Highly Efficient Solution-Processable Nanophosphor with Ambipolar Shell

Article abstract of DOI:10.1002/chem.201705037

Super-resolution display (SRD) is crucial to all super-resolution processing technologies for visualization terminals. Herein, as a proof-of-concept, an iridium-complexed nanoemitter, [Ir(CzPOPBI)₃] (CzPOPBI=9,9′-(3,3′-(4-(1-(3-(4-(diphenylphos

Full text of DOI:10.1002/chem.201705037

A Journal of
Accepted Article
Title: Highly Efficient Solution-Processible Nanophosphor with
Ambipolar Shell
Authors: Hui Xu, Chunmiao Han, and Guohua Xie
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Highly Efficient Solution-Processible Nanophosphor with
Ambipolar Shell
Chunmiao Han,[a] Guohua Xie[b,c] and Hui Xu*[a,c]
Abstract: Super-resolution display (SRD) is crucial to all super-
resolution processing technologies as the visualization terminals.
Herein, as a proof-of-concept, an Iridium-complexed nanoemitter
named Ir(CzPOPBI)3 with core-shell structure for charge and exciton
spatial allocation is developed, whose ambipolar shell can balance
the shell-to-core charge transfer and the excess charge export. As
the result, the top-rank performance of its spin-coated host-free
bilayer devices was realized, owing to the simultaneous exciton
confinement on its core and exciton-charge quenching (ECQ)
suppression. The competence of Ir(CzPOPBI)3 as single-molecular
emissive layers of nano-pixel units shows the great potential of this
kind of organic core-shell systems for high-performance SRD
applications.
electroluminescent (EL) inorganic semiconductors, e.g. quantum
f, 8]
dots[1a,
and perovskites[9], featured non-exciton-involved
spontaneous emission, organic nanoemitters as molecular
luminescent materials characteristic of stimulated emission
suffer from exciton-incorporated quenching effects, such as
triplet-triplet annihilation (TTA) and triplet-polaron quenching
(TPQ).[10] Furthermore, to bring out the advantage of
nanoemitters in saving pixel nanolithography step and cost, a
simple device structure excluding hole-transporting layers (HTL)
should be adopted, putting forward rather high request on
nanoemitters with respect to reducing carrier flux unbalance-
induced TPQ.[11] In this case, one of the bottlenecks for organic
nanoemitters in practical SRD application is how to suppress
exciton quenching.[12]
Introduction
Organic nanoemitter-based organic light-emitting diodes (OLED)
are promising for realizing super-resolution displays (SRD) with
cross-range resolution reaching 10M, in view of each emitter can
be competent as single-molecule emissive layer (EML) of a
nanosize pixel unit.[1] It is known that emission color of organic
luminophors is determined by their structural factors, especially
conjugation and intramolecular electronic effects.[2] Therefore, in
contrast to inorganic nanoemitters with size-dependent emission
characteristics[3], organic nanoemitters, e.g. polymers[4],
dendrimers[5] and oligomers[6], with structure-correlated optical
properties are superior in realizing full-color emissions from
uniform-size pixels, which is crucial for image fidelity as the key
determinant
of
SRDs.[7]
Nevertheless,
different
to
[a]
[b]
[c]
Dr. H. Xu and Dr. C.Han
Key Laboratory of Functional Inorganic Material Chemistry, Ministry
of Education, School of Chemistry and Materials
Heilongjiang University
74 Xuefu Road, Harbin 150080, China
Fax: (+86) 451-86608042
E-mail: hxu@hlju.edu.cn
Dr. G. Xie
Hubei Collaborative Innovation Centre for Advanced Organic
Chemical Materials & Hubei Key Lab on Organic and Polymeric
Optoelectronic Materials
Department of Chemistry
Wuhan University
Wuhan 430072, China.
Key Laboratory for Organic Electronics and Information Displays &
Institute of Advanced Materials (IAM)
Jiangsu National Synergetic Innovation Center for Advanced
Materials (SICAM)
Nanjing University of Posts & Telecommunications
9 Wenyuan Road, Nanjing 210023, China. Department
Institution
Scheme 1. Structural models of Iridium(III) complex-based nano-emitters and
exciton-charge quenching (ECQ) effects in their bilayer SRD units. (a)
Iridium(III) complexes as emissive cores without encapsulation by carrier-
transporting groups, which would suffer from serious ECQ effects. The
interactions between positive and negative charges and excitons (M*) can
generate the corresponding polarons (M+ and M-); (b) Core-shell-structured
nanoemitters with Iridium(III) complex cores and peripheral hole-transporting
groups formed monopolar shells, whose shell-contributed low-lied occupied
molecular orbitals (HOMO-n) can serve as the intermediate orbitals for
Supporting information for this article is given via a link at the end of
the document.
