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Here, a novel deep blue emitter SBABz4 for use in organic light-emittingdiodes (OLED) is investigated. The molecular design of the emitter enablesthermally activated delayed fluorescence (TADF), which we examine bytemperature-dependent time-resolved electroluminescence (trEL) andphotoluminescence (trPL). We show that the dihedral angle between donor andacceptor strongly affects the oscillator strength of the charge transfer statealongside the singlet-triplet gap. The angular dependence of thesinglet-triplet gap is calculated by time-dependent density functional theory(TD-DFT). A gap of 15 meV is calculated for the relaxed ground stateconfiguration of SBABz4 with a dihedral angle between the donor and acceptormoieties of 86{\deg}. Surprisingly, an experimentally obtained energy gap of72+/-5 meV can only be explained by torsion angles in the range of70{\deg}-75{\deg}. Molecular dynamics (MD) simulations showed that SBABz4evaporated at high temperature acquires a distribution of torsion angles, whichimmediately leads to the experimentally obtained energy gap. Moreover, theemitter orientation anisotropy in a host matrix shows an 80% ratio ofhorizontally oriented dipoles, which is highly desirable for efficient lightoutcoupling. Understanding intramolecular donor-acceptor geometry in evaporatedfilms is crucial for OLED applications, because it affects oscillator strengthand TADF efficiency.

journal of physical chemistry. c./journal of physical chemistry. c

Getting the Right Twist: Influence of Donor-Acceptor Dihedral Angle on  Exciton Kinetics and Singlet-Triplet Gap in Deep Blue Thermally Activated  Delayed Fluorescence Emitter