Amorphous metal-free roomerature phosphorescent small molecules with multicolor photoluminescence via a host-guest and dual-emission strategy

Article abstract of DOI:10.1021/jacs.7b12800

Metal-free roomerature phosphorescence (RTP) materials offer unprecedented potentials for photoelectric and biochemical materials due to their unique advantages of long lifetime and low toxicity. However, the achievements of phosphorescence at ambient condition so far have been mainly focused on ordered crystal lattice or on embedding into rigid matrices, where the preparation process might bring out poor repeatability and limited application. In this research, a series of amorphous organic small molecular compounds were developed with efficient RTP emission through conveniently modifying phosphor moieties to β-cyclodextrin (β-CD). The hydrogen bonding between the cyclodextrin derivatives immobilizes the phosphors to suppress the nonradiative relaxation and shields phosphors from quenchers, which enables such molecules to emit efficient RTP emission with decent quantum yields. Furthermore, one such cyclodextrin derivative was utilized to construct a host-guest system incorporating a fluorescent guest molecule, exhibiting excellent RTP-fluorescence dual-emission properties and multicolor emission with a wide range from yellow to purple including white-light emission. This innovative and universal strategy opens up new research paths to construct amorphous metal-free small molecular RTP materials and to design organic white-light-emitting materials using a single supramolecular platform.

Full text of DOI:10.1021/jacs.7b12800

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Amorphous Metal-Free Room-Temperature Phosphorescent
Small Molecules with Multicolor Photoluminescence
via a Host-Guest and Dual-Emission Strategy
Journal of the American Chemical Society is published by the American
Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American
Chemical Society. However, no copyright claim is made to original
U.S. Government works, or works produced by employees of any
Commonwealth realm Crown government in the course of their duties.

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Dengfeng Li, Feifei Lu, Jie Wang, Wende Hu, Xiao-Ming Cao, Xiang Ma, and He Tian
J. Am. Chem. Soc., Just Accepted Manuscript • DOI:
10.1021/jacs.7b12800 • Publication Date (Web): 04 Jan 2018
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Dengfeng Li, Feifei Lu, Jie Wang, Wende Hu, Xiao-Ming Cao, Xiang Ma* and He Tian
Key Laboratory for Advanced Materials and Institute of Fine Chemicals, Center for Computational Chemistry and
Research Institute of Industrial Catalysis, School of Chemistry and Molecular Engineering, East China University of
Science and Technology, Shanghai 200237, P. R. China
ABSTRACT: Metal-free room-temperature phosphorescence (RTP) materials offer unprecedented potentials for
photoelectric and biochemical materials due to their unique advantages of long lifetime and low-toxicity. However, the
achievements of phosphorescence at ambient condition so far have been mainly focused on ordered crystal lattice or on
embedding into rigid matrices, where the preparation process might bring out poor repeatability and limited application.
In this research, a series of amorphous organic small molecular compounds were developed with efficient
room-temperature phosphorescence (RTP) emission through conveniently modifying phosphor moieties to
β-cyclodextrin (β-CD). The hydrogen bonding between the cyclodextrin derivatives immobilizes the phosphors to
suppress the non-radiative relaxation and shields phosphors from quenchers, which enables such molecules to emit
efficient RTP emission with decent quantum yields. Furthermore, one of such cyclodextrin derivatives was utilized to
construct a host-guest system incorporating a fluorescent guest molecule, exhibiting excellent RTP-fluorescence
dual-emission properties and multicolor emission with a wide range from yellow to purple including the white-light
emission. This innovative and universal strategy opens up new research paths to construct amorphous metal-free small
molecular RTP materials and to design organic white-light emitting materials using a single supramolecular platform.
phosphors into solid substrate, silica glass,13 polymer
1
2
14-16
17-20
matrix,
and the cavity of macrocycle hosts.
RTP
Room-temperature phosphorescence (RTP) materials
have attracted significant research interest due to their
distinctive properties such as long decay lifetimes and the
emission could also be enhanced by embedding the
21
phosphor into poly (vinyl alcohol) (PVA) or poly (methyl
22
methacrylate) (PMMA) to suppress the vibrational
1
involvement of triplet states, which have been applied
dissipation. Amorphous rigid steroidal compounds have
also been applied to minimize the quenching of
long-lived triplet excited states and to achieve efficient
phosphorescence in pure organic amorphous guest
2
-4
widely in organic light-emitting diodes (OLED),
5
-6
7-8
chemical sensors,
bio-imaging,
and molecular
9-10
switches. Generally, most RTP materials are inorganic
or organometallic complexes containing noble metals.