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1b).[16]
redundant hole export; (c) Nano-emitters with the feature of ambipolar shell
encapsulated Iridium(III) complex cores, in which the HOMO-n and the low-
lied unoccupied molecular orbitals (LUMO+n) distributed on shells can
establish the channels for excessive hole and electron exports, respectively.
developing
SRD-appliable
emitters
(Scheme
Nevertheless, the polaron/charge-induced exciton quenching
was still remained and even worsened at EML|electron-
transporting layer (ETL) interfaces due to the unipolar features
of the peripheral groups, since p-character of most of them
represented by Cz rendered the direct electron capture on
emissive core. As the result, only few host-free nanoemitter-
based OLEDs can realize EQE more than 10% and especially
Actually, for a pixel unit adopting the single-molecule
nanoemitter-based EML, TTA should be absent;[13] meanwhile,
the embodiment of TPQ becomes the quenching effect of further
injected charge on exciton, namely exciton-charge quenching
(ECQ). Regarding to common organic emitters, e.g. Iridium (III)
power efficiencies (PE) beyond 40 lm W-1 for practical
applications.[5d,
Nevertheless, it can be expected that the
17]
spatial allocation of charge and exciton through CES-type core-
shell structures could completely eliminate TPQ/ECQ in theory if
the ideal balance between charge and exciton confinement on
emissive core and excessive charge export through carrier-
transporting shell (Scheme 1c). In this case, the shell groups
should be crucial for EL performance of nanoemitters with the
concerns on: (i) suitable FMO energy levels and charge transfer
modes to balance shell-to-core charge transfer and intra-shell
charge export; (ii) carrier transportation optimization for charge
flux balance; (iii) direct exciton confinement on core to suppress
shell-to-core energy transfer induced energy loss.
phosphors, with thoroughly overlapped frontier molecular ortbial
14]
(FMO) distributions and exciton state locations,[7,
the
immediately injected positive and negative charges into excited
molecules would make the excitons regress to polarons
(Scheme 1a). In our previous works, a so-called “charge-exciton
separation (CES)” strategy was validated and utilized to reduce
the TPQ effects on host materials and at EML|carrier-
transporting layer (CTL) interfaces.[15] Accordingly, we used
high-density carbazole (Cz) groups to encapsulate the emissive
core and establish the channel for excessive hole export,
achieving an impressive EQE beyond 8% from the host-free
OLEDs, manifesting the effectiveness of CES strategy in
Figure 1. (a) Chemical structures of Ir(PBI)3 as core and its core-shell derivatives Ir(CzPBI)3 and Ir(CzPOPBI)3 with monopolar and ambipolar shells, respectively;
(b) Synthetic procedure of Ir(CzPOPBI)3: i. Ph2PCl, Mg, Et2O, H2O2; ii. BBr3, DCM; iii. TBAB, KOH, 1,3-dichloropropane; iv. TBAB, KOH, 3,6-di-tert-butyl-N-(3-
chloropropyl)-carbazole, THF; v. NaH, TBAB, THF; vi. IrCl3·nH2O, 2-ethoxyethanol, H2O, THF; K2CO3, glycerol.
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In this contribution, as a proof of concept, a nanophosphor
Ir(CzPOPBI)3 with the structure of six hole-transporting 3,6-di-
tert-butyl-carbazole (tBCz) and three electron-transporting
those of Ir(CzPBI)3. Considering the high triplet energy (T1) of
tBCz and TPPO beyond 3.0 eV, the first T1 vibrational level of
the Ir(PBI)3 cores should best match the peripheral groups in
triplet energy (Figure S2). In this case, it is rational that the
monopolar shell of Ir(CzPBI)3 restrains the photo-generated
electron transfer to the core, thereby making the shell-to-core
energy transfer predominant. On the contrary, the ambipolar
triphenylphosphine oxide (TPPO) shelled Ir(PBI)3 (PBI
=
phenylbenzimidazole) core is constructed (Figure 1a). The
almost ideal optoelectronic properties of Ir(CzPOPBI)3 ascribed
to its well-designed ambipolar shell gave rise to the top-rank EL
performance among host-free solution-processed bilayer OLEDs, shell of Ir(CzPOPBI)3 supports the unimpeded charge transfer to
especially the state-of-the-art EQE and PE beyond 12% and 45
lm W-1, respectively, accompanied by the ultra-low turn-on
voltage of 3 V. In comparison to analogue Ir(CzPBI)3 with nine
peripheral tBCz groups-formed monopolar shell, TPQ/ECQ-
induced EQE reduction for Ir(CzPOPBI)3-based devices was
effectively halved, which verified the success of CES strategy in
spatially allocation of charge and exciton and its great potential
for developing SRD-applicable nanoemitters.
its core, rendering the core-originated emissions due to the
negligible incorporation of its shell in intramolecular energy
transfer (IET). Therefore, Ir(CzPOPBI)3 would be superior in
suppressing IET-induced energy loss. In films, these three
complexes showed the same situation (Figure 2b). However, in
contrast to Ir(PBI)3, the solid-state emissions of Ir(CzPBI)3 and
Ir(CzPOPBI)3 are remarkably narrowed owing to the effect of
their shells on preventing the aggregation of their cores, which
can doubtlessly suppress intermolecular interaction-induced
quenching, e.g. TTA. As the result, in solution and film, the
photoluminescence quantum yields (PLQY) of Ir(CzPBI)3 and
Ir(CzPOPBI)3 are equivalent as ~70%, which is comparable to
that of Ir(PBI)3 in solution and four folds of that of Ir(PBI)3 in film
(Table 1).
