A vinylogous Michael addition-triggered quadruple cascade reaction for the enantioselective generation of multiple quaternary stereocenters

Article abstract of DOI:10.1039/c8cc09219b

An efficient organocatalytic quadruple cascade reaction resulting in spiroxindole scaffolds bearing five quaternary stereocenters is reported. The complex cascade reaction is triggered by the scarcely explored vinylogous Michael addition of 3-alkylidene o

Full text of DOI:10.1039/c8cc09219b

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Photon-upconverting chiral liquid crystal:
significantly amplified upconverted circularly
polarized luminescence†
Cite this: Chem. Sci., 2019, 10, 172
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have been paid for by the Royal Society
of Chemistry
c
bd
Xuefeng Yang,ab Jianlei Han,b Yafei Wang
and Pengfei Duan
*
In this work, we demonstrate a room-temperature chiral liquid crystal which shows remarkable photon
upconverted circularly polarized luminescence (UC-CPL). Circularly polarized luminescent materials with
higher dissymmetry factor (glum) underpin the basis for future applications. Since most chiral organic
molecules have only a small glum, it is vital to explore a new pathway to amplify the glum of organic
compounds. Here, by dispersing a chiral emitter and a triplet donor into a room-temperature nematic
liquid crystal, highly efficient triplet–triplet annihilation-based photon upconversion (TTA-UC) and
UC-CPL were observed in the induced chiral nematic liquid crystal (N*LC). Moreover, this system could
simultaneously amplify the promoted circularly polarized luminescence (CPL) and the upconverted
circularly polarized luminescence. The dissymmetry factors glum of CPL and UC-CPL have been
amplified by three orders of magnitude and one order of magnitude, respectively.
Received 25th August 2018
Accepted 2nd October 2018
DOI: 10.1039/c8sc03806f
rsc.li/chemical-science
applications.33–38 Ordinarily, luminescence dissymmetry factor
glum is used to evaluate the level of CPL, whose value is in the
range of ꢀ2 to 2, and is dened as 2(IL ꢀ IR)/(IL + IR), where IL
Introduction
Photon upconversion, the process of converting low energy
photons into high energy photons is interesting, both from
a fundamental and application perspective. Particularly, due to
the wide potential applications ranging from energy to biology,
triplet–triplet annihilation-based photon upconversion (TTA-
UC, Fig. S1†) has attracted attention in recent years. To date,
TTA-UC has been demonstrated extensively in various matrices
including dilute solutions, non-volatile liquids, gels and poly-
mers.1–15 However, the emission behaviours in liquid crystals
were rarely reported. Researchers have tried to tune the emis-
sion direction or the stimuli-responsiveness of TTA-UC through
liquid crystal matrices.16–19 The chiroptical properties, e.g.
circularly polarized luminescence (CPL), of TTA-UC in liquid
crystals have never been explored.
and IR are the intensities of the le- and right-handed circularly
polarized emissions, respectively. Generally, for pure organic
chiral molecules, glum is extremely small within the range of
10ꢀ5 to 10ꢀ3. Thus, exploring new pathways to amplify the glum
of organic compounds is a vital issue in developing chiroptical
materials. Kawai and co-workers had demonstrated that
supramolecular self-assembly could remarkably enhance the
glum in chiral perylene bisimide systems.39,40 Tang and co-
workers had amplied glum by introducing the concept of
aggregation-induced emission (AIE).41 Very recently, we have
found that energy transfer in a hybrid system could signicantly
¨
amplify the glum value, including Forster resonance energy
transfer (FRET) and TTA-UC process.42,43 However, an effective
method to amplify the glum value of upconverted circularly
polarized luminescence (UC-CPL) has never been reported.
In this work, we show the rst example of enhanced UC-CPL
emission in a chiral liquid crystal (N*LC). N*LC could be easily
obtained by blending a chiral emitter R(S)1 (Fig. 1) with an
achiral nematic liquid crystal, whose glum value was three orders
of magnitude higher compared with the dilute solution sample.
Subsequently, by mixing with an appropriate amount of sensi-
tizer, Pt(II)octaethyl porphyrin (PtOEP), both upconversion
emission and upconverted circularly polarized luminescence
(UC-CPL) could be observed. More importantly, compared with
the UC-CPL in dilute solution, the glum value of UC-CPL in the
N*LC was signicantly amplied by one-order of magnitude
(Fig. 1).
