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Amphiphilic disc-shaped penta-alkynes were studied with regard to their molecular organization in Langmuir-Blod- gett (LB) mono- and multilayers. It was found that each compound investigated forms edge-on arranged stable monolayers at the air-water interface. LB-multilayers derived from fivefold pentyl-substituted pentaynes are characterized by an edge-on ordering of the molecules within Y-type bilayers. One of these compounds, containing a hydoxy substituent as hydrophilic head group, is exemplified and two possible rectangular molecular assemblies perpendicular to the substrate, each with a columnar in-plane packing, will be discussed as a result of molecular modelling. Based on the experimental results, hexagonal layer packing in the LB-film of a disc-shaped penta-alkynyl carboxylic acid without lateral substituents proved to be possible, which, furthermore, could be confirmed by molecular mechanics simulation.
Changes of the molecular arrangenemt that can be induced by means of the LB technique in the multilayers of a disc-shaped multialkynyl amphiphile are monitored by means of small angle X-ray diffraction. Studies of the monolayers at the air-water interface reveal "edge-on" orientation of the discs. Specific effects of the counter- ions (Na+, Cd²+, Pb²+, and Ba²+) and sub-solution pH on the monolayer collapse pressure, transfer efficiency and molecular order in the multilayers are found. A correlation between the monolayer properties and the ability for formation of periodic discotic structures in the presence of divalent counterions is established. The discotic molecules retain their "edge-on" arrangement in the highly compressed transferred films with slight irregular interdigtation of the flexible wings and inclination to the substrate normal. The tilt and the inter- digitation are reduced when the discotic monolayers are deposited in alternating LB films with barium arachidate spacer layers.