Intramolecular hydrogen bond-enhanced electroluminescence performance of hybridized local and charge transfer (HLCT) excited-state blue-emissive materials

Article abstract of DOI:10.1039/d0tc04590j

The hybridized local and charge transfer (HLCT) excited state is a successful strategy to produce both high external and internal quantum efficiencies. Based on the HLCT scheme, two isomeric donor-acceptor (D-A)-type excited-state intramolecular proton transfer (ESIPT) chromophores of o-hydroxyphenyl phenanthroimidazole (HPI)-based emissive molecules (mTAHPI and pTAHPI) and their OH-protected derivatives (pTAPI) were designed and explored for organic light-emitting diodes (OLEDs). The photophysical study and density functional theory (DFT) calculations revealed that all molecules possessed the HLCT excited-state characters without exhibiting ESIPT photophysical properties, whereas the nuclear magnetic resonance spectroscopy, single-crystal and physical property analyses discovered the existence of strong intramolecular H bonds and intermolecular interactions in both mTAHPI and pTAHPI. Consequently, their OLEDs displayed blue emissions with a narrow full width at half maximum (65-68 nm) and achieved excellent electroluminescence (EL) performance with a low turn-on voltage of 2.8 V. Particularly, pTAHPI-based devices showed the highest maximum external quantum effciency (EQE) of 8.13% with an ultra-high brightness of 18?100 cd m-2. The maximum singlet exciton utilization efficiency (ηs) of the device was estimated to be as high as 94%, which is among the best results of blue electroluminescence to our knowledge. This journal is

Full text of DOI:10.1039/d0tc04590j

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ARTICLE
Intramolecular hydrogen bond-enhanced electroluminescent
performance of hybridized local and charge transfer (HLCT)
excited state blue emissive materials
Received 00th January 20xx,
Accepted 00th January 20xx
Wan Li,a Pongsakorn Chasing,a Wachara Benchaphanthawee,b Phattananawee Nalaoh,a Thanyarat
Chawanpunyawat,a Chokchai Kaiyasuan,a Nawee Kungwan,b Supawadee Namuangruk,c Taweesak
Sudyoadsuka and Vinich Promarak*ad
DOI: 10.1039/x0xx00000x
The hybridized local and charge-transfer (HLCT) excited state is a successful strategy to produce both high external and
internal quantum efficiency. Based on HLCT scheme, two isomeric donor-acceptor (D-A) type excited state intramolecular
proton transfer (ESIPT) chromophore of o-hydroxyphenyl phenanthroimidazole (HPI)-based emissive molecules (mTAHPI
and pTAHPI) and its OH protected derivative (pTAPI) were designed and explored for organic light-emitting diodes (OLEDs).
The photophysical study and density functional theory (DFT) calculations revealed that all molecules possessed the HLCT
excited state characters without exhibiting ESIPT photophysical properties, whereas the nuclear magnetic resonance
spectroscopy, single-crystal and physical properties analyses discovered the existence of strong intramolecular H-bond and
intermolecular interactions in both mTAHPI and pTAHPI. Consequently, their OLEDs displayed blue emissions with a narrow
full width at half maximum (65-68 nm) and achieved excellent electroluminescent (EL) performance with a low turn-on
voltage of 2.8 V. Particularly, pTAHPI-based device showed the highest maximum external quantum (\54(-5: (EQE) of 8.13%
with an ultra-high brightness of 18100 cd m-2. The maximum singlet exciton utilization efficiency T_s) of the device was
estimated to be as high as 94%, which is among the best results of blue electroluminescence to our knowledge.
25% and the remaining 75% of the electronically excited states
generally relax via non-radiative decay processes during
electroluminescence. Accordingly, the highest theoretical EQE
Introduction
Over the past few decades, we have seen a tremendous
progress in the development of organic light-emitting diode
(OLED) science and technology.1 Many groups have exerted
much effort to improve the OLED efficiency from the points of
view of both new material designs and device architectures.2
Nowadays, OLEDs have been demonstrated to be successful in
the market, including uses in TVs, monitors, smartphones,
wearable devices and lighting. Still, the future retains even
better potential for this technology as it can offer an utterly new
generation of low-cost, lightweight, and flexible electronic
devices. For such applications, external quantum efficiency
(EQE) is one of the vital parameters for OLEDs. Based on spin-
statistics theorem OLEDs using fluorescent materials are
restricted to the theoretical internal quantum efficiency (IQE) of
is limited to only about 5%, assuming a light out-coupling
constant of 20% in devices, which is a major inadequacy for
industrial applications.3 To attain OLEDs with EQEs exceeding
the spin-statistical limit, triplet excitons have been utilized. It
has been shown that electro-phosphorescent OLEDs (PhOLEDs),
utilizing organometallic phosphors of heavy transition metals,
can produce a 100% IQE.4 However, they have some serious
drawbacks such as toxicity of these metals and their rarity,
fabrication cost and device stability of the blue devices. Besides,
many efforts have been also made to utilize triplet excitons to
enlarge the theoretical IQE of fluorescent materials such as
triplet-triplet annihilation (TTA),2d,5 thermally activated delayed
fluorescence (TADF),2b,6 and hybridized local and charge-
transfer (HLCT) technologies,1f,7 but TTA process has a 62.5%
upper limit of singlet exciton utilization efficiency T_s) and TADF
devices suffer from serious roll-off at high current density due
to the long-lived first triplet excited state (T1) excitons in TADF
materials. Hence, HLCT materials holding nondelayed
fluorescent mechanism and the maximum _s approaching
nearly 100% have been the first option for the development of
a new generation of organic electroluminescent materials.7b,8
Moreover, being different from phosphorescent materials,
OLEDs based on HLCT mechanism are cheaper and sufficient for
full-color display especially blue.2b,9 The HLCT excited state has
contemporaneous reactions of local emission (LE) and excited-
a Department of Materials Science and Engineering, School of Molecular Science
and Engineering, Vidyasirimedhi Institute of Science and Technology, Wangchan,
Rayong 21210, Thailand. E-mail: vinich.p@vistec.ac.th
b Department of Chemistry, Faculty of Science, Chiang Mai University, Amphur
Muang, Chiang Mai 50200, Thailand.
c National Nanotechnology Center (NANOTEC), National Science and Technology
Development Agency, Pathum Thani 12120, Thailand
d Research Network of NANOTEC-VISTEC on Nanotechnology for Energy,
Vidyasirimedhi Institute of Science and Technology, Wangchan, Rayong 21210,
Thailand.
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
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reaction of borolane 3 with either bromo phenanthroimidazoles S1, ESI†), suggesting that the intramolecular H-bond of mTAHPI
5 or 6 afforded the related pTAHPI and mTAHPI as pale-yellow becomes strengthened upon photoexcitation. Accordingly, if
solids in good yields. To evaluate the existence and effect of there is ESIPT process taking place in both molecules, mTAHPI
ESIPT process in HPI moiety of the molecules, pTAHPI was then will be more susceptible to ESIPT than pTAHPI. In addition, the
reacted with benzyl bromo in the presence of KOH to give the simulated enol absorption and enol emission spectra based on
O-benzyl-protected pTAPI in 89% yield. All compounds were the vertical electronic transition computed by using TD-CAM-
fully characterized by standard spectroscopic techniques and B3LYP/6-31G(d,p) basis set17 (Fig. 1b) were in good agreement
the results agreed with their expected chemical structures. As with the experimental results. As shown in Fig. 2, for all
shown in Fig. S1 (ESI†), each 1H-NMR spectrum of both pTAHPI molecules, the highest occupied molecular orbitals (HOMO) are
and mTAHPI detected a characteristic hydrogen-bonded OH fully delocalized over TPA and anthracene moieties, while the
proton signal at exceptionally down-fields of 14.26 and 13.52 lowest unoccupied molecular orbitals (LUMO) are mainly
ppm, respectively, indicating the presence of a six-membered localized on the anthracene unit with little distribution on the
ring intramolecular hydrogen-bond system between -OH and - adjacent phenyl rings. Therefore, the HOMO and LUMO
C=N- units (Scheme 1) when they were dissolved in chloroform- distributions hold a large overlap over the anthracene moiety,
d solution.