Results and Discussion
Design, synthesis and morphological stability. Ir(CzPOPBI)3
is designed on the basis of the mixed modifications with carrier-
transporting moieties and aliphatic chains (so-called CT-AC
strategy), corresponding to tBCz and TPPO and propylene,
respectively, in which propylene serves as not only linker but
also insulator for throttling excessive charge transfer to the core.
Simultaneously, the high-density tBCz and TPPO groups with
host function[15b] are correspondingly bonded to N-phenyl and
imidazole groups with the respective contributions to the highest
occupied molecular orbital (HOMO) and the lowest unoccupied
molecular orbitals (LUMO) of Ir(PBI)3 core for efficient shell-to-
core intramolecular charge transfer (ICT). Furthermore, the
tBCz:TPPO ratio is 6:3 to balance the charge flux in EML|ETL-
type bilayer devices.
The ligand of Ir(CzPOPBI)3 was synthesized through
introducing two tBCz and one TPPO groups stepwise in virtue of
acidity difference between –OH and –NH in 3,4-dihydroxyl-
benzimidazole, following by two-step complexation with IrCl3 to
afford Ir(CzPOPBI)3 with a total yield of 7% (Figure 1b). The
1
chemical structure of Ir(CzPOPBI)3 was confirmed with H and
13C NMR, mass spectroscopy and elemental analysis. Similar to
Ir(PBI)3, and Ir(CzPBI)3, Without distinct melting point, its film
preserves the stable amorphous state during heating,
accompanied by the decomposition temperature (Td) beyond
o
300 C, which renders the favourable solution processability in
nanoscale (Figure S1).
Photophysical properties. In comparison to the core, the
contributions of tBCz and TPPO groups to the absorptions of
Ir(CzPBI)3 and Ir(CzPOPBI)3 in solution can be distinguished by
the peaks in the range of 250-350 nm (Figure 2a). Furthermore,
although the emission profiles of these materials are similar, the
shoulder peak intensity around 550 nm for Ir(CzPOPBI)3 is
comparable to that of Ir(PBI)3, but remarkably larger than that of
Ir(CzPBI)3. Further refining the vibrational transition bands at 77
K indicates that the intensities of n→0 transitions (n > 0) for
Ir(PBI)3 and Ir(CzPOPBI)3 are almost equivalent but higher than
Figure 2. (a) Electronic absorption profiles (solid symbol) of the complexes
photoluminescence (PL, hollow symbol) spectra in dilute CH2Cl2 at room
temperature and 77
K
(inset); (b) Absorption (solid symbol) and
photoluminescence (hollow symbol) spectra of Ir(CzPOPBI)3 in films.
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Table 1. Physical Properties of Ir3+ complexes.
Absorption (nm)
Complex
PH (nm)
PLQY[c] (%)
T1[d] (eV)
Td (oC)
HOMO/LUMO (eV)
Lifetime (s)
313, 378, 415, 460[a]
523[a]
76
18[b]
73
Ir(PBI)3
8.3[b]
8.2[b]
8.2[b]
2.41
2.44
2.43
417
346
337
-4.95/-2.44[18]
-5.42/-2.41[16]
-5.28/-2.88[e]
317, 380, 466[b]
540[b]
351, 320, 290, 260, 240[a]
523, 554[a]
520, 552[b]
523, 555[a]
524, 560[b]
Ir(CzPBI)3
351, 300, 288, 266, 238[b]
72[b]
73
352, 320, 299, 292, 266, 238[a]
Ir(CzPOPBI)3
352, 320, 299, 288, 266, 238b
70 [b]
[a] In CH2Cl2 (10-6 mol L-1); [b] in film; [c] calculated by using quinine sulfate in 0.5M sulfuric acid as standard; [d] estimated according to the 0-0 transition of low-
temperature emission spectra; [e] calculated according the onset voltages of redox peaks with the equation of -(Vonset + 4.78) eV.
Electrical performance. To figure out the effects of the shells in
Ir(CzPBI)3 and Ir(CzPOPBI)3 on electrical properties and ICT
process, cyclic voltammetry (CV) analysis of these two
complexes was performed (Figure 3a). Upon the anodic sweep,
the oxidation behaviors of Ir(CzPBI)3 and Ir(CzPOPBI)3 are
similar with the oxidation peaks characteristic of Ir(PBI)3 and
tBCz. For Ir(CzPOPBI)3, an anodic peak at 2.034 V ascribed to
TPPO can be also observed. Meanwhile, the reduction curves
consist of the cathodic peaks attributed to Ir(PBI)3 and TPPO,
excluding any contributions from tBCz. The incorporation of
tBCz and TPPO groups in redox process of Ir(CzPOPBI)3
manifests the ambipolar characteristics of its shell. It is
interesting that in comparison to the HOMO and LUMO levels of
Ir(CzPBI)3 as -5.42 and -2.41 eV, the HOMO level of
Ir(CzPOPBI)3 is elevated by 0.14 eV, accompanied by the
deeper LUMO at -2.88 eV, which should be ascribed to the
polarization effect of the shell dipole field on Ir(PBI)3 core
(Table 1). Furthermore, the shell-core FMO energy gaps of
Ir(CzPOPBI)3 are 0.7 eV for the HOMO and 0.4 eV for the
LUMO, respectively, forming the hole and electron traps deep
enough for charge capture on its core. Therefore, although the
core and shell are separated by insulating linkage according to
CES strategy, the strong spatial field effect of the ambipolar
shell can be utilized to reinforce the electroactivity of the core,
which can accurately regulate the charge migration in the core-
shell systems.
