Stable deep blue organic light emitting diodes with CIE of y < 0.10 based on quinazoline and carbazole units

Article abstract of DOI:10.1016/j.cclet.2019.06.033

Achieving stable deep blue organic light emitting diodes (OLEDs) with narrow full width at half maximum (FWHM) and color gamut in the range of the commission International de L'Eclairage (CIE) of y ≤ 0.10 is still challenging in display and lighting appli

Full text of DOI:10.1016/j.cclet.2019.06.033

Accepted Manuscript
Title: Stable deep blue organic light emitting diodes with CIE
of y < 0.10 based on quinazoline and carbazole units
Authors: Bowen Li, Xiang’an Song, Xi Jiang, Zhiyi Li,
Fengyun Guo, Ying Wang, Liancheng Zhao, Yong Zhang
PII:
DOI:
Reference:
S1001-8417(19)30362-6
https://doi.org/10.1016/j.cclet.2019.06.033
CCLET 5064
To appear in:
Chinese Chemical Letters
Received date:
Revised date:
Accepted date:
19 April 2019
30 May 2019
18 June 2019
Please cite this article as: Li B, Song X, Jiang X, Li Z, Guo F, Wang Y, Zhao
L, Zhang Y, Stable deep blue organic light emitting diodes with CIE of y <
0.10 based on quinazoline and carbazole units, Chinese Chemical Letters (2019),
https://doi.org/10.1016/j.cclet.2019.06.033
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

Please donot adjust the margins
Communication
Stable deep blue organic light emitting diodes with CIE of y < 0.10 based on
quinazoline and carbazole units
Bowen Li a, Xiang’an Song a, Xi Jiang a, Zhiyi Li b, Fengyun Guo a, Ying Wang b, , Liancheng Zhao a,
Yong Zhang a,c *
a
School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China
b Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences,
Beijing 100190, China
c School of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450001, China
 Corresponding authors.
E-mail addresses: yongzhang@hit.edu.cn (Y. Zhang), wangy@mail.ipc.ac.cn (Y.Wang)
Graphical Abstract
We designed and synthesized three deep blue emitters via integrating asymmetric quinazoline (PQ) acceptor with weak donating
carbazole (Cz) donor, which exhibit deep blue emission with the maximum wavelength ≤ 450 nm and narrow FWHM ≈ 60 nm.
Significantly, the deep blue electroluminescence (EL) spectra of these three emitters-based OLED devices are very stable, and the
corresponding CIE coordinates deviation (ΔCIE (x, y)) can be negligible under the applied voltage ranging from 5 V to 9 V.
ARTICLE INFO
Article history:
Received 20 April 2019
Received in revised form 30 May 2019
Accepted 13 June 2019
Available online
ABSTRACT
Achieving stable deep blue organic light emitting diodes (OLED) with narrow full width at half maximum (FWHM) and color gamut in the range of
the commission International de L’Eclairage (CIE) of y ≤ 0.10 is still challenging in display and lighting application. In this investigation, three donor-
acceptor (D-A) deep-blue emitters were designed and synthesized via integrating asymmetric quinazoline (PQ) acceptor with weak donating carbazole
(Cz) donor. The effect of the position and number of Cz group in PQ unit are investigated, which is also first examples for systematic research about
the effect of different position of asymmetric PQ as acceptor on deep OLED. Their bandgaps of 3.12~3.19 eV and the singlet state energy levels of
———

Please donot adjust the margins
3.12~3.19 eV were found to be sufficiently large to achieve deep blue light. As expected, these emitters-based OLED devices exhibit deep blue emission
with the maximum wavelength ≤ 450 nm and narrow FWHM ≈ 60 nm. Especially, a CIE of y = 0.080 was achieved for 4PQ-Cz- based OLED.
Significantly, the deep blue electroluminescence (EL) spectra of these three emitters-based OLED devices are very stable and the corresponding CIE
coordinates deviation (ΔCIE (x, y)) can be negligible under the applied voltage ranging from 5 V to 9 V.
