Multi-color emission with orthogonal input triggers from a diarylethene pyrene-OTHO organogelator cocktail

Article abstract of DOI:10.1039/c9cc08994b

We report on a pyrene-decorated supramolecular gelator based on an oxotriphenylhexanoate (OTHO) that can switch emission profiles between the solution and gel phase. A cocktail of the gelator and a photochromic diarylethene derivative enables four distinct emissive states to be obtained, which are modulated with light and heat as orthogonal input triggers.

Full text of DOI:10.1039/c9cc08994b

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Multi-color emission with orthogonal input
triggers from a diarylethene pyrene-OTHO
Cite this:DOI: 10.1039/c9cc08994b
organogelator cocktail†
Received 18th November 2019,
Accepted 13th December 2019
Mark D. Johnstone,
Chien-Wei Hsu, ‡ Nicolas Hochbaum,‡
Joakim Andreasson * and Henrik Sunden
*
´
´
DOI: 10.1039/c9cc08994b
rsc.li/chemcomm
We report on a pyrene-decorated supramolecular gelator based on photochromic materials using absorption as the information
8
an oxotriphenylhexanoate (OTHO) that can switch emission profiles readout. However, the low sensitivity of UV/Vis absorption
between the solution and gel phase. A cocktail of the gelator and a measurements, and the necessity for external circuitry to deter-
photochromic diarylethene derivative enables four distinct emissive mine the readout value (A = log I
0
/I) limits the utility of this
9
states to be obtained, which are modulated with light and heat as approach. In comparison, fluorescence mode detection offers
1
0
orthogonal input triggers.
much higher sensitivity, making emissive systems that can
switch among multiple emissive states much more attractive.
1
Supramolecular gels resulting from self-assembly of low- Although tunable multicolored emission systems have been
1
1
molecular-weight gelators (LMWGs) present a robust medium reported involving a variety of systems such as nanoparticles,
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13
14
15
for reversible sol–gel transformations that can be controlled micelles, quantum dots, thin films, and gels, these typically
2
by external stimuli, such as heat, ultrasound, ions and light.
involve a maximum of three emissive states. To advance this
Introducing luminescent chromophores to LMWGs enables research field, systems capable of generating four or more
physical transformations to be displayed as optical signals that distinct emissive states must be developed, preferably where
3
can be easily recognized by the naked eye. Phenomena such as the switching is achieved via true orthogonal inputs. Notably,
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5
aggregation induced emission (AIE), and excimer formation,
emissive four-state systems have not been reported in
are commonly employed as a means of modulating emission multistimuli-responsive materials using photoswitching in con-
intensity or color in input responsive systems. Additionally, junction with thermoresponsive gels.
chromophores that give optical responses to changes in their
aggregation state or intermolecular stacking simultaneously micelles and LMWGs, in combination with mixed fluoro-
Recently we reported supramolecular systems based on
1
6
17
provide in situ information on the molecular packing of the gels, phore systems (referred to as ‘‘cocktails’’) that were capable of
6
complementary to infrared and NMR spectroscopic techniques.
multi-color emission via all-photonic modulation. Such systems
Combining chromophores with orthogonal switching involve strategic utilization of energy transfer between chromo-
mechanisms, together with optically responsive LMWGs gels, phores in cocktails consisting of DAEs and fluorescent donor
is crucial for accessing a wider range of colored states. Light is a molecules.
highly appealing input stimuli as the intensity and wavelength
Herein, we report the synthesis, and the rheological and
can be easily tuned, in combination with the unsurpassed photophysical characterization of a pyrene-functionalized oxo-
spatiotemporal control (where and when to apply the stimulus). triphenylhexanoate (OTHO) gelator and its utilization in a
Accordingly, photochromic molecules have received widespread stimuli-responsive multi-color fluorescence system. A modular
attention due to their robust reversible photoinduced isomeriza- synthetic approach to the OTHO enables a fluorescent unit to
7
tion reactions between the two, spectrally well-resolved, isomers.
be readily incorporated into the gelator, which in combination
Photoswitches such as diarylethenes (DAEs) have been used with a fluorescent photoswitch produces a multicolor emission
extensively for generating multiple distinct colored states in system with orthogonal inputs (Fig. 1). The pyrene-decorated
OTHO gelator shows substantial differences between the sol
and gel state emission color, while the addition of a fluorescent
DAE photoswitch enables a larger range of emission colors to
Chalmers University of Technology, Department of Chemistry and Chemical
Engineering, Kemiv a¨ gen 10, 412 96, G o¨ teborg, Sweden.
be produced. Controlling the sol–gel transformation with heat
E-mail: sundenh@chalmers.se, a-son@chalmers.se
2
and the isomeric state of the DAE derivative with light, 4 (2 )
distinct emissive states can be reached using two external stimuli.
