Synthesis and third-order optical nonlinearities of nickel complexes of 8-hydroxyquinoline derivatives

A nickel complex of 5-(acrylamido)methyl-8-hydroxyquinoline, bis-(5-(acrylamido)methyl-8-hydroxyquinolino) nickel(II) (Ni(AAMQ)2) has been synthesized and its third-order nonlinear optical properties was investigated with respect to that of bis-(8-hydroxyquinolino) nickel(II) (NiQ2) by single beam Z-scan technique. The real parts (γR) of the molecular second-order hyperpolarizabilities were −6.0 × 10−46 and −5.5 × 10−46 m5/v2 for NiQ2 and Ni(AAMQ)2, respectively, indicative of similar nonlinear refraction both in sign and in magnitude. After substitution of an acrylamidomethyl group to the 8-hydroxyquinoline (8-HQ) ligand, the nonlinear absorption coefficient of Ni(AAMQ)2 was enhanced by more than two times. The corresponding imaginary part (γI) of the molecular second-order hyperpolarizability was 3.4 × 10−46 m5/v2 for Ni(AAMQ)2 while 1.6 × 10−46 m5/v2 for NiQ2. The increase in nonlinear absorption was attributed to the substitution effect and the enhanced transition dipole moment due to the participation of δ-donor group of CH2 in the molecular conjugation.