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Four new blue light-emitting materials based on benzo[1,2-d:4,5-d′]bisoxazole (BBO) have been synthesized, characterized, and fabricated into organic light-emitting diode (OLED) devices. Using a combination of theoretical and experimental methods, we investigated the effect of conjugation by comparing bulky alkyl groups and planar aromatic groups along the 2,6-axis. Two of these molecules, PB2Cz and PB3Cz, are cross-conjugated cruciform-type BBOs with phenyl and carbazole groups along the 2,6 and 4,8 axes, respectively. The other two molecules, AB2Cz and AB3Cz, have extended conjugation via the carbazole groups along the 4,8-axis and bulky adamantyl groups along the 2,6-axis. Concurrently, we explored the effect of regioisomerism on optoelectronic and device properties arising from attaching carbazole at the 2- (2Cz) or 3- (3Cz) position along the 4,8-axis. The materials’ geometric and electronic properties were predicted using time-dependent density functional theory (TD-DFT) calculations at the mPW3PBE/SV level. The molecules’ photoluminescent properties were measured in solution and film states. The BBO molecules were used as dopants in mixed host/guest OLED devices, producing teal to deep blue emission. Specifically, the AB2Cz and AB3Cz, with adamantyl on the 2,6-axis, exhibit blue to deep-blue emissions of 414–422 nm (CIEx < 0.20, CIEy < 0.10). In comparison, PB2Cz and PB3Cz have slightly longer emission wavelengths of 472–476 nm (CIEx < 0.16, CIEy < 0.28) and high brightness of 2700–3500 cdm–2. The BBOs with 2Cz resulted in more efficient devices with EQEs of ∼2.8–3.2%, while the 3Cz BBOs had EQEs of ∼1.1–1.5%. This work provides insight into designing efficient, purely organic blue-fluorescent OLED materials based on the BBO moiety.
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Benzobisoxazole Cruciforms: A Cross‐conjugated Platform for Designing Tunable Donor/Acceptor Materials
Abstract Four cross‐conjugated molecules based on the benzo[1,2‐d:4,5‐d’]bisoxazole (BBO) moiety have been synthesized from a common synthon. Theoretical studies indicated that these cruciforms had highly segregated HOMO and LUMO levels enabling semi‐autonomous tuning of the LUMO level from the HOMO through substitution along the 2,6‐axis. The experimental data confirms that the HOMO levels within these systems varied by 0.3 eV, whereas the LUMO levels varied by over 1.6 eV when the electron‐density along the 2,6‐axis was increased. The introduction of relatively electron‐deficient moieties along the 2,6‐axis resulted in a bathochromic shift in the absorption profiles concurrent with the stabilization of the LUMO. These substituents also prolonged the photoluminescent lifetimes owing to improved intramolecular charge transfer states between the 4,8‐ and 2,6‐ axis. The BBO cruciforms were evaluated as donor materials in organic solar cells (OSC)s, but the energy‐level mismatches and poor thin film morphology led to poor performance. These results indicate that benzobisoxazole cruciforms are a promising platform for the development of tunable materials for use in organic semiconductors, but improvements in the optical, electronic and film‐forming properties are needed to enable their use in efficient OSCs.
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- PAR ID:
- 10236009
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Asian Journal of Organic Chemistry
- Volume:
- 10
- Issue:
- 1
- ISSN:
- 2193-5807
- Page Range / eLocation ID:
- p. 215-223
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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