Delayed fluorescence by triplet−triplet annihilation from columnar liquid crystal films.
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Date
2022
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Abstract
Delayed fluorescence (DF) by triplet−triplet annihila-
tion (TTA) is observed in solutions of a benzoperylene-imidoester
mesogen that shows a hexagonal columnar mesophase at room
temperature in the neat state. A similar benzoperylene-imide with a
slightly smaller HOMO−LUMO gap, that also is hexagonal columnar
liquid crystalline at room temperature, does not show DF in solution,
and mixtures of the two mesogens show no DF in solution either,
because of collisional quenching of the excited triplet states on the
imidoester by the imide. In contrast, DF by TTA from the imide but
not from the imidoester is observed in condensed films of such
mixtures, even though neat films of either single material are not
displaying DF. In contrast to the DF from the monomeric imidoester
in solution, DF of the imide occurs from dimeric aggregates in the
blend films, assisted by the imidoester. Thus, the close contact of intimately stacked molecules of the two different species in the
columnar mesophase leads to a unique mesophase-assisted aggregate DF. This constitutes the first observation of DF by TTA from
the columnar liquid crystalline state. If the imide is dispersed in films of polybromostyrene, which provides an external heavy-atom
effect facilitating triplet formation, DF is also observed. Organic light-emitting diodes (OLEDs) devices incorporating these liquid
crystal molecules demonstrated high external quantum efficiency (EQE). On the basis of the literature and to the best of our
knowledge, the EQE reported is the highest among nondoped solution-processed OLED devices using a columnar liquid crystal
molecule as the emitting layer.
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Keywords
Optical spectroscopy, Solution-processed OLED
Citation
FRANCA, L. G. et al. Delayed fluorescence by triplet−triplet annihilation from columnar liquid crystal films. ACS Applied Electronic Materials, v. 4, p. 3486−3494, 2022. Disponível em: <https://pubs.acs.org/doi/10.1021/acsaelm.2c00432>. Acesso em: 06 jul. 2023.