Ternary Emission of Fluorescence and Dual Phosphorescence at Room Temperature: A Single-Molecule White Light Emitter Based on Pure Organic Aza-Aromatic Material

Article abstract of DOI:10.1002/adfm.201802407

Herein, a simple aza-aromatic compound dibenzo[a,c]phenazine (DPPZ), which exhibits single-molecule white light with a ternary emission, consisting of simultaneous fluorescence (S₁→S₀) and dual room-temperature phosphorescence (RTP, T₂→S₀ and T₁→S₀) is reported. The Commission Internationale de l' éclairage coordinates of DPPZ powder are (0.28, 0.33). To everyone's knowledge, this is the first case to achieve single-molecule white emission with ternary emission of fluorescence and dual RTP. This finding provides a prototype strategy to realize low-cost, stable pure organic single-molecule white light emission with three standard primary colors through further precise modulation of excited states.

Full text of DOI:10.1002/adfm.201802407

FULL PAPER
White-Light Emitters
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Ternary Emission of Fluorescence and Dual Phosphorescence
at Room Temperature: A Single-Molecule White Light Emitter
Based on Pure Organic Aza-Aromatic Material
Changjiang Zhou, Shitong Zhang, Yu Gao, Haichao Liu, Tong Shan, Xiaoming Liang,
Bing Yang,* and Yuguang Ma
white-light emission, such as phase sepa-
Herein, a simple aza-aromatic compound dibenzo[a,c]phenazine (DPPZ),
which exhibits single-molecule white light with a ternary emission, consisting
of simultaneous fluorescence (S1→S0) and dual room-temperature
phosphorescence (RTP, T2→S0 and T1→S0) is reported. The Commission
Internationale de l’ Éclairage coordinates of DPPZ powder are (0.28, 0.33). To
everyone’s knowledge, this is the first case to achieve single-molecule white
emission with ternary emission of fluorescence and dual RTP. This finding
provides a prototype strategy to realize low-cost, stable pure organic single-
molecule white light emission with three standard primary colors through
further precise modulation of excited states.
ration, color-aging, fabrication complexity,
etc.[3] As a comparison, a single emitter
with dual emission or multiemission
could be a more promising alternative
to realize organic white-light emission
by solving the problems above. Without
exception, more and more dual emission
organic materials have been reported
with single-molecule white light emission
(SMWLE). In principle, dual emission can
be assigned to two emissive sources of
excited state: the lowest singlet (S1) excited
state for blue fluorescence and another
excited state for a largely redshifted emis-
sion, including charge-transfer (CT) state,[4] excimer state,[5]
proton-transfer state,[6] the lowest triplet (T1) excited state
emission for room-temperature phosphorescence (RTP),[7] etc.
What’s more, the latest SMWLE has been discovered with dual
RTP emission by Tang’s group.[8] However, in principle, three-
primary-color system is more convenient for regulating purer
white emission, nevertheless, SMWLE with multiemission
(at least ternary emission) has never been reported so far, let
alone its structure–property relationship.
The development of single-molecule white light material
consisted of pure organic RTP is very challenging for the fol-
lowing reasons. On one hand, in pure organic materials, the
spin–orbit coupling (SOC) is always too small to afford the effi-
cient intersystem crossing (ISC) for triplet exciton generation.
On the other hand, the nonradiative process, including vibra-
tional relaxation, ISC, and exogenous quenching, would further
aggravate the waste of triplet excitons due to the long lifetime.[9]
Accordingly, in order to achieve efficient RTP in pure organic
materials, two key countermeasures should be adopted: one is
to accelerate ISC process for adequate triplet exciton genera-
tion; the other is to suppress nonradiative deactivation of triplet
excitons, but the former is more important. According to the
Fermi’s Golden rule,[10] the efficient radiation of triplet excitons
mostly depend on an adequate accumulation of triplet excitons,
acquiring for the enhancement of SOC to accelerate the ISC
process. In pure organic material system, one way to realize
large SOC is to introduce heavy atom such as halogen (such as
Br and I) and deuterium.[11] However, heavy halogen substitu-
tion seriously affects the chemical stability upon thermal and
electrical treatments, and deuterium substitution is still of large
expenses.