†
‡
Electronic supplementary information (ESI) available. See DOI: 10.1039/c9cc08994b
Chien-Wei Hsu and Nicolas Hochbaum contributed equally to the paper.
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Fig. 1 Design of organogelator with fluorescent pyrene unit and the
cocktail strategy for stimuli-responsive multi-color emission.
ꢀ
1
Fig. 2 (A) Frequency sweep of OTHO5 gel in toluene 10 mg mL , storage
modulus (K) and loss modulus (J), 0.5% strain, 20 1C. (B) Confocal laser
scanning microscopy image of OTHO5 gel, 405 nm laser excitation.
The input triggers are highly orthogonal as the emission from the
DAE photoswitch does not change upon gelation or heat exposure
and likewise light exposure (for DAE isomerization) does
(
C) Emission spectra of pyrene in toluene solution, lex = 340 nm. (D) Emission
not influence the intrinsic spectral properties of the pyrene spectra of OTHO5 in toluene solution and gel, lex = 370 nm.
fluorophore.
The chemical structure of the pyrene-based OTHO gelator
0
independent and the storage modulus (G ) is approximately
and photoswitch DAE8 are shown in Scheme 1. DAE8 was
0
0
1
8
one order of magnitude larger than the loss modulus (G ).
These properties are characteristic for LMWG and other supra-
synthesized according to the literature procedure. The OTHO
gelator was synthesized in an ionic liquid-mediated three-
1
a,20
1
9
molecular entangled fibrillar systems.
Due to the strongly
component reaction where the pyrene-containing chalcone,
cinnamaldehyde, and phenyl-b-D-glucopyranoside were mixed
in the presence of EMIMAc and DBU at room temperature.
Following flash chromatography, OTHO5 was isolated in 66%
fluorescent nature of the pyrene gel, confocal laser scanning
microscopy (CLSM) was used to gain insight into the structure
of the gel. The CLSM images confirm the presence of a highly
entangled fibrillar network in the gel, with the diameter of the
fibers in the order of 1 mm (Fig. 2B).
The fluorescent properties of OTHO5 were investigated
in solution and in the gel phase (Fig. 2). In toluene at low
concentrations (10 M), OTHO5 exhibits monomer-like pyrene
emission (Fig. 2C and D) with a quantum yield of 0.26.
At higher concentrations (410 M), OTHO5 begins to aggre-
gate and assembly into fibrils, where a moderate component
belonging to the excimer emission is present. In the gel phase,
OTHO5 shows a broad emission band with mixed components
from excimers and other restricted conformations present in
the gel. The fluorescence lifetimes of OTHO5 gel in toluene
were determined by time-correlated single photon counting.
The lifetimes of OTHO5 monomer and excimer were substantially
1
13
yield (see ESI† for full characterization data including H,
C
NMR spectra, and HR-MS). The gelating ability of OTHO5 was
investigated using the inverted vial method with a range of
solvents and solvent mixtures. OTHO5 gelates in toluene,
dichlorobenzene, ethyl acetate and in mixtures of toluene and
acetonitrile (Table S1 and Fig. S1, ESI†). The minimum gelation
ꢀ5
ꢀ3
ꢀ
1
concentration of OTHO5 in toluene was 9 mg mL
.
Dynamic shear oscillation experiments were performed to
evaluate the rheological properties of the gel. The gel displays
typical viscoelastic behavior of a physical gel in the frequency
sweep (Fig. 2A), where the moduli are largely frequency
21
shorter than those of pyrene solutions (see Fig. S8 and S9, ESI†).
Interestingly, the risetime observed with pyrene solution excimer
emission is not present in the gel, indicating that excimer
formation is no longer a dynamic process and the pyrene units
22
are confined in the rigid environment of the gel fibers.
