Ellipsometry, Brewster angle microscopy, and thermodynamic studies of monomolecular films of cryptophanes at the air-water interface

The cryptophanes are spherical or ovoid-shaped hollow molecules of nanometric scale capable of forming inclusion complexes with neutral or charged organic species. Certain cryptophanes such as 1-4 form thin films when they are compressed at the air-water interface. These films have been studied by surface pressure measurements, ellipsometry and Brewster angle microscopy. The medium-sized cryptophane 2 and the large cryptophanes 3 and 4 exhibit a reversible monomolecular layer domain limited to a surface pressure of 8-10 mN m(-1) and generated after a plateau corresponding to a gas-liquid transition. In contrast, molecular films of the small cryptophane 1 are not stable and irreversibly collapse to 3D-aggregates when they are compressed.