Circularly polarized luminescence has been attracting
increasing attention20–32 because of its remarkable advantages
including its extensive optical information and lack of angular
dependence, which has been widely used for various
aCollege of Chemistry, Key Lab of Environment-Friendly Chemistry and Application of
the Ministry of Education, Xiangtan University, Xiangtan 411105, P. R. China
bCAS Center for Excellence in Nanoscience, CAS Key Laboratory of Nanosystem and
Hierarchical Fabrication, Division of Nanophotonics, National Center for
Nanoscience and Technology (NCNST), No. 11 ZhongGuanCun BeiYiTiao, Beijing
100190, P. R. China. E-mail: duanpf@nanoctr.cn
cScience and Engineering, Jiangsu Collaboration Innovation Center of Photovoltaic
Science and Engineering, Changzhou University, Changzhou 213164, P. R. China
dUniversity of Chinese Academy of Sciences, Beijing 10049, P. R. China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c8sc03806f
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Fig. 1 N*LC could be obtained by doping chiral acceptor R(S)1 into the nematic liquid crystal, which could emit circularly polarized light by
excitation with a 360 nm light. The dissymmetry factor glum was amplified by three orders of magnitude compared with the diluted solution.
Subsequently both upconverted emission and upconverted circularly polarized emission could be observed sensitized by PtOEP. The glum value
of UC-CPL was amplified by one order of magnitude compared with the diluted solution.
logarithmic plots of the UC emission intensity with the weight
ratio of 10 wt% are shown in Fig. 2d. A slope change from 2 to 1
was clearly observed. The blue and red lines are the tting
Results and discussion
Upconversion behavior in a chiral liquid crystal
First, we fabricated a chiral nematic liquid crystal lm inside
a quartz cell by blending the following components: chiral
emitter R(S)1, sensitizer PtOEP and room-temperature nematic
liquid crystal SLC1717. Before exploring the upconverted
emission properties, we tested the absorption and emission
spectra of S1 and PtOEP in the liquid crystal (Fig. 2a). The S1 in
SLC1717 showed the typical vibrational structure of anthracene,
with its uorescence observed with a maximum at 465 nm,
which is a 20 nm red-shi compared with the spectrum in
toluene solution. On the other hand, PtOEP in SLC1717 (PtOEP/
S1 ¼ 1 mol%) exhibited characteristic Soret- and Q-bands at
385 nm and 535 nm, respectively. Phosphorescence was
observed at 655 nm, which is almost identical to that observed
in dilute solution. Thus, PtOEP could be molecularly dispersed
into the liquid crystal. Fig. 2b shows the N*LC lm aer irra-
diation using a 365 nm UV lamp and a 532 nm laser, respec-
tively. Cyan color emission could be observed from either the
uorescence emission or the TTA-UC emission. The emission
color of the fabricated neat lm showed a slight red-shi from
deep blue to cyan compared with the toluene solution (see the
ESI, Fig. S1†). To get the best UC emission in the liquid crystal,
we have carefully tested the UC emission and UC decay in
various mixing weight ratio samples. It should be noted that no
Fig. 2 (a) Normalized absorption and emission spectra of S1 (10 wt%,
birefringence could be observed using a polarizing optical
microscope (POM) when the weight ratio of S1/SLC1717 reached
40 wt% (see the ESI, Fig. S2†). Thus, the maximum weight ratio
of S1/SLC1717, in this work, was 30 wt%. Fixing the mixing
molar ratio of PtOEP/S1 at 1 mol%, by changing the weight ratio PtOEP/S1 ¼ 1 mol%). (c) Upconversion emission spectra of S1/PtOEP
of S1/SLC1717 from 5, 10, 20 to 30 wt%, UC emission spectra
with different incident power densities using the 532 nm laser
were investigated (Fig. 2c and S3, ESI†). It is clear that a 10 wt%
lex ¼ 360 nm) and PtOEP (1 mol%, lex ¼ 532 nm) in SLC1717. (b) The left
photograph of the neat film was irradiated by a 365 nm UV lamp, and
the right photograph was the upconverted emission sample irradiated
by a 532 nm laser (a short-pass filter was used; S1/SLC1717 ¼ 10 wt%,
with different incident excitation intensities of the 532 nm laser in
SLC1717. (d) Double-logarithmic plots of the UC emission intensity of
S1/PtOEP in SLC1717 as a function of the excitation intensity of the
laser. (e) UC quantum yield FUC of S1/PtOEP in SLC1717 as a function of
mixing ratio sample gave the maximum UC emission and the
minimum residual phosphorescence from PtOEP. Double-
the excitation intensity of the laser. (f) Time-resolved upconverted
emission at 470 nm of the S1/PtOEP in SLC1717 (black square), the tail
fit (red circle) (lex ¼ 532 nm).
