The magic of semi-perfluorinated mixtures: Engineering MR-TADF emission from host-guest mixtures of liquid crystals

Abstract

Two liquid crystalline emitter-host mixtures have been developed, where each of the emitter and host self-assembles into a columnar hexagonal (Col_h) mesophase, as does the mixture. The emitter consists of a modified B-O-Cz multi-resonant thermally activated delayed fluorescence (MR-TADF) core containing lateral semiperfluorinated side chains, while the host is derived from a modified MR-TADF DOBNA core that also contains lateral semiperfluorinated side chains. Unlike the previously used alkoxy side chains in TADF liquid crystalline materials, the semiperfluorinated side chains only minimally perturb the optoelectronic properties of the luminescent cores, this despite the strong aggregation within the Col_ho phase. This was achieved by shielding the emitter moieties from each other within the host mesophase, which mitigates excimer emission from aggregates and by engineering an efficient Förster resonance energy transfer from the host material to the emitter in the blend.