As one of the important elements in natural and artificial electron transfer and energy transfer processes, porphyrin and its derivatives have received much attention in photoelectronics and photoelectronic materials. As our first attempt to relate the π-π electronic couplings between porphyrin macrocycles to apparent third order nonlinear susceptibilities, we measured χ(3) for several porphyrin and chlorophyll a derivatives, including dimers with different configurations. Our preliminary results show that the dimers have enhanced χ(3) compared to those of the monomer. This enhancement is related to the relative orientations between the two macrocycles in the dimers. The parallel dimers with close face-to-face distances seem to have the highest enhancement in χ(3). More model compounds and related theoretical works are in progress before reaching a final conclusion.