Influence of the central metal atom on the nonlinear optical properties of MPcs solutions and thin films

Third order nonlinear optical susceptibility (χ〈3〉) of metallophthalocyanines (MPcs, where M = Co, Cu, Zn, Mg) thin films and solutions was investigated by standard backward degenerate four wave mixing (DFWM) method at 532 nm. Third harmonic generation (THG) measurement at 1064 nm performed on MPcs thin films is also discussed. MPcs thin films were grown by conventional thermal evaporation in high vacuum and solution were dissolved in tetrahydrofuran (THF), in which the studied materials are soluble. In the case of microscopic nonlinearity, we calculated the second order hyperpolarizability (γ) for MPcs solutions. We found that the χ〈3〉 and the γ   values are affected by the nature of the central metal atom. We also found that the χDFWM〈3〉 value is larger than that measured via THG experiment. The variation in χ〈3〉 values occurs due to the different resonance contributions.