Synthesis and Delayed Fluorescent Properties of p-Nido-Carborane-Triarylborane Conjugates with a Methyl-Substituted Phenylene Linker

Article abstract of DOI:10.1002/bkcs.12149

A series of p-nido-carborane-triarylborane conjugates (nido-1-3) in which a methyl group is introduced at the ortho-position to the carborane cage in the phenylene linker was prepared and characterized. All compounds exhibit broad low-energy absorptions (

Full text of DOI:10.1002/bkcs.12149

Article
DOI: 10.1002/bkcs.12149
BULLETIN OF THE
S. Sujith and M. H. Lee
KOREAN CHEMICAL SOCIETY
Synthesis and Delayed Fluorescent Properties of p-Nido-Carborane-
Triarylborane Conjugates with a Methyl-Substituted Phenylene Linker
*
Surendran Sujith and Min Hyung Lee
Department of Chemistry, University of Ulsan, Ulsan 44610, Republic of Korea.
*E-mail: lmh74@ulsan.ac.kr
Received October 8, 2020, Accepted November 4, 2020
A series of p-nido-carborane-triarylborane conjugates (nido-1-3) in which a methyl group is introduced at
the ortho-position to the carborane cage in the phenylene linker was prepared and characterized. All com-
pounds exhibit broad low-energy absorptions (λabs = ca. 350–400 nm) attributable to the intramolecular
charge transfer transition from the nido-carborane donor to the (MePh)BMes2 acceptor. Electrochemical
studies confirm that oxidation occurs at the nido-carborane while the boryl moieties are responsible for
the reduction. All nido-compounds show broad green emissions in tetrahydrofuran (THF) with good
photoluminescence (PL) quantum yields (ΦPL = 24%–78%). In particular, different from the almost non-
thermally activated delayed fluorescence (TADF) properties of unsubstituted para-conjugates, the tran-
sient PL decay curves of nido-1-3 show the existence of weak TADF (τd = 0.9–1.4 μs in THF). The
TADF properties are further supported by the very small singlet-triplet energy splitting below 0.15 eV
and are also observed in poly(methyl methacrylate) (PMMA) films doped with nido-1-3.
Keywords: Thermally activated delayed fluorescence, Nido-carborane, Triarylborane, Para-conjugates
Introduction
In this context, we recently reported nido-carborane-
triarylborane conjugates as a new type of D-A system
(Chart 1).32 It was demonstrated that the conjugates can
exhibit TADF properties and the meta-substitution of the
nido-carborane played a crucial role in attaining TADF.
Although the TADF was weak in solution, the attach-
ment of a steric group (R2 = Me in Chart 1) to the 4-
position of the phenylene linker further enhanced the
TADF properties.33 It was revealed that the additional
methyl group provides large energy barriers to cage rota-
tion, which assists to maintain a perpendicular arrange-
ment between the cage plane (CCb-CCb-B-B-B) and the
Ph ring required for an efficient RISC. This finding
prompted us to consider introducing a methyl group into
the ortho-position to the cage in previous p-nido-car-
borane-substituted dimesitylphenylborane (PhBMes2) com-
pounds. In fact, the unsubstituted para-conjugates showed
almost non TADF because of a substantial electronic conju-
gation between the donor (nido-carborane) and acceptor
(PhBMes2) moieties.32 Thus, it is anticipated that the elec-
tronic conjugation in para-conjugates could be weakened
due to steric hindrance between the cage and methyl
groups, which may improve the TADF properties of the
para-conjugates (nido-1-3 in Chart 1). In this report, we
prepared p-nido-carborane-triarylborane conjugates in
which a methyl group is introduced at the ortho-position to
the cage in the phenylene linker. The investigation of the