Keywords:
Organic light-emitting diodes
Deep blue emitter
Quinazoline
Carbazole
Electroluminescence
Since the invention of OLEDs by Tang et al. in 1987 [1], they have attracted a great deal of attention because of the many advantage
of flexibility, image quality and contrast, and faster response times [2-7]. Although OLEDs have been commercialized in the mobile
phone, such as the fold-screen Huawei Mate X, and displaying, the development of new red, green, and blue-emitter is still essential,
especially deep blue emitting materials with CIE of y ≤ 0.10 [8-12]. Common properties, such as high efficiency, blue emission with
maximum wavelength ≤ 450 nm, and narrow FWHM ≤ 60 nm, are usually required for excellent blue emitters [2]. Up to now, much
efforts in blue emitters are focused on the development of high efficient phosphorescent and thermally activated delayed fluorescent
(TADF) materials owing to the possibility to harvest a theoretical internal quantum efficiency (IQE) of 100% [13-17], unfortunately,
the phosphorescent and TADF OLEDs hardly falls into the deep blue region with CIE of y ≤ 0.10 [18, 19], or even ≤ 0.08 [16]. In
addition, they often suffer from the poor color purity, high cost, and unstable EL spectra under the applied voltages [2, 15], which severely
limited the development of deep blue emitters. Therefore, it is essential to develop new stable deep blue emitting materials with CIE of
y ≤ 0.10, and to further extend deep blue materials family.
Quinazolines are heterocyclic aromatic molecules containing two nitrogen atoms and possess appropriate electron accepting ability
[20]. Its derivatives are ubiquitous in a variety of natural products as well as synthetic pharmaceuticals, and have been widely investigated
and used in medicinal applications, such as being as antimalarial and anticancer agents, etc. [21] However, rare of the quinazoline
derivatives are applied so far in OLEDs. Specifically, to our best knowledge, only limited numbers of quinazoline derivatives have been
introduced into OLEDs as host for red and orange phosphorescent OLEDs. [14, 22] Recently, we first introduced quinazoline as acceptor
to TADF emitters and achieved the promising maximum external quantum efficiency (EQEs) over 20%, and showed that quinazoline is
excellent acceptor moiety for D-A type emitters [20]. However, these quinazoline-based emitters exhibit green to green-yellow EL owing
to the lower singlet state energy (S1) level of below than 2.51 eV.
Considering the S1 energy level can easily adjust by changing the donating electronic ability of donor in D-A type emitters. In this
paper, we select carbazole (Cz) as the weak donor and develop three quinazoline-based emitters, 9-(4-(2-phenylquinazolin-4-yl)phenyl)-
9H-carbazole (2PQ-Cz), 9-(4-(4-phenylquinazolin-2-yl)phenyl)-9H-carbazole (4PQ-Cz) and 9,9'-(quinazoline-2,4-diylbis(4,1-
phenylene))bis(9H-carbazole) (24PQ-Cz). We systematically investigate the effect of the substituted position and number of Cz in PQ
unit on the photophysical and electroluminescent properties. It is found that these emitters have wide bandgaps of 3.12~3.19 eV and
large S1 energy levels of 3.12~3.19 eV, which is sufficiently large to achieve deep blue emission. As expected, these emitters-based
OLED devices exhibit deep blue emission with the maximum wavelength ≤ 450 nm and narrow FWHM ≈ 60 nm. Significantly, the deep
blue EL spectra of these emitters-based OLED devices are very stable and the corresponding ΔCIE (x, y) can be negligible under the
applied voltage ranging from 5 V to 9 V. Additionally, these emitters are also the first examples using quinazoline as acceptor to achieve
stable, high purity color, and deep blue emission with the maximum wavelength ≤ 450 nm and y < 0.10.
The synthetic routes for 2PQ-Cz, 4PQ-Cz, and 24PQ-Cz are showed in Scheme 1, the details are showed in the Supporting information.
