Tailoring Extremely Narrow FWHM in Hypsochromic and Bathochromic Shift of Polycyclo-Heteraborin MR-TADF Materials for High-Performance OLEDs.

Abstract

Developing double boron-based emitters with extremely narrow band spectrum and high efficiency in organic light-emitting diodes (OLEDs) is crucial and challenging. Herein, we report two materials, NO-DBMR and Cz-DBMR, hinge on polycyclic heteraborin skeletons based on role-play of the highest occupied molecular orbital (HOMO) energy levels. The NO-DBMR contains an oxygen atom, whereas the Cz-DBMR has a carbazole core in the double boron-embedded ν-DABNA structure. The synthesized materials resulted in an unsymmetrical pattern for NO-DBMR and surprisingly a symmetrical pattern for Cz-DBMR. Consequently, both materials showed extremely narrow full width at half maximum (FWHM) of 14 nm in hypsochromic (pure blue) and bathochromic (Bluish green) shifted emission without losing their high color fidelity. Furthermore, both materials show high photoluminescence quantum yield (PLQY) of over 82 %, and an extremely small singlet-triplet energy gap (ΔEST ) of 0.04 eV, resulting in high reverse intersystem crossing process (kRISC ) of 105 s-1 . Due to the efficient thermally activated delayed fluorescence (TADF) characteristics, the fabricated OLEDs based on these heteraborins manifested maximum external quantum efficiency (EQEmax ) of 33.7 and 29.8 % for NO-DBMR and Cz-DBMR, respectively. This is the first work reported with this type of strategy for achieving an extremely narrow emission spectrum in hypsochromic and bathochromic shifted emissions with a similar molecular skeleton.