Proceedings of nanoGe Spring Meeting 2022 (NSM22)
DOI: https://doi.org/10.29363/nanoge.nsm.2022.187
Publication date: 7th February 2022
Thermally Activated Delayed Fluorescence (TADF) process has appeared as the most popular design strategy towards reaching 100% internal quantum efficiency for Organic Light-Emitting Diodes (OLEDs). TADF consists in promoting upconversion of triplet excited states into emissive singlet ones through Reverse InterSystem Crossing (RISC), a process driven by spin-orbit coupling (SOC) and requiring a small singlet-triplet gap DEST. The advancement of the TADF field occurred essentially through materials design, the first strategy, as proposed by C. Adachi and co, consisting in connecting electron donating and accepting units to decrease the DEST. However, in doing so, the lower-lying singlet and triplet excited states bear a dominant charge transfer character that translates into a broad emission spectrum.
In this contribution, we will discuss two different topics based on computational considerations:
How doped triangleshaped molecules can lead to (i) concomitant narrow emission, high quantum yield of emission and small DEST resulting in a whole new generation of TADF emitters, the multiresonant TADF emitters and to (ii) a new family of compounds with an inverted singlet-triplet gap and potentially, a downwards energy RISC. To do so, we rely on high level quantum chemical calculations and show that an accurate description of electron correlation effects is key to correctly predict the excited states ordering as well as the optical properties of these compounds.
How the interactions in the solid state can turn RISC from a SOCdriven to a hyperfine interaction (HFI)-driven mechanism. Combining time-resolved and transient electron paramagnetic resonance spectroscopies as well as (time-dependent) density functional theory calculations, we demonstrated that HFI-RISC occurs through delocalized charge transfer states in a curcuminoid derivative.
Y.O. acknowledges funding from the FRS-FNRS under the grant F.4534.21 (MIS-IMAGINE).
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