The N-phenyl-carbazole boronic ester was prepared according to our previous work [23]. The emitters 2PQ-Cz, 4PQ-Cz, and 24PQ-Cz
were then synthesized through Pd-catalyzed Suzuki-Miyaura coupling reaction of 2 with 4-chloro-2-phenylquinazoline (2PQ-Cl), 2-
chloro-4-phenylquinazoline (4PQ-Cl) and 2,4-dichloroquinazoline (24PQ-Cl), respectively. They were purified using column
chromatography on silica gel, and further purified by temperatures-gradient sublimation under vacuum. The structure of the final product
was confirmed by 1H NMR, 13C NMR, and mass spectrometry (Figs. S1-S9 in Supporting information). In addition, the thermal properties
were characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) in nitrogen atmosphere. As shown
in Fig. S10 (Supporting information), 2PQ-Cz, 4PQ-Cz, and 24PQ-Cz display excellent thermal stability with the decomposition
temperature of 371, 375 and 468 oC, respectively, which good enough for application in electroluminescent device.

Please donot adjust the margins
Scheme 1. Synthesis procedures of 2PQ-Cz, 4PQ-Cz and 24PQ-Cz.
To understand the electronic properties of three emitters 2PQ-Cz, 4PQ-Cz, and 24PQ-Cz, we utilized density functional theory (DFT)
in Gaussian 09 at B3LPY/6-31G(d) level to optimize the ground-state geometries and HOMO/LUMO. Since PQ moiety has an
asymmetric structure, the connecting position of Cz may endow different twist angles between Cz donor and PQ acceptor. As shown in
Fig. 1, it can be found that the optimized molecular geometrics of 2PQ-Cz show a dihedral angle of 40.5o between PQ moiety and phenyl
spacer. However, for 4PQ-Cz, the dihedral angle decreases to 1.9o because of the absence of steric hindrance between two nitrogen and
hydrogen atoms. In addition, in the case of 24PQ-Cz, the dihedral angles between PQ moiety and phenyl spacer are 44.8o and 2.2 o,
respectively, which are similar to 2PQ-Cz and 4PQ-Cz. The different molecular geometrics of three emitters result various electron cloud
distribution. For 2PQ-Cz, the HOMO is mainly located on Cz moiety and phenyl spacer, while the LUMO is mainly distributed on PQ
moiety, phenyl spacer, and small portion spreading onto Cz moiety, resulting a lager orbital overlap of HOMO and LUMO on phenyl
spacer. Due to the small twist angle between PQ moiety and phenyl spacer, the HOMO of 4PQ-Cz has a broader distribution over Cz
with a part distribution on PQ. Similarly, the LUMO only distributed on PQ moiety and phenyl spacer compared to 2PQ-Cz. This result
indicates that 2PQ-Cz has deeper HOMO and LUMO levels than 4PQ-Cz, which is consistent with the values of theoretical calculation.
For 24PQ-Cz, the distribution of LUMO can be considered the combination of 2PQ-Cz and 4PQ-Cz, resulting a deeper LUMO level of
-2.12 eV (-2.01 eV for 2PQ-Cz and -2.00 eV for 4PQ-Cz). While the HOMO distribution in 24PQ-Cz is more like HOMO of 4PQ-Cz,
and the HOMO of 24PQ-Cz is calculated to be -5.28 eV, which is very close to -5.25 eV for 4PQ-Cz.
Fig. 1. Chemical structures, HOMO and LUMO distributions for 2PQ-Cz, 4PQ-Cz, and 24PQ-Cz based on TD-DFT at the B3LYP/6-31G(d) level.
