Position Optimization of Bulky Tetraphenylsilane in Multiple Resonance Molecules for Highly Efficient Narrowband OLEDs

Multiple resonance (MR)-type thermally activated delayed fluorescence (TADF) emitters have garnered significant interest due to their narrow full width at half maximum (FWHM) and high electroluminescence efficiency. However, the planar structures and large singlet-triplet energy gaps (ΔE_STs) characteristic of MR-TADF molecules pose challenges to achieving high-performance devices. Herein, two isomeric compounds, p-TPS-BN and m-TPS-BN, are synthesized differing in the connection modes between a bulky tetraphenylsilane (TPS) group and an MR core. This strategy aims to suppress intermolecular interactions, reduce ΔE_ST values, and investigate how connection positions influence photoelectric properties. Both compounds exhibit remarkably small ΔE_ST values (0.08-0.09 eV) and high internal quantum yields (95.0-97.8%). Notably, p-TPS-BN demonstrates a faster reverse intersystem crossing (RISC) with a rate constant of 2.54 × 10⁵ s⁻¹, attributed to its optimal long-range charge transfer (LRCT) process. A narrowband device employing p-TPS-BN achieves a maximum external quantum efficiency of 35.8% with an FWHM of 36 nm. This work offers an effective framework for studying structure-property relationships in MR molecules, paving the way for the development of high-efficiency electroluminescent devices.