Work

Interplay of Excited‐States on Circularly Polarized Thermally Activated Delayed Fluorescent Chiral Exciplexes

Year: 2024

Type: article

Abstract: Molecular emitters that combined thermally activated delayed and circularly polarized fluorescence (CP‐TADF) is of paramount importance for the next generation of displays. While most efforts have thus far focused on covalent donor and acceptor CP‐TADF emitters, a novel strategy based on chiral exciplexes has recently emerged. In this context, we present the synthesis and chiroptical properties of four new CP‐TADF exciplexes, involving two distinct C2‐symmetric bicarbazole systems and two terpyridine‐based derivatives, which serve as the chiral donor and achiral acceptor units, respectively. These exciplexes exhibit CP‐luminescence, with intensity dependent on both the chiral donor and achiral constituents, resulting in emission dissymmetry factors reaching up to 10⁻2 in the thin‐film solid state. Additionally, small singlet‐triplet gaps (∆EST ≤ 0.1 eV) have been measured, leading to TADF characteristics with a photoluminescence quantum yield of 20% for the most efficient emitter, which is also successfully used in non‐optimized organic lightemitting diodes (OLEDs). Interestingly, these chiral exciplexes allow us to explore the impact of the locally‐excited (LE) state of the chiral donor on overall exciplex emission, particularly in relation to the intensity of polarized emission—potentially highlighting a key factor in the design of this type of bimolecular CP‐TADF emitter.

Source: Advanced Optical Materials

DOI: 10.1002/adom.202400725