Fine-Tuned Visible and Near-Infrared Luminescence on Self-Assembled Lanthanide-Organic Tetrahedral Cages with Triazole-Based Chelates

Article abstract of DOI:10.1021/acs.inorgchem.9b00756

The construction of well-defined lanthanide complexes emitting in both the visible and near-infrared regions is of great importance due to their widespread applications in phosphors, light-emitting diodes, biosensors/probes, optical communications, etc. I

Full text of DOI:10.1021/acs.inorgchem.9b00756

Article
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
Fine-Tuned Visible and Near-Infrared Luminescence on Self-
Assembled Lanthanide-Organic Tetrahedral Cages with Triazole-
Based Chelates
†
,‡,§
Xiao-Qing Guo,†,‡,§ Li-Peng Zhou,† and Qing-Fu Sun*,†,‡
Shi-Yu Wu,
†State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of
Sciences, Fuzhou 350002, People’s Republic of China
‡
University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
*
S Supporting Information
ABSTRACT: The construction of well-defined lanthanide
complexes emitting in both the visible and near-infrared
regions is of great importance due to their widespread
applications in phosphors, light-emitting diodes, biosensors/
probes, optical communications, etc. In comparison to the
well-known mononuclear and dinuclear lanthanide complexes,
multinuclear lanthanide supramolecular edifices with bright
luminescence are still scarce. Herein, we report the
coordination self-assembly of strongly luminescent lantha-
nide-organic tetrahedral Ln4L4 cages with a series of
tris(tridentate) ligands based on the triazole chelates.
Among them, the new ligand L3 with triazole-pyridine-
triazole (TPT) chelates manifests an excellent sensitization toward all of the lanthanide ions (Ln = Pr, Nd, Sm, Eu, Tb, Dy, Ho,
Er, Tm, Yb) that emit in both the visible and near-infrared regions, with a record luminescent quantum yield for Tb (L3) (Φ =
4
4
8
2%) being obtained. In contrast, ligands with amido-pyridine-triazole (APT) or TPA chelates show much weaker sensitization
ability. Energy levels for all ligands were measured, and TD-DFT calculations were employed to shed light on the sensitization
mechanism. Finally, white-light emission systems formed by combining the desired luminescent compounds have been
demonstrated. Our strongly luminescent LOPs provide new candidates for photochemical supramolecular devices.
1
4,15
INTRODUCTION
coordinating solvent molecules.
So far, NIR-emitting
■
lanthanide (Ln = Pr, Nd, Sm, Dy, Ho, Er, Tm, Yb) complexes
often suffer from relatively low intensity and short lifetime in
comparison to their visible-emitting Eu and Tb counterparts.
Known strategies to enhance the NIR emission of lanthanide
Lanthanides, a series of peculiar elements in the periodic table
with similar atomic radii and chemical properties, hold unique
1
photophysical properties due to their shielded 4f electrons.
Sharp linelike emission bands, long lifetimes, and large Stokes/
anti-Stoke shifts of the lanthanide luminescence facilitate their
various applications, such as phosphors, light-emitting diodes,
biosensors/probes, and so on.
arising from the direct 4f−4f transitions of lanthanides are very
weak (with molar absorption coefficient ε < 10 M cm )
16,17
complexes include the use of fluorinated ligands
or d-block
18−20
metalloligands
as sensitizers.
2
−5
Coordination self-assembled 3D supramolecular cages have
received growing attention in the past decades, owing to their
versatile structures as exquisite edifices displaying distinct inner
However, the absorptions
2
−1
−1
21−29
6
space and diverse functional sites.
Various supramolecular
due to the Laporte symmetry-forbidden rules. As such,
cages based on transition metals have been designed and
stimulations of luminescence on inorganic lanthanide nano-
particles or clusters often suffer from low brightness (B = εΦ,
where Φ stands for the photoluminescent quantum yield) and
require the irradiation of a high-power laser source. On the
other hand, numerous strong luminescent lanthanide-organic
complexes, especially 3D lanthanide-organic frameworks, have
3
0−40
reported.
In sharp contrast, research on lanthanide-
41−44
directed self-assembly has clearly lagged behind,
because
7
of the lability and unpredictability of lanthanide coordination
numbers and geometries. Though supramolecular mononu-
clear clathrate compounds, bundles, and dinuclear helicates
45−49
8
−11
with lanthanides have been comprehensively investigated,
the rational design of 3D supramolecular lanthanide polyhedra
been reported,
where suitable ligands containing chromo-
phores with strong absorption are used to sensitize the
lanthanide through the so-called “antenna effect”.
