Y. Wang et al.
Organic Electronics 97 (2021) 106275
reported [17,20–23]. To achieve this goal, molecular engineering and
by dichloromethane and water. The organic layer was dried by MgSO4,
then filtered and concentrated in vacuo. Finally, the residue was purified
by column chromatography (elution solvent: petroleum ether) to afford
a white solid (6.42g). Yield, 86%. 1H NMR (400 MHz, CDCl3) δ [ppm]: δ
7.16 (t, J = 7.8 Hz, 12H), 7.07–6.98 (m, 12H), 6.91 (t, J = 7.3 Hz, 6H),
6.42 (s, 3H).
device engineering need a reasonable combination. From molecular
design, multiple resonance core for narrowband TADF emission can be
–
classified as a fused nitrogen/carbonyl (N/C O) system and a fused
–
boron/nitrogen (B/N) system [24–34]. Compared with the fused
–
N/C O system, the fused B/N system exhibits much more multiple
–
structural modifiability, arousing more attention. According to the most
3,5-dichloro-N,N-diphenylaniline (PA-2Cl): The synthetic procedure
was similar to that of PA. White solid was obtained. Yield, 83%. 1H NMR
(400 MHz, CDCl3) δ [ppm]: δ 7.31 (t, J = 7.8 Hz, 4H), 7.11 (t, J = 8.8 Hz,
6H), 6.87 (dd, J = 11.7, 1.5 Hz, 3H).
recent findings of the fused B/N system, the para-disposed two boron
atoms (B-
central
strengths, resulting in large bathochromic shifts of emission. Neverthe-
less, para-disposed boron and nitrogen atoms (B- -N) can reduce the
acceptor and donor strengths, thus realizing a shorter-wavelength
emission [19]. As a result, a fused B/N system with a B- -N structure
is possible for deep-blue emission. Simultaneously, the limited
-conjugation of fused B/N system is also needed [27,28]. Moreover, the
π-B) and para-disposed two nitrogen atoms (N-π-N) in the
π
-core will significantly increase the acceptor and donor
N1,N1,N3,N3-tetrakis(4-(tert-butyl)phenyl)-N5,N5-diphenylbenzene-
1,3,5-triamine (2tPA): The mixture of 1,3,5-tribromobenzene (4.50 g,
14.3 mmol), bis(4-(tert-butyl)phenyl)amine (8.46 g, 30.06 mmol),
Pd2(dba)3 (0.065 g, 0.072 mmol), P(t-Bu)3 (10 wt% in toluene, 0.35 mL,
0.143 mmol) and NaOt-Bu (5.49 g, 57.2 mmol) was suspended in
toluene (70 mL) and refluxed for 18 h under N2 atmosphere at 120 ◦C.
The reaction mixture was cooled to room temperature, toluene was
removed by vacuum distillation. Then the crude product was extracted
by dichloromethane and water. The organic layer was dried by MgSO4,
then filtered and concentrated in vacuo. Finally, the residue was purified
by column chromatography (elution solvent: petroleum ether then pe-
troleum ether/dichloromethane = 9:1) to afford a white solid (6.62g).
Yield, 57%. 1H NMR (400 MHz, CDCl3) δ [ppm]: δ 7.14 (dd, J = 14.4,
8.0 Hz, 12H), 7.02 (d, J = 7.7 Hz, 4H), 6.96 (d, J = 8.6 Hz, 8H), 6.88 (t, J
= 7.3 Hz, 2H), 6.55 (s, 1H), 6.29 (d, J = 1.8 Hz, 2H), 1.37–1.19 (m,
36H).
π
π
π
TADF emitters suffer from aggregation-induced emission quenching and
exciton annihilation processes. The substituents with large steric hin-
drance such as tert-butyl unit are necessary to suppress the negative
effect, thus enhancing luminous efficiency [35–37]. From device engi-
neering, most narrowband TADF-based OLEDs employ bipolar material
as host can improve device efficiency [27–30]. However, the strong
polarity of host will give rise to the interactions between hosts and
emitters, shifting electroluminescence spectra to long-wavelength.
Therefore, it is anticipated that high efficiency and deep-blue emission
can be obtained by cladding large steric hindrance tert-butyl unit at
periphery of multi-resonance emitter with B-
the low polarity host.
π
-N structure and selecting
N1,N1,N3,N3,N5,N5-hexakis(4-(tert-butyl)phenyl)benzene-1,3,5-tri-
amine (3tPA): The synthetic procedure was similar to that of PA. White
solid was obtained. Yield, 91%. 1H NMR (400 MHz, CDCl3) δ [ppm]: δ
7.17 (t, J = 10.4 Hz, 12H), 6.95 (d, J = 8.5 Hz, 12H), 6.44 (s, 3H), 1.26
(s, 54H).