Considering their expenses and toxicity, it is
indispensable to develop metal-free RTP materials with
low cost, versatile molecular design and good
processability. However, it is diffcult for these materials
to emit efficient RTP signals, since the energy of the
excited triplet states of organic molecules could be easily
lost through thermally vibrational and collisional process
or the exposure to the quenchers such as oxygen.
Therefore, the promotion of intersystem crossing (ISC)
efficiency and the suppression of the non-radiative
relaxation process predominate in the construction of
23-25
materials in air.
Recently, a unique pure organic
amorphous RTP system was developed by a simple radical
polymerization of acrylamide and organic phosphors
without extra processing, which could generate efficient
26
RTP emission. Until now, the research of pure organic
compounds emitting RTP have focused mainly on
crystallization-induced phosphorescence due to the rigid
framework for phosphor to retard its molecular
27-31
motion.
However, the demanding growth condition
along with the uncontrollable growth process has greatly
limited the development and application of the metal-free
RTP materials constructed from crystallization. This
indicates the centrality in designing and developing a
convenient and applicable strategy to obtain amorphous
1
1
pure organic RTP materials.
Based on the
aforementioned principles, several methods have already
been developed including the embedding of organic
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organic small molecular compounds with efficient RTP yellow-green light under 254 nm UV light with decent
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emission.
phosphorescent quantum yields (5.9%). The RTP
emission spectrum revealed that BrNp-β-CD was excited
to generate a strong emission peak at about 512 nm and
537 nm (Figure 2). The lifetime of the emission peak at 512
nm reached 1.85 ms, which further verified the RTP
emission (Figure S3). The other three compounds showed
similar properties with BrNp-β-CD and their
photophysical data were collected in Table 1. Comparing
the phosphorescence excitation spectra (Figure S4), we
found that the Stokes shifts of RTP emission reached over
Herein, we described a general design approach to
develop amorphous metal-free organic single compounds
with efficient RTP emission by modifying different
phosphors onto β-CD, which could effectively suppress
the non-radiative relaxation process and enhance the
quantum yield. Strong intermolecular hydrogen bonding
between cyclodextrins (CDs) restricts the vibration of
phosphors and shields phosphorescent moieties from
quenchers. Till now, such non-crystalline metal-free small
compounds with efficient RTP emission have not been
reported. Additionally, the cavity of β-CD was utilized to
incorporate small fluorescent molecules to construct
supramolecular system to engender multicolor emission
including white-light one which was realized through a
fluoroscence-phosphorescence dual-emission strategy.
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230 nm for BrNp-β-CD, 220 nm for BrNpA-β-CD, 200 nm
for both BrHB-β-CD and BrBp-β-CD, respectively, which
manifested their RTP emission characteristics. Moreover,
the X-ray powder diffraction (XRD) was used to explore
the microstructure of these compounds. The results
showed there was no significant crystal characteristics,
verifying their amorphous states (Figure 3). It could be
safely estimated that these pure organic compounds are
RTP emissive in the amorphous solid state rather than in
the solution or crystalline state, which makes them
convenient for both preparation and practical application.
To confirm the applicability of this approach, four
different CD derivatives were prepared which were
modified respectively by 6-bromo-2-naphthol (6-BrNp),
4
4
4
-bromo-4'-hydroxybiphenyl
-(4-bromophenyl)-pyridine
-bromo-1,8-napththalic anhydride (4-BrNpA) (Figure S1,
(4-BrHB),
and
(4-BrBp)
Supporting Information). The structures of these four
compounds were shown in Figure 1.
Figure 1. a) Molecular structures of RTP emissive
cyclodextrin derivatives (BrNp-β-CD, BrHB-β-CD,
BrBp-β-CD and BrNpA-β-CD) and fluorescent guest
molecule AC; b) schematic illustration of the
phosphorescence emission.