50−53
12,13
is still in its infancy.
How-
ever, realization of the near-infrared (NIR) luminescence still
represents a great challenge in these lanthanide complexes due
to the vibrational quenching from organic ligands or
Received: March 15, 2019
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.9b00756
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1
Introduction of lanthanides into coordination self-assembly
will not only diversify the metallasupramolecular structures but
also bring new functionality. From 2015, we reported a series
of studies on the self-assembly of multicomponent supra-
molecular lanthanide edifices, including their ligand design
principles, stereoselectivity, ligand and metal self-sorting
(Figure 1A). H NMR spectra (Figure 1B,C) indicate the
formation of a single species with high symmetry. In contrast
43,53−62
behavior, luminescent photoswitching, and sensing.
Bright visible-emitting tetrahedral cages with Eu and Tb have
been realized by modification of the widely used pyridine-2,6-
diacarboxamide (pcam)-based ligands with oxazoline (L1) and
56,60
triazole (L2) chelating groups (Scheme 1).
In the latter
Scheme 1. Strongly Luminescent Lanthanide-Organic
Tetrahedral Ln L Cages Based on Tris(tridentate) Ligands
4
4
with Different Chelating Groups
case, an unprecedented photoluminescent quantum yield (Φ =
1
5
6.6%) for Eu (L2) was obtained. However, it is worth
Figure 1. (A) Self-assembly from L3 to Eu (L3) . H NMR spectra of
4
4
4
4
pointing out that the NIR emission of lanthanide-organic
polyhedra (LOPs) has been rarely discussed so far. These
precedents motivate our further study on the ligand effects
toward the luminescence of LOPs, especially on their NIR
emission properties.
(B) L3 (600 MHz, DMSO-d
(400 MHz, CD CN/CD OD, 298 K). (D) DOSY spectrum and (E)
ESI-TOF-MS measurement of Eu (L3) (OTf) with insets showing
6 4 4
, 298 K) and (C) Eu (L3) (OTf)12
3
3
4
4
12
8
+
the observed and simulated isotopic patterns for [Eu (L3) (OTf) ] .
4
4
4
Herein, we report fine-tuned luminescence on a series of
Ln L -type cages constructed by two new ligands (L3 and L4)
with the triphenyltriazine core. We find that the fully
conjugated L3, with TPT chelating groups, manifests excellent
sensitization ability toward all the emitting lanthanide ions (Ln
with free L3, the proton signals of the complex show clear
shifting and broadening after coordination with the para-
magnetic Eu ion. Protons on pyridine are shifted dramatically
upfield (Δδ = 1.2−2.7 ppm), and two protons on different
triazole groups display upfield shifts of 0.46 and 1.23 ppm,
4
4
=
Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb) covering both the
respectively. Moreover, H on the terminal isopropyl splits into
i
visible and NIR regions. A record luminescent quantum yield
two doublets with equal integrals, indicating their rigidified
for Tb (L3) is reached (Φ = 82%). As a control, L4 with an
orientation in line with the C -symmetry coordination
4
4
3
1
amido-pyridine-triazole (APT) chelate that differs from the
known L2 only in the relative position of the amido and
triazole groups exhibits weaker sensitization ability on the
LOPs. Finally, white-light emission systems have also been
obtained by combining the desired luminescent compounds.
geometry of Eu ion. A diffusion-ordered H NMR (DOSY)
spectrum also confirms the formation of a single species with a
radius of 1.01 nm as calculated by the Stokes−Einstein
−
10
2 −1
equation (diffusion coefficient D = 5.61 × 10 m s , Figure
1D). ESI-TOF-MS analysis further confirms the composition
of the complex, where a series of peaks corresponding to
RESULTS AND DISCUSSION
n+
■
[Ln
4
(L3)
4
(OTf)12‑n
]
are found with finely resolved isotope
Synthesis and Characterization. Ligands L3 and L4
distribution perfectly matching the simulated results (Figure
were straightforwardly synthesized from bridging C -symmetry
1E and Figure S73). Moreover, Ln (L3) shows good stability
3
4
4
I
2
,4,6-triphenyl-1,3,5-triazine and versatile arms by a Cu -
and solubility in common medium-polarity solvents, including
CH CN, CH OH, and CH NO (Figure S25). Thermogravi-
63
catalyzed azide−alkyne cycloaddition (CuAAC) reaction or
3
3
3
2
64
an HATU condensation reaction. Both ligands were fully
characterized by NMR and high-resolution ESI-TOF-MS (see
the experimental section in the Supporting Information for
details).
metric analysis (TGA) suggests that this cage remains stable
below 380 °C (Figure S91).