photophysical properties of nido-1-3 having different 8-R
groups showed enhanced TADF properties compared with
Carboranes, which are well-known icosahedral boron clusters,
have been actively investigated in the field of boron cluster
chemistry.1–5 The unique properties of carboranes, such as
three-dimensional σ-aromaticity, steric bulkiness, electron-
withdrawing property through C-substitution, high thermal
and chemical stability make them one of the promising
candidates for novel luminophores.6–8 While 1,2-closo-
carboranes (1,2-dicarba-closo-dodecaboranes) are consid-
ered an electron-accepting auxiliary of luminophores owing
to their strong inductive electron-withdrawing effect and
conjugation effect,9–23 7,8-nido-carboranes (7,8-dicarba-
nido-undecaboranes) act as an electron-donating group due to
their anionic nature. Hence, nido-carboranes have often been
employed as a donor in intramolecular charge transfer (ICT)
systems.24–27 However, in contrast with closo-carboranes,
nido-carboranes have been less exploited in luminescent mate-
rials and thereby the photophysical properties of nido-car-
borane-based luminophores are still under investigation. In
particular, the design of novel nido-carborane-based donor-
acceptor (D-A) systems will be challenging because such sys-
tems could be suitable for inducing thermally activated del-
ayed fluorescence (TADF) owing to the steric bulkiness and
electron-donating properties of nido-carboranes.28 In recent
years, TADF compounds are receiving great attention as an
efficient emitting material in organic light-emitting diodes
(OLEDs) since they can harvest nearly 100% singlet (S1) exci-
tons through reverse intersystem crossing (RISC) from triplet
(T1) excitons.29–31
Bull. Korean Chem. Soc. 2020
© 2020 Korean Chemical Society, Seoul & Wiley-VCH GmbH
Wiley Online Library
1

Article
BULLETIN OF THE
ISSN (Print) 0253-2964 | (Online) 1229-5949
KOREAN CHEMICAL SOCIETY
Calcd for C44H77B10N: C, 72.57; H, 10.66; N, 1.92%.
Found: C, 72.21; H, 10.81, N, 1.98%.
[Bu4N][1-(Mes2B)-4-(8-iPr-7,8-nido-C2B9H10)-5-
1
MeC6H3] (nido-3). Yield = 59%. H NMR (acetone-d6): δ
7.26 (d, J = 7.8 Hz, 1H), 7.21 (s, 1H), 7.11–7.04 (m, 1H),
6.82 (s, 4H), 3.50–1.50 (br, 9H, B-H), 3.40 (t, J = 8.6 Hz,
8H), 2.49 (s, 3H), 2.28 (s, 6H, Mes-CH3), 1.98 (s, 12H,
Mes-CH3), 1.81 (quint, J = 7.2 8H), 1.43 (sext, J = 7.5 Hz,
8H), 1.21 (sept, J = 6.6 Hz, 1H), 0.99 (t, J = 7.2 Hz, 12H),
0.95 (d, J = 2.1 Hz, 3H),), 0.58 (t, J = 8.3 Hz, 3H), −2.60
(br s, 1H, B-H-B). 13C NMR (acetone-d6): δ 146.2, 142.6,
141.2, 140.5, 138.8, 134.7, 130.1, 128.9, 59.4 (NBu4),
26.2, 25.3, 24.4 (NBu4), 23.7, 23.6, 21.2, 20.4 (NBu4),
13.8 (NBu4). 11B NMR (acetone-d6): δ 78.3 (br s), −7.9
(2B), −14.2 (1B), −15.9 (2B), −18.6 (2B), −32.8 (1B),
−35.1 (1B). mp = 181ꢀC. Anal. Calcd for C46H81B10N: C,
73.06; H, 10.80; N, 1.85%. Found: C, 73.12; H,
10.69; N, 1.88%.
Chart 1. Meta- and para-nido-carborane-substituted triarylboranes.
those of the unsubstituted conjugates, verifying the rational-
ity of the proposed approach.
Experimental Section
General Synthesis of p-Nido-Carborane-Substituted
Triarylboranes, nido-1-3. Closo-carborane compounds
(0.2 mmol) and tetrabutylammonium fluoride (n-Bu4NF,
TBAF) (1.0 mmol) were combined in tetrahydrofuran
(THF) (20 mL) and the mixture was heated to reflux for
4 days. The mixture was cooled down to room temperature
and the solvent was evaporated. The remaining residue was
subjected to column chromatography on alumina using
CH2Cl2/hexane (1:1, v/v) followed by acetone to afford a
white powder of nido-carborane derivatives (nido-1-3). The
product was further recrystallized from CH2Cl2/hexane.