The experimental HOMO energy levels of three emitters are measured at anhydrous dichloromethane by cyclic voltammetry. It can
find that each molecule exhibited a reversible oxidation wave (Fig. S11 in Supporting information). The HOMO energy levels were
calculated from the onset of oxidation potential and were found to be -5.72 eV, -5.68 eV and -5.32 eV, respectively, for 2PQ-Cz, 4PQ-
Cz, and 24PQ-Cz (Table 1). The LUMO energy levels were at -2.55 eV, -2.49 eV and -2.20 eV, respectively, which were calculated
from the optical bandgap (Eg) from the HOMO energy levels. Similar energies splitting determined experimentally using ΔEST = ES - ET
to DFT calculations, the higher HOMO and LUMO energy levels of 24PQ-Cz compared to that of 2PQ-Cz and 4PQ-Cz is mainly stem
from the special asymmetric D-A-D structure. These results indicated that the asymmetric D-A-D structure plays an important role on

Please donot adjust the margins
tuning the HOMO and LUMO energy levels, which are crucial for facilitating hole and electron injections in organic electroluminescent
device.
Table 1 The HOMO, LUMO, Eg, ES, ET and ΔEST values of 2PQ-Cz, 4PQ-Cz, and 24PQ-Cz.
b
e
f
g
h
Compounds
λPLa/ λPL
HOMO c
LUMO d
Eg
ES
ET
ΔEST
(nm)
(eV)
(eV)
(eV)
(eV)
(eV)
(eV)
2PQ-Cz
4PQ-Cz
24PQ-Cz
439/450
425/442
437/454
-5.72
-5.68
-5.32
-2.55
-2.49
-2.20
3.17
3.19
3.12
3.12
3.19
3.12
2.56
2.53
2.52
0.56
0.63
0.60
a Maximum wavelength of emission measured at toluene solution; b Maximum wavelength of emission measured at neat film; c HOMO were calculated from the
oxidation potential; d LUMO were calculated using HOMO-Eg; e Eg was obtained from the absorption edges of normalized absorption spectra in toluene (1 × 10-4
f
mol/L); Estimated from the onset of fluorescence spectrum in toluene (1 × 10-4 mol/L) at 300 K; g Estimated from the onset of phosphorescence spectrum in
toluene (1 × 10-4 mol/L) at 77 K; h Singlet-triplet.
The UV-vis absorption and photoluminescence (PL) spectra of 2PQ-Cz, 4PQ-Cz, and 24PQ-Cz in dilute toluene (10-4 mol/L) and neat
film are showed in Fig. 2. It can find that these emitters exhibit similar absorption profiles and have an absorption shoulder between 350-
412 nm, which is attributed to the intramolecular charge transfer (ICT) state between PQ unit and Cz moiety. The molar extinction
coefficient of CT transition was measured to be 1.04 × 104, 1.22 × 104, 1.99 × 104 L mol-1 cm-1 for 2PQ-Cz, 4PQ-Cz, and 24PQ-Cz,
respectively, suggesting that 2PQ-Cz has a weaker ICT interaction than 4PQ-Cz and 24PQ-Cz. A slight red-shift in the CT absorption
edge was observed for 24PQ-Cz when compared with 2PQ-Cz, 4PQ-Cz, which likely ascribe to the expanded conjugation of 24PQ-Cz.