which is rather beneficial for boosting the LE component and
It should be realized that the existence of intramolecular H- enhancing the photoluminescence (PL) efficiency of these
bonding in both pTAHPI and mTAHPI can promote the proton molecules.19
transfer through a characteristic four-level photocycle (5- or 6-
membered cyclic transition state) resulting in ESIPT process
a)
b)
mTAHPI
pTAHPI
1.0
272
307
446
occurring in the molecules.14 Many HPI moiety contained
molecules have been observed to exhibit ESIPT via a strong
intramolecular hydrogen bond between its OH proton donor
and -C=N- proton acceptor.12,15 However, it has been reported
that the introduction of an electron-donating triphenylamine
(TPA) group into the side of oxazole of ;RT;mR
hydroxyphenyl)oxazoles and side of azole of 2-(2-
hydroxyphenyl)-azoles (a class of typical ESIPT molecules) can
lead to a sole enol-form emission in PL spectra with +4n(2(-.
polar solutions, and the ESIPT keto-form emission is suppressed
completely.16 The TPA bearing ;RT;mR8:+2,<:>8(-:'V,<)Q,'(*
displayed a deep-blue enol-form emission in both PL and EL
spectra with narrow emission spectra owing to the absence of
the keto-form emission at the long wavelength region.16a Thus,
it is noteworthy to gain a theoretical understanding of the ESIPT
process in HPI moiety of mTAHPI and pTAHPI. Accordingly, the
ground-state potential energy curves (GS-PECs) and excited-
state potential energy curves (ES-PECs) of the proton transfer
(PT) coordinates in gas phase as a function of the O–H bond
length were constructed using the CAM-B3LYP/6-31G(d,p)
approach.17 This approach has been utilized and proven to be
reliable in providing qualitative energetic pathways for the PT
process.18 As depicted in Fig. 1a, all molecules exhibited high
energy barriers in both ground-state (12.46-12.65 kcal/mol) and
excited-state (9.23-12.55 kcal/mol), suggesting that the PT
process in mTAHPI and pTAHPI is unlikely to occur both in the
S0 and S1 states. The optimized structures of mTAHPI and
pTAHPI in the ground state reveal a nearly planar conformation
between phenol and five-membered imidazole ring with small
dihedral angles ( ) of 6-10o, which could be the result of a strong
intramolecular H-bond formed between the two units (Fig. 2).
On the other hand, without the ability to form intramolecular
hydrogen bond the O-benzyl-protected phenol of pTAPI aligns
almost perpendicular to the plane of five-membered imidazole
ring with of 84o. The calculated intramolecular H-bond (N···H)
distance of mTAHPI are shortened from 1.656 Å in the S0 state
to 1.638 Å in the S1 state, while there is no obvious difference
in the N···H distances of the S0 and S1 states of pTAHPI (Table
S1
S0
80
20
enol abs
enol em
9.23
12.46
12.55
12.65
361
mTAHPI
0
273
312
451
S1
S0
80
20
360
enol abs
enol em
pTAHPI
0
1.2
1.4
1.6
1.8
300 400 500 600 700
Wavelength (nm)
O-H Distance (Å)
Fig. 1 a) Calculated potential energy curves in the S0 and S1 and b) simulated enol
absorption and enol emission spectra of mTAHPI and pTAHPI computed at TD-
CAM-B3LYP/6-31G(d,p) level.
6o
75o
75o
74o
Optimized
structure
10o
80o
83o
84o
77o
HOMO
LUMO
mTAHPI
pTAHPI
pTAPI
Fig. 2 The optimized structures with dihedral angles and HOMO-LUMO orbitals of
mTAHPI, pTAHPI and pTAHPI computed at TD-CAM-B3LYP/6-31G(d,p) level.
The UV-vis absorption and photoluminescence (PL) spectra
of mTAHPI, pTAHPI and pTAPI measured in dilute toluene
solutions and neat films are shown in Fig. 3a, and the
characteristics are summarized in Table 1. Their absorption
bands in the short-wavelength region (<350 nm) were
corresponded to the !–!* transition or the n–!* transition of
triarylamine and aromatics, and the typical absorptive bands of
anthracene, while the longest wavelength absorption at "377
nm might derive from an intramolecular charge transfer (ICT)
transition from donor to acceptor. The compounds exhibited
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strong blue emission in the solution with maximum emission dropping to 13-21%, indicating that intermolecular !-!
bands in the rage of 453-459 nm with the #PL measured by interactions exist in the film state causing a strong fluorescence
integrating sphere to be as high as 76-89%. The PL spectrum of quenching. Such intermolecular aggregations have been
pTAHPI was found to match well with PL of its OH-protected detected in several anthracene derivatives.21 The #PL values of
derivative pTAPI. Meanwhile, the stokes shifts between the the molecules in film states could be improved by doping in `mR
absorption and PL spectra of mTAHPI and pTAHPI were K4*TLR5)2K)Q,':'VRB=BmRK4>8(-:' (CBP) film. With the optimum
calculated to be 78-86 nm, which are far too low for ESIPT doping concentration of 20wt% the #PL values of mTAHPI,
molecules.14a,20 A partial overlap of the absorption and PL pTAHPI and pTAPI in doped films were evaluated to be 46%,
spectra was also observed in both cases. These results confirm 43% and 45% respectively. As shown in Fig. S2 (ESI†), the PL
that no ESIPT take place in mTAHPI and pTAHPI and their PL spectra of the doped films are slightly blue shifted as compared
emissions are enol emission, consistent well with the DFT to the neat films with no emission peaks of the CBP host matrix
findings. In the neat films, the PL spectra of mTAHPI, pTAHPI being spotted, indicating a complete energy transfer from the
and pTAPI were somewhat red shifted relative to their toluene CBP host to the dopants.
solutions (Fig. 3a) as well as their #PL values significantly
Table 1 Key physical data of the synthesized compounds.
#PL(%)e
sola/filmb/dfilmc/solidf
Tg/Tm/T5d
(oC)g
Eg
HOMO/LUMO
(eV)i
a
d
opt
Compd
$
$
PL (nm)
sola/filmb/dfilmc
Stokes shift
(nm)a
%
abs
(nm)
(ns)b
(eV)h
mTAHPI
pTAHPI
pTAPI
367
374
378
453/465/462
459/477/468
456/474/462
86
85
78
<1
1
89/13/46/38
87/16/43/28
76/21/45/20
-/293/501
-/325/513
150/-/370
2.73
2.72
2.97
-5.70/-2.97
-5.64/-2.92
-5.64/-2.87
2
c
a Measured in solution of toluene. b Measured in thin film coated on fused silica substrates. Measured in 20 wt% doped CBP thin film coated on fused silica substrates.
e
f
d Transient PL decay life time of the thin films. Absolute PL quantum yield evaluated using an integrating sphere. Obtained from solid powders. g Measured by DSC
opt
i
opt
(2nd scan) and TGA under N2 flow. hEstimated from absorption onset in thin film: Eg = 1240/$onset
. HOMO measured by AC-2 of neat film and LUMO = HOMO + Eg .
solvatochromic shifts of 89-105 nm from blue to orange. In
addition, their PL spectra in low-polarity hexane reveal mild
vibronic structures and then the PL spectra gradually broaden
and become structureless with the increasing of solvent
polarity. Furthermore, the correlation between the Stokes shift
TzaRzf) against the solvent orientational polarizability ('f) was
plotted and linear fitted according to Lippert-Mataga equation
(Table S2, ESI†). The dipole moment ()e) of the excited state,
describing the variation of excited state of the molecules, can
be estimated from the slope of the Lippert-Mataga plots. The
ground-state dipole moments ()g) were estimated using DFT at
the level of B3LYP/6-31G(d,p) to be 5.00 D, 4.89 D and 3.21 D
for mTAHPI, pTAHPI and pTAPI, respectively. As shown in Fig.
