?-conjugated soluble nickel-polyyne copolymer: Synthesis and third-order optical nonlinearity

By means of homogeneous stepwise condensation method, both the Ni–polyyne copolymers with PPh3 and PBu3 ligands, and modified π-conjugated nickel-containing copolymers have been synthesized and confirmed by infrared (IR) analysis. The Ni–polyyne copolymers obtained are yellow powder having a Mw of about 1 ∼ 2 × 104 and a molecular weight distribution (MWD) of less than 3, and they are soluble in tetrahydrofuran (THF), CHCl3, and toluene. Their third-order nonlinear optical properties have been investigated by a degenerate four-wave mixing (DFWM) technique. The effect of the nature of the ligands attached to the nickel atoms, the structure, and the length of π-conjugation between the 2 metal centers in the main chain on the hyperpolarizability γ of the Ni–polyyne polymers have been discussed. The maximum susceptibility χ(3) and hyperpolarizability γ of the Ni–polyyne polymers reach 5.17 × 10−12 and 2.30 × 10−30 esu, respectively.