Phosphorescent 2-phenylbenzothiazole PtIV bis-cyclometalated complexes with phenanthroline-based ligands

Abstract

We describe a family of dicationic heteroleptic complexes of the type [Pt(pbt)₂(N^N)]Q₂, bearing two cyclometalating 2-phenylbenzothiazole (pbt) groups and a N^N phenanthroline-based ligand [N^N = 1,10-phenanthroline (phen) 4, pyrazino[2,3-f][1,10]-phenanthroline (pyraphen) 5, 5-amine-1,10-phenanthroline (NH₂-phen) 6], with two different counteranions (Q = CF₃CO₂ and PF₆). Complexes 4–6-PF₆ and 4–6-CF₃CO₂ were obtained through ligand substitution from cis-[Pt(pbt)₂Cl₂] 2 and cis-[Pt(pbt)₂(OCOF₃)₂] 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 ³IL excited states centered on the cyclometalated pbt, with lower efficiency in 2 in relation to 3 by the presence of closer thermally accessible deactivating ³LMCT excited states in 2. The Pt^IV complexes 4–5-CF₃CO₂/PF₆ display orange emission in CH₂Cl₂ solution, solid state (298, 77 K) or PS films, arising from a ³IL(pbt) emissive state. The NH₂-phen derivatives 6-CF₃CO₂/PF₆ show dual emission associated to two close different emissive states, ³IL′CT (L′ = NH₂-phen) and ³IL(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^IV complexes.