Computational Design of Novel HLCT Materials Composed of Quasi‐Planar Donor and Acceptor Units

The novel emitters were designed based on the combination of the quasi‐planar donor and acceptor moieties including the different chalcogen atoms (O, S, and Se). Time‐dependent density functional theory (DFT) calculations were carried out to understand their specific nature of the photophysical properties in both excited states. The comprehensive analyses of the natural transition orbital (NTO), energy‐level alignment, spin‐orbit coupling matrix element (SOCME) were performed to determine whether the spin‐flip transition occurs or not. Based on these results, the emission mechanism of the designed emitters can be divided into three categories as the pure fluorescence, thermally activated delayed fluorescence, and hybridized local and charge‐transfer chromophores. Among the candidate hybridized local and charge‐transfer chromophores, 7‐(5,9‐dithia‐13b‐boranaphtho[3,2,1‐de]anthracen‐7‐yl)benzo[5,6][1,4]oxazino[2,3,4‐kl]phenoxazine (ONO‐SBS), 7‐(5,9‐diselena‐13b‐boranaphtho[3,2,1‐de]anthracen‐7‐yl)benzo[5,6][1,4]thiazino[2,3,4‐kl]phenothiazine (SNS‐SBS), 7‐(5,9‐dithia‐13b‐boranaphtho[3,2,1‐de]anthracen‐7‐yl)benzo[5,6][1,4]thiazino[2,3,4‐kl]phenothiazine (SNS‐SeBSe), 7‐(5,9‐dithia‐13b‐boranaphtho[3,2,1‐de]anthracen‐7‐yl)benzo[5,6][1,4]selenazino[2,3,4‐kl]phenoselenazine (SeNSe‐SBS), and 7‐(5,9‐diselena‐13b‐boranaphtho[3,2,1‐de]anthracen‐7‐yl)benzo[5,6][1,4]selenazino[2,3,4‐kl]phenoselenazine (SeNSe‐SeBSe) are expected to exhibit a predominant spin‐flip transition pathway from the T 3 to the S 1 states with fast k rISC values on the order of 10 6 ‐10 7 s −1 .