Gelation of OTHO5 occurs rapidly in toluene upon cooling
to room temperature. In acetonitrile, however, it remains in
solution or in a partial gel state. In the case of toluene and
acetonitrile mixtures, there are no observable changes in
gelation at higher toluene/acetonitrile ratio (9 : 1), but with
increasing acetonitrile, the gel forms slowly upon cooling, while
sonication accelerates the gelation process and improves
sample uniformity. When the acetonitrile ratio is more than 50%,
Scheme 1 (A) Three-component synthesis of the OTHO5 gelator.
(
B) Chemical structure of the open (DAE8o) and closed (DAE8c) isomeric
form of the photoswitch.
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Fig. 3 (A) Photos of OTHO5 gel under ambient light. Left: After heating
(
sol). Right: Before heating (gel). (B) Photos of OTHO5 gel under 365 nm
light. Left: After heating (sol). Right: Before heating (gel). (C) Emission
spectra of OTHO5 in solution and gel, lex = 370 nm. (D) CIE diagram of
ꢀ1
OTHO5 in solution and gel. The concentration of OTHO5 is 10 mg mL
toluene/acetonitrile = 2 : 1.
,
OTHO5 does not fully gelate, but instead dissolves or forms a partial
ꢀ
1
Fig. 4 (A) Multicolored emission triggered by solution–gel transforma-
tion (heat) and UV irradiation for isomerization of DAE8o to DAE8c
gel even after sonication. Fig. 3A shows OTHO5 (10 mg mL ) in the
: 1 ratio of toluene/acetonitrile. Here, it remains temporarily in
solution at room temperature (left) but will gelate immediately when
sonication is applied (right). Under UV light irradiation the emission combinations of the input triggers. The concentration of OTHO5 is
2
(l = 380 nm). (B) Mapping the CIE coordinates of the four emission spectra
in the CIE diagram. (C) CIE coordinates of OTHO5/DAE8 with different
ꢀ1
ꢀ4
color is dramatically different in solution and in the gel (Fig. 3B). 10 mg mL , DAE8 is 10 M, toluene/acetonitrile = 2 : 1. The spectra
It can be clearly seen that OTHO5 in the sol-state presents excimer
were recorded at room temperature with lex = 370 nm.
emission centered at 525 nm (Fig. 3C). A tentative explanation is
that this is an effect of the more polar solvent mixture that stabilizes
the excimer in the sol-state as compared to toluene (Fig. 2D). the OTHO5/DAE8o mixture exhibits blue emission in gel state
However, when OTHO5 forms a gel, the excimer emission intensity and green emission in solution state. However, when exposed
is less pronounced. This observation is likely due to self-assembly to UV light DAE8 isomerizes quantitatively from the open form
into initial 1D fibrillar structures and a subsequent breakage to the closed form and emits in the red region (see Fig. S4, ESI†
5a,23
of excimer formation between the pyrene molecules.
Thus, for the emission spectrum of DAE8c). Thus, OTHO5/DAE8c
the excimer emission is much more pronounced in solution displays pink emission in gel state and orange emission in
compared to the gel state. Mapping these emission spectra in the solution state. Although energy transfer from pyrene to DAE8 is
CIE diagram, the coordinates for the solution and the gel are clearly also contributing to the spectral changes, the mechanism is
distinct (Fig. 3D).
