MONOMOLECULAR FILMS OF HYPERPOLARIZABLE P OLYENIC DERIVATIVES AT THE AIR-WATER-INTERFACE

A new family of amphiphilic polyenes of variable length bearing a pola r aldehyde or acid terminus have been prepared. At the air-water inter face, the surface pressure vs. molecular area (pi-A) isotherms for the acid derivatives, recorded as a function of the temperature tin the r ange 5-25 degrees C) and compression, have been found to be strongly c hain-length and temperature-dependent. At low temperature and at low c ompression, 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 p olyenic chain of acids bearing four double bonds is tilted with respec t to the aqueous subphase. At higher compression, the molecular organi zation at the air-water interface changes, and the conjugated chain se ems to become even more perpendicular to the aqueous surface. A simila r effect was observed only for the aldehyde derivative bearing four do uble bonds. (C) Academie des Sciences/Elsevier, Paris.