The third-order optical nonlinearity of two triple-decker mixed plithalocyaninato and porphyrinato Sm complexes, Sm-2(Pc)(2)(TPP) and Sm-2(Pc)(TPP)(2) (Pc=phthalocyanine; TPP=5,10,15,20-tetraphenylporphyrinate), is investigated using the femtosecond time-resolved optical Kerr gate method at 830 nm wavelength. Their second-order hyperpolarizabilities are estimated to be 2.6 x 10(-30) and 2.2 x 10(-30) esu, respectively. Introducing of Lanthanide Sm to the large pi-conjugated system, intermacrocycle interaction and two-photon resonance are considered responsible for the large optical nonlinearity. (C) 2003 Elsevier Science B.V. All rights reserved.