A Quadruple‐Borylated Multiple‐Resonance Emitter with para/meta Heteroatomic Patterns for Narrowband Orange‐Red Emission

Abstract

Hindered by spectral broadening issues with redshifted emission, long‐wavelength (e.g., maxima beyond 570 nm) multiple resonance (MR) emitters with full width at half maxima (FWHMs) below 20 nm remain absent. Herein, by strategically embedding diverse boron (B)/nitrogen (N) atomic pairs into a polycyclic aromatic hydrocarbon (PAH) skeleton, we propose a hybrid pattern for the construction of a long‐wavelength narrowband MR emitter. The proof‐of‐concept emitter B4N6‐Me realized orange‐red emission with an extremely small FWHM of 19 nm (energy unit: 70 meV), representing the narrowest FWHM among all reported long‐wavelength MR emitters. Theoretical calculations revealed that the cooperation of the applied para B‐π‐N and para B‐π‐B/N‐π‐N patterns is complementary, which gives rise to both narrowband and redshift characteristics. The corresponding organic light‐emitting diode (OLED) employing B4N6‐Me achieved state‐of‐the‐art performance, e.g., a narrowband orange‐red emission with an FWHM of 27 nm (energy unit: 99 meV), an excellent maximum external quantum efficiency (EQE) of 35.8 %, and ultralow efficiency roll‐off (EQE of 28.4 % at 1000 cd m−2). This work provides new insights into the further molecular design and synthesis of long‐wavelength MR emitters.

Frontier Molecular Orbital Engineering of Aromatic Donor Fusion: Modularly Constructing Highly Efficient Narrowband Yellow Electroluminescence

“…In the archetypal MR framework, the regularly alternating population of the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) endows the molecular excited state with short-range charge transfer (SRCT) characteristics and long-range complementary resonance interaction, thereby engendering highly efficient TADF with narrowband emission and high Φ PL . At present, MR-TADF materials have covered the entire visible electromagnetic spectrum region, and many significant advancements have been made in blue- and green-emitting materials. − Although there have been some attempts to fabricate MR-TADF materials with emission wavelengths beyond green-emitting materials, − the construction strategies are still limited due to the inherent rigidity and constraint in structural diversity of MR frameworks. Especially for yellow-emitting materials with emission wavelengths residing between green- and orange-emitting materials, more stringent requirements are put forward for the proper design of molecular structure and precise manipulation of the excited state, because the molecular structure chromophore and excited-state behavior of organic luminescent materials are closely pertinent to their photophysical properties.…”

Borylation and rearrangement reactions of azasilaanthracenes to afford B,N-doped nanographenes

“…2–8 In terms of synthesis, many representatives of MR-TADF B n ,N m -PAHs are notable for their convenient accessibility from suitable aryl amines through electrophilic aromatic borylation with BX 3 (X = Br, I). 3,9–12 We recently contributed to this field the B 3 ,N 2 -PAH C (Scheme 1), which is one of the few examples that contain more B than N atoms and thus have a formally electron-deficient π system. 13 Remarkably, in this case the established threefold electrophilic C–H borylation failed for the introduction of the central B atom.…”

Red-Shifted Emission in Multiple Resonance Thermally Activated Delayed Fluorescent Materials through Malononitrile Incorporation

“…Recently, Tang and co-workers demonstrated that appending a triphenylamine group to a blue-green MR-TADF core suppressed ACQ and resulted in aggregation-induced emission enhancement . The preparation of efficient red-emitting MR-TADF compounds is also a challenging task. , The energy gap law dictates that nonradiative decay pathways become significant as the S 0 –S 1 gap becomes smaller, and simply increasing the extent of π-conjugation in the emitter often decreases its solubility, making these materials difficult to synthesize and characterize. Alternatively, red-shifted emission may be realized through the addition of bridging heteroatoms or stronger donating groups.…”