Donor–Acceptor Benzochalcogenazolo-Based N,O‑Coordinated Boron Difluoride Emitters Exhibiting Amplified Spontaneous Emission and Thermally Activated Delayed Fluorescence for Organic Light-Emitting Diodes

A new series of donor–acceptor benzochalcogenazole-based N,O-coordinated boron difluoride complexes (1a,b–3a,b) has been synthesized for applications in organic solid-state lasers and light-emitting diodes. The effect of the chalcogen atom (O, S, Se) in the benzochalcogenazole core on the photophysical properties was systematically studied. While the compounds show negligible fluorescence in solution, they exhibit pronounced aggregation-induced emission and strong solid-state luminescence, with photoluminescence quantum yields up to 48% in the crystalline state and 56% in poly(methyl methacrylate) films. Benzoxazole- and benzothiazole-based derivatives display amplified spontaneous emission with thresholds as low as 10.1 μJ/cm2, which enables to perform efficient organic solid-state lasers. Meanwhile, benzothiazole- and benzoselenazole-containing compounds exhibit both prompt and efficient delayed fluorescence. OLED devices incorporating these emitters demonstrated efficient energy conversion and bright electroluminescence. Benzothiazole-based complexes 2a and 2b achieved maximum external quantum efficiencies of 9.0% and 16.5%, respectively, with luminance values exceeding 23,000 cd/m2. In contrast, the benzoselenazole analogue 3a, despite a higher delayed fluorescence-to-prompt fluorescence ratio, showed lower device efficiency, highlighting the impact of heteroatom selection on exciton dynamics. These findings establish benzothiazole-containing boron difluoride complexes as promising, thermally stable emitters for high-performance solid-state laser and OLED applications. The results underscore the potential of molecular design and heteroatom engineering to further enhance efficiency and operational stability in organic optoelectronic devices.