Octupolar molecular engineering for nonlinear optics

Summary form only given.In the early 90´s, the experimental evidence of frequency doubling in the 1,3,5-trinitro-2,4,6-triaminobenzene (TATB) crystal based on the simplest octupolar extension of paranitroaniline, has triggered the opening of a broader molecular engineering avenue, whereby symmetry-ensured cancellation of the molecular dipole moment is shown to be compatible with non-zero and significantly larger /spl beta/ tensor coefficients than for the purely dipolar scheme. Moreover, earlier one-dimensional (1D) systems have been embedded in the broader realm of multipolar systems whereby the quadratic nonlinearity of any molecule can be decomposed in rotationally invariant dipolar and octupolar components. Full exploitation of the tensorial character of /spl beta/ has thus permitted to enlarge the pool of candidate molecular structures to more isotropic two-dimensional 2D and three-dimensional 3D multipolar systems, whereas a n-level model (where n>2) has been shown to adequately describe the frequency dispersion of multipolar /spl beta/ tensors.