Moreover, the Eg of 24PQ-Cz was calculated to be 3.15 eV, similar with the values of 2PQ-Cz (3.17 eV), 4PQ-Cz (3.19 eV), which
suggests that the expanded conjugation has no obvious influence for emission in this type molecules, and the large Eg values of over 3.0
eV show a blue emission. As expect, the PL spectra in toluene of 2PQ-Cz, 4PQ-Cz, and 24PQ-Cz showed the intense blue emission with
peaks at 423 nm, 438 nm and 439 nm, respectively. Due to the weak ICT character, the emission peak of 2PQ-Cz shows blue-shifted
compared with 4PQ-Cz and 24PQ-Cz, which is similar with others reports.[17, 20] Additionally, the PL spectra of 2PQ-Cz, 4PQ-Cz,
and 24PQ-Cz in the neat film are slightly red-shifted compared with solution state, which should be attributed to the decreased polarity
of neat film relative to toluene solvent [24]. It is well known that the solvent polarity has an effect on the optical properties of the organic
light materials. As shown in Fig. S2, the absorption spectra of 2PQ-Cz, 4PQ-Cz, and 24PQ-Cz have almost no change in various polar
solvents indicating the nonpolar ground states. [23, 25] In contrast, the PL spectra of the three PQ-based emitters exhibited strong
dependence on the solvent polarity (Fig. S12 and Table S1 in Supporting information). 2PQ-Cz, 4PQ-Cz, and 24PQ-Cz, respectively,
with increasing polarity of solvents from n-hexane to DCM. These results also clearly indicate that the emissions of the three PQ-based
emitters are from the ICT states with a more polar than the ground state. In addition, we also measured the low-temperature
phosphorescence (PH) of 2PQ-Cz, 4PQ-Cz, and 24PQ-Cz in toluene at 77 K. It is found that PH spectra display similar vibronic structure,
from which the triplet energy levels (ET) are estimated to be 2.56, 2.53, 2.52 eV, respectively (Table 1). The ETs of three compounds are
exactly similar to its acceptor moiety of 2-phenylquinazoline (ET = 2.48 eV) [20], which indicate that the lowest triplet states of these
compounds are local triplet states and derives from its acceptor. The large singlet-triplet energy gaps of 0.56, 0.63, 0.60 eV for 2PQ-Cz,
4PQ-Cz, and 24PQ-Cz, respectively, suggests that the reverse intersystem crossing process is largely forbidden, which confirmed by Fig.
S13 (Supporting information) [8, 20, 23].
Fig. 2. UV-vis absorption, PL spectra in toluene solution (10-4 mol/L) and in neat film at room temperature and PH spectra in toluene solution at 77 K of 2PQ-Cz,
4PQ-Cz, and 24PQ-Cz.
To evaluate device performances of 2PQ-Cz, 4PQ-Cz, and 24PQ-Cz, multilayer OLEDs were fabricated using thin film of these three
PQ-based emitters in a high triplet energy DPEPO host as an emitting layer (EML). The device architecture, chemical structure of all
materials, and energy level used in the OLEDs device are illustrated in Fig. 3a. The detailed device architectures are as following: glass
substrate/ITO anode/ HATCN (5 nm)/TAPC (30 nm)/mCP (10 nm)/emitters: DPEPO (x) wt% (40 nm)/ DPEPO (5 nm)/TPBi (40 nm)/LiF

Please donot adjust the margins
(0.9 nm)/Al (100 nm). Among them, 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (HATCN) and di-[4-(N,N-ditoly-
amino)-phenyl]cyclohexane (TAPC) were used as a hole injection layer and a hole transporting layer, respectively. 1,3,5-Tris(N-
phenylbenzimidazol-2-yl)benzene (TPBi) and LiF were the electron transporting layer and an electron injection layer, respectively. N,
N-dicarbazolyl-3, 5-benzene (mCP) and (oxybis(2,1-phenylene))bis(diphenylphosphine oxide) (DPEPO) were inserted as excitons
blocking layer.
Through doping concentration optimization (10, 20, 30, 40, 50, 60 wt%), it is found that the doped OLED devices have the better EL
properties at the doped concentration of 40wt% in DPEPO (Figs. S14-S16 in Supporting information). All the optimized 2PQ-Cz-, 4PQ-
Cz-, and 24PQ-Cz- based devices exhibit turn-on voltages of 4.3, 4.3 and 3.9 V, and maximum luminance of 1668, 936, and 3850 cd/m2,
respectively (Table 2). The optimized 2PQ-Cz-based device delivered maximum external quantum efficiency of 2.17% (Fig. S17 and
Table S2 in Supporting information). It is noteworthy that the OLED based on 2PQ-Cz displayed deep blue emission peak at 445 nm
(Fig. 3b), with CIE coordinates of (0.152, 0.099). As discussed above, the asymmetric structure of quinazoline acceptor provides a
possibility to modulate the luminescence properties. As it can see from Fig. 3b, the EL spectrum of 4PQ-Cz based OLED device show
deep blue emission peak at 436 nm with CIE coordinates of (0.157, 0.080), which is very close to the standard blue CIE values of (0.14,
0.08). To date, deep blue OLEDs with y ≤ 0.08 as emitter are very rare. Therefore, the excellent EL spectrum and CIE of 4PQ-Cz-based
OLED devices extend the deep blue emitters family. The maximum external quantum efficiency of 4PQ-Cz- based device is 1.33%.