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gTT;sol
results with slopes of 1.9 and 1.0 in the low and high excitation
intensity ranges, respectively. It involved the TTA process.44 The
threshold excitation intensity (Ith) was 254 mW cmꢀ2, where
TTA became the main deactivation channel for the acceptor
triplet, and consequently the UC quantum yield shows satura-
tion.45 A saturation quantum yield of about 13% was obtained
for S1/PtOEP in SLC1717 (10 wt%) by using Rhodamine B in
SLC1717 as a standard and with the theoretical maximum of
100% (Fig. 2e). These observations provide decisive evidence for
the TTA-UC mechanism in the liquid crystal.
The TTA-UC mechanism could also be conrmed by the
lifetime measurement. When the weight ratio of S1/PtOEP was
10 wt%, the UC emission lifetime at 470 nm was 182 ms, which is
ascribed to the mechanism based on long-lived triplet species
(Fig. 2f). The double-logarithmic plots and UC emission decay
of other weight ratios of S1/SLC1717 are shown in Fig. S4 and
S5,† respectively. In addition, aer comparing the lifetime of
the PtOEP in the TTA-UC process with the phosphorescence
lifetime of PtOEP in SLC1717, we obtained the other evidence to
a0 ¼
(3)
8pDsol
where second-order annihilation gTT,sol could be calculated
using the following equation:45
1
gTT;sol
¼
(4)
2
IthaFΤΤΕΤðsT;sol
Þ
The value of gTT,sol was calculated to be 1.3 ꢁ 10ꢀ11 cm3 sꢀ1
,
while the annihilation distance value a0 was calculated to be
1.2 nm. Considering that the annihilation distance for the
acceptor should be a constant value whether in solution or
liquid crystal, the triplet diffusion coefficient and diffusion
length could be calculated by
gTT;LC
DLC
¼
(5)
8pa0
In the liquid crystal, the second-order annihilation was
prove that 10 wt% was the best weight ratio of S1/SLC1717 for calculated to be gTT,LC ¼ 6.6 ꢁ 10ꢀ10 cm3 sꢀ1. Thus, DLC was
UC emission (see the ESI, Fig. S6†). Subsequently, we compared found to be 2.2 ꢁ 10ꢀ4 cm2 sꢀ1, while the triplet diffusion length
the triplet–triplet energy transfer (TTET) efficiency (FTTET) at LLC was 2.8 mm. As expected, DLC > Dsol, LLC > Lsol, that is to say,
different weight ratios (see the ESI, Table S1†). The FTTET could the capability of triplet diffusion in a liquid crystal is stronger,
be calculated by evaluating the phosphorescence decay before correspondingly the triplet diffusion length of the acceptor in
and aer adding the acceptor S1.46 Although the sample with the liquid crystal is longer than in the solution state. Moreover,
a low mixing weight ratio (5 wt%) showed the highest FTTET the average nearest-neighbor distance between two sensitizers
(90%), UC emission was not the best while even a higher Ith was calculated to be 115 nm.50 These results indicate that even
(517 mW cmꢀ2) was obtained (see the ESI, Fig. S4†).
better triplet diffusion and migration could be observed in the
To date, the TTA-UC in a liquid crystal has rarely been re- liquid crystal; due to the extremely high viscosity, molecular
ported. To carefully examine the triplet diffusion properties in collision was severely suppressed which resulted in the relatively
this kind of room-temperature liquid crystals, we have evalu- weak UC emission efficiency. However, the long diffusion length
ated these parameters in solution state (toluene) and liquid of the triplet was 2.8 mm in the liquid crystal, which was far
crystal phase. Considering the well-ordered structures in the enough to cover the average distance between two sensitizers
liquid crystal phase, the triplet diffusion length should be (115 nm). It is expected that the capability of the triplet acceptor
longer than that in solution. To prove this deduction, we diffusion in the liquid crystal is stronger than in the solution
calculated the triplet diffusion coefficient and diffusion length state, correspondingly the triplet diffusion length of the acceptor
in the liquid crystal (DLC, LLC) and in toluene (Dsol, Lsol). First, in the liquid crystal is longer than in the solution state.
the triplet diffusion coefficient Dsol could be calculated
according to the Stokes–Einstein relationship ([S1] ¼ 1 mM;
CPL behavior in a chiral liquid crystal
[PtOEP] ¼ 0.01 mM),47
Before we test the upconverted circularly polarized lumines-
kbT
Dsol
¼
(1)
cence (UC-CPL) in a chiral nematic liquid crystal, it is necessary
to explore the characteristics of promoted CPL in a N*LC. It has
been widely demonstrated that a N*LC can work as a self-
assembling one dimensional photonic crystal which could be
modulated by tuning the photonic stop band.19,51–53 However, in
this work, the stop band cannot be tuned to the visible light
range because of the weak helical twisting power (HTP) of the
chiral dopant. Anyhow, we have carefully checked the CPL
activity of various mixing weight ratios of S1/SLC1717 in the
liquid crystal cells. The tendency of the CPL dissymmetry factor
glum at different weight ratios of S1/SLC1717 is shown in Fig. 3a.
