Langmuir Films of Anthracene Derivatives on Liquid Mercury II: Asymmetric Molecules

The structure and phase sequence of liquid-mercury-supported Langmuir films (LFs) of anthrone and anthralin were studied by surface tensiometry and surface-specific synchrotron X-ray diffraction. In the low-coverage phase the molecules are both side-lying, rather than the flat-lying orientation found for anthracene and anthraquinone. In the high-coverage phase, the molecules are either standing up (anthrone) or remain side-lying (anthralin) on the mercury surface. In contrast with the symmetric anthracene and anthraquinone, both high-coverage phases exhibit long-range in-plane order. The order is different for the two compounds. The structural details, the role of molecular symmetry, the oxygen side groups, and the asymmetry-induced dipole moments are discussed.