All other Ln (L3) species (Ln = Pr, Nd, Sm, Gd, Tb, Dy,
4
4
Ho, Er, Tm, Yb) and Ln (L4) (Ln = Sm, Eu, Gd, Tb, Dy)
4
4
Ligand L3 (1 equiv) was treated with Ln(OTf) (1.1 equiv)
were synthesized according to the above protocol, and their
structures were confirmed by a combination of NMR (for Ln =
Sm, Eu, Yb only) and high-resolution ESI-TOF-MS (see the
3
in a mixed CD CN/CD OD (v/v 4/1) solvent and stirred for
3
3
3
h at 50 °C, affording a homogeneous faint yellow solution
B
DOI: 10.1021/acs.inorgchem.9b00756
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
experimental section in the Supporting Information for
details).
Self-sorting is a very attractive topic within coordination-
5
4,65−67
driven self-assembly;
hence, we checked the self-sorting
1
behavior of ligands L3 and L4 with the lanthanide metals. H
NMR (Figure S92) and ESI-TOF-MS (Figure S93) suggest a
strong ligand self-sorting potential, but such a behavior is not
1
complete. No change was observed in H NMR when
Eu (L3) and Eu (L4) were blended together after 48 h
4
4
4
4
(Figure S92c), indicating the thermodynamic stability of these
cages. However, mixed-ligand self-assembly of L3, L4 ,and
Eu(OTf) showed that the self-sorted Eu (L3) and Eu (L4)
3
4
4
4
4
were the major products, along with some additional peaks
indicating that new species were also obtained, which were
found to be [Eu (L3) (L4)] and [Eu (L3)(L4) ] by ESI-
4
3
4
3
TOF-MS.
Single crystals of Eu (L3) and Eu (L4) suitable for X-ray
4
4
4
4
diffraction were obtained by slowly diffusing CH Cl into a
2
2
solution of the complex after roughly 2 weeks. As shown in
Figure 2, both complexes give rise to the standard tetrahedral
Figure 3. (A) UV−vis absorption, excitation, and fluorescence spectra
−
5
−5
of L3 (CH Cl , 1 × 10 M, λ = 330 nm)and L4 (CH Cl , 1 × 10
2
2
ex
2
2
M, λex = 366 nm); (B) Emission spectra of Ln (L3) complexes
4
4
−
5
(
CH CN, 1 × 10 M) in the visible region (Ln = Eu, Tb, Sm, Dy).
3
5
extinction coefficients ε > 10 at 320 nm (Figures S32 and
S34). Complexes with different lanthanides display shape-
similar absorption bands, suggesting that the nature of the
68
lanthanide ions only slightly affects their absorbance.
First of all, the photoluminescence of all the complexes with
L3 and L4 are systematically compared in the visible region
(
Table 1, Figure 3B and Figures S37−S48). L3 with the TPT
chelates could universally sensitize Eu, Tb, Sm, and Dy with
lifetimes of 2.711, 1.526, 0.14, and 0.028 ms, respectively. For
Eu (L3) , the characteristic emission bands (579, 593, 616,
Figure 2. Single-crystal X-ray structures of (A) Eu (L3) (OTf) and
4
4
12
(
B) Eu (L4) (OTf) (atom colors: red, Eu; yellow, C; white, H;
4 4 12
pink, O; blue, N).
4
4
6
49.5, 694 nm) of europium are observed under an excitation
5
7
of 330 nm, corresponding to the D → F (J = 0−4)
transitions. In comparison to the known Eu (L2) , the
0
J
structures with four C -symmetry ligands and four nine-
3
4 4
coordinated europium ions defining the faces and vertices,
respectively. Eu (L3) crystallizes in the C2/c space group with
introduction of the second triazole group gives no improve-
ment in the quantum yield of Eu (L3) (Φ = 22.5%).