[Bu4N][1-(Mes2B)-4-(8-H-7,8-nido-C2B9H10)-5-
Photophysical Measurements. Ultraviolet/Visible (UV/
Vis) absorption and photoluminescence (PL) spectroscopic
studies were performed on a Varian Cary 100 and FS5
spectrophotometer, respectively. Photoluminescence quan-
tum yields (PLQYs, ΦPL) of all solution and film samples
were measured on an absolute PL quantum yield spectro-
photometer (Quantaurus-QY C11347-11, Hamamatsu Pho-
tonics, Japan) equipped with a 3.3 inch integrating sphere.
Transient PL decay was recorded on a FS5 spectrophotom-
eter (Edinburgh Instruments, Livingston, UK) using a time-
correlated single-photon counting (TCSPC) method (EPL-
375 ps pulsed diode laser as a light source).
1
MeC6H3] (nido-1). Yield = 65%. H NMR (acetone-d6): δ
7.25 (d, J = 7.8 Hz, 1H), 7.18 (s, 1H), 7.08 (d, J = 7.7 Hz,
1H), 6.82 (s, 4H), 3.5–1.5 (br, 9H, B-H), 3.47 (t, J = 9 Hz,
8H), 2.40 (s, 3H), 2.28 (s, 6H), 1.98 (s, 12H), 1.84 (quint,
J = 9, 8H), 1.68 (s, 1H, CCb-H),1.44 (sext, J = 7.8, Hz,
8H), 0.99 (t, J = 7.5 Hz, 12H), −2.53 (br s, 1H, B-H-B).
13C NMR (acetone-d6): δ 149.9, 140.3, 138.7, 138.1,
137.4, 133.1, 128.1, 128.0, 58.4 (Bu4N), 23.5 (Bu4N),
22.8, 20.3, 19.6, 19.5 (Bu4N), 13.0 (Bu4N). 11B NMR (ace-
tone-d6): δ 79.1 (br s), −8.2 (1B), −9.7 (1B), −13.0 (1B),
−15.4 (1B), −18.1 (2B), −22.9 (1B), −32.4 (1B), −35.2
(1B). mp = 228ꢀC. Anal. Calcd for C43H75B10N: C,
72.32; H, 10.59; N, 1.96%. Found: C, 72.16; H,
10.83, N, 2.01%.
Results and Discussion
Synthesis and Characterization. The synthesis of p-nido-
carborane-triarylborane conjugates (nido-1-3) was achieved
using the analogous methods established previously for the
meta-systems (Scheme 1).32,33 To investigate the substitu-
ent effect on the photophysical properties, we also intro-
i
duced various 8-R groups such as H, Me, and Pr groups
into the 8-position of the nido-carborane cage. The car-
borane cage of the corresponding closo-1-3 was
deboronated with TBAF in refluxing THF, producing nido-
1-3 in good yields (59%–83%, see the SI for details). The
synthesis of closo-1-3 compounds proceeded with slightly
different routes depending on the 8-R group. The 8-H
substituted closo-1 was prepared by the cage forming reac-
tion between (4-ethynylphenyl)dimesitylborane (1b) and
decaborane (B10H14) in the presence of excess Et2S in
refluxing toluene. In the synthesis of closo-2 and -3, a
BMes2 moiety was finally introduced into the 4-
[Bu4N][1-(Mes2B)-4-(8-Me-7,8-nido-C2B9H10)-5-
1
MeC6H3] (nido-2). Yield = 83%. H NMR (acetone-d6): δ
7.25–7.19 (m, 2H), 7.10 (d, J = 7.8 Hz, 1H), 6.82 (s, 1H)
3.5–1.5 (br, 9H, B-H), 3.45 (t, J = 8.9 Hz, 8H), 2.40 (s,
3H), 2.28 (s, 6H), 1.98 (s, 12H), 1.81 (quint, J = 8.3, 8H),
1.45 (sext, J = 7.5, Hz, 8H), 1.01 (s, 3H, CCb-CH3), 0.98 (t,
J = 7.3 Hz, 12H), −2.45 (br s, 1H, B-H-B). 13C NMR (ace-
tone-d6): δ 147.6, 140.4, 139.5, 138.0, 137.1, 132.9, 129.5,
128.1, 58.5 (Bu4N), 23.5 (Bu4N), 22.7, 22.5, 21.0, 20.4,
19.5 (Bu4N), 13.0 (Bu4N). 11B NMR (acetone-d6): δ 78.3
(br s), −6.5 (1B), −9.9 (2B), −13.6 (1B), −15.3 (1B),
−19.7 (2B), −33.2 (1B), −35.6 (1B). mp = 228ꢀC. Anal.