Having found optimal conditions for a heat-controlled sol–gel tion of DAE8. FRET is not efficient here due to the low
transition, corresponding to two signals for optical read-out, we concentration of DAE8 (Rave c R , see ESI†). Mapping the four
mainly ‘‘trivial’’: emission from pyrene is followed by reabsorp-
0
opted for a system containing an additional fluorophore with emission profiles into the CIE diagram (Fig. 4B) clearly shows
tunable spectral properties. We were particularly interested in the four distinct emissive states that can be achieved with these
devising a bi-component system where the input triggers for the input triggers (heat and UV-light). It is interesting to note
two fluorophores are orthogonal, implying that the respective that virtually perfect white light is being generated upon
fluorophore could be addressed with a high degree of selectivity. isomerizing the DAE photoswitch between the open and the
ꢀ1
ꢀ2
Accordingly, OTHO5 gelator (10 mg mL , 1.4 ꢁ 10 M) and closed isomer in the sol-state (actual CIE coordinate (0.33, 0.32)
ꢀ
4
DAE8 (10 M) were dissolved in toluene/acetonitrile (2 : 1). compared to (0.33, 0.33) for perfect white light). As for the
By defining the two input triggers as heat (controlling the concentration of DAE8, there is a tradeoff between the emission
sol–gel transformation, affecting only the pyrene emission in intensity from pyrene in OTHO5/DAE8o (high concentration of
OTHO5) and UV exposure (isomerizing DAE8 quantitatively to DAE8 results in a too low intensity) and the emission intensity
the closed fluorescent isomeric form without affecting the from DAEc in OTHO5/DAE8c (low concentration of DAE8
2
ꢀ4
intrinsic pyrene emission in OTHO5) there will be 4 (2 ) distinct results in a too low intensity). A concentration of 10 M was
states generated. These are OTHO5-Sol/DAE8o, OTHO5- optimal with respect to generating four distinct CIE coordinates
Gel/DAE8o, OTHO5-Sol/DAE8c, and OTHO5-Gel/DAE8c. Fig. 4A with maximal separation to yield a large spread in the observed
shows the overall emission spectra of OTHO5/DAE8 in these four emission colors. Fig. S6B (ESI†) exemplifies the response of the
situations. With the DAE in the open form (no UV exposure), system to differences in the concentration of DAE8.
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To test whether the emission from DAE8c was affected by
switching between the solution and gel state, the emission
spectra were recorded in the presence of an OTHO gelator
lacking the pyrene unit (OTHO3). The absorption and emission
profiles were unchanged between solution and gel state (Fig. S5
4 (a) B.-K. An, D.-S. Lee, J.-S. Lee, Y.-S. Park, H.-S. Song and S. Y. Park,
J. Am. Chem. Soc., 2004, 126, 10232; (b) B.-K. An, J. Gierschner and
S. Y. Park, Acc. Chem. Res., 2012, 45, 544; (c) Z. Zhao, J. W. Y. Lam
and B. Z. Tang, Soft Matter, 2013, 9, 4564; (d) Y. Hong, J. W. Y. Lam
and B. Z. Tang, Chem. Soc. Rev., 2011, 40, 5361.
5
(a) Y. Kamikawa and T. Kato, Langmuir, 2007, 23, 274; (b) C. Dou,
D. Chen, J. Iqbal, Y. Yuan, H. Zhang and Y. Wang, Langmuir, 2011,
f
and S6A, ESI† emission CIE coordinates: 0.644, 0.356, F = 0.25),
27, 6323; (c) N. Yan, Z. Xu, K. K. Diehn, S. R. Raghavan, Y. Fang and
demonstrating that the multi-colored emission system employs
truly orthogonal input triggers.
R. G. Weiss, Langmuir, 2013, 29, 793; (d) C.-B. Huang, L.-J. Chen,
J. Huang and L. Xu, RSC Adv., 2014, 4, 19538.
(a) T. Shu, J. Wu, M. Lu, L. Chen, T. Yi, F. Li and C. Huang, J. Mater.
Chem., 2008, 18, 886; (b) A. Das and S. Ghosh, Angew. Chem., Int. Ed., 2014,
53, 2038; (c) M. A. Castilla, B. Dietrich and J. D. Adams, Gels, 2018, 4.
(a) M. Irie, T. Fukaminato, K. Matsuda and S. Kobatake, Chem. Rev.,
6
7
In summary, a pyrene-modified OTHO that gelates in a
range of solvents has been devised. It manifests different
degrees of pyrene monomer and excimer emission in solution
and gel state owing to the self-assembly and disruption of the
excimer formation. Furthermore, a multi-color readout system
has been realized by combining the photophysical/spectral
changes that accompany the sol–gel transformation with a
fluorescent DAE photoswitch. The use of two highly orthogonal
inputs, heat and light, enables the bi-component OTHO/DAE
cocktail to generate four distinct emissive states. This is a
2014, 114, 12174; (b) S.-Z. Pu, Q. Sun, C.-B. Fan, R.-J. Wang and
G. Liu, J. Mater. Chem. C, 2016, 4, 3075; (c) T. Mosciatti, M. G. del
Rosso, M. Herder, J. Frisch, N. Koch, S. Hecht, E. Orgiu and
P. Samor `ı , Adv. Mater., 2016, 28, 6606.
8
9
(a) M. Morimoto, S. Kobatake and M. Irie, Adv. Mater., 2002,
14, 1027; (b) M. Morimoto, S. Kobatake and M. Irie, J. Am. Chem.
