In Marder's presentation the design guidelines for molecules and materials that have large two-photon absorption cross-sections and large “real” third-order susceptibilities for all optical switching were provided. Specifically, molecules with large two-photon absorption cross-sections, d, are in great demand for a variety of applications including two-photon-excited fluorescence microscopy and three-dimensional optical-data storage. These applications utilize the quadratic scaling of the rate of two-photon absorption with input intensity, which allows for the excitation of chromophores with a high degree of spatial selectivity in three dimensions through using a tightly focused laser beam. A strategy for the design of molecules with large two-photon absorption cross-sections, d, has been developed, which is based on the concept that symmetric charge transfer (upon excitation), either from the ends of a conjugated system to the center or vice versa, is correlated to enhanced values of d. In addition, the synthesis and characterization of materials with large third-order nonlinear susceptibility, ?(3), were discussed.