The third-order optical nonlinearities of thiophene-bearing phthalocyanines studied by Z-scan technique

The third-order optical nonlinearities of thiophene-bearing phthalocyanines (Ni-TPc and Cu-TPc) measured using Z-scan technique at 532 nm have three features: firstly, both Ni-TPc and Cu-TPc showed large molecular cubic hyperpolarizabilities γ whose values were of the order of 10−30 esu; secondly, the nonlinear absorption and the nonlinear refraction contribute almost equally to their molecular cubic hyperpolarizabilities, while for our previous studied phthalocyanines, the contribution from nonlinear refraction was always overwhelming; thirdly, the γ value of Cu-TPc is 1.5 times larger than that of Ni-TPc, which is mainly due to their different nonlinear absorptions. This study may indicate that the incorporation of thiophene rings into phthalocyanines could notably increase the multi-photon absorption cross-section of Pc.