Figure 2. RTP emission spectra of a) BrNp-β-CD, b)
BrHB-β-CD, c) BrBp-β-CD and d) BrNpA-β-CD
(
phosphorescence mode; excitation slim =10 nm; emission
Synthesis.
slim =10 nm; excitation wavelength of a) 285 nm, b) 300
nm), c) 350 nm, d) 365 nm) in solid state. Inset:
luminescent delay lifetimes of a) BrNp-β-CD at 512 nm, b)
BrHB-β-CD at 500 nm, c) BrBp-β-CD at 500 nm and d)
BrNpA-CD at 585 nm. Photographs of the solid powder of
e) BrNp-β-CD, BrHB-β-CD, BrBp-β-CD under 254 nm
UV light and BrNpA-β-CD under 365 nm UV light.
Mono[6-O-(4-methyl-phenylsulfonyl)]-β-cyclodextrin
(6-OTs-β-CD) or 6-amino-β-cyclodextrin (6-NH -β-CD)
2
was reacted with the organic phosphorescent functional
groups to yield RTP-emissive cyclodextrin derivatives.
The guest molecule AC was obtained through alkylation
coupling between coumarin and amantadine and
subsequent protonation by hydrochloric acid.
Photophysical properties of CD derivatives. As
anticipated, a strong RTP emission was observed from the
four CD derivatives in the amorphous solid state. Their
fluorescence emissions were weak because of the
heavy-atom effect from the Br substitutes. As shown in
Figure 2, the BrNp-β-CD powder emitted visible
Mechanism analysis for the enhancement of RTP
emission. The previous reports revealed that the
orientation of phosphorescent emission at room
temperature could be attributed to both the internal
factors such as the molecular structure design for efficient
2
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Table 1. Photophysical data of BrNp-β-CD, BrHB-β-CD,
BrBp-β-CD and BrNpA-β-CD.
amorphous state. Figure 4 and Figure S5 showed that the
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frontier molecular orbits of CD derivatives and their
corresponding phosphors mainly concentrated on the
phosphor moieties, indicating that CD was not involved
in the efficient spin-orbital coupling. More was found
through comparing the energy levels of the singlet and
triplet excited states of the phosphors and the coupled
λ
ex
λ
em
τ
p
Φ
p
Compound
[nm]
[nm]
[%]
[ms]
BrNp-β-CD
BrHB-β-CD
BrBp-β-CD
BrNpA-β-CD
285, 327 512, 537 1.85
5.9
300
340
365
500
500
585
0.96 2.8
2.67 16.9
CD derivatives that the energy gap (ΔEST) between S
1
and
T
1
was nearly unchanged with a moderate value, which
3
3
was favorable for the ISC process. This highlighted the
critical role of the matrix roles in the process of RTP
emission. The potential hydrogen bonding environment
was also studied to develop insights into the matrix part
and the hydroxy group around the CD molecules. The
hydrogen bonding between the adjacent CDs might
immobilize the phosphorescent moieties to suppress the
1.27
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vibrational dissipation and provide
a
secluded
environment away from oxygen to a certain degree. Since
the hydrogen bond could be broken during dissolution in
the
relatively
polar
solvent,
an
N,
N-dimethylformamide/ethyl acetate (DMF/EA) mixed
soluble/insoluble solvent system was applied to study the
effect. Specific concentration of BrNp-β-CD suspension
(
0.3 mg/mL) was prepared with different ratios of the
Figure 3. X-ray powder diffraction (XRD) patterns of
BrNp-β-CD, BrHB-β-CD, BrBp-β-CD and
AC@BrNp-β-CD powder (molar ratio AC: BrNp-β-CD =
:1).
mixed solvents ranging from 0 to 0.3 (volume ratio). As
shown in Figure 5, the RTP emission decreased
remarkably with the increase of the DMF content when it
was irradiated with 254 nm light. Similar characters
applied to BrHB-β-CD, BrBp-β-CD and BrNpA-β-CD,
which demonstrated the conclusion above. Besides,
1
spin-orbital coupling32 and the external factors such as
the environmental matrix for the suppression of
6
-BrNp was mixed with its equivalent of β-CD and
1
5
non-radiative decay. Furthermore, it could be inferred
that cyclodextrin was least likely to promote the ISC
process, since, without its unsaturated group, it could
hardly participate in the electron transition process. To
confirm the influence of cyclodextrin unit on the
methyl-β-cyclodextrin (Me-β-CD) in DMF respectively
before their powder was collected in vacuum. 6-BrNp
embedded with β-CD still exhibited obvious
phosphorescent emission due to the existence of
hydrogen bond between cyclodextrins. However, the RTP
emission of 6-BrNp became weak when embedded with
enhanced
TD)-B3LYP/6-311+G* calculations were implemented to
study the phosphors and four CD derivatives in the
RTP
emission
in
this
system,
(
Figure 4 Calculated HOMO and LUMO for the ground states and calculated energies for excited singlet state (S
1
), excited
triplet state (T
1
) and ΔEST for CD derivatives BrNp-β-CD, BrHB-β-CD, BrBp-β-CD and BrNpA-β-CD.
