Isomeric thermally activated delayed fluorescence emitters based on indolo[2,3-b]acridine electron-donor: a compromising optimization for efficient orange-red organic light-emitting diodesElectronic supplementary information (ESI) available. See DOI: 10.1039/c8tc06081a
Energy differences (Δ E ST s) between the lowest singlet and triplet excited states as well as the oscillator strengths ( f s) are two contradictory factors controlling performance of thermally activated delayed fluorescence (TADF) emitters. To figure out their optimum balance, we developed two oran...
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Main Authors | , , , , , , , , , |
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Format | Journal Article |
Language | English |
Published |
07.03.2019
|
Online Access | Get full text |
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Summary: | Energy differences (Δ
E
ST
s) between the lowest singlet and triplet excited states as well as the oscillator strengths (
f
s) are two contradictory factors controlling performance of thermally activated delayed fluorescence (TADF) emitters. To figure out their optimum balance, we developed two orange-red isomeric TADF emitters 12-(13,13-dimethyl-5-phenyl-5,13-dihydro-11
H
-indolo[2,3-
b
]acridin-11-yl)dibenzo[
a
,
c
]dipyrido[3,2-
h
:2′,3′-
j
]phenazine (
IDAC-BPPZ
) and 12-(13,13-dimethyl-11-phenyl-11,13-dihydro-5
H
-indolo[2,3-
b
]acridin-5-yl)dibenzo[
a
,
c
]dipyrido[3,2-
h
:2′,3′-
j
]phenazine (
ACID-BPPZ
), which are constructed with the same electron-donor (D) and the same electron-acceptor (A) cores
via
different connecting sites.
ACID-BPPZ
has a weaker D-A conjugation and realizes an extremely small Δ
E
ST
of 0.02 eV, but its
f
is also very small (0.001). These factors are better compromised in
IDAC-BPPZ
which has a more conjugated D-A connections. This successfully realizes a much higher
f
of 0.068 and a reasonably small Δ
E
ST
of 0.07 eV. As a result, the orange-red OLEDs using
IDAC-BPPZ
as emitter achieve a maximum external quantum efficiency 18.3% comparing to that of 14.7% in the
ACID-BPPZ
-based device. The results suggest that a balance between Δ
E
ST
and
f
is important for developing high performance TADF emitters.
A combination of small Δ
E
ST
and higher
f
in an orange-red TADF emitter results in better performances. |
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Bibliography: | 10.1039/c8tc06081a Electronic supplementary information (ESI) available. See DOI |
ISSN: | 2050-7526 2050-7534 |
DOI: | 10.1039/c8tc06081a |