Soc., 2003, 125, 11080; (c) K. Higashiguchi, K. Matsuda, N. Tanifuji
and M. Irie, J. Am. Chem. Soc., 2005, 127, 8922; (d) T. J. Wigglesworth
and N. R. Branda, Chem. Mater., 2005, 17, 5473.
A. J. Myles and N. R. Branda, Adv. Funct. Mater., 2002, 12, 167.
powerful approach to multi-wavelength readout systems, offering 10 T. B. Norsten and N. R. Branda, J. Am. Chem. Soc., 2001, 123, 1784.
1
1 (a) S. Ishida, T. Fukaminato, D. Kitagawa, S. Kobatake, S. Kim,
T. Ogata and S. Kurihara, Chem. Commun., 2017, 53, 8268; (b) J. Chen,
P. Zhang, G. Fang, P. Yi, F. Zeng and S. Wu, J. Phys. Chem. B, 2012,
116, 4354; (c) L. Zhu, W. Wu, M.-Q. Zhu, J. J. Han, J. K. Hurst and
A. D. Q. Li, J. Am. Chem. Soc., 2007, 129, 3524; (d) S. Ishida,
T. Fukaminato, S. Kim, T. Ogata and S. Kurihara, Chem. Lett., 2017,
a situation where substantially more information can be encoded,
compared to the binary on–off situations displayed by systems
built on single fluorophore emission. Increasing the number of
3
inputs to three stimuli could potentially generate 8 (2 ) distinct
24
output states, although this becomes increasingly challenging
with mixed chromophore systems if orthogonal switching is
desired. Moreover, accessing a larger region of the CIE space
would undoubtedly add to the appeal, and could imply the
inclusion of a green emitter. Efforts along these lines are presently
being undertaken in our laboratory.
4
6, 1182; (e) K. Watanabe, H. Hayasaka, T. Miyashita, K. Ueda and
K. Akagi, Adv. Funct. Mater., 2015, 25, 2794; ( f ) S. Kim, S.-J. Yoon and
S. Y. Park, J. Am. Chem. Soc., 2012, 134, 12091; (g) J. Bu, K. Watanabe,
H. Hayasaka and K. Akagi, Nat. Commun., 2014, 5, 3799.
2 C. Li, Y. Zhang, J. Hu, J. Cheng and S. Liu, Angew. Chem., Int. Ed.,
2010, 49, 5120.
3 (a) S. A. D ´ı az, L. Giordano, T. M. Jovin and E. A. Jares-Erijman, Nano
Lett., 2012, 12, 3537; (b) S. A. D ´ı az, F. Gillanders, K. Susumu, E. Oh,
I. L. Medintz and T. M. Jovin, Chem. – Eur. J., 2017, 23, 263.
1
1
We gratefully acknowledge the Swedish Research council
(
VR and Formas) for funding and Carl-Tryggers foundation and 14 (a) H.-J. Kim, D. R. Whang, J. Gierschner, C. H. Lee and S. Y. Park,
Angew. Chem., Int. Ed., 2015, 54, 4330; (b) W. Tian, J. Zhang, J. Yu, J. Wu,
the Swedish Energy Agency for providing postdoc fellowships
for C.-W. H. and M. D. J., respectively. Chalmers Excellence
Initiative in Nano-science and Nanotechnology, Adlerbert Research
Foundation and Wilhelm and Martina Lundgren Research
Foundation are also acknowledged for funding.
J. Zhang, J. He and F. Wang, Adv. Funct. Mater., 2018, 28, 1703548.
5 (a) J. W. Chung, S.-J. Yoon, S.-J. Lim, B.-K. AnandS. Y. Park,Angew. Chem.,
Int. Ed., 2009, 48, 7030; (b) A. Kishimura, T. Yamashita and T. Aida, J. Am.
Chem. Soc., 2005, 127, 179; (c)D. Kim, J. E. KwonandS. Y. Park, Adv. Funct.
