Stabilization and large nonlinearity of gold nanoparticles functionalized with a pi-conjugated polymer

Gold nanoparticles protected by a novel pi-conjugated polymer [poly(p-phenylene ethynylene) containing pendent disulfide and bipyridine groups] are synthesized and characterized. The polymer can stabilize the gold nanoparticles effectively. The nonlinear optical properties of the gold nanoparticle colloid solutions in toluene are investigated by using the Z-scan technique at a wavelength of 532 nm and pulse width of 4 ns. The gold-nanoparticle colloid solutions show an exceptional nonlinear absorption effect, which simultaneously contains the saturated absorption resulting from third-order nonlinearity and a large reverse-saturated absorption resulting from fifth-order nonlinearity. In addition, asymmetric self-focusing refractive effects are investigated in the colloid solutions.