When the mixing weight ratio of S1/SLC1717 was 10 wt%, the
highest glum value (0.2) could be observed, the corresponding
mirror-image CPL and CD signals are shown in Fig. 3b and S7.†
It is already widely acknowledged that the handedness of
a N*LC could be determined by the CPL signal direction in that
6phR
where kb is the Boltzmann constant, T is the temperature (293
K), h is the viscosity of toluene at 293 K, and R is the molecular
˚
radius of the acceptor (8.5 A). The Dsol value (in toluene solu-
tion) was calculated to be 4.3 ꢁ 10ꢀ6 cm2 sꢀ1. The triplet
diffusion length Lsol could be calculated using the following
expression:48
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Lsol
¼
DsolsT;sol
(2)
where sT,sol is the lifetime of an acceptor excited triplet, namely
twice the value of the lifetime of the upconversion (568 ms). The
value of Lsol (in toluene solution) was calculated to be 0.49 mm.
The annihilation distance of the triplets (a0) could be calculated
by the equation49
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checked the inuence of different weight ratios of the acceptor
in a liquid crystal on the UC-CPL. The upconverted glum
exhibited the same tendency between promoted and upcon-
verted CPL (Fig. 4a), while the sample with 10 wt% mixing ratio
showed the highest upconverted glum value. As expected,
a mirror-image UC-CPL signal was observed under excitation by
a 532 nm green laser (Fig. 4b). It should be emphasized that the
UC-CPL signal was consistent with the CPL in the liquid crystal,
which indicated that the upconverted emission followed the
regulation of a N*LC. With increasing the excitation intensity of
the incident light, the UC-CPL increased. However, aer con-
verting to the glum value, the intensity was almost the same in all
emission ranges (Fig. 4c). Compared with the glum of UC-CPL in
dilute toluene solution, glum in the liquid crystal was one order
of magnitude higher (Fig. 4d). These results indicated that
whether it is promoted CPL or upconverted CPL, the optical
properties of N*LC play a critical role in determining the
emission properties.
Although the mechanism of photon upconversion amplied
circularly polarized luminescence in dilute solution is not clear,
the development of various approaches to further promote the
level of upconverted circularly polarized luminescence is
ongoing. The present liquid crystal system offers unprece-
dented opportunities for the efficient TTA-based upconversion,
circularly polarized emission and upconverted circularly polar-
ized emission. The use of room-temperature liquid crystals
allows exploring the luminescence and chiroptical properties in
the liquid crystal phase. The orientation of chiral acceptor
molecules in the N*LC enables highly efficient triplet energy
transfer and migration which might facilitate the TTA-UC. This
Fig. 3 (a) The tendency of CPL dissymmetry factor glum with different
weight ratios of S1/SLC1717 (lex ¼ 360 nm). (b) CPL spectra of 10 wt%
R(S)1 in SLC1717. R1 induced SLC1717 to a right-handed N*LC, S1
induced SLC1717 to a left-handed N*LC (lex ¼ 360 nm, |glum| ¼ 0.2). (c)
S1 in solution has the opposite glum value in the liquid crystal. The blue
square represents the glum of S1 in toluene solution ([S1] ¼ 10ꢀ5 M); the
red square represents the glum of 10 wt% S1 in the liquid crystal. The
values of glum in all emission ranges with intensity were almost the
same. (d) POM image of a chiral liquid crystal. The weight ratio of
S1/SLC1717 was 10 wt%.
