Binuclear platinum(II) complexes based on 2-mercaptobenzothiazole 2-mercaptobenzimidazole and 2-hydroxpyridine as brigding ligands: Red and near-infrared luminescence originated from MMLCT transition

Six new binuclear platinum (II) complexes were successfully designed and synthesized named (ppy)2Pt2(ns2)2(1), (ppy)2Pt2(n2s)2 (2), (dpq)2Pt2(ns2)2(3), (dpq)2Pt2(n2s)2(4), (dpq)2Pt2(2-opy)2 (5)and (bzq)2Pt2(2-opy)2 (6), where 2-phenylpyridine (hppy), 2,3-diphenylquinoxaline (hdpq), 7,8-benzoquinoline (hbzq) were used as cyclometalated ligands and 2-mercaptobenzothiazole (hns2), 2-mercaptobenzimidazole (hn2s), 2-hydroxpyridine (2-hypy) served as bridging ligands, respectively. Their crystal structure, photophysical and electrochemical characteristics were investigated. Four red or near-infrared luminescent compounds were obtained for 1 to 4 with emission peaks at 639, 632, 744 and 745 nm in solution at room temperature respectively, while emission spectra of 5 and 6 could not be measured. The X-ray structure of 1 and 5 showed that Pt(II)-Pt(II) distance were 2.9694 (3) and 2.8802 (3) Å respectively, which proved luminescence of the complexes benefited from metal-metal-to-ligand charge transfer (MMLCT) transitions. Among of them, the quantum efficiency of 1 was biggest at 16.5% in solution.