Vibronic absorption spectra of the angular fused bisindolo- and biscarbazoloanthracene blue fluorophores for OLED applications

Stereo effects for efficient synthesis of orange-red multiple resonance emitters centered on a pyridine ring

Despite theoretical difficulties, we herein demonstrate an effective strategy for the inaugural synthesis of an orange-red multiple resonance (MR) emitter centered on a pyridine ring via stereo effects. Compared to conventional benzene-centered materials, the pyridine moiety in the novel MR material acts as a co-acceptor. This results in a significant spectral redshift and a narrower spectrum, as well as an improved photoluminescence quantum yield (PLQY) due to the formation of intramolecular hydrogen bonds. As envisioned, the proof-of-concept emitter Py-Cz-BN exhibits bright orange-red emission peaking at 586 nm with a small full width at half maximum (FWHM) of 0.14 eV (40 nm), exceeding both the wavelength and FWHM achieved with benzene-centered BBCz-Y. Benefiting from high PLQYs (>92%) and suppressed chromophore interactions, the optimized organic light-emitting diodes achieved high maximum external quantum efficiencies of 25.3-29.6%, identical small FWHMs of 0.18 eV (54 nm), and long lifetimes over a wide range of dopant concentrations (1-15 wt%). The performance described above demonstrates the effectiveness of this molecular design and synthesis strategy in constructing high performance long-wavelength MR emitters.

Fusion of Multi-Resonance Fragment with Conventional Polycyclic Aromatic Hydrocarbon for Nearly BT.2020 Green Emission

Herein, we report a general strategy for achieving ultra-pure green emissions by suppressing the shoulder peaks in the emission spectra of conventional polycyclic aromatic hydrocarbons (PAHs). Through precise synthetic fusion of multi-resonance (MR) fragments with conventional PAH, extended π-conjugation lengths, increased molecular rigidity, and reduced vibrational frequency could be simultaneously realized. The proof-of-concept emitters exhibited ultra-pure green emissions with dominant peaks at ca. 521 nm, photoluminescence quantum yields that are greater than 99 %, a small full-width-at-half-maximum of 23 nm, and CIE coordinates of (0.16, 0.77). The bottom-emitting organic light-emitting diode (OLED) exhibited a record-high CIEy value of 0.74 and a high maximum external quantum efficiency of 30.5 %. The top-emitting OLED not only achieved a BT.2020 green color (CIE: 0.17, 0.78) for the first time but also showed superior performance among all green OLED devices, with a current efficiency of 220 cd A^- .