Narrowband Emissive Thermally Activated Delayed Fluorescence Materials

Abstract

Organic thermally activated delayed fluorescence (TADF) materials have attracted significant research interest in the field of organic electronics because of their inherent advantage of 100% exciton utilization capability in organic light‐emitting diodes (OLEDs) without the use of noble metals. However, despite their high internal electroluminescence quantum efficiencies approaching unity, broad emission spectra with sizable full width at half maxima (FWHM; 60–100 nm) present a critical issue that must be solved for their application in ultrahigh‐definition OLED displays. Recently, a new paradigm of TADF materials featuring the multiple resonance (MR) effect based on heteroatom‐doped polycyclic aromatic frameworks, referred to as MR‐TADF materials, has emerged and garnered considerable research interest owing to their remarkable features of efficient narrowband emissions with extremely small FWHMs (≤30 nm). Currently, MR‐TADF materials occupy a prominent position in the cutting‐edge research on organic light‐emitting materials from both chemical and physical perspectives. This review article focuses on recent progress in narrowband emissive MR‐TADF systems from the perspective of molecular design, photophysical properties, and electroluminescence performance in OLEDs. The current status and future prospects of this advanced material technology are discussed comprehensively.

Carbonyl‐Containing Thermally Activated Delayed Fluorescence Emitters for Narrow‐Band Electroluminescence

“…[54] The boron-based MR-TADF emitters exhibit the best device performance among these different MR-TADF systems. [55] However, rare works including ketone derivatives focus on device stability issues.…”

Facile dimerization strategy for producing narrowband green multi-resonance delayed fluorescence emitters

“…Boron-and nitrogen-embedded polycyclic aromatic hydrocarbons (B,N-PAHs) have recently attracted burgeoning interest, [1][2][3][4][5][6][7][8][9] which is ascribable to their promising use in optoelectronic devices as typified by organic light-emitting diodes (OLEDs). The opposite resonance characteristics of mutually orthodisposed B and N atoms in B,N-PAHs are capable of inducing the multiple-resonance (MR) effect, leading to the localization and separation of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) on different constituent atoms.…”

“…5,6 This MR feature endows B, N-PAHs with a small singlet-triplet energy gap (DE ST ) and thermally activated delayed fluorescence (TADF) properties as a consequence. [4][5][6][7][8][9] The biggest advantage of such an MR-TADF emitter is its narrowband emission capability, with an extremely small full width at half maximum (FWHM o 40 nm) enabled by suppressing structural relaxation and vibronic coupling in excited states. Combining the capabilities of full exciton use and narrowband emission leads to ideal emitters for OLED applications, with superior electroluminescence (EL) efficiencies and color purities.…”

“…8 High-efficiency green MR-TADF emitters have recently been developed by extending p-systems via additional ring fusion. 9,[24][25][26][27] Herein, we unveiled a simple but effective dimerization strategy for producing pure green MR-TADF emitters. Two isomeric MR dimers, namely p-CzB and m-CzB, were designed by tethering two BBCz-SB fragments through different linking positions (Fig.…”

Double boron-embedded multiresonant thermally activated delayed fluorescent materials for organic light-emitting diodes

“…At the same time, HOMOs will be restricted on the electron-donating atoms (N or O) and at the meta positions relative to electron-withdrawing atoms 37,38 . This MR effect-suppressed vibronic coupling leads to a narrow full width at half maximum (FWHM), and the rigid molecular structure helps realize a minimal Stokes shift below 30 nm, resulting in a low reorganization energy and high photoluminescence quantum yield (PLQY) [39][40][41][42][43][44] . Notably, compared to conventional TADF emitters, the MR-TADF emitters have significant advantages such as high color purity (high PLQY) and narrow emission spectra with FWHM of ~30 nm 35,38,39,[45][46][47] .…”