a positive CPL signal indicates a right-handed chiral liquid
crystal while a negative CPL signal means a le-handed chiral
liquid crystal. Thus, it can be clearly claried that chiral emitter
R1 will induce the nematic liquid crystal to a right-handed N*LC
while the addition of S1 to SLC1717 will result in a le-handed
N*LC.54 It should be noted that the direction of the CPL signal
in the liquid crystal was opposite to the one in toluene solution,
which leads to the opposite value of glum (Fig. 3c). This could be
explained as follows. The CPL activity in solution should be due
to the intrinsic chiral emission property of the chiral emitter
R(S)1. However, aer dispersing into the nematic liquid crystal,
the nal CPL sign is decided by the handedness of the induced
N*LC. We have also checked the polarizing optical microscope
images of S1 in SLC1717 (Fig. 3d). The typical ngerprint texture
proved that the N*LC had been induced successfully by the
chiral emitter. In addition, we prepared the sample S1/SLC1717
with various mixing ratios from 5 to 30 wt% to measure the
X-ray diffraction (XRD) (see the ESI, Fig. S8†). The results indi-
cated that all mixing ratios showed similar diffraction patterns
to those of the original nematic liquid crystal SLC1717. There
was no obvious crystallization diffraction peak even at the high
mixing ratio of 30 wt%, which indicated that the dopant S1
could well disperse into the liquid crystal matrix. Differential
scanning calorimetry (DSC) revealed that the clearing point of
SLC1717 showed a slight decline when blending with the chiral
emitter (see the ESI, Fig. S9†).
Fig. 4 (a) The tendency of UC-CPL dissymmetry factor glum with
different weight ratios of acceptor in the liquid crystal (PtOEP/S1 ¼
1 mol%, lex ¼ 532 nm). (b) UC-CPL spectra of 10 wt% R(S)1 in SLC1717
with 1 mol% PtOEP, |glum| was nearly 0.04 (lex ¼ 532 nm). (c) UC-CPL
spectra of 10 wt% S1 with different incident power densities of
a 532 nm laser in a liquid crystal. The arrow indicates the spectral
changes with increasing incident power density from 15.3 to
31.6 W cmꢀ2. The corresponding glum value was almost the same as
the emission value. (d) UC-CPL dissymmetry factor glum versus
wavelength. The black square represents R(S)1/PtOEP in toluene
solution ([R(S)1] ¼ 10ꢀ5 M, lex ¼ 532 nm); the red square represents
Upconverted circularly polarized luminescence in a chiral
liquid crystal
The most interesting result in this work is that UC-CPL could be
signicantly amplied in a liquid crystal. Similarly, we have also R(S)1/PtOEP in SLC1717 (R(S)1/SLC1717 ¼ 10 wt%, lex ¼ 532 nm).
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will be a better complement to the system of triplet energy
migration-based photon upconversion (TEM-UC) which has
been extensively demonstrated by Kimizuka et al.55
In addition, the well-ordered chiral acceptor–acceptor
arrangements would facilitate the chiral emission and upcon-
verted chiral emission in this kind of liquid crystal phase. Thus,
the integration of a chiral nematic liquid crystal amplifying CPL
with TTA-based photon upconversion thus renovates the eld of
CPL-active functional materials and TTA-UC.
Characterization and methods
The sample used to investigate the UV-vis and uorescence
spectra, lifetime, upconversion emission and UC-CPL was
fabricated by the following method. Firstly, 1 mg S1 and 9 mg
SLC1717 were added into a 1 mL centrifuge tube, and then
mixed with 1 mL toluene. Aer that, the resulting solution was
sonicated for about 1 min to obtain a good solution. Finally,
400 mL of the solution was transferred into a quartz cell and
toluene was evaporated slowly using a vacuum pump. The thin
chiral nematic liquid crystal lm was generated in the inner
face of the quartz cell. It should be noted that evaporation of
toluene should be carried out at an appropriate velocity,
otherwise the generated chiral nematic liquid crystal will not be
uniform. The chiral nematic liquid crystal containing the PtOEP
was fabricated in the same way, 10.6 mL PtOEP (10ꢀ3 M) should
be added with 1 mg S1. The UV-vis spectra were recorded from
200 nm to 800 nm. Emission spectra were recorded with an
excitation wavelength of 360 nm. The samples were excited with
an incidence angle of 45ꢂ to the quartz cell surface and the
uorescence was detected along the normal. Time-resolved
upconverted emission spectra were measured with an excita-
tion wavelength of 532 nm laser and detected at 470 nm. The
upconverted lifetimes have been tted with a single exponential
decay. Spectra of UC emission and UC-CPL were measured with
the excitation wavelength of a 532 nm laser. The semiconductor
laser used in our experiment was bought from Changchun New
Industries Optoelectronics Technology Co., Ltd. The bandwidth
was < 0.2 nm, Gaussian beam in spatial mode TEM00, with
a polarization ratio of 1 : 100, the polarization direction being
horizontal. The sample used for CPL spectra was fabricated by
the following method. Firstly, 2 mg S1 and 18 mg SLC1717 were
dissolved in 1 mL toluene. Aer drying the toluene, N*LC was
added into the liquid crystal cell. CPL spectra were recorded
with the excitation wavelength of a 360 nm Xe-lamp. The sample
used for CD spectra and POM measurement was prepared by
the following method. 1 mg S1 and 9 mg SLC1717 were dis-
solved in 1 mL toluene. Subsequently, the resulting solution was
sonicated for about 1 min to obtain a solution. 50 mL of the
solution was transferred to a 0.1 mm quartz cell and the solvent
was evaporated. CD spectra were recorded from 200 nm to
800 nm. By casting the solution on a quartz plate, uniform lm
could be formed aer evaporating the solvent. The lm sample
could be used for POM measurement and XRD measurement.
