A series of new organic emitters was prepared by introducing various donors (Ds) to the meta-position of the boron atom in the central phenyl ring in the acceptor (A) of 5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (OBA). Moreover, their thermal, photophysical, electrochemical and electroluminescent (EL) properties were characterized in detail. The photophysical results revealed that these OBA-based molecules adopted a D–A configuration and exhibited efficient thermally activated delayed fluorescence (TADF) properties with a reverse inter-system crossing constant (k_RISC) in the order of 10⁵ s⁻¹. It has been shown that introducing the –Br group to the OBA acceptor could increase k_RISC by 2 to 3 times. Importantly, the deep-blue TADF emitter OBA-O showed a high photoluminescent quantum yield (PLQY) of 0.84, while its blue analog OBA-BrO with the –Br group exhibited an even higher PLQY of 0.92 in the doped film state. Benefitting from their high PLQYs as blue-emitting TADF emitters, the doped organic light-emitting diodes (OLEDs) based on these OBA-based TADF emitters exhibited attractive electroluminescent (EL) performances. The blue-emitting OLEDs with CIE (0.17, 0.17) showed the maximum external quantum efficiency (η_ext) of 17.8%, current efficiency (η_L) of 33.2 cd A⁻¹ and power efficiency (η_P) of 34.2 lm W⁻¹, while that for the bluish-green device were 22.5%, 49.2 cd A⁻¹ and 56.9 lm W⁻¹, respectively. Thus, the great potential of these TADF emitter-based OBA acceptors was clearly demonstrated by their EL data. In addition, these asymmetric OBA-based molecules will enrich the structural diversity of this type of TADF emitter.

Time-dependent density functional theory (TDDFT) with and without a spin-flip scheme is extensively compared in on-the-fly trajectory surface hopping molecular dynamics with a global switching (GS) algorithm. The simulation is performed for cis–trans azobenzene photoisomerization following the excitation to the S₁(nπ*) state that is involved in a conical intersection (CI) between ground and first excited states. This CI is found correctly to be a single-cone (artificial double-cone) structure computed by the TDDFT method with (and without) spin-flip. Nevertheless, simulated quantum yields and lifetimes are in very good agreement; 0.43 and 63 fs (0.34 and 62 fs) for cis-to-trans isomerization, and 0.11 and 2200 fs (0.13 and 1040 fs) for trans-to-cis isomerization, by TDDFT with (and without) a spin-flip scheme. Distributions of excited-state decay, hopping spots and products, as well as typical trajectories have similar patterns and behaviors with and without spin-flip. The global switching trajectory surface hopping method is demonstrated to be well suited to TDDFT on-the-fly dynamic simulation with and without spin-flip. For comparison, previous simulations with the CASSCF method and Tully's fewest-switches trajectory surface hopping method are also addressed.