3c, all molecules displayed to two different fitted slopes in low-
polarity and high-polarity regions, and accordingly two )e values
were calculated to be 17.30 D and 31.31 D for mTAHPI, 17.60 D
and 32.09 D for pTAHPI and 16.29 D and 31.77 D for pTAPI.
These results signify the coexistence of CT and LE components,
which are consistent with the description of HLCT state.23 In
other words, mTAHPI, pTAHPI and pTAPI possess HLCT
character. The HLCT is a valuable excited state which originates
from a state-mixing of the weak binding energy of CT state and
large radiative transition rate of LE state.7b,8b The presence of
HLCT state could ensure a relatively high photoluminescence
(PL) efficiency and a large fraction of singlet exciton generation
in electroluminescence (EL).24 Notably, both )g and )e values of
mTAHPI and pTAHPI are bit higher than pTAPI in both high-
polarity or low-polarity regions, which could be the effect of the
intramolecular H-bonding in mTAHPI and pTAHPI. This could
influence the properties of mTAHPI and pTAHPI in solution and
thin film when compared with pTAPI. As listed in Table S2, all
molecules showed high #PL in different solutions. Generally, the
4
3
2
1
0
a)
c) 9k
8k
mTAHPI
linear fit
pTAHPI
linear fit
pTAPI
mTAHPI
pTAHPI
pTAPI
1
31.31 D
7k
linear fit
32.09 D
31.77 D
6k
17.30 D
5k
17.60 D
16.29 D
4k
0
0.00 0.05 0.10 0.15 0.20 0.25 0.30
300 350 400 450 500 550 600 650
'f
Wavelength (nm)
b)
89 nm
d)103
Hexane
Toluene
Chloroform
Hexane
mTAHPI
mTAHPI
Toluene
102
101
1,4-dioxane
Chlorobenzene
100
103
95 nm
Chloroform
Ethyl Ether
Ethyl Acetate
THF
DCM
Acetone
Acetonitrile
pTAHPI
pTAHPI
102
101
100
103
105 nm
DCM
pTAPI
pTAPI
102
101
100
DMF
Acetone
Acetonitrile
400
500
600
700
800
0
20
40
60
80
100
Time (ns)
Wavelength(nm)
Fig. 3 a) The absorption and v0,2(*5(-5( spectra in toluene solution (solid line)
and in neat w'1* (dashed line) coated on fused silica substrates. b) PL spectra in
various polarity solvents. c) linear w..4-3 of the Lippert–Mataga plots ('f,
orientation polarizability of solvent media; (ay(f, Stokes shift a: absorption; f:
v0,2(*5(-5(VC d) Transient PL decay spectra in in various polarity solvents.
To further investigate the photophysical properties and
fluorescent characteristics of mTAHPI, pTAHPI and pTAPI, the
absorption and PL spectra in various solvent systems were
thoroughly evaluated. This solvatochromic experiment is
generally used to inspect the excited state properties for CT-
state molecule.7b,22 As depicted in Fig. 3b, from low-polarity
hexane to high-polarity acetonitrile, all molecules show large
4 | J. Name., 2012, 00, 1-3
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molecules based on CT state always show low radiative similar and NTOs of S0*S1 clearly displayed the HLCT transition
transition rate and poor PL (Sw54(-5:= which is mainly caused by characteristics (Fig. 4a) as it is comprised of both LE and CT
the spatially separated transition orbital of CT state, as well as transitions. The hole is mainly distributed on the TPA and
the CT state being a dark state in solutions with high polarity.25 anthracene, while the particle is largely spread over the
However, their high #PL values (60-82%) in polar solutions anthracene with a slight residue on the phenyl of TPA and
(acetone and acetonitrile) are the indication of the highly state- phenol of HPI. The hole and particle distributions are totally
mixed CT and LE states (or HLCT) in the molecules. Further study overlapped on the anthracene ring, indicating the LE-like
by time-resolved fluorescence spectroscopy revealed transition, whereas the hole and particle distributions do not
fluorescence traces of mTAHPI, pTAHPI and pTAPI with a single- overlap on the entire TPA unit, indicating a CT-like transition. As
exponential decay in +4n(2(-. solvent polarities (Fig. 3d), is evident from the energy landscape plots (Fig. 4b), in all cases
verifying that fluorescence evolves from only one excited state the energy gaps between the S1 and T2 states (<0.08 eV) are
and HLCT state was supposed to be formed rather than a simple substantially narrower than that between T2 and T1 states
mixture of the LE and CT states. (>1.25 eV), indicating that the RISC rate (kRISC) from the T2 to S1
To inspect the excited-state properties and confirm the state should be higher than the internal conversion rate (kICT
)
HLCT character of mTAHPI, pTAHPI and pTAPI, the W0)-.4w(+ from the T2 to T1 states, giving rise to a possibly hot-exciton
natural transition orbitals (NTOs) of S0*S1 were calculated channel for the RISC of the T2*S1 process according to the El-
using the TDA-B3LYP/6-31G(d,p) method based on the Sayed rule.26 Therefore, when the triplet excitons relax to the
optimized lowest singlet excited state geometry.17 In all lowest vibration level of T1, some of them can be converted to
molecules, the spatial distributions of holes and particles were singlet excitons through the T2*S1 channel.
Hole
Particle
a)
b)
S0 S1
+ = 0.279
83%
Singlets
Triplets
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
S
'EST = 0.06 eV
2
'EST = 0.08 eV
mTAHPI
'EST = 0.05 eV
T
T
3
2
LE + CT
S
1
S0 S1
+ = 0.808
87%
1.19 eV
1.25 eV
1.22 eV
T
1
pTAHPI
pTAPI
LE + CT
S0 S1
+ = 0.125
90%
S
0
pTAPI
mTAHPI
pTAHPI
LE + CT
Fig. 4 a) Natural transition orbitals (NTOs) of S0*S1 transition (+ represents the oscillator strength. The percentage indicates the possibility of the transition) and b) the
energy landscape of singlet and triplet excited states obtained from TDA-B3LYP/6-31G(d,p) calculations.