1. Introduction
Organic white-light materials are closely related to our daily life,
due to its wide applications in lighting and display systems.[1]
In chroma theory, the white-light emission can be mainly
obtained by two ways: one is the mixture of two complemen-
tary colors (yellow and blue), and the other is the most widely
used complex of three primary colors (red, green, and blue).[2]
Therefore, multicomponent emitters with different emission
colors are usually required to combine white-light emission.
However, there are still many defects for the multiemitter
C. Zhou, Dr. S. Zhang, Dr. Y. Gao, Dr. H. Liu, T. Shan, Prof. B. Yang
State Key Laboratory of Supramolecular Structure and Materials
Jilin University
Changchun 130012, P. R. China
E-mail: yangbing@jlu.edu.cn
C. Zhou, Dr. S. Zhang, Dr. Y. Gao, Dr. H. Liu, T. Shan, Prof. B. Yang
College of Chemistry
Jilin University
Changchun 130012, P. R. China
Dr. S. Zhang
Institute of Theoretical Chemistry
Jilin University
Changchun 130012, P. R. China
X. Liang, Prof. Y. Ma
State Key Laboratory of Luminescent Materials and Devices
South China University of Technology
Guangzhou 510640, P. R. China
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/adfm.201802407.
DOI: 10.1002/adfm.201802407
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Figure 1. The chemical structure, absorption and emission spectra of a) DPPZ and b) DPAN in THF solution under 298 and 78 K. The insets are the
photos of the steady-state emission of DPPZ and DPAN, respectively. The excitation wavelength for DPPZ and DPAN are 390 and 330 nm, respectively.
In principle, some light heteroatoms can also play a similar
role as that of heavy atoms, which provide the lone pair elec-
trons to strengthen SOC and to facilitate ISC process between
n→π* and π→π* character states according to the El-Sayed
rule,[12] for instance, involving boron atom or carbonyl sub-
stitution in pure organic system.[13] Furthermore, the other
heteroatoms need to be systematically examined for the expan-
sion of pure organic RTP material family. In this contribution,
a SMWLE is harvested with the mixing three emissions of
fluorescence and dual RTP of a nitrogen (N)-containing het-
erocyclic aromatic compound dibenzo[a,c]phenazine (DPPZ),
as shown in Figure 1. Experimental and theoretical investi-
gations reveal that the dual RTP is composed of a normal T1
phosphorescence and an unusual T2 phosphorescence from
high-lying triplet state (exception to Kasha’s rule). More impor-
tantly, the two RTP components of DPPZ are proved to be rela-
tively independent, which creates a possibility of the rational
excited state regulation for the desired SMWLE materials with
standard tricolor. Our results not only provide a new concept
for designing pure organic SMWLE material, but also propose
a prototype strategy to design a single-molecule true white-light
emitter with three standard primary colors in the future.
measured for a nitrogen-free counterpart DPAN in Figure 1b.
As a matter of course, DPAN shows structured PL spectrum,
corresponding to a π→π* transition character.
In usual cases, the fluorescence of an organic emitter will
hide the weak phosphorescence in its PL spectrum, since the
radiative transition rate of phosphorescence is three or four
orders of magnitude lower than that of fluorescence in pure
organic materials. Therefore, to detect the phosphorescent
emission, low-temperature circumstance is often adopted to
suppress the nonradiation decay, and time-resolved measure-
ments are always further adapted to exclude the interference
of fluorescence signals. However, in DPPZ solution, we are
surprised to find out that the steady-state PL is dominated by a
structured π→π* phosphorescence with a long lifetime of 2.7 µs
(Figure S1, Table S1, Supporting Information), and the fluores-
cence is only a residue at low temperature (78 K). This unusual
phenomenon can be initially understood by the El-Sayed rule
that ISC process takes places more easily, as a result of the dis-
tinct transition pattern between singlet and triplet states. In the
case of DPPZ, the fluorescence is of structureless n→π* transi-
tion character while its phosphorescence is assigned to π→π*
transition (refer to Figure 4a), which efficiently facilitates ISC
process that contributes to the adequate triplet exciton genera-
tion for such significant steady-state phosphorescence. An evi-
dence to well support this point is that the phosphorescence
of DPAN cannot be observed under the same condition, indi-
cating that N-heteroatom of DPPZ plays the key role in efficient
triplet exciton generation, which is a crucial structure basis for
RTP property. Notably, compared with DPAN (8.66 ns), the flu-
orescence lifetime of DPPZ is very short (0.072 ns, reported by
Tian’s group)[14] and it could not even be resolved with a pico-
second laser (Figure S3, Supporting Information), indicating
that very fast ISC process is expected to occur from S1 excited
state in DPPZ.