For further insight in the nature of the optoelectronic effects
from ambipolar shell, density functional theory (DFT) simulation
on the FMOs of Ir(CzPOPBI)3 is performed (Figure 3b and
Figure S3). It is showed that the molecular diameter of
Ir(CzPOPBI)3 reaches to 3 nm. Similar to Ir(PBI)3, the HOMO
and HOMO-1 of Ir(CzPOPBI)3 are mainly localized on N-phenyl
of its core; whereas, its LUMO, LUMO+1 and LUMO+2 are
contributed by PBI and Ir3+, reflecting the exclusion of the
peripheral tBCz and TPPO groups from optical process as
shown by photophysical analysis. Furthermore, the HOMO-n (n
= 2~7) are successively dispersed on the peripheral six tBCz
groups. On contrary, the LUMO-n (n = 3~5) is located on three
TPPO groups, respectively. In accord with CV analysis, the
core-shell FMO gaps are ~0.3 eV for effective charge trapping.
Simultaneously, the HOMO-n energy levels are almost
equivalent so the same as the situation of LUMO-n, which
establishes the barrier-free hole and electron migration channels
on tBCz and TPPO groups for charge export, respectively. In
Figure 3. (a) Cyclic voltammograms of Ir(CzPBI)3 and Ir(CzPOPBI)3
measured at room temperature under N2; (b) Contours and energy levels of
the first four occupied and unoccupied molecular orbitals for Ir(CzPOPBI)3
calculated by DFT simulation.
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opposite, the monopolar shell of Ir(CzPBI)3 renders the
dispersion of LUMO+3 on tBCz groups, reflecting the hole-
export and electron-shielding effect.[16] Thus, the ambipolar shell
can perfectly utilize the superiority of core-shell system in spatial
effect on balancing ICT and charge export for exciton generation
and ECQ reduction. In addition, tBCz groups in Ir(CzPBI)3 can
form exciton based on their simultaneous contributions to FMOs,
afterwards giving rise to the shell-to-core energy transfer. On
contrary, the HOMO-n and LUMO-n of Ir(CzPOPBI)3 are
spatially separated on tBCz and TPPO groups, respectively,
which suppresses the formation of shell-localized excitons and
IET-induced energy-loss.
Device performance. To identify the potential of Ir(CzPOPBI)3
for SRD applications and the superiority of its ambipolar shell in
exciton confinement and TPQ/ECQ suppression, the non-doped
OLEDs with the bilayer configuration of ITO|PEDOT:PSS (30
nm)|Ir3+ complexes (40 nm)|TmPyPB (40 nm)|Liq (1 nm)|Al (100
nm) were fabricated through spin coating, in which PEDOT:PSS
and
Liq
are
poly(3,4-ethylenedioxythiophene):
poly(styrenesulfonate) and 8-hydroxyquinoline Lithium(I) as hole
and electron injecting layers and 1,3,5-tri[(3-pyridyl)-phen-3-
yl]benzene (TmPyPB) is ETL, respectively (Figure 4a). All the
devices showed the EL spectra exactly consistent with the solid-
state PL spectra of these complexes, verifying the electro-
generated exciton confinement on the emissive cores (inset of
Figure 4b).
Figure 4. (a) Device configuration and energy level scheme of the bilayer non-doped devices and the chemical structures of the involved materials; (b) EL spectra
(inset) and luminance-current density (J)-voltage curves; (c) Efficiency vs. luminance relationships.
The full-conjugated structure of Ir(PBI)3 and its strong
intermolecular interactions facilitate the carrier injection and
transportation in its film. Therefore, among these emitters,
Ir(PBI)3 supported the highest current density (J) to its devices,
accompanied by the highest luminance when voltage less than 8
V (Figure 4b). In contrast, due to the inert propylene-induced
electroactivity reduction, J of Ir(CzPOPBI)3-based devices was
reduced, but which was still 10 folds of that of Ir(CzPBI)3-based
analogues. In this case, the monopolar shell in Ir(CzPBI)3
doubtlessly shielded the electron injection and transportation in
its film, rendering the smallest J, as well as the exponentially
decreased luminance, for its devices. It is noteworthy that with
the smaller J, Ir(CzPOPBI)3 endowed its devices with the
operation voltages comparable to those of Ir(PBI)3-based
analogues. The exactly balanced charge flux supported by
Ir(CzPOPBI)3 was further verified by the linear relationship
between luminance and J of its devices in logarithmic scale,
manifesting the effect of the ambipolar shell on remedying the
defect of CES-type systems in electrical performance (Figure 5).