Conclusions
In conclusion, the signicance of the present study is three-fold.
First, by adding the chiral acceptor molecule R(S)1 and the
sensitizer PtOEP into the nematic liquid crystal, highly efficient
TTA-UC could be observed in the N*LC. Moreover, efficient
triplet energy diffusion and long migration length were calcu-
lated in the liquid crystal for the rst time. Second, the N*LC
induced by the chiral emitter exhibited good promoted CPL,
while the corresponding dissymmetry factor glum was amplied
by three orders of magnitude to 10ꢀ1 compared with the solu-
tion state. Third, signicant amplication of UC-CPL could be
observed in this N*LC system. Upconverted dissymmetry factor
showed one order amplication. This work will promote the
design and fabrication of chiroptical materials with not only
better UC-CPL emission but also rational emission efficiency for
more practical application.
Materials and methods
Materials
The commercial room-temperature nematic liquid crystal,
SLC1717, was bought from the Chengzhi Yonghua Display
Material Co., Ltd. Pt(II)octaethyl porphyrin (PtOEP) was bought
from Frontier Scientic, Inc. Rhodamine B was bought from
Acros Organics.
Instrumentation
UV-vis spectra were recorded on a Hitachi U-3900 spectro-
photometer. Fluorescence spectra were measured on an
F-4500 uorescence spectrophotometer. CD and CPL spectra
were measured on JASCO J-1500 and JASCO CPL-200 spec-
trophotometers, respectively. Lifetime measurements were
recorded on the spectrometer using time-correlated single
photon counting (TCSPC). Upconverted emission spectra
were recorded on a Zolix Omin-l500i monochromator with
a photomultiplier tube PMTH-R 928 using an external exci-
tation source. POM images were recorded on a Leica
DM2700M upright materials microscope. Upconverted CPL
spectra were recorded on a JASCO CPL-200 spectrophotometer
Determination of TTA-UC quantum yield by a relative method
The upconverted emission quantum efficiency was determined
relative to a standard according to the following equation:
ꢀ
ꢁꢀ ꢁꢀ
ꢁ
2
Astd
IUC
hUC
hstd
FUC ¼ 2Fstd
AUC
Istd
with an external excitation source, a 532 nm semiconductor where F, A, I and h represent the quantum yield, intensity of
laser. DSC spectra were recorded on a PerkinElmer Diamond absorbance at 532 nm, integrated photoluminescence spectral
TG/DTA. XRD spectra were measured on a Panalytical Empy- prole, and refractive index of the solvents used as a standard,
rean. Quantum yield was measured on an Edinburg FLS-980 respectively. The subscripts UC and std denote the parameters
uorescence spectrometer with
sphere.
a
calibrated integrating of the upconversion and standard systems. Since the standard
and the UC dyes are doped in the same liquid crystal, the
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refractive indices are the same. Therefore, under our experi- 13 C. Fan, W. Wu, J. J. Chruma, J. Zhao and C. Yang, J. Am.
mental conditions, the upconverted emission quantum effi- Chem. Soc., 2016, 138, 15405–15412.
ciency FUC could be calculated using the equation. For the UC 14 C. Ye, L. Zhou, X. Wang and Z. Liang, Phys. Chem. Chem.
system, the weight ratio of S1/SLC1717 was 10 wt%, the molar Phys., 2016, 18, 10818–10835.
ratio of PtOEP/S1 was 1%. For the standard system, the 15 X. Cui, J. Zhao, Y. Zhou, J. Ma and Y. Zhao, J. Am. Chem. Soc.,
concentration of Rhodamine B was the same as the concen- 2014, 136, 9256–9259.
tration of PtOEP. The UC system was tested from 400 nm to 16 K. Borjesson, P. Rudquist, V. Gray and K. Moth-Poulsen, Nat.
530 nm, and the standard system was tested from 540 nm to Commun., 2016, 7, 12689.
750 nm. The UC quantum yield was determined relative to 17 Z. Jiang, M. Xu, F. Li and Y. Yu, J. Am. Chem. Soc., 2013, 135,
a standard, Rhodamine B in SLC1717 (Fstd ¼ 0.441) under 16446–16453.