i
bromobenzene intermediates having an 8-R (R = Me, Pr)
substituted closo-carborane (2b and 3b), which could be
obtained via deprotonation of 8-H in 2a with NaH,
followed by reaction with a respective alkyl iodide.
The formation of the closo- and nido-compounds was
identified by nuclear magnetic resonance (NMR)
Bull. Korean Chem. Soc. 2020
© 2020 Korean Chemical Society, Seoul & Wiley-VCH GmbH
www.bkcs.wiley-vch.de
2

BULLETIN OF THE
Article
p-Nido-Carborane-Triarylborane Conjugates
KOREAN CHEMICAL SOCIETY
Figure 1. UV/Vis absorption spectra of nido-1-3 in THF
(2.0 × 10−5 M) at 298 K.
oxidations occur at similar potentials (Eox = 0.47 V for
nido-2 and 0.49 V for nido-3) (Table S1).
This result indicates that nido-carborane-centered HOMO
level could be controlled by the 8-R group. In the case of
reduction, while triarylboron-centered reductions are
observed for all compounds, they are not completely
reversible (quasi-reversible). Nevertheless, the reduction
potentials are very similar to each other (Ered = −2.42 V to
−2.45 V) probably owing to the same boryl acceptor moi-
ety. Accordingly, the band gap (Eg) of compounds is
governed by their HOMO levels, leading to the largest
value for nido-1. These electrochemical results further indi-
cate that HOMO (nido-carborane) and LUMO ((MePh)
BMes2) are well separated within a molecule due to the
additional Me group at the ortho-position to the cage and
the lowest-energy electronic transition involves the nido-
carborane to boryl ICT transition.
The PL spectra of nido-1-3 exhibit a broad emission cen-
tered at 520–535 nm in THF, which is typical for CT tran-
sition (Figure 3 and Table 1). Among the three compounds,
nido-1 shows the most blue-shifted emission because of the
largest band gap. All compounds have good PL quantum
yields (PLQY, ΦPL) in oxygen-free THF (ΦPL = 24%–
78%). The 8-H containing nido-1 is the most emissive
among the compounds, as similarly found for previous
Scheme 1. Synthesis of closo-1-3 and nido-1-3. i) Pd(PPh3)4, CuI,
i
ethynyltrimethylsilane, Pr2NH, 0ꢀC; ii) n-BuLi, ether, −78ꢀC,
then FBMes2; iii) TBAF, THF, RT; iv) B10H14, Et2S, toluene, r/x;
i
v) NaH, DMF, 0ꢀC, then RI (R = Me for 2b and Pr for 3b); vi)
TBAF, THF, r/x, 4 days.
spectroscopy and elemental analyses (see the SI for details).
For nido-1-3, broad 1H NMR resonances at δ − 2.3 to
−2.8 ppm can be attributed to the bridging B-H-B hydro-
gen of the nido-carborane. The 11B NMR spectra showed
two sets of signals, that is, a weak broad signal at δ ca.
78 ppm and sharp signals at δ −6 to −36 ppm, which con-
firmed the presence of both tri-coordinated boron and nido-
carboranyl boron atoms.