4
4
4
4
half of the cage skeleton (two unique L3 and two Eu ions) in
the asymmetric unit. In contrast, Eu (L4) crystallized in a
However, L3 shows excellent sensitization ability on Tb (L3)
4 4
(Φ = 82%) and Sm (L3) (Φ = 3.2%). It is worth pointing out
4
4
4
4
space group of much higher symmetry (P4
̅
3n), so that only
that the quantum yield of Tb (L3) was a new record for
4 4
one-third of the L4 and Eu ions are located in the asymmetric
unit. The Eu−Eu distances in Eu (L3) and Eu (L4) are
multinuclear LOPs. In contrast, L4 with the APT chelates
displays relatively poor sensitization ability on the lanthanide
tetrahedra. For example, the quantum yield for Eu (L4) is
4
4
4
4
measured to be 19.0 and 16.9 Å, respectively. Thus, a larger
4
4
inner cavity for Eu (L3) is defined. Consistent with a previous
determined to be Φ = 8.9%. Meanwhile, the emission band of
4
4
6
0
report, the four metal centers on both tetrahedral cages
exhibit a cooperative ΔΔΔΔ or ΛΛΛΛ chirality. As none of
them crystallize in a chiral space group, two enantiomers
coexist in both crystals.
L4 could be clearly observed in the cases of Tb (L4) and
4
4
Sm (L4) . No characteristic luminescence of Dy is observed in
4
4
the case of Dy (L4) .
4
4
To gain further insight into the differences observed in
visible emission on the complexes, phosphorescence spectra of
Gd (L3) and Gd (L4) were tested at 77 K under an Ar
Photophysical Properties. The UV−vis absorption and
luminescence spectra of L3 and L4 are shown in Figure 3A.
The maximum absorption peaks of the two ligands are located
at 320 and 334 nm, with molar extinction coefficients (ε) of
4
4
4
4
atmosphere using gating technique, from which the triplet state
energy levels of L3 and L4 are estimated to be 22421 and
.83 × 10 and 6.11 × 104
4
M
−1
cm , respectively.
−1
20704 cm , respectively (Figures S50 and S51). The triplet
−1
69
1
Interestingly, the absorption of L4 shows a clear red shift
and relatively higher molar extinction coefficient in comparison
to L3. On excitation at 330 nm, the ligands’ fluorescence
spectra show maximum emission positions at 400 and 450 nm
for L3 and L4, respectively. UV−vis absorption spectra of
typical Ln (L3) and Ln (L4) complexes (Ln = Eu, Tb, Sm,
state energy level of L3 is higher than that of L2 (21858
−
1
60
−1
5
cm ) and 5221 cm higher than the energy level of D of
0
III
Eu , causing decreased sensitization efficiency. However, such
a high energy level of L3 better suits the emitting D energy
level of Tb (20500 cm ), with an energy gap of 1921 cm .
The much lower ligand level of L4 could only sensitize Eu and
Sm, and the energy gap is too small to sensitize Tb.
Nonetheless, in comparison to the previous oxazoline-based
5
4
III
−1
−1
4
4
4
4
Dy) were also measured and displayed very small red shifts
<13 nm) in comparison with the free ligands, with high molar
(
C
DOI: 10.1021/acs.inorgchem.9b00756
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 1. Photophysical Data for Typical Ln L Cages Emitting in the Visible Region
4
4
εmax (10 M cm−1
5
−1
)
λex (nm)
τ (ms)
Φsens (%)
Φoverall (%)
LOP
Eu (L3)4
3.059
2.057
4.061
2.426
4.284
332
330
333
330
365
2.711
1.526
0.14
0.028
1.913
45
22.5
82
3.2
2.9
8.9
4
Tb (L3)4
4
Sm (L3)4
4
Dy (L3)4
4
Eu (L4)4
4
22
5
6
Eu (L1) , Eu (L4) with the triazole chelates still has a
could only sensitize Nd, Sm, Dy, Er, and Yb and L4 could only
sensitize Nd, Sm, and Yb. Moreover, the most detectable NIR
spectra of Ln (L3) show a higher signal to noise ratio in
4
4
4
4
better luminescence quantum yield (from 1.4% to 8.9% under
the same experimental conditions). Thus, we conclude that
triazole is a better sensitization group in similar lanthanide-
organic tetrahedral systems.