532 nm excitation. The result of upconverted emission 18 K. Mase, Y. Sasaki, Y. Sagara, N. Tamaoki, C. Weder, N. Yanai
quantum efficiency was the mean value for parallel testing three
times.
and N. Kimizuka, Angew. Chem., Int. Ed., 2018, 57, 2806–
2810.
19 J.-H. Kang, S.-H. Kim, A. Fernandez-Nieves and
E. Reichmanis, J. Am. Chem. Soc., 2017, 139, 5708–5711.
20 L. Shi, L. Zhu, J. Guo, L. Zhang, Y. Shi, Y. Zhang, K. Hou,
Y. Zheng, Y. Zhu, J. Lv, S. Liu and Z. Tang, Angew. Chem.,
Int. Ed., 2017, 56, 15397–15401.
Conflicts of interest
There are no conicts to declare.
21 H. Nishimura, K. Tanaka, Y. Morisaki, Y. Chujo,
A. Wakamiya and Y. Murata, J. Org. Chem., 2017, 82, 5242–
5249.
22 R. Aoki, R. Toyoda, J. F. Koegel, R. Sakamoto, J. Kumar,
Y. Kitagawa, K. Harano, T. Kawai and H. Nishihara, J. Am.
Chem. Soc., 2017, 139, 16024–16027.
23 T. Goto, Y. Okazaki, M. Ueki, Y. Kuwahara, M. Takafuji,
R. Oda and H. Ihara, Angew. Chem., Int. Ed., 2017, 56,
2989–2993.
24 S. Huo, P. Duan, T. Jiao, Q. Peng and M. Liu, Angew. Chem.,
Int. Ed., 2017, 56, 12174–12178.
Acknowledgements
This work was supported by the Ministry of Science and Tech-
nology of China (2016YFA0203400, 2017YFA0206600), National
Natural Science Foundation of China (51673050, 51773021).
P. D. is grateful for the support of “New Hundred-Talent
Program” research fund from the Chinese Academy of
Sciences. Y. W. is grateful for the support of the Talent Project of
Jiangsu Specially-Appointed Professor.
25 Y. Shi, P. Duan, S. Huo, Y. Li and M. Liu, Adv. Mater., 2018,
30, 1705011.
Notes and references
1 S. Baluschev, T. Miteva, V. Yakutkin, G. Nelles, A. Yasuda and 26 E. M. Sanchez-Carnerero, F. Moreno, B. L. Maroto,
G. Wegner, Phys. Rev. Lett., 2006, 97, 143903.
2 T. N. Singh-Rachford and F. N. Castellano, Coord. Chem. Rev.,
2010, 254, 2560–2573.
A. R. Agarrabeitia, M. J. Ortiz, B. G. Vo, G. Muller and S. de
la Moya, J. Am. Chem. Soc., 2014, 136, 3346–3349.
27 T. Kimoto, N. Tajima, M. Fujiki and Y. Imai, Chem.–Asian J.,
2012, 7, 2836–2841.
3 J. Zhao, S. Ji and H. Guo, RSC Adv., 2011, 1, 937–950.
4 A. Monguzzi, R. Tubino, S. Hoseinkhani, M. Campione and 28 J. Han, J. You, X. Li, P. Duan and M. Liu, Adv. Mater., 2017,
F. Meinardi, Phys. Chem. Chem. Phys., 2012, 14, 4322–4332. 29, 1606503.
5 Y. C. Simon and C. Weder, J. Mater. Chem., 2012, 22, 20817– 29 J. Zhang, W. Feng, H. Zhang, Z. Wang, H. A. Calcaterra,
20830.
B. Yeom, P. A. Hu and N. A. Kotov, Nat. Commun., 2016, 7,
6 S. H. C. Askes, A. Bahreman and S. Bonnet, Angew. Chem., Int.
Ed., 2014, 53, 1029–1033.
7 Y. Y. Cheng, B. Fueckel, R. W. MacQueen, T. Khoury,
10701.
30 R. Carr, N. H. Evans and D. Parker, Chem. Soc. Rev., 2012, 41,
7673–7686.
R. G. C. R. Clady, T. F. Schulze, N. J. Ekins-Daukes, 31 F. Song, G. Wei, X. Jiang, F. Li, C. Zhu and Y. Cheng, Chem.
M. J. Crossley, B. Stannowski, K. Lips and T. W. Schmidt,
Energy Environ. Sci., 2012, 5, 6953–6959.
8 Z. Huang and M. L. Tang, J. Am. Chem. Soc., 2017, 139, 9412–
9418.
