Search for: All records

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. 

The color tuning of benzobisoxazole-based OLEDs to achieve white emission with high brightness is reported. 

Post-synthetic phase transfer ligand exchange has been established as a simple, reliable, and versatile method for the synthesis of chiral, optically active colloidal nanocrystals displaying circular dichroism (CD) and circularly polarized luminescence (CPL). Herein we present a water-free and purification-free cyclohexane → methanol ligand exchange system that led to the synthesis of stable, non-aggregating chiral and fluorescent cadmium sulfide quantum dots (CdS QDs). Absorption and emission studies revealed that the carboxylate capping ligands can tune the band gap by up to 65 meV as well as control the band gap and deep trap emission pathways. The CD data revealed that the addition of a 2nd stereogenic center did not automatically lead to an increase of the CD anisotropy of QDs, but rather match/mismatch cooperativity effects must be considered in the transfer of the chirality from the capping ligands to the achiral nanocrystals. Variation in position of the functional groups as well as the chemical identity of the functional groups impacted both the shape and anisotropy of the induced CD spectra and revealed the importance of the functional groups’ coordination and polarity on the binding geometry and induced chiroptical properties. Finally, we describe the first example where CD spectra of QDs capped with the same ligand and dissolved in the same solvent displayed very different spectral profiles. This work provides deeper insight into induced CD of QDs and paves the path to rational design of chiral nanomaterials.