The presence of intramolecular H-bond and its impact on PL efficiency in neat film state of the molecule. The packing
molecular interactions, crystallinity, morphology and thermal interactions are also observed through edge-to-face C—H!}
stability of the materials were investigated. The single crystal of interactions between the phenyl group of imidazole unit and
mTAHPI was successfully grown from
a mixture of phenanthrene ring center, and among the triphenylamine units
dichloromethane:hexane and examined by single crystal X-ray (with molecular distances of 2.622-2.780 Å) (Fig. 5a, highlighted
diffraction (SCXRD). The crystallographic data are given in the in green and yellow colors, respectively). Moreover, such strong
Supporting Information (Table S3, ESI†). As shown in Fig. 5a, the interactions may rigidify the molecular structure for efficient
molecular structure shows the intramolecular H-bonding of radiative transition and narrow emission spectrum.19
O1—H1!N3 with the distance of 1.879 Å, indicating strong H- Accordingly, the #PL values of mTAHPI and pTAHPI in solid
bonds. The strong intramolecular H-bonds bring about a powder were recorded to be somewhat higher than pTAPI. The
relatively small of 12.9o between phenol and five-membered crystallinity of these as-synthesized mTAHPI, pTAHPI and pTAPI
imidazole ring as compared to that between phenol and solid powders was further evaluated by powder x-ray diffraction
anthracene ring (66.1o), resulting in a high degree of planarity (PXRD). As illustrated in Fig. 5b, the PXRD profile of mTAHPI
in o-hydroxyphenyl phenanthroimidazole (HPI) plane. The reveals amounts of intense diffraction peaks, indicating the
crystal packing shows the intermolecular interactions and presence of a long-range ordered structure and crystalline
stacking in a face-to-face manner, observing between the behavior of the material. The XRD pattern of pTAHPI was
anthracene units with the centroid-centroid distances of 4.024 roughly similar to that of mTAHPI but with relatively lower peak
Å (Fig. 5a, highlighted in red color). These separations are close intensity, while that of pTAPI displayed strong diffraction peak
to an effective intermolecular interaction distance (3.7 Å), at low ;~ value of bCYYÄ with few low-intensity peaks at higher
signaling the strong }–} stacking which could trigger a serious ;~C Hence, pTAPI was suspected to have a less crystallinity or
fluorescence aggregation-caused quenching, giving rise to low molecular interactions when compared to mTAHPI and pTAHPI.
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Fig. 5 a) Crystal structure packing of mTAHPI. Intramolecular hydrogen bonding of
O1-H1!N3 and intermolecular interactions showing }–} facial stacking of
anthracene, C-H!} stacking between phenyl ring and phenanthroimidazole unit
of HPI and C-H!} stacking of TPA group are highlighted in magenta, red, green,
and yellow, respectively. The distances are given in Å. b) Powder x-ray diffraction
patterns of solid samples. c) DSC (2nd heating scan) and TGA thermograms.
To investigate morphology and thermal stability of the
materials, thermogravimetry (TG) and differential scanning
calorimetry (DSC) were carried out (Fig. 5c, Table 1). The
decomposition temperatures (T5d, at 5% weight loss) of mTAHPI
o
and pTAHPI were over 500 C, which is much higher than that
o
of pTAPI (370 C), indicating the superior thermal stability of
To explore the effect of molecular structure on the EL
properties of the designed HPI derivatives, the optimized OLED
devices with mTAHPI, pTAHPI and pTAPI as the emitters were
fabricated with configuration of ITO/PEDOT:PSS:Nf (40
nm)/emitter 20wt% in CBP (40 nm)/TmPyPb (30 nm)/LiF (0.5
nm)/Al (100 nm) (Fig. 6c, insert). With a view to simplify the
device structure while at the same time maintaining high-
mTAHPI and pTAHPI over pTAPI. Also, mTAHPI and pTAHPI
exhibited high melting temperatures (Tm) of 293 oC and 325 oC,
while for pTAPI only glass transition temperature (Tg) was
detected to be 150 oC. Furthermore, mTAHPI and pTAHPI
showed high T5d and crystalline structure resulting from the
existence of strong intramolecular H-bond and intermolecular
interactions in the molecules, while pTAPI had a morphology of
amorphous solid. The high T5d and Tm have proved that the
compounds possess good thermal stability which is an essential
aspect for device fabrication by thermal evaporation as well as
for achieving a good device performance,27 since they can
endure high temperatures and would not decompose during
device fabrication process under vacuum thermal deposition.
Electrochemical behaviours of mTAHPI, pTAHPI and pTAPI
were investigated using cyclic voltammetry (CV) in
dichloromethane solutions in the presence of n-Bu4NPF6 as a
supporting electrolyte (Fig. S3, ESI†). All molecules exhibited
good electrochemical stability and reversibility, as their
repeated CV scans demonstrated unchanged CV traces. This
implied that the highly reactive radical cations of TPA-
anthracene formed during the first oxidation (E1/2 " 0.98 V) were
fairly stable to an oxidative coupling dimerization on the surface
of a working electrode, believably due to an effective !-electron
delocalization between TPA and anthracene units.13d,28 The
HOMO energy levels of the materials in thin film were
determined by photoelectron yield spectroscopy (AC-2) in air
(Fig. S4, ESI†). The LUMO energy levels were deduced from the
HOMO and optical band gaps (Egopt) by using the equation of
LUMO = HOMO + Egopt. The corresponding HOMO/LUMO levels
for mTAHPI, pTAHPI and pTAPI were estimated to be -5.70/-
2.97 eV, -5.64/-2.92 eV and -5.64/-2.87 eV, respectively (Table
1).
efficiency,
Nafion
(Nf)
doped
poly(3,4-
ethylenedioxythiophene):poly(4-styrene sulfonate (PEDOT:PSS)
with ratio of 1:4 was applied as hole injection layers (HIL) with a
work function of 5.50 eV (Fig. 6a and S4, ESI†). It has been
reported that the work function of PEDOT:PSS as HIL can be
fine-tuned by mixing with Nafion in different rations.29 An
appropriate match between the work functions of HIL and
HOMO level of emissive layer (EML) can reduce the charge
injection barrier between the two layers, giving rise to a better
charge carrier balance within the EML caused by the efficient
hole injection from HIL to EML.30 The high electron mobility and
suitable LUMO level (-2.73 eV) of 1,3,5-tris(3-pyridyl-3-
phenyl)benzene (TmPyPb) was employed as electron
transporting layer (ETL). The optimized energy band alignment
of the device would facilitate hole/electron accumulation and
confine exciton recombination zone within the EML.31 As EML,
in order to reach their optimal PL efficiency, different host
materials and doping concentrations were tried to reach the
best performances of the devices. Successfully, the emitters
were doped in CBP at 20 wt%. The characteristic curves and
device data are shown in Fig. 6b-e and Table 2. As depicted in
Fig. 6e and the insert photo, the mTAHPI, pTAHPI and pTAPI -
based OLEDs exhibited strong blue emission colours with the EL
emission peaks at 463, 472 and 467 nm and Commission
Internationale de I’Eclairage (CIE) coordinates of (0.14, 0.17),
(0.15, 0.23) and (0.19, 0.25), respectively. Moreover, the
mTAHPI- and pTAHPI-devices showed EL spectra with the full
width half maximum (FWHM) values of 65-68 nm, which are
relatively narrower than that of pTAPI device. This might be a
result of strong H-bonding interactions which stiffen the
molecular structure to generate narrow emission. EL spectra of
all devices fitted well with their PL spectra in the thin film
without emission peaks of TmPyPB (470 nm)32 and CBP (390
nm)33 at lower wavelengths. Notably, these EL were unchanged
under the applied voltages ranging from 6 V to 10 V (Fig. S5,
ESI†), implying effective charge injection and recombination in
the EML, and excimer emission as well as exciplex emission
from EML/TmPyPB interface being efficiently suppressed. All
three devices had low turn-on voltages of 2.8-3.2 V at 1 cd m-2,
indicating the effective charge injection and transfer of the
devices. Considering that these molecules possess D-A
properties, a host containing electron donor unit may also
contribute to the balanced transportation of carriers. Among
them, pTAHPI-based device delivered the best overall EL
a)
12.9o
(Intramolecular H-bond)
66.1o
mTAHPI
b)
c)15
100
80
60
40
20
0
mTAHPI
pTAHPI
pTAPI
mTAHPI
pTAHPI
pTAPI
10
5
0
-5
-10
-15
5
10 15 20 25 30 35 40
100 200 300 400 500 600 700
Temperature (oC)
2Theta (Degree)
6 | J. Name., 2012, 00, 1-3
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Table 2 Electroluminescent data of solution-processed devices.a
EML
Hole mobility
(cm2 O-1 s-1)b
3.99 x 10-6
4.33 x 10-6
1.02 x 10-7
Von
(V)
2.8
2.8
3.2
$
Lmax
(cd m-2)
13630
18100
3358
EQE/LE/PE (%, cd A-1, lm W-1)c
CIE
FHWM
(nm)
65
,
EL
s
(nm)
463
472
467
(x, y)
(%)d
73
maximum
@ 1000 cd m-2
2.92/4.05/2.05
3.33/5.60/3.05
0.69/1.18/0.96
mTAHPI
pTAHPI
pTAPI
6.73/9.78/8.10
8.13/12.43/10.39
3.13/5.34/4.72
0.14, 0.17
0.15, 0.23
0.19, 0.25
68
94
77
34
a
b
ITO/PEDOT:PSS:Nf (40 nm)/EML 20% doped in CBP (40 nm)/TmPyPb (30 nm)/LiF (0.5 nm):Al (100 nm). ITO/NBP (10 nm)/ EML 20% doped in CBP (90 nm)/NBP (10
nm)/Al (100 nm). c External quantum efficiency/luminance efficiency/power efficiency. d Singlet exciton utilization efficiency.
