Synthesis, crystal structure, photophysical property and metal ion-binding behavior of a cyclometalated platinum(ii) terpyridylacetylide with efficient π-conjugation degree

Abstract

A cyclometalated Pt(II) acetylide derivative bearing a carbazole donor and a terpyridine (TPY) receptor has been successfully synthesized and characterized. X-ray crystallography shows its monoclinic crystal system with the P2(1)/c space group and the three-component co-planarity molecular structure. This efficient π-conjugation system displays an intense low-energy absorption band (ε = 1.51 × 10⁴ dm³ mol⁻¹ cm⁻¹) at λ_max = 442 nm and a strong phosphorescence emission (Φ = 0.045) at λ_max = 596 nm in an air-saturated CH₂Cl₂ solution at room temperature, resulting from the dπ(Pt) → π*(C^N^N) metal-to-ligand charge transfer (MLCT) mixing with the π(CC–Ar) → π*(C^N^N) ligand-to-ligand charge transfer (LLCT) transition. With the introduction of the TPY receptor, this complex possesses ca. 1.6-fold luminescence-enhancing response for Zn²⁺ and Cd²⁺ but dramatic luminescence quenching response toward other common transition metal cations. Consecutive titrations exhibit that the added metal ions bond to its free TPY receptor with 1 : 2 stoichiometry to form the heterotrinuclear (Pt–M–Pt) complex. The Fe²⁺-quenched and Zn²⁺-enhanced luminescence behaviors with the maximum PET efficiency of 92.4% and 62.7%, respectively, strongly suggest the presence of the intra-molecular energy transfer between the [M(TPY)₂]²⁺ core and the terminal phosphorescent Pt(II) complex units.