Series of C^N^C Cyclometalated Pt(II) Complexes: Synthesis, Crystal Structures, and Nonlinear Optical Properties in the Near-Infrared Region

Abstract

It is currently challenged that nonlinear optical (NLO) properties in the near-infrared region (NIR) of metal complexes can be tunable with an assistant ligand. Herein, the linear and nonlinear photophysical properties of the novel C^N^C cyclometalated Pt(II) complexes with different substituents as auxiliary ligands are presented. The complexes displayed intense triplet metal/ligand-to-ligand charge-transfer (³MLCT/³LLCT) and intraligand ³π, π* emission at low-temperature. The excited-state characteristics are further confirmed over the TD-DFT calculations, transient absorption, and emission lifetimes. The Pt-3 possesses a relatively high quantum yield (9.1%), a moderate triplet excited-state lifetime (5.32 μs), and a broad excited-state absorption from the visible to the near-IR region. Interestingly, it was found that Pt-3 exhibited high 2PA cross section values (σ₂ up to 367 GM at 820 nm), as well as good optical limiting properties over a tunable femtosecond laser. The relationships between the structures and properties were systematically investigated on the basis of crystal structural information. Hence, cyclometalated Pt(II) complexes would become candidates for the application of the NIR NLO materials.