Phosphorescent 2-phenylbenzothiazole Pt IV bis-cyclometalated complexes with phenanthroline-based ligands.

We describe a family of dicationic heteroleptic complexes of the type [Pt(pbt)(N^N)]Q, bearing two cyclometalating 2-phenylbenzothiazole (pbt) groups and a N^N phenanthroline-based ligand [N^N = 1,10-phenanthroline (phen) 4, pyrazino[2,3-][1,10]-phenanthroline (pyraphen) 5, 5-amine-1,10-phenanthroline (NH-phen) 6], with two different counteranions (Q = CFCO and PF). Complexes 4-6-PF6 and 4-6-CF3CO2 were obtained through ligand substitution from -[Pt(pbt)Cl] 2 and -[Pt(pbt)(OCOF)] 3, respectively. The molecular structures of 2, 3 and 4-PF6 and the photophysical and electrochemical properties of all complexes were studied in detail. The precursors 2 and 3 exhibit high-energy emissions from IL excited states centered on the cyclometalated pbt, with lower efficiency in 2 in relation to 3 by the presence of closer thermally accessible deactivating LMCT excited states in 2. The Pt complexes 4-5-CF3CO2/PF6 display orange emission in CHCl solution, solid state (298, 77 K) or PS films, arising from a IL(pbt) emissive state. The NH-phen derivatives 6-CF3CO2/PF6 show dual emission associated to two close different emissive states, IL'CT (L' = NH-phen) and IL(pbt), depending on the medium and the excitation wavelength. DFT and time-dependent TD-DFT calculations support these assignments and allow explain the luminescence of these tris-chelate Pt complexes.