2. Results and Discussions
2.1. Photophysical Properties
2.1.1. Dispersed Condition
DPPZ is facilely synthesized using a one-step cyclization reac-
tion with a high yield (Supporting Information). First, the
absorption and emission spectra of DPPZ are recorded at dif-
ferent temperature in tetrahydrofuran (THF) for its S1 and T1
energy levels. As shown in Figure 1, DPPZ demonstrates a
structured absorption, while its photoluminescence (PL) spec-
trum is structureless arising from the n→π* transition char-
acter induced by nitrogen heteroatom. Due to the rigidity of
planar structure, DPPZ shows very small Stokes shift between
absorption and emission at room temperature (298 K). For the
purpose of comparison, both absorption and emission are also
Similar to the low-temperature, nonradiative transition can
also be alleviated or suppressed to certain extent by rigid sur-
rounding medium and intermolecular aggregation. Typically, a
large number of molecules have been observed with enhanced
PL emission upon the increase of viscosity or aggregation
degree, knowing as the famous aggregation-induced emission
(AIE) phenomenon, such as silole and tetraphenylethylene
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be ascribed to the emission from high-lying triplet Tn excited
state as an exception to Kasha’s rule rather than a high-lying
singlet Sn emission, since the peak of the new emission band is
redshifted relative to the S1 emission.
2.1.2. Single-Molecule White Light Emission in Aggregated
Condition
Interestingly, the mixed emissions of S1, T1, and Tn are observed
even more clearly in the neat powder of DPPZ, especially for T1
and Tn mixed RTP, as shown in Figure 3a. Thus, the powder
of DPPZ exhibits pure, stable white-light emission with a
Commission Internationale de L’Eclairage (CIE) coordinate of
(0.28, 0.33), with a photoluminescence quantum yield (PLQY)
of 1%, as a result of the good continuity of PL spectrum that
covers the whole visible region from 400 to 700 nm. Importantly,
this simultaneous ternary emission may provide a prototype
of SMWLE with standard three-primary-color mixing mecha-
nism. Furthermore, these three different emissive components
(fluorescence and dual phosphorescence) can be confirmed
by the time-resolved PL spectra (Figure 3b). At a delay time of
160 µs, the fluorescence component of DPPZ disappears com-
pletely, and only dual phosphorescence (Tn and T1) remained
obviously. What’s more, relative to T1 phosphorescence, the Tn
emission band from 480 to 530 nm demonstrates a synchro-
nous and faster decay in a timescale of 1.4 ms, assigning to
a vibronic splitting of RTP from high-lying Tn excited state in
DPPZ, which could also be revealed by further peak fitting of
the PL spectra of DPPZ (Figure 3a). Another solid evidence
for the existence of Tn emission is the PL grinding effect and
oxygen quenching effect in DPPZ neat powder (Figure S9,
Supporting Information). In fact, according to the typical AIE
experiment on DPPZ (PL spectra in the mixed solvent of water
and tetrahydrofuran, Figure S10, Supporting Information),
we found that RTP of DPPZ largely depends on its aggrega-
tion degree.[17] Although tentatively we could not obtain high-
quality crystal of DPPZ for molecular aggregation details, the
powder X-ray diffraction (pXRD) reveals a partially crystalline
state in DPPZ neat powder. After thoroughly grinding, the crys-
talline structure of DPPZ is fully destructed, and both T1 and
Tn RTP emissions exhibit more serious quenching comparing
to that of fluorescence and shows more obvious sensitivity to
the oxygen quenching, indicating that the phosphorescence is
more dependent on the aggregation degree of DPPZ, which is
essentially consistent with their phosphorescence instinct.
More importantly, the two RTP components of DPPZ
are relatively independent to each other, which is benefi-
cial to the emission stability that could guarantee the contin-
uous white PL of DPPZ. In Figure 3c, instead of the Tn-RTP,
the T1-RTP of DPPZ shows obvious enhancement upon the
increasing of temperature, which not only implies that the
S1→T1 ISC process is very efficient in DPPZ, but also reveals
that the T1→Tn thermally activated reversed inner conversion
mechanism[8,18] is invalid in DPPZ, otherwise an enhance-
ment on the PL of Tn-RTP should be observed. As a result of
the independency of its RTP components, DPPZ demonstrates
obvious excitation wavelength dependency, revealing the dif-
ferent exciton resources of three emissive species. In Figure 3d,
Figure 2. The PL spectra of DPPZ-doped film in PMMA at different tem-
peratures. The excitation wavelength is chosen as 390 nm.