3
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Me-β-CD (Figure 6a). By analyzing the phosphorescence
NMR experiments were conducted to validate the
inclusion behavior. As presented in Figure S9, there were
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properties listed in Figure 6c, it could be deduced that the
hydrogen bonding atmosphere might benefit the
enhancement of the RTP emission by restricting the
vibration of phosphors to suppress the non-radiative
decay.
three sets of protons in the AD moiety marked as H
a
, H
b
1
c
and H . With the addition of BrNp-β-CD, the H NMR
signals corresponding to these protons broadened. H
proton shifted upfield (ΔδH = - 0.06 ppm) whilst H , H
protons downfield (ΔδH = + 0.02 ppm, ΔδH = + 0.04
ppm). This indicated that H proton has been deeply
included in the cavity while H , H protons remained at
the periphery of the wider rim of BrNp-β-CD. This was
a
a
b
c
6-BrNp and β-CD in the aqueous solution could form a
1:1 inclusion complex 6-BrNp@β-CD with a relatively low
b
c
a
-
1
constant of K
a
= 840 M , which would emit weak RTP
b
c
3
4
signals. Nevertheless, the pre-assembly of 6-BrNp with
β-CD (6-BrNp@β-CD) in the aqueous solution would
promote the densification of hydrogen bonding
surrounding for phosphors in the solid state. Figure 6
showed that the solid inclusion complex emitted stronger
RTP signals than in the random mixture. The 2D ROESY
NMR spectrum of BrNp-β-CD (Figure S7) showed weak
signals between the protons of 6-BrNp group and CD,
which implied that 6-BrNp might enter into the cavity of
CD. Therefore, it was also necessary to evaluate the
influence of the host-guest interaction in this solid system.
It is well known that the inclusion complexes formed by
β-CD and guests are influenced by the solvent effect
because of the hydrophobic property of the β-CD
4
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consistent with the previously reported literature.
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Furthermore, 2D ROESY NMR spectrum of the complex
AC@BrNp-β-CD in D2O showed strong ROE signals
between protons Ha-c and BrNp-β-CD (Figure S10). Few
other correlation signals were observed between the
protons of other aromatic rings and BrNp-β-CD. It was
definitely deduced that the cavity of BrNp-β-CD was only
occupied by the AD moiety. Another evidence to confirm
3
5-36
cavity
and normally instable in non-aqueous
3
7
solution. BrNp-β-CD was dissolved in dry DMF or H
2
O,
respectively, and then evaporated the solvents to get the
samples in vacuum. Figure S7 depicted the RTP spectra of
BrNp-β-CD powder obtained from the aqueous or
non-aqueous solution under the same test conditions,
which showed no obvious difference in their emission
intensities. Therefore, the hydrogen bonding interaction
dominates the enhancement of RTP intensity in our
designed molecules in this research, ascribed to the steric
hindrance obstructing the host-guest inclusion. With the
aim of demonstrating the role of modification in the
efficient RTP emission, the control experiments between
BrNp-β-CD and the complex 6-BrNp@β-CD were
implemented. In comparison with the emission intensity
and the quantum yield, BrNp-β-CD manifested better
RTP-emissive property superior to the complex (Figure 6b
and 6c), which indicated that the covalent bonding from
modification could preferably restrict the activity of
phosphors to a great extent.
Application in multicolor materials including
white-light emitting ones. The cavity of CD derivatives
endows them with the ability to accommodate diverse
guest molecules. Adamantane (AD) derivatives can form
3
8-39
stable inclusion complexes with β-CD.
