Monomolecular films of hyperpolarizable polyenic derivatives at the air-water interface

A new family of amphiphilic polyenes of variable length bearing a polar aldehyde or acid terminus have been prepared. At the air-water interface, the surface pressure vs. molecular area (pi-A) isotherms for the acid derivatives, recorded as a function of the temperature tin the range 5-25 degrees C) and compression, have been found to be strongly chain-length and temperature-dependent. At low temperature and at low compression, the isotherms for compounds bearing less than three double bonds show the existence of a particular molecular organization where the polyenic chain is nearly parallel to the interface, whereas the polyenic chain of acids bearing four double bonds is tilted with respect to the aqueous subphase. At higher compression, the molecular organization at the air-water interface changes, and the conjugated chain seems to become even more perpendicular to the aqueous surface. A similar effect was observed only for the aldehyde derivative bearing four double bonds. (C) Academie des Sciences/Elsevier, Paris.