Furthermore, the throughout linear luminance-J relationship of
Ir(CzPOPBI)3-based devices strongly evidenced the effectively
reduced roll-off. When voltage exceeded 8 V, the luminance of
Ir(CzPOPBI)3-based device became larger than that of Ir(PBI)3-
based analogues, which should be ascribed to the suppressed
quenching effects at high exciton concentrations in the former.
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As designed, Ir(CzPOPBI)3 realized the state-of-the-art EL
efficiencies with the maxima of 44.1 cd A-1 for current efficiency
(CE), 46.2 lm W-1 for PE and 12.5% for EQE, respectively, which
is among the best results for bilayer spin-coated host-free
devices to date (Figure 4c). In comparison, the efficiencies of
Ir(CzPBI)3-based devices were almost halved, e.g. the peak
values of 23.5 cd A-1 and 6.9%, however, which were still about
50% higher than those of Ir(PBI)3-based analogues. Therefore,
both monopolar and ambipolar shells in Ir(CzPBI)3 and
Ir(CzPOPBI)3 can provide the effective and comparable
suppression effects on TTA. In this sense, their disparity in EL
efficiencies should be attributed to the differences of their shells
in electrical properties, especially in charge flux balance and
correlated ECQ/TPQ suppression.
of an ambipolar shell as proved with Ir(CzPOPBI)3, the shell-to-
core charge transfer and shell-supported excess charge export
can be optimized to effectively suppress ECQ/TPQ effect by
more than 55%. Therefore, the superiority of CES-type core-
shell organic nanoemitters in controlling exciton recombination
and quenching verifies their great potential as single-emitter
EMLs of nano-pixel units, which paves the way for realizing
high-efficiency SRD devices.
Experimental Section
Materials and instruments. All the reagents and solvents were
purchased from Aldrich and Acros companies and used without further
purification.
1H NMR spectra were recorded using a Varian Mercury plus
400NB spectrometer relative to tetramethylsilane (TMS) as internal
standard. Molecular masses were determined by a FINNIGAN LCQ
Electro-Spraying Ionization-Mass Spectrometry (ESI-MS), or a MALDI-
TOF-MS. Elemental analyses were performed on a Vario EL III elemental
analyzer. Absorption and photoluminescence (PL) emission spectra of
the target compound were measured using a SHIMADZU UV-3150
spectrophotometer and a SHIMADZU RF-5301PC spectrophotometer,
respectively. Thermogravimetric analysis (TGA) and differential scanning
calorimetry (DSC) were performed on Shimadzu DSC-60A and DTG-60A
thermal analyzers under nitrogen atmosphere at a heating rate of 10 °C
min-1. Cyclic voltammetric (CV) studies were conducted using an Eco
Chemie B. V. AUTOLAB potentiostat in a typical three-electrode cell with
a platinum sheet working electrode, a platinum wire counter electrode,
and
a
silver/silver nitrate (Ag/Ag+) reference electrode. All
nitrogen
electrochemical experiments were carried out under
a
atmosphere at room temperature in dichloromethane. Phosphorescence
spectra were measured in dichloromethane using an Edinburgh FPLS
920 fluorescence spectrophotometer at 77 K cooling by liquid nitrogen.
The time decay spectra was measured using Time-Correlated Single
Photon Counting (TCSPC) method with a microsecond pulsed Xenon
light source for 1 μs-10 s lifetime measurement, the synchronization
photomultiplier for signal collection and the Multi-Channel Scaling Mode
of the PCS900 fast counter PC plug-in card for data processing.
Figure 5. Luminance-J relationships of the bilayer non-doped devices.
Assuming the influences of TTA effects in Ir(CzPBI)3 and
Ir(CzPOPBI)3-based devices can be excluded, the relative
variation of ECQ/TPQ effects in these two devices can be
estimated according to equation (1):
Synthetic procedure. 4-Methoxyphenyl-diphenylphosphine oxide (1): In
Ar, 13 mL (0.1 mol) of 4-bromoanisole was added dropwise at 0 oC to
kTBPQ
kTAPQ
B0  B
A0  A
(1)

2.43
g (0.1 mol) of magnesium chips. After 1h, 16 mL of
chlorodiphenylphosphine was added dropwise and the mixture was
stirred for 12h. The reaction was quenched with water and extracted with
dichloromethane. The organic layer was dried with anhydrous Na2SO4.
