How alkyl substituents in thermally activated delayed fluorescence luminogens affect the performance of the corresponding organic light-emitting diode

Thermally activated delayed fluorescence (TADF) materials are a promising route to highly efficient, wide color gamut organic light-emitting diode (OLED) displays. Unlike strategies that modify π-conjugated configurations, alkyl chains engineering subtly tunes solid-state packing without altering the excited-state electronic structures. Employing this strategy, five TADF emitters (TDBA-A1–A5) were synthesized by extending the alkyl chains on the acridine donor from methyl to pentyl. All the emitters show identical solution emission at 461 nm in toluene and high luminescent efficiency (82%–87%) in polymethyl methacrylate films. Crystallographic and computational analyses reveal that elongation of alkyl chains promotes tighter π-π overlap and stronger intermolecular interactions. OLEDs based on TDBA-A2–A5 achieve maximum external quantum efficiencies of 20.2%, 23.8%, 24.1%, and 23.5%, respectively, representing 1.22- to 1.45-fold enhancements over the TDBA-A1-based device (16.6%). This work validates that fine-tuning alkyl chain length is an effective strategy to boost TADF-OLED performance through controlled molecular packing.