Simple Molecular Design Strategy for Multiresonance Induced TADF Emitter: Highly Efficient Deep Blue to Blue Electroluminescence with High Color Purity

Abstract

Thermally activated delayed fluorescence (TADF) materials based on multiple resonance (MR) effect exhibit enormous potentials in organic light‐emitting diodes (OLEDs) with high color purity due to their intrinsically narrow emission. However, most of MR‐TADF emitters are limited to the boron‐nitrogen‐based rigid skeleton. In this work, three novel MR‐TADF emitters, namely CzBNO, DMAcBNO and DPAcBNO, are elaborately constructed, the TADF properties of which are realized by virtue of opposite MR effect of boron and nitrogen/oxygen atom. CzBNO‐based deep blue‐emitting OLEDs achieve a maximum external quantum efficiency (EQE) of 13.6% with a small FWHM of 36 nm, as well as a Commission Internationale de l'Eclairage (CIE) coordinate of (0.14,0.08). While the other two emitter‐based devices exhibit blue emission with a maximum EQE of up to 23.0%. To further improve the OLEDs performances, DMAcBNO and DPAcBNO‐based devices assisted by a sensitizer exhibit an excellent EQE of up to 29.6% with a relatively small efficiency roll‐off.

Fine-tuned asymmetric blue multiple resonance thermally activated delayed fluorescence emitters with high efficiency and narrow emission band

“…35 The twisted phenyl unit of diphenylamine may relieve intermolecular interaction compared to other planar groups of phenoxy or carbazole in the MR TADF materials. 34,36 As a result of the calculation, the HOMO levels were −4.96 eV for B-dpa-Cz , −4.76 eV for B-dpa-dmAc , and −4.79 eV for B-dpa-SpiroAc , following the relative donor strength of Cz, dmAc and SpiroAc. The HOMO-LUMO gaps were calculated as 3.51, 3.50, and 3.49 eV for B-dpa-Cz , B-dpa-dmAC and B-dpa-SpiroAC , respectively.…”

“…It was slightly increased in the asymmetric MR TADF emitters compared to the symmetric MR TADF emitters due to the disordered MR structure. 36 Phosphorescence spectra were measured at 77 K using frozen THF solution after a delay time of 1.0 ms. The lowest singlet energy (S 1 ) and triplet energy (T 1 ) of the materials were predicted by the onset energy of the fluorescence and phosphorescence spectra.…”

A Chiral Dual‐Core Organoboron Structure Realizes Dual‐Channel Enhanced Ultrapure Blue Emission and Highly Efficient Circularly Polarized Electroluminescence

“…In addition, the EQE max , the maximum luminance (L max ), and the maximum current efficiency (CE max ) are 14.6%, 6935 cd m −2 , and 16.1 cd A −1 , respectively, which are close to the results of reported homogeneous structures. [51][52][53] However, with an increased doping concentration from 5% to 8%, the FWHM of SOBN-based devices increased from 47 to 58 nm, exhibiting a poorer color purity. We assume that the reasons mainly come from two aspects: i) the relatively large reorganization energy of SOBN enhances coupling of electronic transition and vibrational level in polar environments, resulting in spectral broadening; ii) as the doping concentration increases, the intermolecular interaction of the planar SOBN structure is significantly enhanced, further broadening the spectrum, which may be the most important reason.…”

Extending the π‐Skeleton of Multi‐Resonance TADF Materials towards High‐Efficiency Narrowband Deep‐Blue Emission

“…Though the conceptual advancement has derived a burgeoning number of MR-TADF emitters covering the entire visible spectrum, corresponding devices often suffer from severe triplet-involved annihilation process caused by the moderate ΔE ST and RISC rate constant (k RISC � 10 4 s À 1 ). [10][11][12][13][14][15][16][17][18][19][20][21] To fully exploit the potential of MR-OLEDs, the energy transition processes for these emitters must be optimized. The most adopted strategy to tackle this issue is by enlarging the degree of mixing between singlet and triplet states through peripheral functionalization or heteroatom insertion to the core skeleton.…”