Commun., 2013, 49, 5772–5774.
32 H. Zheng, W. Li, W. Li, X. Wang, Z. Tang, S. X.-A. Zhang and
Y. Xu, Adv. Mater., 2018, 30, 1705948.
33 M. Schadt, Annu. Rev. Mater. Sci., 1997, 27, 305–379.
9 P. Duan, N. Yanai, H. Nagatomi and N. Kimizuka, J. Am. 34 C. Wagenknecht, C.-M. Li, A. Reingruber, X.-H. Bao,
Chem. Soc., 2015, 137, 1887–1894.
A. Goebel, Y.-A. Chen, Q. Zhang, K. Chen and J.-W. Pan,
10 V. Gray, D. Dzebo, M. Abrahamsson, B. Albinsson and
Nat. Photonics, 2010, 4, 549–552.
K. Moth-Poulsen, Phys. Chem. Chem. Phys., 2014, 16, 35 G. Muller, Dalton Trans., 2009, 9692–9707.
10345–10352.
36 M. C. Heffern, L. M. Matosziuk and T. J. Meade, Chem. Rev.,
11 S. P. Hill, T. Dilbeck, E. Baduell and K. Hanson, ACS Energy
Lett., 2016, 1, 3–8.
2014, 114, 4496–4539.
37 F. Zinna and L. Di Bari, Chirality, 2015, 27, 1–13.
12 R. Vadrucci, C. Weder and Y. C. Simon, Mater. Horiz., 2015, 38 Y. Yang, R. C. da Costa, M. J. Fuchter and A. J. Campbell, Nat.
2, 120–124.
Photonics, 2013, 7, 634–638.
This journal is © The Royal Society of Chemistry 2019
Chem. Sci., 2019, 10, 172–178 | 177

View Article Online
Chemical Science
Edge Article
39 H. Tsumatori, T. Nakashima and T. Kawai, Org. Lett., 2010, 47 P. Duan, N. Yanai and N. Kimizuka, Chem. Commun., 2014,
12, 2362–2365. 50, 13111–13113.
40 J. Kumar, T. Nakashima, H. Tsumatori and T. Kawai, J. Phys. 48 S. Hisamitsu, N. Yanai, H. Kouno, E. Magome, M. Matsuki,
Chem. Lett., 2014, 5, 316–321.
41 J. Liu, H. Su, L. Meng, Y. Zhao, C. Deng, J. C. Y. Ng, P. Lu,
T. Yamada, A. Monguzzi and N. Kimizuka, Phys. Chem.
Chem. Phys., 2018, 20, 3233–3240.
M. Faisal, J. W. Y. Lam, X. Huang, H. Wu, K. S. Wong and 49 J. Jortner, J. L. Katz, S. A. Rice and S. I. Choi, Phys. Rev. Lett.,
B. Z. Tang, Chem. Sci., 2012, 3, 2737–2747. 1963, 11, 323.
42 D. Yang, P. Duan, L. Zhang and M. Liu, Nat. Commun., 2017, 50 A. Ito, D. J. Stewart, T. E. Knight, Z. Fang, M. K. Brennaman
8, 15727. and T. J. Meyer, J. Phys. Chem. B, 2013, 117, 3428–3438.
43 J. Han, P. Duan, X. Li and M. Liu, J. Am. Chem. Soc., 2017, 51 D. Zhao, H. He, X. Gu, L. Guo, K. S. Wong, J. W. Y. Lam and
139, 9783–9786. B. Z. Tang, Adv. Opt. Mater., 2016, 4, 534–539.
44 A. Haefele, J. Blumhoff, R. S. Khnayzer and F. N. Castellano, 52 J. Schmidtke and W. Stille, Eur. Phys. J. B, 2003, 31, 179–194.
J. Phys. Chem. Lett., 2012, 3, 299–303.
53 A. L. Rodarte, C. Gray, L. S. Hirst and S. Ghosh, Phys. Rev. B,
45 A. Monguzzi, J. Mezyk, F. Scotognella, R. Tubino and
F. Meinardi, Phys. Rev. B, 2008, 78, 195112.
2012, 85, 035430.
54 T. Hamamoto and M. Funahashi, J. Mater. Chem. C, 2015, 3,
46 A. Monguzzi, M. Frigoli, C. Larpent, R. Tubino and
F. Meinardi, Adv. Funct. Mater., 2012, 22, 139–143.
6891–6900.
55 N. Yanai and N. Kimizuka, Chem. Commun., 2016, 52, 5354–
5370.
178 | Chem. Sci., 2019, 10, 172–178
This journal is © The Royal Society of Chemistry 2019