Synthesis, characterization and theoretical investigation of the structure, electronic and third-order nonlinear optical (NLO) properties of M(dnpi)2 (M = Mn2+ and Ni2+)

Two coordination compounds have been synthesized following the Davidson method. The crystal structures of the two complexes of M(dnpi)2 (M = Mn2+ and Ni2+; dnpi = 4,5-diphenyl-2-(4-nitrophenyl)-1H-imidazole) were obtained. The grown crystals were characterized by elemental analysis, FTIR, UV–vis, single crystal X-ray diffraction, and DTA/TGA. The equilibrium geometry and molecular orbitals (MO) of the complexes are calculated based on B3LYP using LANL2DZ basis sets. The third-order nonlinear optical (NLO) properties were measured by the Z-scan technique with a pulse width of 4 ns at 532 nm and a 10 Hz repetition rate generated from a Q-switched frequency-doubled Nd:YAG laser. The nonlinear absorption coefficient, β, is 3.5 × 10−12 m/W for Ni(dnpi)2 and 2.3 × 10−11 m/W for Mn(dnpi)2, which has a nonlinear refractive index, γ, of −1.2 × 10−12 m2/W and elicits self-defocusing properties.