The work presented in this thesis concerns the design and synthesis of organic and metallo-organic chromophores for use in non-linear optics. The non-linear optical (NLO) properties have been quantified using hyper-Rayleigh scattering (HRS) studies to measure β, and using the two-state model βο values have been determined. Stark spectroscopy has also been used to derive βο values indirectly. Twenty four X-ray crystal structures have been solved, with six of these showing non-centrosymmetric (NCS) packing arrangements. HRS measurements have also been applied to two series of known co-ordination complexes in order to probe structure-activity relationships.