derivates.[15] Likewise, the concept of AIE can also apply to the
RTP, such as doping in rigid matrix (e.g., polymethyl-meth-
acrylate, PMMA), crystallization, etc. In fact, for DPPZ, PMMA
doping could be some effective access to RTP. In Figure 2, rela-
tive to that in THF solution, the DPPZ doped film (5% w/w
in PMMA) demonstrates an extra tailing peak from 500 to
650 nm, which can be assigned to phosphorescence emission.
As for the reason, the PL decay at 546 nm is fit with a long
lifetime of 20.11 µs, which is obviously distinguished from the
short one as 0.3 ns of DPPZ fluorescence at 428 nm. Moreover,
this RTP could also be confirmed by time-resolved PL meas-
urement. With a delay time of 50 µs, an obvious phosphores-
cent emission can be observed with vibrational fine structure
between 541 and 586 nm, while the fluorescence emission
fades to an inconspicuous residue, which is similar to that of
THF solution at 78 K.
However, it seems to be impossible that we could still observe
the “fluorescence component” of DPPZ with a long delay time of
50 µs (Figure S5, Supporting Information), since the lifetime of
the fluorescence component has been proved to be very short.
Therefore, the fluorescence-like residue should originate from
other emissive species. Considering that low temperature could
restrict the nonradiative processes, we further carry out tem-
perature-dependent experiment to clarify the origin of this flu-
orescence-like residue. Under a set of decreasing temperatures
from 320 to 80 K, the phosphorescence of DPPZ-doped film
gradually enhances (Figure S6, Supporting Information), with
almost no change on the spectral shape. When the temperature
is further lowered to 10 K, not only the fluorescence exhibits an
enhancement due to the further suppressed nonradiation of S1
excited state, but also an obvious new emission band emerges
from 460 to 520 nm between fluorescence at 424 nm and phos-
phorescence at 541 nm (Figure 2), corresponding to the residue
emission peak. According to the Kasha’s rule,[16] the emission
of an organic molecule should result from the lowest singlet
(S1) or triplet (T1) excited state in general, nevertheless, both
S1 and T1 emissions do coexist with the new emission band
at 10 K. As a result, the new emission band at 10 K should
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Figure 3. The RTP properties of DPPZ neat powder. a) PL spectrum and peak fitting of DPPZ neat powder under ambient conditions. b) Normalized
time-resolved PL spectra of DPPZ neat powder. The spectra are normalized to the T1 emission for comparison. c) Temperature-dependent PL spectra
from 80 to 240 K. d) Excitation spectra of DPPZ at different emission wavelengths (440–620 nm). The spectra of (a) and (b) are given as normalized
ones to guarantee that the results are comparable relative strengths.
the obvious excitation of T1-RTP only appears at ≈445 nm with
negligible contribution from higher excitations, corresponding
to the ISC channel of S1→T1. As a comparison, the excitations
of Tn-RTP (emission wavelengths from 480 to 540 nm) dem-
onstrate three series of markedly bands at ≈330, ≈420, and
≈445 nm, respectively, indicating that Tn-RTP could be efficiently
generated through multiple alterative ISC channels. In this
regard, it is convincing that T1-RTP and Tn-RTP have totally
different origins. For Tn-RTP, two main ISC channels can be
probably assigned to S1→T2 and S2→T2 upon the excitations
at ≈420 and ≈445 nm, respectively. Additionally, it should be
mentioned that the influence of triplet absorption can be excluded
here, since the triplet absorption of DPPZ has been confirmed
to be very weak and of even lower energy level (≈550 nm).[14]
the two sp2-N heteroatoms, a p-orbital character of lone pair
electron was obviously observed, indicating n-electron char-
acter of “hole” wavefunction. On the other hand, the “particles”
possess such nodal section along molecular plane, and are
all delocalized over the whole molecular skeleton, which are
of obvious π-bonding character. Thus, both S1 and T2 excited
states of DPPZ should be attributed to n→π* transition. As a
contrast, both S2 and T1 excited states should be assigned to
π→π* transition.[20] According to the El-Sayed rule, the ISC pro-
cesses along S1→T1 and S2→T2 are expected to occur efficiently
in DPPZ (Figure 4a) due to the different transition patterns,
which are in good agreement with the excitation-wavelength-
dependent results. Second, the SOC for S1→T1 and S2→T2 are
estimated by Beijing Density Function (BDF) program[21] as
10.33 and 6.03 cm−1, respectively, which can well rationalize the
efficient ISC processes of S1→T1 and S2→T2, especially for the
generation and accumulation of T2 excitons. The last but not
the least, the existence of T2-RTP reveals that DPPZ does not
only benefit from adequate exciton resources, a fast radiative
rate of T2 excited state is also needed. The radiation rate con-
stants of T2 and T1 excited states are calculated to be 4.00 × 105
and 1.82 × 105 s−1, respectively,[22] which is in correspondence
of their characterful lifetimes (13.33 and 24.68 µs, respectively,
Table S1, Supporting Information).