Photophysical and Electrochemical Properties. UV/Vis
absorption and PL spectroscopic studies were performed in
THF to investigate the photophysical properties (Figures 1
and 3, and Table 1). All nido-1-3 exhibit similar strong
absorptions at ca. 318 nm, which are mainly assignable to
(MePh)BMes2-centered π(Mes) ! pπ(B) CT transition. In
addition, a weak absorption is observed in the low-energy
region of ca. 350–400 nm. This absorption can be ascribed
to the ICT transition from the nido-carborane donor to the
(MePh)BMes2 acceptor.32,33
The redox properties and the nature of highest occupied
molecular orbital (HOMO) and lowest unoccupied molecu-
lar orbital (LUMO) of compounds were investigated by an
electrochemical study (Figure 2 and Table 1). All nido-1-3
show an irreversible oxidation (HOMO) typical for nido-
carboranes.34,35 Owing to the presence of different 8-R
groups, the oxidation potentials are slightly different among
the compounds; nido-1 bearing a less electron-donating 8-
H group exhibits a larger oxidation potential (Eox = 0.56 V)
than those of the 8-alkyl substituted nido-2 and -3 whose
Figure 2. Cyclic voltammograms of nido-1-3 (1.0 × 10−3 M in
DMF, scan rate = 100–200 mV/s).
Bull. Korean Chem. Soc. 2020
© 2020 Korean Chemical Society, Seoul & Wiley-VCH GmbH
www.bkcs.wiley-vch.de
3

BULLETIN OF THE
Article
p-Nido-Carborane-Triarylborane Conjugates
KOREAN CHEMICAL SOCIETY
Table 1. Photophysical data of nido-1-3.
HOMO/LUMOd ΔEST
e
Compd λabsa (nm)
λPL (nm)
THFa filmf THFa (N2/air) filmf
ΦPLb (%)
τp (ΦPF) [ns (%)]c
THFa filmf
τd (ΦDF) [μs (%)]c
(eV)
(eV)
THFa
filmf
nido-1
nido-2
nido-3
319
318
318
520
535
529
459
484
487
78/40
40/16
24/11
80
70
44
28.9 (94) 18.9 (97) 0.9 (6)
33.2 (94) 38.0 (89) 1.4 (6)
31.5 (90) 46.3 (98) 0.9 (10)
0.6 (3)
3.6 (11)
1.5 (2)
−5.36/−2.38
−5.27/−2.37
−5.29/−2.35
0.020
0.041
0.145
a In oxygen-free THF at 298 K (2.0 × 10−5 M).
b Absolute photoluminescence quantum yields (PLQYs).
c Prompt (τp) and delayed (τd) PL lifetimes. Relative portions (%) of the prompt (ΦPF) and delayed (ΦDF) components are provided in parentheses.
d From electrochemical oxidation (HOMO) and reduction (LUMO).
e ΔEST = ES − ET. Singlet (ES) and triplet (ET) energies from the fluorescence and phosphorescence spectra in THF at 77 K.
f Spin-coated PMMA films doped with 10 wt% of compounds.
Figure 3. PL spectra of nido-1-3 in N2-filled and aerated THF (2.0 × 10−5 M) at 298 K. λexc = 320 nm for nido-1 and 2; 325 nm for nido-
3. Insets: Transient PL decay curves of nido-1-3 in N2-filled and aerated THF at 298 K. λexc (laser) = 375 nm.
nido-carborane-substituted triarylboranes.32,33 Note that the
emission wavelength and PLQY of the 8-alkyl substituted
nido-2 and -3 are almost comparable albeit a slightly higher
PLQY for nido-2. Next, to investigate the TADF properties,
transient PL decay for the CT emission of the compounds
was measured in oxygen-free THF (Insets in Figure 3 and
Table 1). For comparison, the decay curves in air-saturated
THF are also obtained. The PL decay of all compounds
exhibits microsecond-range decay components, as well as
nanosecond-range prompt components. The estimated del-
ayed emission lifetimes (τd) are of ca. 1 μs at 298 K. How-
ever, the intensities of the decay components are
considerably weak for all compounds, exhibiting relative
portions of the delayed components (ΦDF) less than 10%.
The absence of long-lived decay components and the much
reduced emission intensities in aerated solutions indicates
that the delayed emission of nido-1-3 can be assigned to
TADF originating from the T1 ! S1 RISC process (Fig-
ure 3). Although these results are poorer than those of previ-
ous meta-systems, which showed strong delayed emission
with long lifetimes,33 they are promising when compared
with the almost non-TADF properties of unsubstituted para-
conjugates.32 This in turn indicates that the introduction of a
steric group (Me) into the ortho-position to the cage in the
phenylene linker can enhance TADF properties by restricting
cage rotation which is favorable for maintaining a perpendic-
ular arrangement between the cage plane and the Ph ring.