4
4
comparison to Ln (L2) and Ln (L4) under the same
4
4
4
4
conditions.
NIR-emitting lanthanide complexes have attracted increas-
ing attention, as they are widely used for bioimaging, optical
TD-DFT Calculations. TD-DFT calculations were per-
formed to shed light on the relationship between the ligand
structures and the photoluminescent performances of our
lanthanide complexes. TD-DFT calculations and the exper-
imental UV−vis spectra are displayed in Figure S31. According
3
,9,70
communication, and so on.
However, research into the
NIR emission properties of multinuclear lanthanide supra-
molecular cages is still rare. Inspired by the thrilling
sensitization abilities of L3, isostructural Ln (L3) complexes
to the TD-DFT results, the calculated λ values of L2, L3,
4
4
max
with NIR-emitting lanthanide centers were synthesized. As
and L4 are located at 319, 317, and 331 nm, respectively,
which agree very well with the experimental λmax values (L2,
shown in Figure 4, the NIR emissions of Ln (L3) (Ln = Dy,
4
4
315 nm; L3, 320 nm, L4, 334 nm). The LUMOs of L2 and L3
focus on the central triphenyltriazine groups, while the LUMO
of L4 extends to the peripheral pyridine groups. The HOMOs
of L2 and L3 dominate on the tridentate chelates, while the
HOMO of L4 is located on the phenyl rings (Figure 5A,B).
Figure 4. Emission spectra of the Ln (L3) complexes (CH CN, 1 ×
4
4
3
−
5
1
0
M) in the NIR region (Ln = Tm, Dy, Sm, Yb, Ho, Pr, Nd, Er).
Tm, Nd, Sm, Yb, Pr, Er) are distinctly observed with the main
character emission peaks corresponding to each lanthanide ion
(
for details see Figures S62−S69 and Table S3). For example,
Nd (L3) and Yb (L3) exhibit characteristic NIR emission
bands at 1068 and 978 nm, corresponding to the F → I
11/2
and F → F transitions, respectively. In all cases, the NIR
4
4
4
4
4
4
3/2
2
2
5
/2
7/2
lifetimes concentrate on a microsecond scale, and the
maximum lifetime of 142 μs is noted for Sm (L3) .
4
4
Perfluorinated ligand and d-block sensitizers have been
proven successful to improve lanthanide NIR emission. From
the above results, we propose that the use of a fully conjugated
rigidified ligand provides an alternative strategy to improve the
NIR emission. To test this assumption, the NIR spectra of
Ln4L4 (L = L2, L3, L4) are compared (Table 2). For
Ln (L3) , the distinct characteristic peaks of all eight
Figure 5. TD-DFT (B3LYP\6−31G*) calculated (A) LUMOs and
(B) HOMOs and the charge density transfer diagrams (red, electronic
increase; blue, electronic decrease) corresponding to the (C)
strongest absorption bands of L2, L3, and L4.
4
4
lanthanides are observed. The weakest signal is noticed for
Ho (L3) , but still a clear emission band is noticed at 974 nm,
4
4
7
1
5
5
The charge density transfer diagrams corresponding to the
strongest absorption bands also suggest that the presence of
the inner amido group on L4 has a dramatic influence on the
electron transfer directions from central triphenyltriazine
chromophores to peripheral chelates (Figure 5C), which may
have a great effect on the energy transfer from the ligands to
the lanthanide centers.
corresponding to its F → I transition. In clear contrast, L2
5
7
Table 2. Comparison of the NIR Emission on Ln L with
4
4
Triazole-Based Ligands
NIR emission
Pr
Nd
Sm
Dy
Ho
Er
Tm
Yb
White-Light Emission. White-light-emitting diodes
WLEDs) have attracted a great deal of attention in recent
In principle, an ideal white-light-emitting material
should meet three main requirements: CIE coordinates (0.33,
L2
L3
L4
×
√
×
√
√
√
√
√
√
√
√
×
×
√
×
√
√
×
×
√
×
√
√
√
(
72−75
years.
