Steric Modulation of Spiro Structure for Highly Efficient Multiple Resonance Emitters
Yang‐Kun Qu, Dong‐Ying Zhou, Fan‐Cheng Kong, Qi Zheng, Xun Tang, Yuan‐Hao Zhu, Chen‐Chao Huang, Ziqi Feng, Jian Fan, Chihaya Adachi, Liang‐Sheng Liao, Zuo‐Quan Jiang
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.