Synthesis and luminescent study of diphosphine-Pt-disulfide complexes for OLED

Three novel diphosphine-Pt-disulfide complexes were synthesized and characterized by ¹H NMR, mass spectrometry and elemental analysis. As a diphosphine, 1,8-bis(diphenylphosphino)naphthalene (dppn), rac-2,2^′-bis(diphenylphosphino)-1,1^′-binaphthyl (dppbn), or 1,1^′-bis(diphenylphosphino)ferrocene (dppf) was employed and chelated to the Pt(II) center. As an anion, p-tolylsulfide (4-SC₆H₄CH₃) was incorporated to Pt(II) center subsequently, yielding (dppn)Pt(4-SC₆H₄CH₃)₂ (1), (dppbn)Pt(4-SC₆H₄CH₃)₂ (2), or (dppf)Pt(4-SC₆H₄CH₃)₂ (3). The photophysical properties of the resulting Pt complexes were investigated with UV–VIS spectroscopy, photoluminescence (PL) spectroscopy and transient PL. Charge Transfer absorptions between the metal and the ligand of 2 and 3 were observed at 320–350 nm in the UV–VIS spectra whereas such noticeable absorption was not observed in 1. The solid films of 1 and 3 showed luminescence at 600 and 580 nm, respectively, while that of 2 did not show emission at the room temperature. The complex 3 exhibited two excited state lifetimes, 23 and 125 ns, at room temperature, and the weighting factor for 125 ns state is only 10% of that for 23 ns one. It means that the prominent luminescence was fluorescence and the intersystem crossing through LS coupling is relatively weak.