In this work, N,N,5,9-tetraphenyl-5,9-dihydro-5,9-diaza-13b-
boranaphtho[3,2,1-de]anthracen-7-amine (PAB) with B-π-N structure
was designed as a parent molecule. By partial and full periphery clad-
ding with tert-butyl unit, 2,12-di-tert-butyl-5,9-bis(4-(tert-butyl)phenyl)-
N,N-diphenyl-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2,1-de]anthra-
cen-7-amine (2tPAB) and 2,12-di-tert-butyl-N,N,5,9-tetrakis(4-(tert-
butyl)phenyl)-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2,1-de]
anthracen-7-amine (3tPAB) were further synthesized. The results
N,N,5,9-tetraphenyl-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2,1-de]
anthracen-7-amine (PAB): Boron tribromide (3.19 mL, 33.1 mmol) was
added to a solution of PA (3.21 g, 3.5 mmol) in o-dichlorobenzene (100
mL) at room temperature under a nitrogen atmosphere. After stirring at
180 ◦C for 20 h, the reaction mixture was allowed to cool to 0 ◦C. After
addition of N, N-diisopropylethylamine (20.5 mL, 124.2 mmol), the
solvent was removed in vacuo. The crude product was washed with
acetonitrile and recrystallized by toluene and acetonitrile to afford a
yellow solid (3.55g). Yield, 73%. 1H NMR (400 MHz, CDCl3) δ [ppm]: δ
8.90 (dd, J = 7.7, 1.4 Hz, 2H), 7.48 (dd, J = 17.1, 9.7 Hz, 4H), 7.37 (ddd,
J = 8.6, 5.0, 1.9 Hz, 4H), 7.27–7.17 (m, 6H), 7.08 (dd, J = 10.2, 5.5 Hz,
4H), 6.97–6.86 (m, 6H), 6.71 (d, J = 8.4 Hz, 2H), 5.61 (s, 2H). 13C NMR
(101 MHz, CDCl3) δ [ppm]: δ 146.65, 142.17, 134.84, 130.66, 130.35,
130.13, 128.78, 128.09, 125.62, 123.49, 116.83. FTMS (APCI): calcu-
lated for C42H30BN3, 587.5330; found, 588.2595.
showed all new emitters with B-π-N structure exhibited deep-blue
narrowband TADF emission with peak at 449–456 nm and FHWM of
23–26 nm in toluene solution. Under the periphery cladding of tert-butyl
units, the intermolecular interactions were suppressed, and the PLQY of
emitter was enhanced. However, the singlet-triplet splitting (ΔEST) was
increased, which reduced reverse intersystem crossing rate constant
(kRISC). By using 1,3-di(9H-carbazol-9-yl)benzene (mCP) with low po-
larity as host, 3tPAB-based device achieved the best performance with
the maximum external quantum efficiency (EQEmax) of 19.3% and CIE
coordinates of (0.141, 0.076), respectively. To our knowledge, this is the
first report about narrowband TADF OLEDs with single host that EQEmax
approached 20% while CIE coordinates met the NTSC blue-light
standard.
2,12-di-tert-butyl-5,9-bis(4-(tert-butyl)phenyl)-N,N-diphenyl-5,9-dihy-
dro-5,9-diaza-13b-boranaphtho[3,2,1-de]anthracen-7-amine
(2tPAB):
The synthetic procedure was similar to that of PAB. Yellow solid was
obtained. Yield, 61%. 1H NMR (400 MHz, CDCl3) δ [ppm]: δ 8.96 (d, J =
2.4 Hz, 2H), 7.46 (dd, J = 8.7, 3.4 Hz, 6H), 7.13 (d, J = 8.5 Hz, 4H),
7.10–7.02 (m, 4H), 6.99–6.85 (m, 6H), 6.76 (d, J = 9.0 Hz, 2H), 5.47 (s,
2H), 1.47 (s, 18H), 1.33 (s, 18H). 13C NMR (101 MHz, CDCl3) δ [ppm]: δ
150.91, 147.97, 146.59, 145.88, 141.46, 139.45, 130.78, 129.50,
128.66, 127.92, 127.37, 125.94, 123.49, 116.52, 34.65, 34.32, 31.76,
31.42. FTMS (APCI): calculated for C58H62BN3, 811.9650; found,
812.5106.
2. Experimental section
2.1. Materials and reagents
All the solvents and reagents used for target compounds were pur-
chased from commercial suppliers without further purification.
2,12-di-tert-butyl-N,N,5,9-tetrakis(4-(tert-butyl)phenyl)-5,9-dihydro-
5,9-diaza-13b-boranaphtho[3,2,1-de]anthracen-7-amine (3tPAB): The
synthetic procedure was similar to that of PAB. After recrystallization,
the crude product was purified by column chromatography (elution
solvent: petroleum ether). Yellow solid was obtained. Yield, 30%. 1H
NMR (400 MHz, CDCl3) δ [ppm]: δ 8.93 (d, J = 2.4 Hz, 2H), 7.49–7.42
(m, 6H), 7.15 (d, J = 8.5 Hz, 4H), 7.07 (t, J = 5.7 Hz, 4H), 6.86–6.80 (m,
4H), 6.63 (d, J = 9.0 Hz, 2H), 5.70 (s, 2H), 1.46 (s, 18H), 1.33 (s, 18H),
1.27 (s, 18H). 13C NMR (101 MHz, CDCl3) δ [ppm]: δ 151.00, 147.78,
2.2. Synthesis
N1,N1,N3,N3,N5,N5-hexaphenylbenzene-1,3,5-triamine
(PA):
The
mixture of 1,3,5-tribromobenzene (4.00 g, 12.7 mmol), diphenylamine
(6.70 g, 39.40 mmol), Pd2(dba)3 (0.17 g, 0.19 mmol), P(t-Bu)3⋅HBF4
(0.13 g, 0.44 mmol) and NaOt-Bu (3.66 g, 38.1 mmol) was suspended in
toluene (60 mL) and refluxed for 18 h under N2 atmosphere at 120 ◦C.
The reaction mixture was cooled to room temperature, toluene was
removed by vacuum distillation. Then the crude product was extracted
2