Mater., 2018, 28, 1706213; (d) Q. Chen, D. Zhang, G. Zhang, X. Yang,
Y. Feng, Q. Fan and D. Zhu, Adv. Funct. Mater., 2010, 20, 3244.
1
1
1
6 (a) M. B ¨a lter, S. Li, M. Morimoto, S. Tang, J. Hernando, G. Guirado,
M. Irie, F. M. Raymo and J. Andr ´e asson, Chem. Sci., 2016, 7, 5867;
(
b) G. Naren, C.-W. Hsu, S. Li, M. Morimoto, S. Tang, J. Hernando,
Conflicts of interest
G. Guirado, M. Irie, F. M. Raymo, H. Sund ´e n and J. Andr ´e asson, Nat.
Commun., 2019, 10, 3996.
7 C.-W. Hsu, C. Sauv ´e e, H. Sund ´e n and J. Andr ´e asson, Chem. Sci.,
There are no conflicts to declare.
2018, 9, 8019.
References
18 K. Uno, H. Niikura, M. Morimoto, Y. Ishibashi, H. Miyasaka and
M. Irie, J. Am. Chem. Soc., 2011, 133, 13558.
1
(a) P. Terech and R. G. Weiss, Chem. Rev., 1997, 97, 3133; (b) J. W. 19 (a) A. Axelsson, L. Ta and H. Sund ´e n, Eur. J. Org. Chem., 2016, 3339;
Steed, Chem. Commun., 2011, 47, 1379.
(a) C. D. Jones and J. W. Steed, Chem. Soc. Rev., 2016, 45, 6546;
b) E. R. Draper and D. J. Adams, Chem. Commun., 2016, 52, 8196;
c) Z. Sun, Q. Huang, T. He, Z. Li, Y. Zhang and L. Yi, Chem-
(b) L. Ta, A. Axelsson, J. Bijl, M. Haukka and H. Sund ´e n, Chem. – Eur.
J., 2014, 20, 13889; (c) A. Axelsson, L. Ta and H. Sund ´e n, Catalysts,
2015, 5, 2052; (d) C. Sauv ´e e, A. Str ¨o m, M. Haukka and H. Sund ´e n,
Chem. – Eur. J., 2018, 24, 8071.
2
(
(
PhysChem, 2014, 15, 2421; (d) S. Yagai and A. Kitamura, Chem. 20 P. Terech, D. Pasquier, V. Bordas and C. Rossat, Langmuir, 2000, 16, 4485.
Soc. Rev., 2008, 37, 1520; (e) Z. Ding, Y. Ma, H. Shang, H. Zhang and 21 J. B. Birks, D. J. Dyson, I. H. Munro and H. Flowers Brian, Proc. R.
S. Jiang, Chem. – Eur. J., 2019, 25, 315; ( f ) X. Wang, Z. Ding, Y. Ma,
Y. Zhang, H. Shang and S. Jiang, Soft Matter, 2019, 15, 1658; 22 (a) J. Matsui, M. Mitsuishi and T. Miyashita, J. Phys. Chem. B, 2002,
Soc. London, Ser. A, 1963, 275, 575.
(
2
g) X. Cao, Y. Li, Y. Yu, S. Fu, A. Gao and X. Chang, Nanoscale,
019, 11, 10911; (h) J. W. Steed, Chem. Soc. Rev., 2010, 39, 3686;
106, 2468; (b) T. Yamazaki, N. Tamai and I. Yamazaki, Chem. Phys.
Lett., 1986, 124, 326.
(
i) M.-O. M. Piepenbrock, G. O. Lloyd, N. Clarke and J. W. Steed, 23 (a) J. Lee, H. Jung, H. Shin, J. Kim, D. Yokoyama, H. Nishimura,
Chem. Rev., 2010, 110, 1960.
(a) S. S. Babu, V. K. Praveen and A. Ajayaghosh, Chem. Rev., 2014,
A. Wakamiya and J. Park, J. Mater. Chem. C, 2016, 4, 2784; (b) C. Wang,
Z. Wang, D. Zhang and D. Zhu, Chem. Phys. Lett., 2006, 428, 130.
3
1
14, 1973; (b) S. Wang, W. Shen, Y. Feng and H. Tian, Chem. 24 Fig. S10 (ESI†) demonstrates that eight distinct CIE coordinates can be
Commun., 2006, 1497; (c) S. Xiao, Y. Zou, M. Yu, T. Yi, Y. Zhou,
F. Li and C. Huang, Chem. Commun., 2007, 4758.
accomplished with three different stimuli. However, those CIE coordi-
nates are very close to each other due to the inefficient of FRET.
Chem. Commun.
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