Results are presented on the design, preparation and characterization of Langmuir-Blodgett films formed from stearyl (S) derivatives of DAN, MAP and NPP. Molecular dynamics modelling of trilayers composed of simplified molecules reveals buckling at the interface owing to disordering of the strongly interacting head groups. Model calculations show weak dielectric interactions between neighbouring layers, and reveal major effects of molecular tilt on the quadratic and cubic susceptibilities. SDAN forms good films but SNPP and SMAP do not form stable films even in mixtures with stearic or behenic acid. All three materials give SHG as powders and as LB films. The film SHG coefficients are some 10% of those for crystals of the underivatized molecules.