Molecular Order within Langmuir-Blodgett Films of Two Amphiphilic Octasubstituted Phthalocyanines Studied by Atomic Force Microscopy

Y-type Langmuir-Blodgett films of the octasubstituted amphiphilic phthalocyanines 1 and 2 deposited onto hydrophobic glass have been investigated by atomic force microscopy (AFM). The technique has been used to measure the thicknesses of one, two, and three bilayer films, and the results show that each bilayer is of the same thickness. This characteristic thickness is the same as the repeat spacing measured using low-angle X-ray diffraction methods on thicker samples, and thus we demonstrate that the order of the molecules in the monolayers after several cycles of deposition remains constant. We have detected considerable differences with respect to the consistency of the films of 1 and 2 and their resistance to the pressure exerted by the AFM tip during the scanning process required to obtain the images. Films of 1 are more robust and we have observed the columnar arrangement of the molecules at the surfaces of one, two, and three bilayers. However, under the same imaging conditions it was not possible to observe molecular order before perturbing the surface of the films formed by 2. The lateral extent of the ordered regions at the surfaces of the films of 1 covers areas of at least 10μm² . There is very clear evidence that there is a predominant alignment. Inspection of 82 images taken of different regions of the film indicates that ca. 83% show columns whose axes are aligned to within ±30° of the dipping direction.