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 λmax = 442 nm and a strong phosphorescence emission (Φ = 0.045) at λmax = 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.