Tuning of the Coordination and Emission Properties of 4-Amino-2,1,3-Benzothiadiazole by Introduction of Diphenylphosphine Group

Sukhikh, Taisiya S.; Khisamov, Radmir M.; Bashirov, Denis A.; Komarov, Vladislav Yu; Molokeev, Maxim S.; et al. Crystal Growth & Design. https://doi.org/10.1021/acs.cgd.0c00406

A novel amino-benzothiadiazole bearing diphenylphosphine groups (L) was designed and synthesized. A number of its coordination compounds of Cu(I) (1·0.75C7H8, 2a,b), Pd(II) (4), and Pt(II) (5) were prepared demonstrating the coordination of L ligand via N and/or P atoms. The reaction with strong Lewis acid Zn(II) resulted in the rearrangement of P—N—P to P–P–N moiety and formation of complex 3. The structures of L, 2–5 were determined by single crystal X-ray (XRD) diffraction, while that of 1·0.75C7H8 was determined by powder XRD analysis. Intermolecular secondary bonding of S···S interactions in the compounds, unusual for benzothiadiazoles, was discussed supported by quantum chemical calculations. Differences in the structures of the compounds cause significant changes of photophysical properties. In particular, the position of the electronic absorption band is featured by the conformation of L, viz., the dihedral angle between the benzothiadiazole unit and the P—N—P moiety, as proved by TD-DFT calculations performed on model molecules. The photophysical properties of the compounds also strongly depend on the coordination mode of L: the presence of a bond between the metal and the N atom of the thiadiazole unit plays an essential role in defining the position of the absorption and emission bands as well as emission lifetime of these compounds. The thermally activated delayed fluorescence and phosphorescence mechanisms in a thermal equilibrium were determined for 1·0.75C7H8. Complex 5 features a broad emission band spanning the entire visible region; moreover, it shows an unusual clear-white luminescence, which remains visible even in the daylight.