A proposed strategy to design molecules predisposed to in-plane orientation in Langmuir-Blodgett films

Assuming that in-plane orientation in Langmuir-Blodgett (LB) films can be obtained from compounds having an anisotropic shape within the plane of the Langmuir film, this particular alignment is expected for calamitic compounds with a side-on polar head or with a hydrophilic function linked to the end of a tilted rodlike group. According to such hypothesis, various calamitic molecules were synthesized and showed indeed in-plane orientation. Clearly, these molecules can be described as two-dimensional calamitic compounds forming a new family of molecules with a different orientation than that of the classical disklike derivatives. These experiments demonstrate that analysis of the molecular shape anisotropy enables one to predict in-plane orientation in LB films and to control the main orientation of the compounds within the plane of the multilayers.