CH2Cl2 solvent. On the basis of the optimized configuration of
the ground state (S0), the high excitation energy levels of singlet
and triplet states were computed by TDA-B3LYP/6-31G(d,p)
method. Natural transition orbitals (NTOs) were evaluated for
the S1 states. In order to gain further insights into the ESIPT
character, potential energy curves were constructed using
CAM-B3LYP with 6-31G(d,p) theoretical level and the simulated
enol optical spectra were computed at TD-CAM-B3LYP/6-
31G(d,p) level.
Experimental
Materials and methods: All reagents and solvents were without
further purification. All NMR spectra were recorded on Bruker
Ascend III HD (600 MHz) spectrometer using CDCl3 as a solvent
in all cases. High resolution mass analysis was performed on
Bruker LC-QTOF-MS/MS. UV-Visible spectra were recorded on
Perkin Elmer Lambda 1050 UV/Vis/NIR spectrometer.
Fluorescence emission spectra and photoluminescence decay
profiles were measured using Edinburgh Instruments FLS980
spectrometer. Absolute fluorescence quantum yield (#F) was
measured by integrating sphere on Edinburgh Instruments FLS
980. Electrochemical analysis was operated on Autolab
PGSTA101 with three electrode system fitted with a Pt as
counter electrode, a glassy carbon as working electrode and an
Ag/AgCl as reference electrode at scan rate of 50 mV s-1 by using
TBAPF6 as electrolyte under argon. HOMO of samples in film
states are measured by Riken-Keiki ultraviolet photoelectron
spectrometer AC-2 in air. Differential scanning calorimetry
(DSC) and thermogravimetric analysis (TGA) were done on
Device fabrication and measurements: The patterned indium
tin oxide (ITO) glass substrates with a sheet resistance of 12 ã
sq-1 were thoroughly cleaned by successive ultrasonic
treatment in Liquinox detergent, deionized water, acetone, and
isopropanol and brew with nitrogen for drying. The cleaned ITO
was then treated by UV ozone for 15 min, then a 40 nm hole
injection
layer
(poly(3,4-ethylenedioxythiophene:poly(4-
styrene sulfonate) (PEDOT:PSS, CLEVIOSTM P VP Al 4083) and
Nafion in a ratio 1:4 (v/v)) was spin coated above ITO at a spin
speed of 5000 rpm for 30 s and dried at 120 oC for 30 min. A 40
nm thick EML and CBP layer was deposited simultaneously at an
thermal evaporation rate of 0.8 Å s-1 and 0.2 Å s-1, respectively,
from low temperature evaporation sources using a Kurt J.
Lasker mini SPECTROS 100 thin film deposition system under a
base pressure of 5 x 10-6 mbar to form an active diode area of 4
mm2. The film thickness was monitored using a quartz oscillator
thickness sensor. A 30 nm thick TmPyPb, 0.5 nm thick LiF and
150 nm thick aluminium layers were subsequently deposited.
The hole-only devices were also fabricated as mentioned above.
Current density-voltage-luminescence (J-V-L) characteristics
were measured simultaneously using a Keithley 2400 source
meter and a Hamamatsu Photonics PMA-12 multi-channel
analyzer. The absolute external quantum efficiency (EQE) of
OLED devices was obtained by Hamamatsu Photonics C9920-12
External Quantum Efficiency Measurement System utilizing an
integrating sphere under ambient atmosphere at room
temperature.
PerkinElmer DSC-8500 and Perkin–Elmer TGA Pyris
1
instrument, respectively, under nitrogen gas flow with heating
rate of 10 oC min-1. Melting points were measured using a Krüss
KSP1N melting point meter and are uncorrected. Powder XRD
patterns were collected using
a Bruker D8 ADVANCE
+4n2)5.,1(.(2 at 40 kV, 40 mA for Cu MÖ= TÜ = 1.5418 Å) from
two theta of 2 to 40° with a step size of 0.01° and scanning rate
of 0.6° min-1. Single crystals data were collected on a Bruker D8
Venture diffractometer using à and â scans with Mo MÖ
radiation at 298 K. The crystal structures were solved with the
ShelXT and OLEX2 programs using Levenberg-Marquardt
minimization method. The crystal data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam. ac.uk/data_request/cif (CCDC: 2007054).
All quantum chemical calculations were performed using
the Gaussian 09 package.17 The ground state geometries,
HOMO and LUMO distributions, and HOMO, LUMO energy
levels were calculated by B3LYP/6-31G(d,p) level of theory in
Synthesis of mTAHPI and pTAHPI: A mixture of 5 or 6 (200 mg,
0.43 mmol), 3 (284 mg, 0.52 mmol), Pd(PPh3)4 (50 mg, 0.043
mmol), 2M Na2CO3 aqueous solution (10 ml) and THF (30 ml)
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Journal Name
ARTICLE
was degassed with nitrogen for 15 min while stirring. Then the 21H), 7.17 (s, 4H), 7.12 (d, J = 8.4 Hz, 1H), 7.09 (t, J = 7.2 Hz, 2H),
stirring reaction was heated and refluxed under nitrogen 6.95 (s, 1H), 4.86 (s, 2H); 13C NMR (151 MHz, CDCl3) å = 155.66,
atmosphere for 24 h. The mixture was cooled to room 148.47, 146.48, 145.92, 140.97, 136.93, 136.27, 136.02, 135.00,
temperature after confirming consumption of the starting 134.70, 131.43, 131.11, 130.78, 130.73, 128.69, 128.29, 128.08,
materials by TLC in 30% v/v CH2Cl2-hexane. Then the mixture 127.85, 127.70, 127.68, 127.64, 127.07, 126.91, 126.38, 126.18,
was added with brine solution (30 ml) and extracted with CH2Cl2 126.07, 125.98, 125.78, 125.72, 125.38, 124.86, 124.13, 123.88,
(3 x 30 ml). The organic extract was washed with water (50 ml), 123.69, 123.51, 123.41, 122.76, 122.40, 121.81, 121.75, 121.73,
dried over anhydrous Na2SO4, filtered, concentrated under 121.54, 119.77, 118.65, 114.15, 68.77. HRMS (APCI): m/z clacd.
reduced pressure, and finally purified by silica gel column for C66H45N3O: 895.3563 (M+), found: 896.3590 (MH+).
chromatography eluting with 30% v/v CH2Cl2-hexane. The
product was recrystallized in CH2Cl2-MeHO.
