Benzochalcogenazolo-based N,O-coordinated boron difluoride complexes as gain media for organic solid-state lasers†

Three N,O-coordinated benzochalcogenazolo-based boron difluoride complexes have been designed, synthesized, and spectroscopically characterized using their solutions, solid state, and the films of dye-doped polymers. The structural analysis demonstrated that dyes adopt twisted molecular structures with the torsion angle ranging from 24° to 37°, attributed to the steric effect of the cyano group. The obtained compounds exhibit aggregation-induced emission and blue to cyan emission (455–487 nm) in the solid state with a photoluminescence quantum yield ranging from 21% to 85% and a short excited-state lifetime of 0.80–2.27 ns. These characteristics facilitate the amplified spontaneous emission (ASE) with the progressive reduction in the full width at half maximum observed across the series of benzoxazole → benzothiazole → benzoselenazole derivatives up to 15 nm, 11 nm, and 8 nm, respectively, and also the low ASE threshold values of 18.7–40.3 μJ cm⁻². The successful application of the dyes in the fabrication of organic solid-state lasers results in a laser threshold of 46.1 μJ cm⁻², 28.0 μJ cm⁻², and 58.6 μJ cm⁻² for the devices based on benzoxazole, benzothiazole, and benzoselenazole-based boron difluoride complexes, respectively. Our work opens the pathway for a novel class of heavy atom-containing organic laser dyes, which can be used for both organic optically and electrically pumped lasers.