Anisotropic floating monolayers of 2-docosylamino-5-nitropyridine studied by second-harmonic generation

We demonstrate that a significant in-plane anisotropy is present in monolayers of 2-docosylamino-5-nitropyridine at an air-water interface. The floating monolayers were studied by in situ transmission second-harmonic generation under normal incidence and shown to have C-1h symmetry. The formation of such anisotropic monolayers was studied as a function of the surface pressure of the layers. The process was initiated by the formation of domains in which the molecules are preferentially aligned parallel rather than antiparallel to each other.