Orientation of cavitands at air/water and air/solid interfaces studied by second harmonic generation

Surface second harmonic generation (SHG) was used to probe orientation of cavitand molecules deposited on water as Langmuir films and on fused silica substrates either bare or functionalized with a surfactant. Measurements performed during compression of the Langmuir films reveal that while the surface density may vary, molecules always appear more or less oriented with their long axis perpendicular to the water surface. Phase measurements indicate that the vase-like heads of the molecules cover the water for Langmuir films, but face the air for monolayers spread on surfactant-coated substrates.