Lapachol is a naphthoquinone that was first isolated by E. Paterno from Tabebuia avellanedae (Bignoniaceae) in 1882. A wide spectrum of therapeutic activities have been attributed to lapachol or its derivatives viz., anti-abscess, anti-ulcer, antileishmanial, anticarcinomic, antiedemic, anti-inflammatory, antimalarial, antiseptic, antitumor, antiviral, bactericidal, fungicidal, insectifugal, pesticidal, protisticidal, respiradepressant, schistosomicidal, termiticidal, and viricidal. Originally isolated from species of the Bignoniaceae family, lapachol can also be found in other families such as Verbenaceae, Proteaceae, Leguminosae, Sapotaceae, Scrophulariaceae, and Malvaceae. The interesting and most usefull knowledge on lapachol, which is reviewed in this paper, can be used as a starting point in future research endeavors.

Recent studies have demonstrated that in thermally activated delayed fluorescence (TADF) materials, efficient reverse intersystem crossing occurs from non-radiative triplet states to radiative singlet states due to a small singlet-triplet energy gap. This reverse intersystem crossing significantly influences exciton annihilation processes and external quantum efficiency roll-off in TADF based organic light-emitting diodes (OLEDs). In this work, a comprehensive exciton quenching model is developed for a TADF system to determine singlet-singlet, singlet-triplet, and triplet-triplet annihilation rate constants. A well-known TADF molecule, 3-(9,9-dimethylacridin-10(9H)-yl)-9H-xanthen-9-one (ACRXTN), was studied under intensity-dependent optical and electrical pulse excitation. Our model shows singlet-singlet annihilation dominates under optically excited decays, whereas singlet-triplet annihilation and triplet-triplet annihilation have strong contribution in electroluminescence decays under electrical pulse excitation. Furthermore, the efficiency roll-off characteristics of ACRXTN OLEDs at steady state was investigated through simulation. Finally, singlet and triplet diffusion length were calculated from annihilation rate constants.

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