The solvent was removed in vacuo. The residue was dissolved in
where k is ECQ/TPQ index, 0 and  refer to the theoretical
EQE value estimated by PLQY and outcoupling ration of 0.25
and the practical maximum EQE, and A and B represent two
different devices, respectively. As the result, the ECQ/TPQ-
induced efficiency decrease in Ir(CzPOPBI)3-based devices was
dramatically reduced by 55% in contrast to Ir(CzPBI)3-based
analogues, which was further evidenced by the remarkably
limited efficiency roll-offs at high luminance for the former.
dichloromethane. Hydrogen peroxide was added at
0
oC, and the
reaction mixture was stirred for 4h. The reaction was extracted with
saturated sodium hydrogensulfite solution. The organic layer was dried
with anhydrous Na2SO4. Then, the solvent was removed in vacuo. The
residue was purified by flash column chromatography. Yield: 22 g of
white powder (60%). 1H NMR (TMS, CDCl3, 400 MHz): δ = 7.53-7.58 (m,
4H), 7.50-7.60 (m, 4H), 7.40-7.45 (m, 4H), 6.97(dd, J1 = 2.0 Hz, J2 = 8.8
Hz, 2H), 3.84 (s, 3H). MALDI-TOF: m/z (%): 308 (100) [M+]; elemental
analysis (%) for C19H17O2P: C 74.02, H 5.56; found: C 74.07, H 5.53.
Conclusions
4-Hydroxyphenyl-diphenylphosphine oxide (2): In Ar, 10 mL (80
mmol) of BBr3 was added dropwise at -78 oC to a solution of 1 (15 g, 40
mmol) in dichloromethane. After 1h, the reaction mixture was warm to
room temperature and stirred for another 12h. The reaction was
A simple and effective strategy for developing nanoemitters for
SRD applications was demonstrated with the feature of charge-
exciton spatial allocation through core-shell structures. In virtue
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quenched with water and extracted with dichloromethane. The organic
layer was dried with anhydrous Na2SO4. The solvent was removed in
vacuo. The residue was purified by flash column chromatography. Yield:
12 g of white powder (80%). 1H NMR (TMS, CDCl3, 400 MHz): =7.61-
J = 8.0 Hz, 3H). MALDI-TOF: m/z (%): 1000 (100) [M+]; elemental
analysis (%) for C57H39IrN6: C 68.45, H 3.93, N 8.40; found: C 68.40, H
3.95, N 8.41.
Ir(CzPBI)3: prepared according to the literature procedures.[16] 1H
NMR (TMS, CDCl3, 400 MHz): δ = 8.050 (s, 6H), 8.027 (s, 12H) , 7.214-
7.316 (m, 27H), 7.139 (d, J = 8.8 Hz, 6H), 6.867 (d, J = 8.4 Hz, 6H),
6.886 (t, J = 7.6 Hz, 3H), 6.691 (d, J = 8.4 Hz, 3H) , 6.546-6.592 (m, 6H),
6.128 (d, J = 8 Hz, 3H) , 4.360-4.520 (m, 6H) , 4.200-4.360 (m, 12H),
4.000-4.100 (m, 6H) , 3.820-3.920 (m, 12H), 2.280-2.320 (m, 6H),
2.180-2.260 (m, 6H), 1.960-2.100 (m, 6H), 1.357 (s, 54H) , 1.331 (s,
54H) , 1.304 (s, 54H); 13C NMR (CDCl3, 100 MHz): δ = 162.042, 162.024,
159.415, 150.943, 150.924, 142.298, 142.038, 141.601, 139.100,
138.839, 138.594, 135.119, 126.904, 123.594, 123.432, 122.927,
122.838, 122.775, 121.572, 121.521, 121.464, 116.407, 116.335,
116.234, 113.399, 108.996, 108.064, 107.992, 107.770, 82.798, 67.903,
65.252, 42.149, 42.125, 40.228, 40.104, 40.083, 40.045, 40.023, 34.630,
34.604, 32.043, 30.955, 29.606, 28.928, 28.733 ppm; MALDI-TOF: m/z
(%): 3743 (100) [M+]; elemental analysis (%) for C246H288IrN15O6: C 78.9,
H 7.75, N 5.61; found: C 79.0, H 7.71, N 5.66.
7.66 (m, 4H), 7.41-7.45 (m, 2H), 7.32-7.38 (m, 4H), 7.35-7.40 (dd, J1
=
11.8 Hz, J2 = 8.6 Hz，2H), 6.92-6.95 (dd, J1 =2.4Hz, J2 = 8.8 Hz, 2H).
MALDI-TOF: m/z (%): 294 (100) [M+]; elemental analysis (%) for
C18H15O2P: C 73.46, H 5.14; found: C 73.49, H 5.15.
4-(3-Chloropropoxy)phenyl-diphenylphosphine oxide (3): A mixture
of 2 (5.56 g, 20 mmol), TBAB (0.1612 g, 0.5 mmol), KOH (2.24 g,
40 mmol) and 1,3-dichloropropane (40 mL, 400 mmol) was heated to 90
oC and stirred for 12h. The reaction was quenched with water and
extracted with dichloromethane. The organic layer was dried with
anhydrous Na2SO4. The solvent was removed in vacuo. The residue was
purified by flash column chromatography. Yield: 4.5 g of white powder
(75%). 1H NMR (TMS, CDCl3, 400 MHz): = 7.51-7.56 (m, 4H),
7.45-7.53 (m, 2H), 7.25-7.41 (dd, J1 = 11.8 Hz, J2 = 8.6 Hz, 2H), 7.31-
7.34 (m, 4H), 6.90-6.95 (dd, J1 = 2.4 Hz, J2 = 8.8 Hz, 2H), 4.02-4.05 (d, J
= 8 Hz, 2H), 3.72-3.75 (d, J = 8.6 Hz，2H), 2.21-2.24 ppm (m, 2H).
