| Abstract
| - The organization of an amphiphilic azobenzene derivative, 4-octyl-4‘-(5-carboxy- pentamethyleneoxy)azobenzene (8A5), in monolayers at the air−water interface is strongly controlled by association phenomenadue to intermolecular interactions of the azobenzene moiety. The monolayer behavior has been investigatedby measuring surface pressure−area and surface potential-area isotherms as well as by Brewster anglemicroscopy (BAM) and reflection spectroscopy. In particular, dimers are formed that reorient from a flat orslightly tilted orientation to an orientation nearly normal to the water surface and forming H-aggregates uponmonolayer compression. The BAM images clearly show domains with long range tilt orientational order.The observed shifts of the reflection maximum as well as the intensities of the band are accounted for by amodel of molecular association and reorientation. The intermolecular interactions are strongly modified byvariation of the subphase pH controlling the dissociation of the hydrophilic carboxyl group. On a subphasepH = 9.4, flat lying monomers are observed at low surface pressure and dimers form upon compression,however, no domains are detected by BAM in this case.
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