Six acridone (quinacridone) derivatives containing either carbazole or phenoxazine substituents were designed and synthesized with the aim of elucidating the effect of the donor (D) and acceptor (A) linking pattern...
Motivated to minimize the effects of solid-state solvation
and
conformation disorder on emission properties of donor–acceptor-type
emitters, we developed five new asymmetric multiple donor–acceptor
type derivatives of tert-butyl carbazole and trifluoromethyl
benzene exploiting different electron-accepting anchoring groups.
Using this design strategy, for a compound containing four di-tert-butyl carbazole units as donors as well as 5-methyl
pyrimidine and trifluoromethyl acceptor moieties, small singlet-triplet
splitting of ca. 0.03 eV, reverse intersystem crossing
rate of 1 × 106 s–1, and high photoluminescence
quantum yield of neat film of ca. 75% were achieved.
This compound was also characterized by the high value of hole and
electron mobilities of 8.9 × 10–4 and 5.8 ×
10–4 cm2 V–1 s–1 at an electric field of 4.7 × 105 V/cm, showing relatively good hole/electron balance, respectively.
Due to the lowest conformational disorder and solid-state solvation
effects, this compound demonstrated very similar emission properties
(emission colors) in non-doped and differently doped organic light-emitting
diodes (OLEDs). The lowest conformational disorder was observed for
the compound with the additional accepting moiety inducing steric
hindrance, limiting donor–acceptor dihedral rotational freedom.
It can be exploited in the multi-donor–acceptor approach, increasing
the efficiency. Using an emitter exhibiting the minimized solid-state
solvation and conformation disorder effects, the sky blue OLED with
the emitting layer of this compound dispersed in host 1,3-bis(N-carbazolyl)benzene displayed an emission peak at 477 nm,
high brightness over 39 000 cd/m2, and external
quantum efficiency up to 15.9% along with a maximum current efficiency
of 42.6 cd/A and a maximum power efficiency of 24.1 lm/W.
Using the newly designed
exciplex-forming 1,2,3-triazole-based
acceptors with fast and efficient singlet → triplet intersystem
crossing (ISC) processes, carbazole and benzoyl-1
H
-1,2,3-triazole derivatives were synthesized by Dimroth-type 1,2,3-triazole
ring formation and Ullmann–Goldberg C–N coupling reactions.
Due to the exciplex formation between covalently bonded electron-donating
(carbazole) and 1,2,3-triazole-based electron-accepting moieties with
small singlet-triplet splitting (0.07–0.13 eV), the compounds
exhibited ISC-assisted bluish–green thermally activated delayed
fluorescence. The compounds were characterized by high triplet energy
levels ranging from 2.93 to 2.98 eV. The most efficient exciplex-type
thermally activated delayed fluorescence was observed for ortho-substituted
carbazole-benzoyl-1
H
-1,2,3-triazole which was selected
as a host in the structure of efficient solution-processed white light-emitting
diodes. The best device exhibited a maximum power efficiency of 10.7
lm/W, current efficiency of 18.4 cd/A, and quantum efficiency of 7.1%.
This device also showed the highest brightness exceeding 10 thousand
cd/m
2
. Usage of the exciplex-forming host allowed us to
achieve a low turn-on voltage of 3.6 V. High-quality white electroluminescence
was obtained with the close to nature white color coordinates (0.31,
0.34) and a color rendering index of 92.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.