Very small energy splitting (ΔEST) between the excited sin-
glet (S1) and triplet (T1) states below 0.15 eV for all com-
pounds further supports the TADF properties of nido-1-3
(Table 1 and Figure S4).
Figure 4. PL spectrum and transient PL decay curve (right inset)
of PMMA film doped with 10% nido-2. λexc = 320 nm. PLQY
(%) and delayed lifetime (τd) are provided.
Bull. Korean Chem. Soc. 2020
© 2020 Korean Chemical Society, Seoul & Wiley-VCH GmbH
www.bkcs.wiley-vch.de
4

BULLETIN OF THE
Article
p-Nido-Carborane-Triarylborane Conjugates
KOREAN CHEMICAL SOCIETY
8. N. S. Hosmane, Boron Science: New Technologies and Appli-
cations, CRC Press, New York, 2012.
9. H. Naito, K. Nishino, Y. Morisaki, K. Tanaka, Y. Chujo,
Angew. Chem. Int. Ed. 2017, 56, 254.
10. D. Tu, P. Leong, S. Guo, H. Yan, C. Lu, Q. Zhao, Angew.
Chem. Int. Ed. 2017, 56, 11370.
11. N. V. Nghia, S. Park, Y. An, J. Lee, J. Jung, S. Yoo, M. H. J.
Lee, Mater. Chem. C 2017, 5, 3024.
12. N. V. Nghia, J. Oh, J. Jung, M. H. Lee, Organometallics
2017, 36, 2573.
13. R. Furue, T. Nishimoto, I. S. Park, J. Lee, T. Yasuda, Angew.
Chem. Int. Ed. 2016, 55, 7171.
14. Y. Kim, S. Park, Y. H. Lee, J. Jung, S. Yoo, M. H. Lee,
Inorg. Chem. 2016, 55, 909.
Finally, the photophysical properties of nido-1-3 were
investigated in the rigid state using poly(methyl methacry-
late) (PMMA) films. All PMMA films doped with 10 wt%
compounds exhibit CT emission with increased PLQYs
(ΦPL = 80%–44%) (Figures 4 and S5). The PL emission
underwent rigidochromic blue shifts by ca. 40–60 nm in
comparison with that in THF. The emission peak positions
follow the same trend as that observed in THF solutions,
showing the most blue-shifted peak for nido-1. In particu-
lar, the weak delayed fluorescence with emission lifetimes
(τd) of 0.6–3.6 μs is also observed for all film samples, con-
firming the existence of TADF in the rigid state.
15. J. Park, Y. H. Lee, J. Y. Ryu, J. Lee, M. H. Lee, Dalton
Trans. 2016, 45, 5667.
Conclusion
16. B. H. Choi, J. H. Lee, H. Hwang, K. M. Lee, M. H. Park,
Organometallics 2016, 35, 1771.
17. Y. H. Lee, J. Park, S.-J. Jo, M. Kim, J. Lee, S. U. Lee, M. H.
Lee, Chem. Eur. J. 2015, 21, 2052.
18. H. Naito, Y. Morisaki, Y. Chujo, Angew. Chem. Int. Ed.
2015, 54, 5084.
19. H. J. Bae, H. Kim, K. M. Lee, T. Kim, Y. S. Lee, Y. Do,
M. H. Lee, Dalton Trans. 2014, 43, 4978.
20. K.-R. Wee, Y.-J. Cho, J. K. Song, S. O. Kang, Angew. Chem.
Int. Ed. 2013, 52, 9682.
21. C. Shi, H. Sun, X. Tang, W. Lv, H. Yan, Q. Zhao, J. Wang,
W. Huang, Angew. Chem. Int. Ed. 2013, 52, 13434.
22. T. Kim, H. Kim, K. M. Lee, Y. S. Lee, M. H. Lee, Inorg.
Chem. 2013, 52, 160.