Compared to these two D-A emitters, the asymmetry D-A-D 24PQ-Cz exhibits a better EL properties and afford a EQE of 2.64%.
However, the CIE of y is large 0.10, which is due to a larger conjugate length.

Please donot adjust the margins
Table 2 Summary of OLED performances using 2PQ-Cz, 4PQ-Cz and 24PQ-Cz as dopants.
a
c
d
e
λEL
FWHMb
(nm)
Von
EQEmax
(%)
Lmax
Emittes
CIE(x,y) a
ΔCIE(x,y) f
(nm)
(V)
(cd/m2)
2PQ-Cz
4PQ-Cz
24PQ-Cz
445
436
448
63
61
57
4.3
4.3
3.9
2.17
1.33
2.64
1668
936
(0.152, 0.099)
(0.157, 0.080)
(0.151, 0.113)
(0.000, 0.002)
(0.003, 0.005)
(0.001, 0.003)
3850
a Measured at 7 V; b Full width at half maximum; c Turn-on voltage at 1 cd/m2; d Maximum external quantum efficiency; e Maximum luminance; f CIE coordinates
deviation.
Fig. 3. (a) The energy level diagrams, OLED device structure, and the chemical structure of the materials used in the TADF devices. Performance of 2PQ-Cz-,
4PQ-Cz-, and 24PQ-Cz-based OLED with doped concentration of 40% in DPEPO. (b) Current density and luminance versus voltage (J-V-L) characteristics. (c)
EL spectra of the TADF OLEDs at 7 V.
It is known that color purity is an important parameter for good color quality in display for OLED. Generally, emitters with classical
charge-transfer excited states often display broad emission spectra and poor color purity [8]. It is notably that the EL spectra of 2PQ-Cz-
, 4PQ-Cz-, and 24PQ-Cz-based OLED devices have narrow FWHM of 63, 61, and 57 nm, respectively. More importantly, EL spectra
and CIE of these three emitters based OLED devices are almost completely consistent ranging from 5 V to 9 V, which indicate that the
deep blue EL emissions are fairly stable under the applied voltage range (Fig. 4a). Furthermore, the corresponding ΔCIE (x, y) of (0.000,
0.002), (0.003, 0.005), and (0.001, 0.003) can be negligible for 2PQ-Cz-, 4PQ-Cz-, and 24PQ-Cz-based OLED devices, respectively
(Fig. 4b).
Fig. 4. (a) EL spectra of 2PQ-Cz-, 4PQ-Cz-, and 24PQ-Cz-based OLED from 5 V to 9 V. (b) CIE coordinates deviation of 2PQ-Cz-, 4PQ-Cz-, and 24PQ-Cz-
based OLED devices from 5 V to 9 V.
In conclusion, we have developed three new deep blue emitters, namely, 2PQ-Cz, 4PQ-Cz and 24PQ-Cz, by connecting quinzonline
acceptor with carbazole donor. Their bandgaps of 3.17, 3.19, 3.12 eV are found to be sufficiently large to achieve deep blue light,
responding the singlet state energy levels of 3.12, 3.19, and 3.12 eV, respectively. These emitters-based OLEDs exhibit deep blue
emission with the maximum wavelength ≤ 450 nm and narrow FWHM ≈ 60 nm. Especially, a CIE of y = 0.080 is achieved for 4PQ-Cz-
based OLED. This result indicates that the asymmetric quinazoline as acceptor not only can achieve deep blue materials for OLED, but
also can effectively modulate the luminescence properties. Moreover, EL spectra and CIE of these three emitters based OLED devices
are almost completely consistent ranging from 5 V to 9 V, which indicate that the deep blue EL emissions are fairly stable under the

Please donot adjust the margins
applied voltage range. The corresponding ΔCIE (x, y) of (0.000, 0.002), (0.003, 0.005), and (0.001, 0.003) can be negligible for 2PQ-Cz-
, 4PQ-Cz-, and 24PQ-Cz-based OLED devices, respectively.
