The ultrafast tunable saturable absorption of metal complexes containing redox-active 1-(2-pyridylazo)-2-acenaphthequinol ligands

Abstract The extraordinary ultrafast tunable saturable absorption properties of metal complexes M(PAAL) 2 (M = Co, Ni, Cu, Zn) containing redox-active 1-(2-pyridylazo)-2-acenaphthequinol ligands (PAAL) were investigated by Z-scan and pump-probe system. The obtained third-order nonlinear optical (NLO) absorption and refraction coefficient of each metal complex reach ∼10 −2 cm/GW and ∼10 −6 cm 2 /GW at 510 nm wavelength, respectively. Meanwhile, an ultrafast carrier relaxation process of approximately (200 ± 50) fs is observed for all of them. Furthermore, we found that the third-order nonlinear absorption coefficient of M(PAAL) 2 is proportional to the central metal proton number. All the NLO properties indicate that those metal complexes posses potential applications for fabricating photonic devices.