Electrochromic and proton-induced phosphorescence properties of Pt(ii) chlorides with arylamine functionalized cyclometalating ligands

Abstract

Two cyclometalated Pt(II) complexes, [(L¹)PtCl] and [(L²)PtCl] (where HL¹ = 4-[p-(N-octyl-N-phenyl)amino]-phenyl-6-phenyl-2,2′-bipyridine and HL² = 4-{p-[p-(N,N′-dioctyl-N′-phenyl)phenyldiamino]}-phenyl-6-phenyl-2,2′-bipyridine), have been synthesized and characterized by ¹H NMR, mass spectrometry (MS) and elemental analysis. The structure of complex [(L¹)PtCl] has been revealed by X-ray crystallography. Both of the complexes possess the intense and red-shifted metal-to-ligand charge transfer (¹MLCT) (dπ(Pt) → π*(L)) transitions (ε ∼ 10⁴ dm³ mol⁻¹ cm⁻¹). Complex [(L¹)PtCl] displays strong phosphorescence (λ_max = 597 nm) in CH₂Cl₂ solution at room temperature and efficient electropolymerization behavior to form an electrochromic film with times of 5.8 s for the coloration step and 5.2 s for the bleaching step, an optical contrast of 70.5%, a black coloration efficiency of 441.4 C⁻¹ cm² and a bleaching efficiency of 489.1 C⁻¹ cm². Complex [(L²)PtCl] shows sensitive pH dependent luminescent properties, which are attributed to the inhibition of the intramolecular charge transfer (ICT) process through the protonation of the aniline dimer unit in the cyclometalating ligand.