The unique optoclectric feature of structurally simple surfactants was presented. Phosphonium salts as a novel class of thermotropic liquid crystals were used to explore the spatial arrangement of ions in multilayer self-assemblies based on the surfactant complexes. Through the evaluation of second-order nonlinear optical property of the phosphonium self-assemblies, it was revealed that the phosphonium thin film assemblies can be regarded as a polar thin film consisting of two-dimensional ionic layers with noncentrosymmetric atomic arrangement. Such spontaneous formation of the in-plane polar structure was assumed to originate from the variety of bonding manner (i.e., the characteristic electronic structure) of phosphorus atom. Furthermore, it was also found that the macroscopic polar order is enhanced by application of an external electric field.