Polyhalogenated 2,1,3-Benzochalcogenadiazoles: A Small-Molecule Platform for Multicentered Spin-Orbit Coupling Affecting Optical Properties (Chalcogens = S, Se, Te; Halogens = F, Cl, Br, I).

2,1,3-Benzochalcogenadiazoles and their halogen derivatives (chalcogen = S, Se, Te; halogen = F, Cl, Br, I) are widely employed in organic optoelectronics as chromophoric/fluorophoric electron-acceptor building blocks. In this work they are specified as an advantageous small-molecule platform for multicentered (Se, Te; Cl, Br, I) spin-orbit coupling (SOC) affecting optical properties of π-organics. Electronic absorption and emission/photoluminescence spectra of 4,7-di- and 4,5,6,7-tetrahalogenated 2,1,3-benzochalcogenadiazoles E/X' and E/X, respectively (E = chalcogen, X = halogen), have been studied in solid-state and THF solutions experimentally and theoretically. It has been found that the nature of E is the key factor controlling the photophysical properties of E/X' and E/X, such as energy levels, Stokes shifts, and the photoluminescence quantum yields, while X serves for further fine tuning of the properties. Combined E and X variation allows target-oriented design of absorptive and emissive materials for metal-free SOC-controlled optoelectronics and emerging spin-orbitronics.