Nonlinear-optical investigations of new materials are important for 2 complementary reasons. first, the requirements for materials to be used in device applications that utilize nonlinear interactions are very demanding. New approaches to materials research can yield materials with favorable properties compared to traditional nonlinear materials, as shown recently in several supramolecular systems (Cox et a1. 1990; Stucky and MacDougall 1990; Clays et a1. 1993; Kelderman et a1. 1993; Kauranen et a1. 1995; Lehn 1995). This is particularly true for 2nd-order nonlinear optics that require noncentrosymmetric materials (Prasad and Williams 1991). On the other hand. nonlinear-optical processes can provide new techniques to study the properties of new materials. The nonlinear techniques have the potential of being more sensitive than the existing techniques or providing information that is not accessible at all using the existing techniques (Shen 1984). Here again, 2nd-order processes are particularly important because they provide an extremely sensitive tool to study symmetry properties of materials.