeiting coding.
Molecular Switches. Angew. Chem., Int. Ed. 2015, 54, 11338−11349.
(c) Harris, J. D.; Moran, M. J.; Aprahamian, I. New Molecular
Switch Architectures. Proc. Natl. Acad. Sci. U.S.A. 2018, 115,
9414−9422. (d) Natali, M.; Giordani, S., Molecular Switches as
Photocontrollable "Smart" Receptors. Chem. Soc. Rev. 2012, 41,
4010−4029. (e) Feringa, B. L. The Art of Building Small: From
Molecular Switches to Motors. Angew. Chem., Int. Ed. 2017, 56,
11059−11078. (f) Klajn, R.; Stoddart, J. F.; Grzybowski, B. A.
Nanoparticles Functionalised with Reversible Molecular and
Supramolecular Switches. Chem. Soc. Rev. 2010, 39, 2203−2237.
(2) (a) Qu, D. H.; Wang, Q. C.; Zhang, Q. W.; Ma, X.; Tian, H.
Photoresponsive Host-Guest Functional Systems. Chem. Rev.
2015, 115, 7543−7588. (b) Shang, M. M.; Li, C. X.; Lin, J. How to
Produce White Light in a Single-Phase Host? Chem. Soc. Rev.
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9
Conclusions
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In summary, a general strategy of dynamic covalent optical
switches and reaction networks was developed, and the use
in the control of multicolor emitters and vapor sensitive
materials was further explored. A suite of fluorescent
probes exhibiting aldehyde based ring-chain tautomerism
as well as broad spectral range was prepared. The
manipulation of open/cyclic isomers through base or
dynamic covalent reactions with amines allowed the
activation of switching, and moreover, diverse signaling
patterns dependent on structural features of probes were
revealed. By taking advantage of differential reactivity of
aldehydes and amines multistate communicating
networks were constructed in situ, further achieving
addressable color modulator, including white emission.
Finally, reversible and recyclable multi-responsive
luminescent materials were facilely constructed for
sensing of various types of vapors. To the best of our
knowledge, it is the first example of creating tunable
multicolor emissive systems based on dynamic covalent
networks. The strategies and results presented should find
wide utility in a variety of chemistry endeavors.
Su,
C.
Y.
Single-Phase
White-Light-Emitting
and
Photoluminescent Color-Tuning Coordination Assemblies. Chem.
Rev. 2018, 118, 8889−8935. (d) Wu, H.; Chen, Y.; Dai, X.; Li, P.;
Stoddart, J. F.; Liu, Y. In Situ Photoconversion of Multicolor
Luminescence and Pure White Light Emission Based on Carbon
Dot-Supported Supramolecular Assembly. J. Am. Chem. Soc. 2019,
141, 6583−6591. (e) Watanabe, K.; Hayasaka, H.; Miyashita, T.;
Ueda, K.; Akagi, K. Dynamic Control of Full-Colored Emission and
Quenching of Photoresponsive Conjugated Polymers by
Photostimuli. Adv. Funct. Mater. 2015, 25, 2794−2806.
(3) (a) Yamashina, M.; Sartin, M. M.; Sei, Y.; Akita, M.; Takeuchi,
S.; Tahara, T.; Yoshizawa, M. Preparation of Highly Fluorescent
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Zhang, Q. W.; Li, D. F.; Li, X.; White, P. B.; Mecinovic, J.; Ma, X.;
Agren, H.; Nolte, R. J. M.; Tian, H. Multicolor Photoluminescence
Including White-Light Emission by a Single Host-Guest Complex.
J. Am. Chem. Soc. 2016, 138, 13541−13550. (d) Ji, X. F.; Wu, R. T.;
Long, L. L.; Ke, X. S.; Guo, C. X.; Ghang, Y. J.; Lynch, V. M.; Huang,
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M.; Stoddart, J. F. Dynamic Covalent Chemistry. Angew. Chem.,
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W. Recent Advances in Dynamic Covalent Chemistry. Chem. Soc.
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Herrmann, A. Dynamic Combinatorial/Covalent Chemistry: a
Tool to Read, Generate and Modulate the Bioactivity of
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Sanders, J. K. M.; Otto, S. Dynamic Combinatorial Chemistry.
Chem. Rev. 2006, 106, 3652−3711. (b) Moulin, E.; Cormos, G.;
Giuseppone, N. Dynamic Combinatorial Chemistry as a Tool for
the Design of Functional Materials and Devices. Chem. Soc. Rev.
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ASSOCIATED CONTENT
Experimental details, characterization, NMR, mass, and
fluorescence spectra, as well as X-ray data. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*lyou@fjirsm.ac.cn
Author Contributions
§These authors contributed equally.
Notes
The authors declare no competing financial interest..
ACKNOWLEDGMENT
We thank NSFC (21672214), the Recruitment Program of
Global Youth Experts, and the Strategic Priority Research
Program (XDB20000000) and the Key Research Program of
Frontier Sciences (QYZDB-SSW-SLH030) of the CAS for
funding. We also thank The CAS/SAFEA International
Partnership Program for Creative Research Teams.
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O
O
O
N
O
N
O
S
O
O
S
O
S
S
N
N
NH2
H
H
CHO
OH
NH
N
9
O
S
O
O
S
O
N
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N
CHO
N
Multistate
Fluorescence
Switching
Communicating
Multicolor
Networks
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