Weissenseel, SebastianDrigo, Nikita A.Kudriashova, Liudmila G.Schmid, MarkusMorgenstern, ThomasLin, Kun-HanPrlj, AntonioCorminboeuf, ClemenceSperlich, AndreasBruetting, WolfgangNazeeruddin, Mohammad KhajaDyakonov, Vladimir2019-12-042019-12-042019-12-042019-11-1410.1021/acs.jpcc.9b08269https://infoscience.epfl.ch/handle/20.500.14299/163531WOS:000497260100055Here, a novel deep blue emitter SBABz4 for use in organic light-emitting diodes (OLED) is investigated. The molecular design of the emitter enables thermally activated delayed fluorescence (TADF), which we examine by temperature-dependent time-resolved electroluminescence (trEL) and photoluminescence (trPL). We show that the dihedral angle between donor and acceptor strongly affects the oscillator strength of the charge transfer state alongside the singlet-triplet gap. The angular dependence of the singlet-triplet gap is calculated by time-dependent density functional theory (TD-DFT). A gap of 15 meV is calculated for the relaxed groundstate configuration of SBABz4 with a dihedral angle between the donor and acceptor moieties of 86 degrees. Surprisingly, an experimentally obtained energy gap of 72 +/- 5 meV can only be explained by torsion angles in the range of 70-75 degrees. Molecular dynamics (MD) simulations showed that SBABz4 evaporated at high temperature acquires a distribution of torsion angles, which immediately leads to the experimentally obtained energy gap. Moreover, the emitter orientation anisotropy in a host shows an 80% ratio of horizontally oriented dipoles, which is highly desirable for efficient light outcoupling. Understanding intramolecular donor-acceptor geometry in evaporated films is crucial for OLED applications, because it affects oscillator strength and TADF efficiency.Chemistry, PhysicalNanoscience & NanotechnologyMaterials Science, MultidisciplinaryChemistryScience & Technology - Other TopicsMaterials Scienceexternal quantum efficiencydiodessimulationmoleculesenergytext::journal::journal article::research article