Based on the
properties above, a simple host-guest system was hence
developed, which consisted of BrNp-β-CD host and a
linear fluorescent guest molecule AC containing an AD
moiety and a coumarin unit at each end linked by a
(
CH2)4 alkyl chain. By mixing these two components in
Figure 5. Normalized RTP intensities of a) BrNp-β-CD at
512 nm, b) BrHB-β-CD at 500 nm, c) BrBp-β-CD at 500
nm and d) BrNpA-β-CD at 585 nm at different volume
mixing ratios of DMF/EA. The corresponding
photographs of a) BrNp-β-CD, b) BrHB-β-CD, c)
BrBp-β-CD under 254 nm irradiation and d)
BrNpA-β-CD under 365 nm irradiation.
the aqueous solution, host-guest complex
a
AC@BrNp-β-CD was obtained because of the firm
inclusion of AC in the cyclodextrin cavity of BrNp-β-CD.
A job’s plot by UV-Vis absorption spectroscopy was
conducted, confirming that BrNp-β-CD and AC
1
interacted in a 1:1 binding stoichiometry (Figure S8). H
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To investigate the optical properties of this complex,
the formation of the 1:1 host-guest complex was supported
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by Matrix-Assisted Laser Desorption/Ionization Time of
Flight Mass Spectrometry (MALDI-TOF-MS). A strong
peak at 1708.5961 corresponding to [AC + BrNp-β-CD –
Cl] was observed, showing an ideal match between the
calculated and measured mass peaks for the 1:1 host-guest
complex (Figure S11).
the absorption spectra were measured in an aqueous
solution. Figure S15 depicted the absorption spectra of
BrNp-β-CD, AC and AC@BrNp-β-CD as well as the
reference compound 6-BrNp. The spectrum of
AC@BrNp-β-CD showed the three sets of characteristic
absorption peaks at around 235 nm, 275 nm and 325 nm,
which belonged to the chromophore pieces contained in
AC@BrNp-β-CD compared with the reference compound
6-BrNp and AC. A more careful comparison revealed that
the intensity of the absorption peaks assigned to 6-BrNp
moiety increases due to the competitive inclusion of AC.
PL spectroscopy studies of AC@BrNp-β-CD assembled in
different ratio of two components in the solid state were
carried out. The PL spectra of the solid inclusion complex
+
As the demonstration of the actual formation of the
inclusion complex in solution cannot persuasively
guarantee its existence in the solid state, extra analytical
techniques are necessary for the characterization of
AC@BrNp-β-CD solid system, including FT-IR, TGA and
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SEM.
The FT-IR spectra of AC, BrNp-β-CD, the
physical mixture PM (AC and BrNp-β-CD with molar
ratio 1:1) and solid inclusion complex AC@BrNp-β-CD are
shown in Figure S12. For AC, the stretching frequencies of
N-H and C-H belonging to AD were observed in 3436.11
-
1
-1
cm and 2919.84 cm , respectively. However, most of
them diminished in intensity or even disappeared in
AC@BrNp-β-CD, suggesting that AC was involved into
the inclusion process. In contrast, the subtle
characteristic peaks of AC and BrNp-β-CD were shown on
the FT-IR spectrum of PM, which could be regarded as a
simple superimposition of the host and guest molecule.
TGA curves in Figure S13 showed mass losses indicating
the following orders of the thermal stability of the
samples: BrNp-β-CD > AC@BrNp-β-CD > PM > AC.
o
Compared with AC (ca. 226 C), the fact that a higher
o
decomposition temperature (ca. 256 C) needed for
AC@BrNp-β-CD suggests the formation of the inclusion
complex. SEM helps to evidence the morphological
changes related to the interactions between the
components in the solid inclusion complexes. As shown
in Figure S14, the SEM images of BrNp-β-CD, AC, PM and
AC@BrNp-β-CD revealed a completely different shape
and size between AC@BrNp-β-CD and PM, which
reflected the formation of solid inclusion complex.