2.2. Theoretical Analysis of the Single-Molecule White
Light Emission
To further clarify the essence of the dual RTP in DPPZ, time-
dependent density functional theory (TDDFT) calculations
are carried out.[19] First, the Tn-RTP species of DPPZ could be
specified as a T2-RTP emission. To confirm this point, we cal-
culated the natural transition orbital (NTO) of relevant excited
states to understand their transition characters, as shown in
Figure 4a. On one hand, the “hole” of S1 and T2 excited states
do not possess any nodal section along molecular plane,
assigning to σ-bonding character between any two atoms. For
Additionally, due to the different transition patterns between
T2 and T1, the internal conversion (IC) of T2→T1 should be
probably slowed down to some extent.[23] Meanwhile, the n→π*
transition character of T2 unblocks the radiative transition of
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Figure 4. a) Natural transition orbitals (NTO) images of the S1, S2, T1, and T2 excited states of DPPZ. The NTO images of each excited states
represent for their transition forms from the “hole” unity to the “particle” unity, respectively, and the percentages on the arrows are the proportions of
the transitions. b) Schematic Jablonski diagram with SOC matrix elements of RTP-related ISC processes in DPPZ.
T2→S0.[8] Thus, the radiative transition of T2→S0 can com-
pete with the limited IC process of T2→T1, and finally leading
to the dual phosphorescent emission of a T2→S0 RTP with
a short lifetime and a T1→S0 RTP with a little long lifetime,
which is consistent with the excitation-wavelength-dependent
results. Finally, besides ISC channels of S2→T2 and S1→T1, the
S1→T2 channel is also active. Although the SOC of S1→T2 is
relatively small (0.23 cm−1), the calculated energy gap between
them is very small (ES1 − ET1 = 0.14 eV, Figure S15, Supporting
Information), which is identical to the excitation band of
T2-RTP around 440 nm in Figure 3d. As a comparison, the
large SOC is not found in the nitrogen-free counterpart DPAN,
indicating that nitrogen heteroatom surely plays a crucial role
in the RTP of DPPZ, and it is an important molecular design
prototype to achieve simultaneous multiemission based on
single molecule.
mixing through a precise manipulation on the energy levels
of three different excited states in the future.
4. Experimental Section
All the reagents and solvents used for the synthesis were purchased
from Aldrich and Acros companies and used without further purification.
The synthesis procedure was presented in Scheme S1 (Supporting
Information). The 1H NMR and 13C NMR spectra were recorded on
AVANCE 500 spectrometers at 298 K by utilizing deuterated dimethyl
sulfoxide (DMSO) and deuterated chloroform (CDCl3) as solvents and
tetramethylsilane (TMS) as a standard, respectively. The compounds
were characterized by a Flash EA 1112, CHNS-O elemental analysis
instrument. The matrix-assisted laser desorption/ionization time of flight
mass spectrometry (MALDI-TOF-MS) mass spectra were recorded using
an AXIMA-CFR plus instrument. Thermal gravimetric analysis (TGA) was
undertaken on a PerkinElmer thermal analysis system at a heating rate of
10 °C min−1 and a nitrogen flow rate of 80 mL min−1. UV–vis absorption
spectra were recorded on a UV-3100 spectrophotometer. PL spectra
of original powder and ground powder in air, N2, and O2 were carried
out with Edinburgh FLS-980. The time-resolved PL spectra of doped
film were measured on a Horiba Fluoromax-4 spectrofluorometer. PL
efficiency of powder was measured on quartz plate using an integrating
sphere apparatus. The temperature-dependent spectra and lifetimes were
measured on an Edinburgh FLS-980 with an EPL-375 optical laser. The time-
resolved PL spectra of powder were measured on an Edinburgh LP-920. All
the density functional theory (DFT) calculations and natural transitional
orbital (NTO) analysis were carried out using Gaussian 09 (version
D.01) package on a Power Leader cluster. The excited-state geometry was
optimized by time-dependent density functional theory (TDDFT) with the
B3LYP functional at the basis set level of 6-31G(d, p). The energy levels of
singlet and triplet were obtained using TDDFT with the B3LYP functional at
the basis set level of 6-31G(d, p) at the optimized excited state S1 and T1
geometries, respectively. The SOC matrix elements were calculated using
a BDF package. The radiative rate constants were calculated using the
Molecular Materials Property Prediction Package (MOMAP).