D
DOI: 10.1021/acs.inorgchem.9b00756
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
.33), a color rendition index (CRI) exceeding 80, and a
Article
0
CONCLUSIONS
■
correlated color temperature (CCT) between 2500 and 6500
In summary, the luminescent properties of supramolecular
lanthanide cages have been thoroughly investigated with a
series of ligands featuring the triazole-based chelates. A record
high luminescence quantum yield (Φ = 82%) in the visible
region for a terbium cage was reached among all multinuclear
LOPs. Moreover, a fully conjugated rigid ligand that can
universally sensitize the LOPs luminescence spanning the
visible and NIR regions was obtained. This study offers
important design principles toward strongly NIR emitting
LOPs. Moreover, these strongly luminescent LOPs provide
new candidates for photochemical supramolecular devices.
7
6
K. In addition, color stability, reproducibility, and quantum
yield of the materials are also crucial for practical WLED
application. Some pioneering works using lanthanides as
77−79
stabilized light source have been reported.
Recently,
Gunnlaugsson’s group reported the design of white-light
emitters based on directed self-assembly of two f metals in
solution, resulting in a successful emission of white light with
80
CIE coordinates of (0.33, 0.34). Due to the unpromising
luminescence of previous LOPs architectures, their white-light
regulation has never been studied before. Thus, the high
quantum yields of our LOPs persuaded us to further study
their WLE potentials.
ASSOCIATED CONTENT
■
In view of the weak blue emission performance of Gd L , we
4
4
*
S
Supporting Information
decided to choose the ligands as the blue-ray source. First of
all, the quantum yields of all the ligands were determined and
the best value was obtained for L2 (Φ = 5.1%; Φ = 1.7%;
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.9b00756.
L2
L3
Φ
= 1.6%). Then, the concentration-dependent lumines-
cence of L2 was measured to determine its blue-emitting
performance in solution. An optimal concentration of 140 μM
L4
Additional synthetic and structural details, crystallo-
graphic data, and additional figures and tables as
described in the text (PDF)
in CH Cl /CH OH (v/v 1/1) was confirmed, above which the
2
2
3
broad featureless excimer luminescent band (at ca. 490 nm)
became apparent (Figure S70). Under this condition, the CIE
coordinates for the emission of the ligand was calculated to be
Accession Codes
CCDC 1903502 and 1903518 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(
0.24, 0.27). Then the red Eu (L2) and green Tb (L2)
4 4 4 4
emitters, with CIE coordinates of (0.65, 0.34) and (0.36, 0.54),
respectively, were added to the ligand solution. Finally, the CIE
coordinates for [Eu (L2) ] [Tb (L2) ][L2] in CH Cl /
4
4 2
4
4
35
2
2
CH OH (v/v 1/1) solution was determined to be (0.33,
3
0
.33), which is the ideal value for a WLE system (Figure 6).
AUTHOR INFORMATION
■
Corresponding Author
E-mail for Q.-F.S.: qfsun@fjirsm.ac.cn.
*
ORCID
Li-Peng Zhou: 0000-0003-3820-2591
Qing-Fu Sun: 0000-0002-6419-8904
Author Contributions
§
S.-Y.W. and X.-Q.G. contributed equally.
Notes
The authors declare no competing financial interest.
Figure 6. (A) White-light emission of [Eu (L2) ] [Tb (L2) ][L2]
35
4
4
2
4
4
in CH Cl /CH OH (v/v 1/1) solution excited at 347 nm. (B) Shifts
ACKNOWLEDGMENTS
2
2
3
■
of the CIE coordinates for [Eu (L2) ] [Tb (L2) ] [L2] with
4
4
x
4
4
y
35
This work was supported by the National Natural Science
Foundation of China (Grant Nos. 21825107, 21601183),
Natural Science Foundation of Fujian Province (Grant No.
different amounts of [Eu (L2) ] and [Tb (L2) ] added (A, 0, 0; B,
4
4
4
4
0
.5, 0.25; C, 1, 0.25; D, 1, 0.25; E, 2, 0.625; F, 2, 1) correspondingly
(c = 4 μM for Tb (L2) ).
4
4
2
016J05051), and the Strategic Priority Research Program of
the Chinese Academy of Sciences (Grant No. XDB20000000).
Generally, sharp emission of lanthanide compounds usually
leads to low CRI values. However, the broad emission of L2
can efficiently overcome this drawback, giving a higher CRI
value of 93 and moderate CCT of 4594 K. Moreover, the
absolute quantum yield for such a system in solution was
measured to be 8.0% by excitation at 347 nm. Moreover,
white-light emission from [Eu (L3) ][Tb (L3) ][L3] and
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