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Title: Inductive effects of diphenylphosphoryl moieties on carbazole host materials: Design rules for blue electrophosphorescent organic light-emitting devices

Abstract

We show that the inductive electron-withdrawing effect of diphenylphosphoryl (Ph2P=O) groups stabilizes both the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of a carbazole chromophore. This improves electron injection from a cathode without affecting the high triplet exciton energy (ET ~ 3.0 eV) of the host material. Three new carbazole derivatives 3,6-bis(diphenylphosphoryl)-9-ethylcarbazole (PO10), 3,6-bis(diphenylphosphoryl)-9-phenylcarbazole (PO9) and N-(4-diphenylphosphoryl phenyl) carbazole (MPO12) were investigated as host materials in blue phosphor-doped organic light-emitting devices (OLEDs). Photophysical characterization showed all three carbazole derivatives exhibit monomer UV fluorescence (367-385 nm) in solution and contributions from molecular aggregates in solid-state films (378-395 nm). The polar MPO12 derivative exhibited solvatochromism and had the highest propensity for aggregate formation in the solid-state. Testing of OLEDs using PO9, PO10 and MPO12 as host materials for the sky blue organometallic phosphor, iridium(III)bis(4,6-(di-fluorophenyl)-pyridinato-N,C2') picolinate (FIrpic) gave external quantum efficiencies (EQE) and operating voltages at a similar current density (J = 13 mA/cm2) of 6 - 8 % at < 7V. The best device performance was exhibited using MPO12 as the host when an appropriate hole blocking layer was implemented. At a brightness of 800 cd/m2 an EQE of 9.09 ± 0.12% at 4.8 V was achieved. The highermore » performance of MPO12 was attributed to the ambipolar charge transporting character of the polar carbazole derivative. However, exciton relaxation on nonradiative aggregate or excimer states of all host materials studied may limit further improvements in device efficiencies.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
937035
Report Number(s):
PNNL-SA-58590
830403000; TRN: US0806060
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry C, 112(21):7989-7996
Additional Journal Information:
Journal Volume: 112; Journal Issue: 21
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; BRIGHTNESS; CARBAZOLES; CATHODES; CURRENT DENSITY; DEPLETION LAYER; DESIGN; ELECTRONS; EXCITONS; FLUORESCENCE; MONOMERS; PERFORMANCE; RELAXATION; SKY; TESTING; TRIPLETS

Citation Formats

Sapochak, Linda S, Padmaperuma, Asanga B, Cai, Xiuyu, Male, Jonathan L, and Burrows, Paul E. Inductive effects of diphenylphosphoryl moieties on carbazole host materials: Design rules for blue electrophosphorescent organic light-emitting devices. United States: N. p., 2008. Web. doi:10.1021/jp800079z.
Sapochak, Linda S, Padmaperuma, Asanga B, Cai, Xiuyu, Male, Jonathan L, & Burrows, Paul E. Inductive effects of diphenylphosphoryl moieties on carbazole host materials: Design rules for blue electrophosphorescent organic light-emitting devices. United States. doi:10.1021/jp800079z.
Sapochak, Linda S, Padmaperuma, Asanga B, Cai, Xiuyu, Male, Jonathan L, and Burrows, Paul E. Thu . "Inductive effects of diphenylphosphoryl moieties on carbazole host materials: Design rules for blue electrophosphorescent organic light-emitting devices". United States. doi:10.1021/jp800079z.
@article{osti_937035,
title = {Inductive effects of diphenylphosphoryl moieties on carbazole host materials: Design rules for blue electrophosphorescent organic light-emitting devices},
author = {Sapochak, Linda S and Padmaperuma, Asanga B and Cai, Xiuyu and Male, Jonathan L and Burrows, Paul E},
abstractNote = {We show that the inductive electron-withdrawing effect of diphenylphosphoryl (Ph2P=O) groups stabilizes both the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of a carbazole chromophore. This improves electron injection from a cathode without affecting the high triplet exciton energy (ET ~ 3.0 eV) of the host material. Three new carbazole derivatives 3,6-bis(diphenylphosphoryl)-9-ethylcarbazole (PO10), 3,6-bis(diphenylphosphoryl)-9-phenylcarbazole (PO9) and N-(4-diphenylphosphoryl phenyl) carbazole (MPO12) were investigated as host materials in blue phosphor-doped organic light-emitting devices (OLEDs). Photophysical characterization showed all three carbazole derivatives exhibit monomer UV fluorescence (367-385 nm) in solution and contributions from molecular aggregates in solid-state films (378-395 nm). The polar MPO12 derivative exhibited solvatochromism and had the highest propensity for aggregate formation in the solid-state. Testing of OLEDs using PO9, PO10 and MPO12 as host materials for the sky blue organometallic phosphor, iridium(III)bis(4,6-(di-fluorophenyl)-pyridinato-N,C2') picolinate (FIrpic) gave external quantum efficiencies (EQE) and operating voltages at a similar current density (J = 13 mA/cm2) of 6 - 8 % at < 7V. The best device performance was exhibited using MPO12 as the host when an appropriate hole blocking layer was implemented. At a brightness of 800 cd/m2 an EQE of 9.09 ± 0.12% at 4.8 V was achieved. The higher performance of MPO12 was attributed to the ambipolar charge transporting character of the polar carbazole derivative. However, exciton relaxation on nonradiative aggregate or excimer states of all host materials studied may limit further improvements in device efficiencies.},
doi = {10.1021/jp800079z},
journal = {Journal of Physical Chemistry C, 112(21):7989-7996},
number = 21,
volume = 112,
place = {United States},
year = {2008},
month = {5}
}