Two bipolar host materials
Despite the excellent physical properties of single‐component Eu3+–Tb3+‐containing metallopolymers, the development of their flexible white polymer light‐emitting diodes (WPLEDs) for portable full‐color flat displays remains a formidable challenge. Herein, the WPLEDs from a metallopolymer
- NSF-PAR ID:
- 10457521
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Optical Materials
- Volume:
- 7
- Issue:
- 22
- ISSN:
- 2195-1071
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract 3‐CBPy and4‐mCBPy are reported. These hosts are structural analogs of the common host materials CBP and mCBP wherein the phenyl rings have been replaced with pyridines. The two materials possess deep highest occupied molecular orbital (HOMO) and shallow lowest unoccupied molecular orbital (LUMO) levels along with sufficiently high energyS 1andT 1states that make them suitable hosts for yellow emitters in electroluminescent devices. Yellow‐emitting thermally activated delayed fluorescence organic light‐emitting diodes are fabricated using 2,4,6‐tris (4‐(10H‐phenoxazin‐10‐yl)phenyl)‐1,3,5‐triazine (tri‐PXZ‐TRZ) as the dopant emitter with either3‐CBPy or4‐mCBPy employed as the host. Their device performance is compared to analogous devices using CBP and mCBP as host materials. The pyridine‐containing host devices show markedly improved external quantum efficiencies (EQE) and decreased roll‐off. The 7 wt% tri‐PXZ‐TRZ‐doped device exhibits very low turn‐on voltage (2.5 V for both3‐CBPy and4‐mCBPy ) along with maximum external quantum efficiencies (EQEmax) reaching 15.6% (for3‐CBPy ) and 19.4% (for4‐mCBPy ). The device using4‐mCBPy also exhibits very low efficiency roll‐off with an EQE of 16.0% at a luminance of 10 000 cd m−2. -
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ABSTRACT Triplet arylnitrenes may provide direct access to aryl azo‐dimers, which have broad commercial applicability. Herein, the photolysis of
p ‐azidostilbene (1 ) in argon‐saturated methanol yielded stilbene azo‐dimer (2 ) through the dimerization of tripletp ‐nitrenostilbene (31N ). The formation of31N was verified by electron paramagnetic resonance spectroscopy and absorption spectroscopy (λ max ~ 375 nm) in cryogenic 2‐methyltetrahydrofuran matrices. At ambient temperature, laser flash photolysis of1 in methanol formed31N (λ max ~ 370 nm, 2.85 × 107 s−1). On shorter timescales, a transient absorption (λ max ~ 390 nm) that decayed with a similar rate constant (3.11 × 107 s−1) was assigned to a triplet excited state (T) of1 . Density functional theory calculations yielded three configurations for T of1 , with the unpaired electrons on the azido (TA) or stilbene moiety (TTw, twisted and TFl, flat). The transient was assigned to TTwbased on its calculated spectrum. CASPT2 calculations gave a singlet–triplet energy gap of 16.6 kcal mol−1for1 N ; thus, intersystem crossing of11N to31N is unlikely at ambient temperature, supporting the formation of31N from T of1 . Thus, sustainable synthetic methods for aryl azo‐dimers can be developed using the visible‐light irradiation of aryl azides to form triplet arylnitrenes. -
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