Acknowledgments
The authors thank the supports from the National Key Research and Development Plan (No. 2016YFB0401004). Y. Zhang thanks the
supports from the Open Fund of Beijing National Laboratory for Molecular Sciences (BNLMS) (No. BNLMS20160131) and the
Fundamental Research Funds for the Central Universities (Harbin Institute of Technology).

Please donot adjust the margins
References
[1] C.W. Tang, S.A. VanSlyke, Appl. Phys. Lett. 51 (1987) 913-915.
[2] S. Kim, B. Kim, J. Lee, et al., Mater. Sci. Engin. R. 99 (2016) 1-22.
[3] M.Y. Wong, E. Zysman-Colman, Adv. Mater. 29 (2017) 1605444.
[4] L. Gan, Z. Xu, Z. Wang, et al., Adv. Funct. Mater. (2019) 1808088.
[5] S. Chen, J. Lian, W. Wang, et al., J. Mater. Chem. C 6 (2018) 9363-9373.
[6] Y. Xu, X. Liang, X. Zhou, et al., Adv. Mater. 31 (2019) e1807388.
[7] Y. Xiong, J. Zeng, B. Chen, et al., Chin. Chem. Lett. 30 (2019) 592-596.
[8] Z. Li, C. Li, Y. Xu, et al., J. Phys. Chem. Lett. 10 (2019) 842-847.
[9] X. Xu, X. Li, S. Wang, et al., J. Mater. Chem. C 6 (2018) 9599-9606.
[10] W. Sun, N. Zhou, Y. Xiao, et al., Dyes Pigments 154 (2018) 30-37.
[11] Y.X. Zhang, Y. Yuan, Q. Wang, et al., Dyes Pigments 158 (2018) 396-401.
[12] H. Park, J. Lee, I. Kang, et al., J. Mater. Chem. 22 (2012) 2695-2700.
[13] N. Jürgensen, A. Kretzschmar, S. Höfle, et al., Chem. Mater. 29 (2017) 9154-9161.
[14] Z. Zhang, J. Xie, H. Wang, et al., Dyes Pigments 125 (2016) 299-308.
[15] D.H. Ahn, S.W. Kim, H. Lee, et al., Nature Photon. 13 (2019) doi: 10.1038/s41566-019-0415-5.
[16] J. Lee, H.F. Chen, T. Batagoda, et al., Nature Mater. 15 (2015) 92-98.
[17] K. Nakao, H. Sasabe, R. Komatsu, et al., Adv. Opt. Mater. 5 (2017) 1600843.
[18] R. Komatsu, T. Ohsawa, H. Sasabe, et al., ACS Appl. Mater. Interfaces 9 (2017) 4742-4749.
[19] J.W. Sun, J.Y. Baek, K.H. Kim, et al., Chem. Mater. 27 (2015) 6675-6681.
[20] B. Li, Z. Wang, S.J. Su, et al., Adv. Opt. Mater.7 (2019) 1801496.
[21] F.E. Held, A.A. Guryev, T. Frohlich, et al., Nat. Commun. 8 (2017) 15071.
[22] S.M. Kim, J.H. Yun, S.H. Han, et al., J. Mater. Chem. C 5 (2017) 9072-9079.
[23] B. Li, Z. Li, T. Hu, et al., J. Mater. Chem. C 6 (2018) 2351-2359.
[24] J. Guo, X.L. Li, H. Nie, et al., Chem. Mater. 29 (2017) 3623-3631.
[25] M. Liu, X.L. Li, D.C. Chen, et al., Adv. Funct. Mater. 25 (2015) 5190-5198.