mTAHPI as light-yellow solids (71%). M.p = 302-303 oC; 1H NMR
(600 MHz, CDCl3) å = 13.52 (s, 1H), 8.80 (d, J = 7.8 Hz, 1H), 8.77
(d, J = 8.4 Hz, 1H), 8.73 (d, J = 7.8 Hz, 1H), 7.81 (d, J = 8.4 Hz, 3H),
7.71 (t, J = 7.8 Hz, 1H), 7.53 (d, J = 7.8 Hz, 4H), 7.50 (t, J = 7.8 Hz,
1H), 7.41 – 7.32 (m, 11H), 7.29 (t, J = 9.0 Hz, 9H), 7.21 (t, J = 7.8
Hz, 1H), 7.17 (t, J = 7.2 Hz, 1H), 7.09 (t, J = 7.2 Hz, 2H), 7.06 (d, J
= 8.4 Hz, 1H), 6.92 (s, 1H); 13C NMR (151 MHz, CDCl3) å = 158.29,
148.54, 147.84, 147.16, 138.66, 136.72, 136.22, 134.88, 134.05,
132.72, 132.21, 132.09, 130.71, 130.17, 130.04, 129.97, 129.60,
129.53, 129.39, 128.66, 128.58, 128.52, 127.56, 127.32, 127.13,
126.90, 126.52, 126.11, 125.98, 125.30, 124.84, 124.78, 124.68,
124.17, 123.25, 123.20, 123.10, 123.08, 122.67, 122.66, 120.93,
117.89, 113.17; HRMS (APCI): m/z clacd. for C59H39N3O (M+):
805.3093, found: 806.2729 (MH+).
pTAHPI as light-yellow solids (76%). M.p = 331-332 oC; 1H NMR
(600 MHz, CDCl3) å = 14.27 (s, 1H), 8.81 (d, J = 7.8 Hz, 1H), 8.78
(d, J = 8.4 Hz, 1H), 8.75 (d, J = 8.4 Hz, 1H), 7.85 – 7.75 (m, 10H),
7.72 (t, J = 7.2 Hz, 1H), 7.56 (t, J = 7.8 Hz, 1H), 7.40 – 7.27 (m,
18H), 7.09 (t, J = 6.6 Hz, 2H), 7.08 (d, J = 7.2, 1H), 6.95 (d, J = 7.8
Hz, 1H), 6.64 (d, J = 7.8 Hz, 1H); 13C NMR (151 MHz, CDCl3) å =
159.36, 148.51, 147.84, 147.17, 139.19, 136.01, 134.52, 132.62,
132.18, 132.07, 131.05, 130.76, 130.04, 129.61, 129.56, 129.39,
129.17, 128.56, 127.60, 127.18, 127.04, 126.92, 126.61, 126.15,
125.86, 125.76, 125.34, 125.06, 124.98, 124.70, 124.25, 123.27,
123.14, 123.09, 122.67, 121.50, 121.13, 120.94, 112.40. HRMS
(APCI): m/z clacd. for C59H39N3O (M+): 805.3093, found:
806.1889 (MH+).
Conclusions
In conclusion, we successfully synthesized and studied two
isomeric D-A molecules containing ESIPT chromophore of o-
hydroxyphenyl phenanthroimidazole (HPI) mTAHPI and
pTAHPI, and its OH protected derivative pTAPI. Their properties
were systematically investigated and compared. The theoretical
calculation and optical studies demonstrated that mTAHPI and
pTAHPI did not show ESIPT characteristics due to high potential
energy of proton transfer process in the excited state, while
solvatochromic experiments proved that they exhibited an
HLCT excited state, which is advantageous to the improvement
of EL efficiency. Single-crystal analysis of mTAHPI revealed
intramolecular H-bond and intermolecular interactions that
were capable of efficiently repressing the inevitable excited
state geometric relaxation. The optimized EL devices based on
mTAHPI and pTAHPI showed highly efficient EL performance.
Especially, pTAHPI-based device achieved an EQE of 8.13% with
an ultra-high brightness 18100 cd m-2, narrow emission (FHWM
= 68 nm) and _s value as high as 94%, while its OH protected
derivative pTAPI demonstrated rather low EL efficiency and _s
value of 34%. These results hint that such superior EL
efficiencies originate from the RISC process arising from the
HLCT excited state character which is efficiently enhanced by
the intramolecular H-bonding between phenol hydroxyl and
phenanthroimidazole. As a result, 3a features a high PL
efficiency and exhibits a high exciton utilization efficiency of
nearly 100% with EQE up to 7.1% in OLEDs. The results of this
work have demonstrated that HPI-based D-A materials are good
fluorescent emitters for blue OLEDs and provided a useful guide
in the future for designing efficient electroluminescent
materials for high-efficiency and high color purity OLEDs by
taking advantage of intramolecular H-bond interaction and the
HLCT excited state.
Synthesis of pTAPI: A solution of pTAHPI (50 mg, 0.06 mmol) in
anhydrous DMF (20 ml) was stirred and cooled down to 0 oC for
10 min. KOH (9 mg, 0.16 mmol) was added into the mixture and
stirred continuously for another 30 min. The reaction was set
under room temperature for 12h after adding benzyl bromide
(16 mg, 0.09 mmol). The consumption of the starting materials
was confirmed by TLC in 50% v/v CH2Cl2-hexane before
termination of reaction. Then the mixture was added to brine
solution (20 ml) and extracted with CH2Cl2 (3 x 30 ml). The
organic extract was washed with water (50 ml), dried over
anhydrous Na2SO4, filtered, concentrated under reduced
pressure and finally purified by silica gel column
chromatography eluting with 30% v/v CH2Cl2-hexane. The
product was recrystallized in CH2Cl2-MeOH to give light-yellow
solids (40 mg, 70%). M.p = 310-311 oC; 1H NMR (600 MHz, CDCl3)
å = 8.98 (d, J = 7.8 Hz, 1H), 8.81 (d, J = 8.4 Hz, 1H), 8.76 (d, J =
8.4 Hz, 1H), 7.84 (d, J = 8.4 Hz, 2H), 7.79 (t, J = 7.2 Hz, 1H), 7.74
(d, J = 7.2 Hz, 1H), 7.69 (t, J = 7.8 Hz, 1H), 7.57 (d, J = 8.4 Hz, 2H),
7.53 (q, J = 7.2 Hz, 2H), 7.47 (t, J = 7.8 Hz, 2H), 7.44 – 7.27 (m,
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
This work was financially supported by the TRF (RTA6080005)
and the NANOTEC, NSTDA, Ministry of Science and Technology,
Thailand, through its program of Research Network NANOTEC.
Thanks also go to VISTEC for the support of both Postdoctoral
Fellowship (to T. S.) and equipment.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
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Journal Name
S. J. Su and Y. Ma, Dye. Pigment., 2018, 149, 430.
Notes and references
11 (a) D. Tu, P. Leong, Z. Li, R. Hu, C. Shi, K. Y. Zhang, H. Yan and Q.
Zhao, Chem. Commun., 2016, 52, 12494; (b) S. Lukman, K.
Chen, J. M. Hodgkiss, D. H. P. Turban, N. D. M. Hine, S. Dong, J.
Wu, N. C. Greenham and A. J. Musser, Nat. Commun., 2016, 7,
13622.
1
(a) C. W. Tang and S. A. Vanslyke, Appl. Phys. Lett., 1987, 51,
913; (b) P. Funchien, P. Chasing, T. Sudyoadsuk and V.
Promarak, Chem. Commun., 2020, 56, 6305; (c) M. Godumala,
S. Choi, M. J. Cho and D. H. Choi, J. Mater. Chem. C, 2019, 7,
2172; (d) J. H. Lee, C. H. Chen, P. H. Lee, H. Y. Lin, M. K. Leung,
T. L. Chiu and C. F. Lin, J. Mater. Chem. C, 2019, 7, 5874; (e) X.
Lv, M. Sun, L. Xu, R. Wang, H. Zhou, Y. Pan, S. Zhang, Q. Sun, S.
