Highly Efficient Multi‐Resonance Thermally Activated Delayed Fluorescence Material with a Narrow Full Width at Half‐Maximum of 0.14 eV

Abstract

Multi‐resonance thermally activated delayed fluorescence (MR‐TADF) material, which possesses the ability to achieve narrowband emission in organic light‐emitting diodes (OLEDs), is of significant importance for wide color gamut and high‐resolution display applications. To date, MR‐TADF material with narrow full width at half‐maximum (FWHM) below 0.14 eV still remains a great challenge. Herein, through peripheral protection of MR framework by phenyl derivatives, four efficient narrowband MR‐TADF emitters are successfully designed and synthesized. The introduction of peripheral phenyl‐based moieties via a single bond significantly suppresses the high‐frequency stretching vibrations and reduces the reorganization energies, accordingly deriving the resulting molecules with small FWMH values around 20 nm/0.11 eV and fast radiative decay rates exceeding 108 s−1. The corresponding green OLED based on TPh‐BN realizes excellent performance with the maximum external quantum efficiency (EQE) up to 28.9% without utilizing any sensitizing host and a relatively narrow FWHM of 0.14 eV (28 nm), which is smaller than the reported green MR‐TADF molecules in current literatures. Especially, the devices show significantly reduced efficiency roll‐off and relatively long operational lifetimes among the sensitizer‐free MR‐TADF devices. These results clearly indicate the promise of this design strategy for highly efficient OLEDs with ultra‐high color purity.

Identifying the Molecular Origins of Green BN‐TADF Material Degradation and Device Stability via in situ Raman Spectroscopy

“…The photophysical behaviors of three molecules including ultraviolet‐visible (UV‐vis), photoluminescence (PL), and phosphorescence (77 K) spectra were studied in Figure 1a–c, and the key data were listed in Table 1. The absorption bands from 250 nm to 350 nm could be assigned to the π‐π* and n‐π* transitions of the benzene rings, while the strongest absorption bands of three molecules around 470 nm in the toluene solution arose from the ICT characters [5p,6] . The three molecules displayed a similar fluorescent characteristic with the emission peaks of 485 nm, 486 nm, and 486 nm and narrow FWHMs of 26 nm, 26 nm, and 24 nm for BN‐PhOH, BN‐PhOCH 3 , and BN‐PhN(CH 3 ) 2 , respectively.…”

“…BN-PhOH, BN-PhOCH 3 , and BN-PhN(CH 3 ) 2 demonstrated small reorganization energies of 0.1220, 0.1174, and 0.1269 eV, respectively, which indicated that the linked phenyl moieties were effective to inhibit the vibrational coupling and remain the color purity (Supporting Information, Figure S9). [6] The electrochemical behaviors of the three molecules were further determined from the cyclic voltammograms (CV) (Supporting Information, Figure S10) and the key data were listed in Table 1. The HOMO energy levels of BN-PhOH, BN-PhOCH 3 , and BN-PhN(CH 3 ) 2 are À 5.32 eV, À 5.37 eV, and À 5.15 eV, respectively, according to the onset potential of the oxidation curves.…”

“…BN‐PhN(CH 3 ) 2 demonstrated a smaller dihedral angle of 35° between the BN core and dimethylaniline group compared to that of 39°of BN‐PhOH and 38° of BN‐PhOCH 3 . BN‐PhOH, BN‐PhOCH 3 , and BN‐PhN(CH 3 ) 2 demonstrated small reorganization energies of 0.1220, 0.1174, and 0.1269 eV, respectively, which indicated that the linked phenyl moieties were effective to inhibit the vibrational coupling and remain the color purity (Supporting Information, Figure S9) [6] . The electrochemical behaviors of the three molecules were further determined from the cyclic voltammograms (CV) (Supporting Information, Figure S10) and the key data were listed in Table 1.…”

High Efficiency of over 25% and Long Device Lifetime of over 500 h at 1000 nit in Blue Fluorescent Organic Light‐Emitting Diodes

“…Interestingly, the FWHM of t‐DABNA‐dtB was 22 nm, which was smaller than that of t‐DABNA (26 nm), indicating that the di‐tert‐butylphenyl substituent suppressed vibrational coupling and relaxation. [ 23,24 ] Phosphrescence spectra were measured at 77 K in frozen tetrahydrofuran (THF) with 2.0 ms delay time. The emission peak wavelengths of t‐DABNA and t‐DABNA‐dtB were 489 and 503 nm, respectively, and the triplet energies estimated from onset wavelength of the phosphorescence spectra were 2.62 and 2.58 eV, respectively.…”

73‐1: Invited Paper: Decoration Strategy in Para Boron Position: An Effective Way to Achieve Ideal Multi‐Resonance Emitters

“…[7] Copyright 2021, Wiley-VCH), TW-BN, TPh-BN, pCz-BN, and mCz-BN (Adapted with permission. [8] Copyright 2021, Wiley-VCH). BN all could considerably inhibit interchromophore interactions to give the quenching-resistant MR emitters.…”