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

Abstract

Establishing a simple and versatile design strategy to finely modulate emission colors while retaining high luminescence efficiency and color purity remains an appealing yet challenging task for the development of multi-resonanceinduced thermally activated delayed fluorescence (MR-TADF) materials. Herein, we demonstrate that the strategic introduction of electron-withdrawing imine and electrondonating amine moieties into a versatile boron-embedded 1,3-bis(carbazol-9-yl)benzene skeleton enables systematic hypsochromic and bathochromic shifts of narrowband emissions, respectively. By this method, effective electroluminescence color tuning was accomplished over a wide visible range from deep-blue to yellow (461-571 nm), using the same MR molecular system, without compromising very narrow spectral features. Deep-blue to yellow organic light-emitting diodes with maximum external quantum efficiencies as high as 19.0-29.2 % and superb color purity could be produced with this family of color-tunable MR-TADF emitters.

Recent advances in green thermally activated delayed fluorescence emitters towards high colour purity and good electroluminescence performance

“…Just increasing the donor strength of BN core and effect on HOMO distribution tend to show bathochromic shifted emission of 512 nm, and which is comparably large shift from the parent BN core (477 nm-Cz-B). This design concept did not show much effect on FWHM broadening (solution FWHM-27; device FWHM-30 nm), and the EQE was 29.2% with the green emission of 515 nm [47][48].…”

“…With the help of high PLQY (98%) and horizontal ratio of 94%, green device was able to achieve high EQE of 32.2% with the emission wavelength of 524 nm. Although the efficiency values were high, but the color purity was not satisfactory due to its wider FWHM of 37 nm [48,51].…”

Thermally activated delayed fluorescence dendrimers achieving 20% external quantum efficiency for solution-processed OLEDs

“…The construction of multiple organic functional layers for vacuum-deposited OLEDs has been proved to be efficient. [6][7][8] However, due to the limited deposited space, low material utilization and high manufacturing costs, the development of vacuum-deposited OLEDs has been restricted. Therefore, it is more important to develop solution-processed OLEDs.…”

Isomeric thermally activated delayed fluorescence emitters based on a quinolino[3,2,1-de]acridine-5,9-dione multiple resonance core and carbazole substituent

“…32 These kinds of TADF emitters with narrow FWHM were thus widely studied and more MR-TADF systems are worth exploring. [33][34][35][36][37][38][39][40][41][42] In 2019, our group proposed another example, quinolino[3,2,1-de]acridine-5,9-dione (QAO) bearing MR-TADF activity aside from the prevalent B/N system, which consisted of a triphenylamine having two para-disposed carbonyl bridges, and its electroluminescent device achieves the external quantum efficiency (EQE) of 19.4% with the narrow FWHM of 39 nm. 43 From these cores, new MR-TADF emitters can thus be designed by (i) varying the donor patterns, (ii) fusing the conjugated system or (iii) substituting functional groups.…”