Molecular design of thermally activated delayed fluorescent emitters for narrowband orange–red OLEDs boosted by a cyano-functionalization strategy

Abstract

The establishment of simple molecular design strategy to realize red-shifted emission while maintaining good color purity for multi-resonance induced thermally activated delayed fluorescent (MR-TADF) materials remains an appealing yet challenging...

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

“…By the virtue of MR effect induced by the exquisite combination of boron, nitrogen, and sulfur atoms, the radiative decay rate constant (k r ) of BSBS-N1 in the doped film was calculated to be as high as 9.0 10 7 s À1 , which is comparable to those of other reported MR-TADF materials. [8][9][10][11][12][13][14][15] Moreover, BSBS-N1 was found to exhibit a notably high RISC rate constant (k RISC ) of 1.9 10 6 s À1 , which is reasonably consistent with the foregoing short exciton life-time and large F d /F p ratio. To the best of our knowledge, this k RISC is the highest ever reported value among the MR-TADF materials (typically k RISC % 10 3 -10 5 s À1 ; 2.0 10 5 s À1 for n-DABNA), [9] suggesting an enhanced SOC between the associated excited states with different spin multiplicities governing the RISC.…”

Molecular Design Strategy for Orange Red Thermally Activated Delayed Fluorescence Emitters in Organic Light‐Emitting Diodes (OLEDs)

“…In 2021 Bin et al reported that the attachment of a cyano (CN) functionality at the LUMO position of the MR-TADF skeleton can promote attractive red-shifted emission due to the exceptional electronwithdrawing capacity of the CN group, which represents the first example of orange-red MR-TADF emitters. [43] Meanwhile, the linear CN group adopts a coplanar conformation with the MR-framework to restrict structure relaxation associated with rotation, which is beneficial to maintain a small full-width at half-maximum. With the support of high PLQY (90 %) and high radiative of 2.2 × 10 7 s À 1 , an excellent EQE of 33.7 % was recorded with a narrow FWHM below 50 nm.…”

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.…”