Synthesis, tunable photophysics and nonlinear absorption of terpyridyl Pt(II) complexes bearing different acetylide ligands

A series of 4-phenyl-2,2′; 6′,2″-terpyridyl Pt(II) complexes bearing different σ-alkynyl ancillary ligands (1a-1f) were synthesized and characterized. All complexes exhibit strong ¹π,π∗absorption bands in the UV region; and broad, structureless metal-to-ligand charge transfer (¹MLCT)/ligand-to-ligand charge transfer (¹LLCT) absorption bands in the visible region. When excited at the charge-transfer absorption band, the complexes exhibit yellow to red luminescence (λ_max = 553-608 nm) in CH₃CN at room temperature, which is attributed to the ³MLCT/³LLCT state, except 1c. The emitting state of 1c exhibits a significant intraligand ³π,π∗character, which is originated from the naphthalimide acetylide ligand. Complexes 1a-1c exhibit moderate triplet transient absorptions from visible to NIR region, where reverse saturable absorption (RSA) occurs. The photophysical, electrochemical and nonlinear absorption properties of these Pt(II) complexes can be tuned drastically by the different acetylide ligand, which would be useful for rational design of broadband nonlinear absorption materials.