Xue and W. Yang, Chem. Sci., 2020, 5058; (f) S. Kim, H. J. Kwon,
S. Lee, H. Shim, Y. Chun, W. Choi, J. Kwack, D. Han, M. Song, S.
Kim, S. Mohammadi, I. Kee and S. Y. Lee, Adv. Mater., 2011, 23,
3511; (g) W. Zeng, H. Y. Lai, W. K. Lee, M. Jiao, Y. J. Shiu, C.
Zhong, S. Gong, T. Zhou, G. Xie, M. Sarma, K. T. Wong, C. C. Wu
and C. Yang, Adv. Mater., 2018, 30, 1704961; (h) Y. Yin, M. U.
Ali, W. Xie, H. Yang and H. Meng, Mater. Chem. Front., 2019, 3,
970.
12 (a) S. Park, J. E. Kwon and S. Y. Park, Phys. Chem. Chem. Phys.,
2012, 14, 8878; (b) V. S. Padalkar and S. Seki, Chem. Soc. Rev.,
2016, 45, 169.
13 (a) J. Huang, J. H. Su and H. Tian, J. Mater. Chem., 2012, 22,
10977; (b) A. Slodek, M. Filapek, E. Schab-Balcerzak, M.
Grucela, S. Kotowicz, H. Janeczek, K. Smolarek, S. Mackowski, J.
G. Malecki, A. Jedrzejowska, G. Szafraniec-Gorol, A. Chrobok,
B. Marcol, S. Krompiec and M. Matussek, European J. Org.
Chem., 2016, 2016, 4020; (c) K. Danel, T. H. Huang, J. T. Lin, Y.
T. Tao and C. H. Chuen, Chem. Mater., 2002, 14, 3860; (d) A.-
M. Thangthong, D. Meunmart, N. Prachumrak, S.
2
(a) M. Y. Wong and E. Zysman-Colman, Adv. Mater., 2017, 29,
1605444; (b) A. Maheshwaran, V. G. Sree, H. Y. Park, H. Kim, S.
H. Han, J. Y. Lee and S. H. Jin, Adv. Funct. Mater., 2018, 28,
1802945; (c) J. Tagare and S. Vaidyanathan, J. Mater. Chem. C,
2018, 6, 10138; (d) Y. Xu, X. Liang, X. Zhou, P. Yuan, J. Zhou, C.
Wang, B. Li, D. Hu, X. Qiao, X. Jiang, L. Liu, S. J. Su, D. Ma and Y.
Ma, Adv. Mater., 2019, 31, 1807388; (e) Q. Wei, N. Fei, A.
Islam, T. Lei, L. Hong, R. Peng, X. Fan, L. Chen, P. Gao and Z. Ge,
Adv. Opt. Mater., 2018, 6, 1800512; (f) Z. Xu, B. Z. Tang, Y.
Wang and D. Ma, J. Mater. Chem. C, 2020, 8, 2614.
Jungsuttiwong, T. Keawin, T. Sudyoadsuk and V. Promarak,
Chem. Commun., 2011, 47, 7122.
14 (a) K. Benelhadj, J. Massue, P. Retailleau, G. Ulrich and R.
Ziessel, Org. Lett., 2013, 15, 2918; (b) P. Majumdar and J. Zhao,
J. Phys. Chem. B, 2015, 119, 2384.
15 K. Skonieczny, A. I. Ciuciu, E. M. Nichols, V. Hugues, M.
Blanchard-Desce, L. Flamigni and D. T. Gryko, J. Mater. Chem.,
2012, 22, 20649.
16 (a) B. Li, G. Tang, L. Zhou, D. Wu, J. Lan, L. Zhou, Z. Lu, and J.
You, Adv. Funct. Mater., 2017, 27, 1605245, (b) A. I. Ciuciu, K.
Skonieczny, D. Koszelewski, D. T. Gryko and L. Flamigni, J. Phys.
Chem. C, 2013, 117, 791.
3
4
B. Zhao, T. Zhang, B. Chu, W. Li, Z. Su, H. Wu, X. Yan, F. Jin, Y.
Gao and C. Liu, Sci. Rep., 2015, 5, 10697.
(a) F. Kessler, Y. Watanabe, H. Sasabe, H. Katagiri, M. K.
Nazeeruddin, M. Grätzel and J. Kido, J. Mater. Chem. C, 2013,
1, 1070; (b) X. Ban, K. Sun, Y. Sun, B. Huang, S. Ye, M. Yang and
W. Jiang, ACS Appl. Mater. Interfaces, 2015, 7, 25129.
(a) H. Liu, L. Kang, J. Li, F. Liu, X. He, S. Ren, X. Tang, C. Lv and P.
Lu, J. Mater. Chem. C, 2019, 7, 10273; (b) W. Liu, S. Ying, R.
Guo, X. Qiao, P. Leng, Q. Zhang, Y. Wang, D. Ma and L. Wang, J.
Mater. Chem. C, 2019, 7, 1014; (c) Y. J. Luo, Z. Y. Lu and Y.
Huang, Chinese Chem. Lett., 2016, 27, 1223.
17 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.
Robb, J. R. Cheeseman, G. Scalmani, V. Barone, G. A.
Petersson, H. Nakatsuji, X. Li, M. Caricato, A. V. Marenich, J.
Bloino, B. G. Janesko, R. Gomperts, B. Mennucci, H. P.
Hratchian, J. V. Ortiz, A. F. Izmaylov, J. L. Sonnenberg, Williams,
F. Ding, F. Lipparini, F. Egidi, J. Goings, B. Peng, A. Petrone, T.
Henderson, D. Ranasinghe, V. G. Zakrzewski, J. Gao, N. Rega, G.
Zheng, W. Liang, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J.
Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai,
T. Vreven, K. Throssell, J. A. Montgomery Jr., J. E. Peralta, F.
Ogliaro, M. J. Bearpark, J. J. Heyd, E. N. Brothers, K. N. Kudin, V.
N. Staroverov, T. A. Keith, R. Kobayashi, J. Normand, K.
Raghavachari, A. P. Rendell, J. C. Burant, S. S. Iyengar, J.
Tomasi, M. Cossi, J. M. Millam, M. Klene, C. Adamo, R. Cammi,
J. W. Ochterski, R. L. Martin, K. Morokuma, O. Farkas, J. B.
Foresman and D. J. Fox, 2016, Gaussian 09, Revision A.02,
Gaussian, Inc., Wallin.
5
6
7
(a) T. T. Bui, F. Goubard, M. Ibrahim-Ouali, D. Gigmes and F.
Dumur, Beilstein J. Org. Chem., 2018, 14, 282; (b) Y. Liu, C. Li, Z.
Ren, S. Yan and M. R. Bryce, Nat. Rev. Mater., 2018, 3, 18020.
(a) W. Z. Yuan, X. Bin, G. Chen, Z. He, J. Liu, H. Ma, Q. Peng, B.
Wei, Y. Gong, Y. Lu, G. He and Y. Zhang, Adv. Opt. Mater.,
2017, 5, 1700466; (b) W. Li, Y. Pan, L. Yao, H. Liu, S. Zhang, C.
Wang, F. Shen, P. Lu, B. Yang and Y. Ma, Adv. Opt. Mater.,
2014, 2, 892; (c) Y. Liu, H. Liu, Q. Bai, C. Du, A. Shang, D. Jiang,
X. Tang and P. Lu, ACS Appl. Mater. Interfaces, 2020, 12,
16715.
18 (a) N. Kanlayakan, K. Kerdpol, C. Prommin, R. Salaeh, W.
Chansen, C. Sattayanon and N. Kungwan, New J. Chem., 2017,
41, 8761; (b) B. An, S. Feng, K. Wen, W. Wu, H. Yuan, Q. Zhu, X.
