Dibenzothiophene-platinated complexes: probing the effect of ancillary ligands on the photophysical performance

Cyclometalation of dibenzothienyl-pyridine (HPyDBT) afforded a series of platinum(ii) complexes Pt(PyDBT)(L)Cl (L = DMSO, 1; P(p-C₆H₄-X)₃ (X = H, 2; CF₃, 3; OMe, 4; NPh₂, 5); 1,3,5-triaza-7-phosphaadamantane, 6; 2,6-dimethylphenyl isocyanide, 7). Chelating bidentate LL ligands formed cationic compounds [Pt(PyDBT)(LL)]⁺ (LL = 1,2-bis(diphenylphosphino)benzene, 8; 2,2′-bipyridine, 9; 1,10-phenanthroline, 10). Oxidation of a thienyl sulfur atom allowed for the isolation of the sulfone derivative Pt(PyDBT)(PPh₃)Cl (11). The title complexes were characterized crystallographically (except 7). Investigation of their photophysical behavior revealed solid state phosphorescence with quantum yields up to 0.45 for neat powders. The ancillary ligands L show a minor influence on the emission energies of the neutral compounds, but affect dramatically the intensity of luminescence. In contrast, the cationic species with diimine ligands demonstrate a significant contribution of the LL fragments into the emissive T₁ states that leads to a certain mixing of ³IL and ³LL′CT transitions and causes a substantial bathochromic shift of emission.