MALDI-TOF: m/z (%): 370 (100) [M+]; elemental analysis (%) for
C
21H20ClO2P: C 68.02, H 5.44; found: C 68.05, H 5.42.
Ir(CzPOPBI)3: In Ar, 5 (1.32 g, 1.1 mmol) and IrCl3.nH2O (n= 1-3,
0.164 g, 0.5 mmol) were dissolved in 2-ethoxyethanol (15 mL), H2O (15
mL) and THF (5 mL). The mixture was heated to 110 oC and stirred for
24h. Then, the system was cooled to room temperature. The precipitate
was collected by filtration and washed with anhydrous ethanol (3×10 mL)
to afford the crude chlorobridged dimer as greenish yellow powder, which
was directly used in the next step without further purification. Then, 5
(0.593 g, 0.5 mmol), dimer (1.3 g, ~0.25 mmol), and K2CO3 (0.345 g, 2.5
mmol) were suspended in glycerol (15 mL). The mixture was heated to
240 °C and stirred for 72 h. Then, the system was poured into water (50
mL) and extracted with CH2Cl2 (3×50 mL). The organic phase was
combined and dried with anhydrous Na2SO4. After removal of solvent,
the residue was purified by flash column chromatography. Yield: yellow
powder with the total yield of 7%. 1H NMR (TMS, CDCl3, 400 MHz): =
8.006 (d, J = 3.2 Hz, 12H), 7.580 (q, J1 = 11.6 Hz, J2 = 7.2 Hz, 12H),
7.531-7.439 (m, 12H), 7.435-7.342 (m, 12H), 7.318-7.119 (m, 33H),
6.843 (t, J = 7.6 Hz, 3H), 6.671 (d, J = 7.2 Hz, 6H), 6.599 (s, 3H), 6.505 (t,
J = 7.4 Hz, 3H), 6.016 (d, J = 7.2 Hz, 3H), 4.547-4.435 (m, 6H), 4.428-
4.328 (m, 6H), 4.319-4.123 (m, 6H), 3.975-3.745 (m, 12H), 3.622-3.487
(m, 6H), 2.323-2.186 (m, 6H), 2.128-1.885 (m, 12H), 1.324 (s, 54H),
1.299 (s, 54H). 13C NMR (TMS, CDCl3, 100 MHz): = 161.995, 161.167,
161.140, 159.140, 150.606, 142.417, 142.049, 141.613, 141.546,
139.052, 139.011, 138.797, 135.737, 133.946, 133.836, 133.463,
133.432, 133.412, 132.434, 132.373, 132.043, 131.945, 131.822,
131.798, 130.960, 128.492, 128.372, 126.892, 124.600, 123.509,
123.376, 123.317, 122.688, 122.536, 121.565, 121.449, 116.227,
116.193, 115.567, 114.486, 114.355, 112.933, 109.177, 107.977,
107.948, 67.688, 65.150, 63.809, 40.740, 39.963, 39.838, 34.558,
34.524, 31.999, 31.981, 29.551, 29.102, 28.690. MALDI-TOF: m/z (%):
3790 (100) [M+]; elemental analysis (%) for C240H261IrN12O12P3: C 76.04,
H 6.94, N 4.43; found: C 76.01, H 6.97, N 4.45.
9,9'-(3,3'-(4-(1H-benzo[d]imidazol-2-yl)-1,2-
phenylene)bis(oxy)bis(propane-3,1-diyl))bis(3,6-di-tert-butyl-9H-
carbazole) (4): In Ar, the prepared benzimidazole derivatives[16] (0.226 g,
1 mmol), TBAB (0.0644 g, 0.2 mmol), KOH (0.112 g, 2 mmol), and 3,6-di-
tert-butyl-N-(3-chloropropyl)-carbazole (0.67 g, 2 mmol) were dissolved in
10 mL of THF. The mixture was heated to 70 oC and stirred for 24 h. The
reaction was quenched with water and extracted with dichloromethane.
The organic layer was dried with anhydrous Na2SO4. The solvent was
removed in vacuo. The residue was purified by flash column
chromatography. Yield: 0.65 g of white powder (75%). 1H NMR (TMS,
CDCl3, 400 MHz): = 8.121-8.132 (m, 4H), 7.626-7.637 (m, 2H), 7.473-
7.505 (m, 2H), 7.409-7.443 (m, 5H), 7.338-7.390 (m, 4H), 7.192-7.214 (m,
2H), 6.707-6.735 (m, 1H), 4.573 (t, J = 6.4 Hz, 2H), 4.424 (t, J = 6.2 Hz,
2H), 2.387-2.413 (m, 2H), 2.213-2.223 (m, 2H), 1.446 ppm (s, 36).
