Nonlinear absorption in ionic liquids with transition metallic atoms in the anion

•Synthesis of new ionic liquids with transition metallic atoms in the anion.•NMR and mass spectroscopy analysis have been done.•Heat capacity and linear absorption between 300 nm and 1000 nm is characterized.•Nonlinear absorption induced by femtosecond laser pulses at 810 nm is reported.

Nonlinear absorption has been investigated by open aperture Z-scan in ionic liquids obtained by combination of 1-butyl-3-methyl-imidazolium cations with anions containing a transition metal (Co, Zn, Cu or Ni) and thiocyanate groups. The laser source was a Ti:Sapphire oscillator (80-fs pulses, λ = 810 nm, repetition rate of 80.75 MHz). All liquids present quite low heat capacities that favor the development of strong thermal effects. Thermal effects and nonlinear absorption make them potential materials for optical limiting purposes.