Figure 7. a) PL emission spectra of AC@BrNp-β-CD
(different molar ratio BrNp-β-CD:AC); b) the
yellow/purple (Y/P) emission intensity ratio and c)
calculated
PL
emission
color
coordinates
of
AC@BrNp-β-CD in the CIE 1931 chromaticity diagram as
a function of BrNp-β-CD:AC (molar ratio 0:1, 4:1, 6:1, 8:1
and 10:1, respectively). d) PL emission spectra of
AC@BrNp-β-CD (molar ratio BrNp-β-CD:AC =10:1, using
different excitation wavelength), e) the yellow/purple
Figure 6. RTP emission spectra of a) mixtures 6-BrNp:
β-CD and 6-BrNp:Me-β-CD (molar ratio 1:1) powder
prepared from DMF solution and b) BrNp-β-CD and the
complex 6-BrNp@β-CD (1:1) powder obtained from mixed
(
Y/P) emission intensity ratio and f) calculated PL
emission color coordinates in the CIE 1931 chromaticity
diagram as a function of excitation wavelength (285, 295,
solution (ethanol (v): H
and quantum yield (Φ ) of solid samples mentioned above.
Excitation voltage for a) 600 V, b) 500 V; excitation slim =
0 nm; emission slim = 10 nm; excited at 285 nm.
2
O (v) = 1:9). c) RTP lifetime (τ
p
)
p
3
05, 315, 325, 335, 345 and 355 nm); g) photographs of AC,
AC@BrNp-β-CD and BrNp-β-CD under daylight and UV
irradiation, respectively. All the measurements were
carried out in the solid state.
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AC@BrNp-β-CD were found to show noticeable broad fluorescent guest ones to successfully generate
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dual emission peaks, recognized as the emission of
coumarin group at 400 nm (blue-purple band) and the
BrNp group emission at 512 nm and 537 nm (yellow-green
band) (Figure 7). As showed in Figure S16, the blue-purple
emission is excited at 330 nm, whereas the excitation for
the yellow-green emission was at 285 nm and 327 nm.
Furthermore, the PL emission of the solid powder of AC
was found to emit at 400 nm when excited at 360 nm. On
the basis of the PL spectra above, it could be legitimately
inferred that the dual emissions of AC@BrNp-β-CD
originate from AC and BrNp-β-CD.
white-light emission by using the host-guest interaction.
Additionally, this system exhibits unique dual emission
bands in the solid state. It can be modulated in a dual
model by altering the proportion of BrNp-β-CD and AC
and the excitation wavelength, which may contribute to
the prospect of the multicolor emitting materials.
Supporting Information. The detailed experiments,
computational simulation and additional spectroscopic
data. This material is available at http://pubs.acs.org.
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Additionally, how to modulate the PL emission was also
investigated by tuning the molar ratio of the two
components AC and BrNp-β-CD or by turning the
excitation wavelength. The pre-organization of
BrNp-β-CD:AC with different molar ratios generated a
series of powder with muticolor emission (including
white-light one) under the UV irradiation. The emission
spectroscopy studies revealed that the intensity of the
yellow-green band increased gradually at the expense of
the intensity of the blue-purple band as a function of
BrNp-β-CD:AC (Figure 7). The variation of excitation
wavelength led to different emissions of the host-guest
complex. When BrNp-β-CD was excited using the light
above 350 nm, its RTP emission became negligible.
Similar results could be observed in the complex
consisting of BrNp-β-CD and AC, which primarily
emitted the blue-purple light emission upon light
irradiation at 365 nm. When excited at diverse excitation
wavelengths, the PL emission of the complex with
different ratios corresponding to a CIE coordinate and the
values were collected in Table S1. Interestingly, almost
pure white-light emission with the CIE coordinates
calculated as (0.29, 0.33) was realized when BrNp-β-CD
incorporated with 0.1 equivalent of AC under the
excitation at 295 nm (Figure 7). Ascribed to the modest
water solubility, BrNp-β-CD was sensitive to ambient
humidity and hence emitted intensity-variable RTP when
*
maxiang@ecust.edu.cn
#
These two authors (D. Li and F. Lu) contributed equally
to this work.
We gratefully acknowledge the financial support from
NSFC/China (21788102, 21722603, 214210004, 21476075 and
21790361), Programme of Introducing the Talents of
Discipline to Universities (B1607), Innovation Program of
Shanghai Municipal Education Commission and the
Fundamental Research Funds for the Central Universities
(WJ1514309 and 222201717003). The authors also thank
Miss J. Wu for helping draw figures, Dr. Q. Zhang and Dr.
H. Chen for helpful discussions, and Dr. X. Rao for
refining the manuscript.
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O solution
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Figure S17). AC@BrNp-β-CD retained the properties of
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white-light emitting materials,
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