MALDI-TOF: m/z (%): 864 (100) [M+]; elemental analysis (%) for
C59H68N4O2: C 81.90, H 7.92, N 6.48; found: C 81.95, H 7.93, N 6.48.
9,9'-(3,3'-(4-(1-(3-(4-(Diphenylphosphoryl)phenoxy)propyl)-1H-
benzo[d]imidazol-2-yl)-1,2-phenylene)bis(oxy)bis(propane-3,1-
diyl))bis(3,6-di-tert-butyl-9H-carbazole) (5): In Ar,
a mixture of NaH
(0.0288 g, 1.2 mmol), 4 (0.53 g, 0.6 mmol), TBAB (0.02 g, 0.06 mmol)
and 3 (0.44 g, 1.2 mmol) was dissolved in 10 mL of THF. The reaction
mixture was heated to 70 oC and stirred for 24h. The reaction was
quenched with water and extracted with dichloromethane. The organic
layer was dried with anhydrous Na2SO4. The solvent was removed in
vacuo. The residue was purified by flash column chromatography. Yield:
0.58 g of white powder (80%). 1H NMR (TMS, CDCl3, 400 MHz): =
8.096 (s, 2H), 8.068 (s, 2H), 7.777 (d, J = 7.6 Hz, 1H), 7.598-7.647 (m,
4H), 7.361-7.523 (m, 16H), 7.232-7.303 (m, 3H), 7.141-7.189 (m, 2H),
6.782 (d, J = 8Hz, 1H), 6.714-6.741 (dd, J1 = 1.6 Hz, J2 = 8.8 Hz, 2H),
4.559-4.608 (m, 4H), 4.399 (t, J = 3.2 Hz, 2H), 4.078 (t, J = 3.2 Hz, 2H),
4.037 (t, J = 3.2 Hz, 2H), 3.732 (t, J = 3.2 Hz, 2H), 2.396-2.448 (m, 4H),
2.199-2.138 (m, 2H), 1.477 (s, 18H), 1.386 ppm (s, 18H). MALDI-TOF:
m/z (%): 1198 (100) [M+]; elemental analysis (%) for C80H87N4O4P: C
80.10, H 7.31, N 4.67; found: C 80.15, H 7.30, N 4.69.
DFT calculations. DFT computations were carried out with different
parameters for structure optimizations and vibration analyses. The
ground states of molecules in vacuum were optimized without any
assistance of experimental data by the restricted and unrestricted
formalism of Beck's three-parameter hybrid exchange functional[19] and
Lee, and Yang and Parr correlation functional[20] (B3LYP) for C, H, N,
and O and effective core potential (ECP) of LANL2DZ for Ir. The
optimization was performed at the level of 6-31G(d). The fully optimized
stationary points were further characterized by harmonic vibrational
frequency analysis to ensure that real local minima had been found
without imaginary vibrational frequency. The total energies were also
Ir(PBI)3: prepared according to the literature procedures.[5a] 1H
NMR (TMS, CDCl3, 400 MHz): = 7.55-7.65 (m, 9H)，7.42-7.53 (dd, J1
= 14.2 Hz, J2 = 5.6 Hz, 6H)，7.01-7.09 (m, 6H)，6.86-6.88 (d, J = 8.4 Hz,
3H)，6.80-6.83 (t, J = 7.4 Hz, 3H)，6.70-6.74 (t, J = 7.0 Hz, 3H)，6.61-
6.63 (d, J = 7.6 Hz, 3H)，6.51-6.54 (t, J = 7.4 Hz, 3H)，6.38-6.40 ppm (d,
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10.1002/chem.201705037
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corrected by zero-point energy both for the ground state. All
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cleaned respectively with acetone and ethanol in an ultrasonic bath. After
treated with UV-ozone for 20 min, a layer of PEDOT:PSS for enhancing
hole injection was spin-coated onto the substrate and then baked at 120
oC for 10 min. The emitting layer was dissolved in chlorobenzene and
then spin-coated onto the PEDOT:PSS covered substrates. Afterwards,
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controlled with a customized software to simultaneously record the
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Acknowledgements
CH and GX contributed equally to this work. This project was
financially supported by Changjiang Scholar Program of Chinese
Ministry of Education (Q2016208), NSFC (21672056, 61605042
and 21602048), National Postdoctoral Program for Innovative
Talents (BX201600048), Heilongjiang Postdoctoral Special Fund
(Postdoctoral Youth Talent Program) (LBH-TZ1617), Science
and Technology Bureau of Heilongjiang Province (JC2015002)
and Education Bureau of Heilongjiang Province (HDRCCX-
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Octhterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J.
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Entry for the Table of Contents (Please choose one layout)
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A core-shell-structured
nanophosphor named
Chunmiao Han, Guohua Xie and Hui
Xu*
Ir(CzPOPBI)3 is developed,
whose ambipolar shell can
effectively balance the shell-to-core
charge transfer and excess charge
export and thereby suppress
exciton-charge quenching effects in
the solution-processed bilayer
OLED for super-resolution display
applications.
Page No. – Page No.
Highly Efficient Solution-Processible
Nanophosphor with Ambipolar Shell
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