Fused‐Nonacyclic Multi‐Resonance Delayed Fluorescence Emitter Based on Ladder‐Thiaborin Exhibiting Narrowband Sky‐Blue Emission with Accelerated Reverse Intersystem Crossing

Abstract

Developing organic luminophores with unique capability of strong narrowband emission is both crucial and challenging for the further advancement of organic light‐emitting diodes (OLEDs). Herein, a nanographitic fused‐nonacyclic π‐system (BSBS‐N1), which was strategically embedded with multiple boron, nitrogen, and sulfur atoms, was developed as a new multi‐resonance thermally activated delayed fluorescence (MR‐TADF) emitter. Narrowband sky‐blue emission with a peak at 478 nm, full width at half maximum of 24 nm, and photoluminescence quantum yield of 89 % was obtained with BSBS‐N1. Additionally, the spin‐orbit coupling was enhanced by incorporating two sulfur atoms, thereby facilitating the spin‐flipping process between the excited triplet and singlet states. OLEDs based on BSBS‐N1 as a sky‐blue MR‐TADF emitter achieved a high maximum external electroluminescence quantum efficiency of 21.0 %, with improved efficiency roll‐off.

Wide‐Range Color Tuning of Narrowband Emission in Multi‐resonance Organoboron Delayed Fluorescence Materials through Rational Imine/Amine Functionalization

“…More recently, led by the pioneering work by Hatakeyama et al in 2016, [5] a new paradigm of TADF emitters featuring the multi-resonance (MR) effect has emerged and attracted immense interest with the astonishing potential for overcoming the aforementioned drawbacks of D-A-structured TADF systems. [5][6][7][8][9][10][11][12][13][14][15] In the design of so-called MR-TADF molecules, as represented by the renowned DABNA analogs, a triphenylborane core is planarized and stabilized [16] by connecting with nitrogen atoms (amine moieties) to construct a rigid polycyclic aromatic framework, giving rise to opposite resonance effects by the mutually ortho-disposed boron and nitrogen atoms. [5,6] This electronic feature enables the resulting polycyclic molecules to have an alternating (atomically separated) HOMO/LUMO pattern, with a small DE ST and large Frank-Condon overlap integral, and hence exhibit efficient narrowband TADF.…”

Fused‐Nonacyclic Multi‐Resonance Delayed Fluorescence Emitter Based on Ladder‐Thiaborin Exhibiting Narrowband Sky‐Blue Emission with Accelerated Reverse Intersystem Crossing

“…One of the two crystallographically independent molecules is shown here. [23] respectively, from the measured fluorescence and phosphorescence peaks in the doped film (Supporting Information), affording DE ST of 0.14 eV. This DE ST value was small enough to induce effective RISC with the support of ambient thermal energy.…”

“…Hydrogen atoms and disordered t-Bu groups are omitted for clarity. One of the two crystallographically independent molecules is shown here [23].…”

Wide‐Range Color Tuning of Narrowband Emission in Multi‐resonance Organoboron Delayed Fluorescence Materials through Rational Imine/Amine Functionalization

“…More recently, led by the pioneering work by Hatakeyama et al in 2016, [5] a new paradigm of TADF emitters featuring the multi-resonance (MR) effect has emerged and attracted immense interest with the astonishing potential for overcoming the aforementioned drawbacks of D-A-structured TADF systems. [5][6][7][8][9][10][11][12][13][14][15] In the design of so-called MR-TADF molecules, as represented by the renowned DABNA analogs, a triphenylborane core is planarized and stabilized [16] by connecting with nitrogen atoms (amine moieties) to construct a rigid polycyclic aromatic framework, giving rise to opposite resonance effects by the mutually ortho-disposed boron and nitrogen atoms. [5,6] This electronic feature enables the resulting polycyclic molecules to have an alternating (atomically separated) HOMO/LUMO pattern, with a small DE ST and large Frank-Condon overlap integral, and hence exhibit efficient narrowband TADF.…”

“…All of these MR-TADF materials were readily prepared using a synthetic protocol similar to that of the parent Cz-B, which consists of the nucleophilic aromatic substitution (S N Ar) and tandem lithiation-borylation-annulation reactions, [12] by merely changing the carbazole analogous peripheries (see the Supporting Information for detailed synthesis procedures and characterization data). The simplicity of this protocol, in comparison with the complexity of synthesis of DABNA derivatives, [5,6] facilitates the easy expansion of the materials library.…”