Steric Modulation of Spiro Structure for Highly Efficient Multiple Resonance Emitters

Abstract

A multiple resonance thermally activated delayed fluorescence (MR‐TADF) molecule with a fused, planar architecture tends to aggregate at high doping ratios, resulting in broad full width at half maximum (FWHM), redshifting electroluminescence peaks, and low device efficiency. Herein, we propose a mono‐substituted design strategy by introducing spiro‐9,9′‐bifluorene (SBF) units with different substituted sites into the MR‐TADF system for the first time. As a classic steric group, SBF can hinder interchromophore interactions, leading to high device efficiency (32.2–35.9 %) and narrow‐band emission (≈27 nm). Particularly, the shield‐like molecule, SF1BN, seldom exhibits a broadened FWHM as the doping ratio rises, which differs from the C3‐substituted isomer and unhindered parent emitter. These results manifest an effective method for constructing highly efficient MR‐TADF emitters through a spiro strategy and elucidate the feasibility for steric modulation of the spiro structure in π‐framework.

Triphenylamine‐Functionalized Multiple‐Resonance TADF Emitters with Accelerated Reverse Intersystem Crossing and Aggregation‐Induced Emission Enhancement for Narrowband OLEDs

“…[12,20] Recently, Jiang and co-workers introduced spirobifluorene groups into the BNCz system to hinder interchromophore interactions to improve EL efficiencies. [21] However, it was also worth noting that modification of the π-conjugated framework with bulky substituents is generally difficult because the steric hindrance prevents coupling reactions. [22] Therefore, facilely accessible approaches to circumvent the ACQ issue of MR-TADF emitters are highly desirable.…”

Sequential Multiple Borylation Toward an Ultrapure Green Thermally Activated Delayed Fluorescence Material

“…The most effective protocol to construct boron-based MR structures is the “one-pot borylation” method involving lithiation, transmetalation, and tandem bora-Friedel–Crafts reaction (electrophilic arene borylation), which was first reported in 2011 and subsequently established for the synthesis of DOBNA and DABNA (Figure a). Although this protocol provides a synthetically accessible chemical space for MR-TADF emitters, it requires directing groups or halogen atoms for borylation, thus limiting the number of boron atoms introduced. Therefore, in 2018, we developed “one-shot borylation,” which involved inter- and intramolecular tandem bora-Friedel–Crafts reactions (Figure b).…”

Exceeding 30 % External Quantum Efficiency in Non‐doped OLEDs Utilizing Solution Processable TADF Emitters with High Horizontal Dipole Orientation via Anchoring Strategy

“…5CzBN as a classical TADF material, has been used as emitter or sensitizer for vacuum-deposited OLEDs due to the high PLQY and efficient RISC process induced by small ΔE ST , [9] however, whose poor solubility limits the application in solution processable OLEDs. To achieve the processability of the solution, as shown in Figure 1a, naked hexane groups are firstly attached to 5CzBN core to establish a compound, 5CzBN-Hex.…”