  Here, 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 ground state
configuration of SBABz4 with a dihedral angle between the donor and acceptor
moieties of 86{\deg}. Surprisingly, an experimentally obtained energy gap of
72+/-5 meV can only be explained by torsion angles in the range of
70{\deg}-75{\deg}. 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 matrix 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.