23. L. Weber, J. Kahlert, R. Brockhinke, L. Böhling, A.
Brockhinke, H.-G. Stammler, B. Neumann, R. A. Harder,
M. A. Fox, Chem. Eur. J. 2012, 18, 8347.
24. M. Z. Shafikov, A. F. Suleymanova, R. Czerwieniec, H.
Yersin, Chem. Mater. 2017, 29, 1708.
We prepared and characterized p-nido-carborane-
triarylborane conjugates (nido-1-3) in which a methyl group
is introduced at the ortho-position to the cage in the
phenylene linker. Different from the almost non-TADF
behavior of previous unsubstituted para-conjugates, nido-1-3
exhibited TADF properties in both solution and solid state
irrespective of 8-R groups. All compounds showed very
small ΔEST values as a consequence of a perpendicular
arrangement between the cage plane and the Ph ring induced
by the steric hindrance between the two moieties. The results
in this study demonstrate that TADF properties of nido-car-
borane-triarylborane D-A conjugates can be improved by
employing a steric group between the donor (cage) and
acceptor (PhBMes2) groups and the proposed approach will
also be useful for designing nido-carborane-based TADF
compounds.
Acknowledgments. This work was supported by the 2020
Research Fund of University of Ulsan.
25. K. C. Song, H. Kim, K. M. Lee, Y. S. Lee, Y. Do, M. H.
Lee, Dalton Trans. 2013, 42, 2351.
26. R. Visbal, I. Ospino, J. M. López-de-Luzuriaga, A. Laguna,
M. C. Gimeno, J. Am. Chem. Soc. 2013, 135, 4712.
27. F. Lerouge, A. Ferrer-Ugalde, C. Viñas, F. Teixidor, R.
Sillanpää, A. Abreu, E. Xochitiotzi, N. Farfán, R. Santillan,
R. Núñez, Dalton Trans. 2011, 40, 7541.
Supporting Information. Additional supporting informa-
tion may be found online in the Supporting Information
section at the end of the article.
28. H. Uoyama, K. Goushi, K. Shizu, H. Nomura, C. Adachi,
Nature 2012, 492, 234.
References
29. X. Cai, S.-J. Su, Adv. Funct. Mater. 2018, 28, 1802558.
30. M. Y. Wong, E. Zysman-Colman, Adv. Mater. 2017, 29,
1605444.
1. R. Núñez, M. Tarrés, A. Ferrer-Ugalde, F. F. de Biani, F.
Teixidor, Chem. Rev. 2016, 116, 14307.
2. R. Núñez, I. Romero, F. Teixidor, C. Viñas, Chem. Soc. Rev.
2016, 45, 5147.
3. R. N. Grimes, Dalton Trans. 2015, 44, 5939.
4. R. N. Grimes, Carboranes, 2nd ed., Academic Press,
London, 2011.
5. Z. Chen, R. B. King, Chem. Rev. 2005, 105, 3613.
6. J. Ochi, K. Tanaka, Y. Chujo, Angew. Chem. Int. Ed. 2020,
59, 9841.
31. Y. Tao, K. Yuan, T. Chen, P. Xu, H. Li, R. Chen, C. Zheng,
L. Zhang, W. Huang, Adv. Mater. 2014, 26, 7931.
32. N. V. Nghia, S. Jana, S. Sujith, J. Y. Ryu, J. Lee, S. U. Lee,
M. H. Lee, Angew. Chem. Int. Ed. 2018, 57, 12483.
33. S. Sujith, E. B. Nam, J. Lee, S. U. Lee, M. H. Lee, Inorg.
Chem. Front. 2020, 7, 3456.
34. E. Hao, B. Fabre, F. R. Fronczek, M. G. H. Vicente, Chem.
Mater. 2007, 19, 6195.
7. Y. H. Lee, J. Park, J. Lee, S. U. Lee, M. H. J. Lee, Am.
Chem. Soc. 2015, 137, 8018.
35. B. Fabre, J. C. Clark, M. G. H. Vicente, Macromolecules
2006, 39, 112.
Bull. Korean Chem. Soc. 2020
© 2020 Korean Chemical Society, Seoul & Wiley-VCH GmbH
www.bkcs.wiley-vch.de
5