The structural properties of Langmuir monolayers on aqueous substrates of a metal free phthalocyanine, 2,9,16,23-tetrakis(phenylthio)-29H,31H-phthalocyanine and an Aluminum centered phthalocyanine, Aluminum 2,9,16,23-tetrakis(phenylthio)-29H,31H-phthalocyanine chloride are reported here. Their structure is investigated under progressive lateral compression by grazing incidence diffuse X-ray scattering out of the specular plane to determine specular reflectivity-like information where the phase change of the molecules from "flat-lying" on the surface to "edge-standing" perpendicular to the surface was directly observed. Furthermore grazing incident X-ray diffraction is used to investigate the in-plane ordering of the system where it has been found that at high density states the systems can be considered as monolayers consisting of arrays of side-by-side cofacially aggregated cylindrical rodlike entities.