Stabilization of Au nanoparticles prepared by laser ablation in chloroform with free-base porphyrin molecules

Laser ablation (LA) of a Au foil immersed in chloroform and/or in diluted 5,10,15,20-tetrakis-4-pyridylporphine (TPyP) chloroform solutions was carried out using 1064 nm nanosecond laser pulses. The products were characterized by UV-visible-NIR optical extinction and IR absorption measurements, Raman spectroscopy and transmission electron microscopy (TEM). They were found to be strongly influenced by the convergence of the incident laser beam and delivered energy per pulse. Our results show that with highly focused laser beam chloroform underwent photochemical reactions and no nanoparticles with observable surface plasmon extinction (SPE) band were formed whereas at particular focusing conditions Au nanoparticles with the SPE band typical for Au organosols were created. Au organosols in pure chloroform showed a limited stability, the SPE band disappeared in a few hours after the preparation. When a small amount of TPyP was present in the course of LA both the efficiency of Au nanoparticles formation and the stability of the resulting organosols were improved. A possible mechanism of LA of the Au target in chloroform and in diluted TPyP chloroform solutions is discussed.