White light emission from a green cyclometalated platinum(ii) terpyridylphenylacetylide upon titration with Zn(ii) and Eu(iii )

Abstract

The cyclometalated Pt(II) acetylide derivative with a 1,3-bis(N-octyl-benzimidazol-2-yl)benzene (N^C^N) ligand and a free terpyridine (TPY) receptor has been successfully synthesized and characterized. X-ray crystallography shows its inefficient conjugation degree between the [(N^C^N)Pt] and TPY planes. This bifunctional complex shows an enhanced ¹MLCT/LLCT absorption band (ε = 3.30 × 10⁴ dm³ mol⁻¹ cm⁻¹) centered at λ_max = 365 nm, and the well-resolved vibronic-structured ³MLCT/LLCT emission bands (Φ = 0.08, τ = 3.43 μs) in the range of ca. 475–700 nm. Consecutive titrations show that added Zn²⁺ and Eu(HFA)₃ bond to its free TPY receptor with 1 : 2 and 1 : 1 stoichiometry to form the heterotrinuclear Pt–Zn–Pt (K_a = 3.48 × 10⁴ mol⁻¹ dm³) and heterodinuclear Pt–Eu (K_a = 1.73 × 10⁴ mol⁻¹ dm³) complexes, respectively. A sensitizing effect of Zn²⁺ on the TPY unit, and the incomplete d → f energy transfer from the [(N^C^N)Pt(II)] antenna donor to the Eu(III) center with maximum efficiency of 51.8% are observed. Using an in situ mixed titration strategy, the R/G/B emission triads consisted of red [(TPY)Eu(HFA)₃] and green [(N^C^N)Pt(II)] dual phosphorescence and blue [(TPY)Zn(TPY)] fluorescence, which can be well balanced to realize the white-light-emission with CIE coordinates (x = 0.36, y = 0.36) by precisely controlling the molar ratio (9 : 1 : 2) of the parent complexes, Eu(HFA)₃ and Zn(ClO₄)₂.