Guo and J. Zhang, Org. Electron., 2017, 45, 1.
8
9
(a) W. Li, D. Liu, F. Shen, D. Ma, Z. Wang, T. Feng, Y. Xu, B. Yang
and Y. Ma, Adv. Funct. Mater., 2012, 22, 2797; (b) W. Li, Y. Pan,
R. Xiao, Q. Peng, S. Zhang, D. Ma, F. Li, F. Shen, Y. Wang, B.
Yang and Y. Ma, Adv. Funct. Mater., 2014, 24, 1609.
19 X. Qiu, Y. Xu, C. Wang, M. Hanif, J. Zhou, C. Zeng, Y. Li, Q. Jiang,
R. Zhao, D. Hu and Y. Ma, J. Mater. Chem. C, 2019, 7, 5461.
20 K. I. Sakai, S. Tsuchiya, T. Kikuchi and T. Akutagawa, J. Mater.
Chem. C, 2016, 4, 2011.
(a) C. Fu, S. Luo, Z. Li, X. Ai, Z. Pang, C. Li, K. Chen, L. Zhou, F. Li,
Y. Huang and Z. Lu, Chem. Commun., 2019, 55, 6317; (b) B. Liu,
Z. W. Yu, D. He, Z. L. Zhu, J. Zheng, Y. D. Yu, W. F. Xie, Q. X.
Tong and C. S. Lee, J. Mater. Chem. C, 2017, 5, 5402.
21 (a) Y. C. Chang, S. C. Yeh, Y. H. Chen, C. T. Chen, R. H. Lee and R.
J. Jeng, Dye. Pigment., 2013, 99, 577; (b) Y. H. Chen, S. L. Lin, Y.
C. Chang, Y. C. Chen, J. T. Lin, R. H. Lee, W. J. Kuo and R. J. Jeng,
10 X. Tang, X. L. Li, H. Liu, Y. Gao, Y. Shen, S. Zhang, P. Lu, B. Yang,
10 | J. Name., 2012, 00, 1-3
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Journal of Materials Chemistry C
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DOI: 10.1039/D0TC04590J
Journal Name
Org. Electron., 2012, 13, 43.
ARTICLE
22 C. Zhou, D. Cong, Y. Gao, H. Liu, J. Li, S. Zhang, Q. Su, Q. Wu
and B. Yang, J. Phys. Chem. C, 2018, 122, 18376.
23 D. Hu, L. Yao, B. Yang and Y. Ma, Philos. Trans. R. Soc. A Math.
Phys. Eng. Sci., 2015, 373, 20140318.
24 Y. Pan, J. Huang, W. Li, Y. Gao, Z. Wang, D. Yu, B. Yang and Y.
Ma, RSC Adv., 2017, 7, 19576.
25 Q. Luo, L. Li, H. Ma, C. Lv, X. Jiang, X. Gu, Z. An, B. Zou, C. Zhang
and Y. Zhang, Chem. Sci., 2020, 11, 6020.
26 (a) R. Chen, Y. Tang, Y. Wan, T. Chen, C. Zheng, Y. Qi, Y. Cheng
and W. Huang, Sci. Rep., 2017, 7, 6225; (b) N. Sharma, M. Y.
Wong, D. Hall, E. Spuling, F. Tenopala-Carmona, A. Privitera, G.
Copley, D. B. Cordes, A. M. Z. Slawin, C. Murawski, M. C.
Gather, D. Beljonne, Y. Olivier, I. D. W. Samuel and E. Zysman-
Colman, J. Mater. Chem. C, 2020, 8, 3773.
27 (a) S. Tao, Y. Zhou, C. S. Lee, S. T. Lee, D. Huang and X. Zhang, J.
Phys. Chem. C, 2008, 112, 14603; (b) M. G. Shin, S. O. Kim, H. T.
Park, S. J. Park, H. S. Yu, Y. H. Kim and S. K. Kwon, Dye.
Pigment., 2012, 92, 1075; (c) S. Ye, J. Chen, C. A. Di, Y. Liu, K.
Lu, W. Wu, C. Du, Y. Liu, Z. Shuai and G. Yu, J. Mater. Chem.,
2010, 20, 3186.
28 N. Prachumrak, S. Namuangruk, T. Keawin, S. Jungsuttingwong,
T. Sudyoadsuk and V. Promarak, European J. Org. Chem., 2013,
3825.
29 (a) J. Hossain, Q. Liu, T. Miura, K. Kasahara, D. Harada, R.
Ishikawa, K. Ueno and H. Shirai, ACS Appl. Mater. Interfaces,
2016, 8, 31926; (b) S. H. Kim, J. Kim, S. Nam, H. S. Lee, S. W.
Lee and J. Jang, ACS Appl. Mater. Interfaces, 2017, 9, 12637; (c)
A. Pachariyangkun, W. Senapak, T. Sudyoadsuk, S.
Namuangruk and V. Promarak, Org. Electron., 2020, 85,
105897.
30 R. A. K. Yadav, D. K. Dubey, S. Z. Chen, T. W. Liang and J. H. Jou,
Sci. Rep., 2020, 10, 9915.
31 (a) S. H. Rhee, K. B. Nam, C. S. Kim, M. Song, M. Cho, S. H. Jin
and S. Y. Ryu, ECS Solid State Lett., 2014, 3, R19; (b) S. Wu, S. Li,
Q. Sun, C. Huang and M. K. Fung, Sci. Rep., 2016, 6, 4.
32 F. X. Yu, Y. Zhang, Z. Y. Xiong, X. J. Ma, P. Chen, Z. H. Xiong and
C. H. Gao, Org. Electron., 2017, 50, 480.
33 B. B. W. D. Andrade, J. Brooks, V. Adamovich, M. E. Thompson
and S. R. Forrest, Adv. Mater., 2002, 14, 1032.
34 Y. Li, R. G. Clevenger, L. Jin, K. V. Kilway and Z. Peng, J. Mater.
Chem. C, 2014, 2, 7180.
35 (a) S. W. Culligan, A. C. A. Chen, J. U. Wallace, K. P. Klubek, C.
W. Tang and S. H. Chen, Adv. Funct. Mater., 2006, 16, 1481; (b)
J. H. Jou, S. Kumar, M. Singh, Y. H. Chen, C. C. Chen and M. T.
Lee, Molecules, 2015, 20, 13005.
36 (a) J. Jayabharathi, G. Goperundevi, V. Thanikachalam and S.
Panimozhi, ACS Omega, 2019, 4, 15030; (b) C. Wang, X. Li, Y.
Pan, S. Zhang, L. Yao, Q. Bai, W. Li, P. Lu, B. Yang, S. Su and Y.
Ma, ACS Appl. Mater. Interfaces, 2016, 8, 3041.
This journal is © The Royal Society of Chemistry 20xx
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Journal of Materials Chemistry C
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DOI: 10.1039/D0TC04590J
Graphical Abstract
Intramolecular hydrogen bond-enhanced electroluminescent performance of hybridized local
and charge transfer (HLCT) excited state blue emissive materials
Wan Li, Pongsakorn Chasing, Wachara Benchaphanthawee, Thanyarat Chawanpunyawat, Chokchai
Kaiyasuan, Phattananawee Nalaoh, Nawee Kungwan, Supawadee Namuangruk, Taweesak
Sudyoadsuk and Vinich Promarak*
OLED device based on o-hydroxyphenyl phenanthroimidazole (HPI)-based emissive molecules
showed high maximum external quantum efficiency (EQE) of 8.13% with an ultra-high brightness
of 18100 cd m-2. The maximum singlet exciton utilization efficiency (ηs) of the device was
estimated to be as high as 94%, which is among the best results of blue electroluminescence to our
knowledge.
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