3. Conclusion
To sum up, we synthesized a pure-organic aromatic com-
pound dibenzo[a,c]phenazine (DPPZ), and successfully
achieved a pure organic single-molecule white-light emission
at ambient condition. The CIE coordinate of DPPZ emis-
sion is (0.28, 0.33), as a result of the continuous PL emission
covering the whole visible region from ternary emissions:
S1-fluorescence, T1-RTP, and T2-RTP (exception to Kasha’s
rule). Theoretical calculation combined with photophysical
property characterization proves that T1-RTP and T2-RTP
have relatively independent origin, which is beneficial for the
continuity and stability of the white emission of DPPZ. The
aromatic system containing nitrogen heteroatom turns out to
be a promising candidate to enhance SOC, leading to the effi-
cient ISC in pure organic metal-free RTP materials, instead
of commonly used heavy atoms (e.g., bromine, iodine, or
deuterium) and carbonyl group. Our results not only provide
a new molecular system to develop environmental-friendly,
low-cost, stable pure organic SMWLE materials, but also
suggest a prototype mechanism to realize single-molecule
true white light emission with standard three-primary-color
The synthesis of dibenzo[a,c]phenazine followed the procedure
described in previous report.[24]
A
mixture of phenanthrene-
9,10-dione (1.04 g, 5 mmol) and benzene-1,2-diamine (0.54 g, 5 mmol)
in acetic acid (80 mL) was heated to reflux for 8 h. After cooling to room
temperature, the resulting mixture was poured into ethanol (200 mL),
and then filtered. The solid was washed with ethanol several times. The
crude product was purified by column chromatography on silica gel
(eluent: dichloromethane) and dried under vacuum to give the desired
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compound as a white solid in 80% yield (1.12 g). H NMR (500 MHz,
DMSO) δ 9.32 (d, J = 7.9 Hz, 2H), 8.84 (d, J = 8.1 Hz, 2H), 8.38 (dd, J =
6.4, 3.4 Hz, 2H), 8.02 (dd, J = 6.4, 3.3 Hz, 2H), 7.92 (t, J = 7.5 Hz, 2H),
7.85 (t, J = 7.5 Hz, 2H). 13C NMR (126 MHz, CDCl3) δ 142.60, 142.20,
132.01, 130.31, 129.68, 129.47, 127.94, 126.28, 122.92. MALDI-TOF MS
(mass m/z): 280 [M]+. Anal. calcd for C20H12N2: C 85.69, H 4.31, N 9.99;
found: C 85.95, H 4.21, N 9.92.
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Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
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Acknowledgements
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C.Z. and S.Z. contributed equally to this work. This work was supported
by the National Natural Science Foundation of China (51473063,
91233116, and 51673083), the National Key Basic Research and
Development Program of China (Grant Nos. 2016YFB0401001,
2013CB834801, and 2015CB655003), the Postdoctoral Innovation Talent
Support Project (BX201700097), and the China Postdoctoral Science
Foundation (2017M620108).
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Conflict of Interest
[19] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci,
G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian,
A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada,
M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima,
Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery Jr.,
J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers,
K. N. Kudin, V. N. Staroverov, T. Keith, R. Kobayashi, J. Normand,
K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi,
M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross,
V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski,
R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth,
P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas,
J. B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian 09,
Revision D.01, Gaussian, Inc., Wallingford, CT 2013.
The authors declare no conflict of interest.
Keywords
high-lying triplet, room-temperature phosphorescence, spin–orbital
coupling, ternary emission, white light
Received: April 9, 2018
Revised: May 15, 2018
Published online:
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