Segregation of lipid in Ir-dye/DMPA mixed monolayers as strategy to fabricate 2D supramolecular nanostructures at the air–water interface

Abstract

A novel pseudospherical fluorinated iridium(III) derivative, Ir-dye/PF₆, [Ir(F₂-ppy)₂(bpy)]PF₆ (F₂-ppy = 2-(2,4-difluoro)phenylpyridine, bpy = 2,2′-bipyridine), has been organized by using a lipid matrix, DMPA (dimyristoyl-phosphatidic acid), in several molar ratios at the air–water interface. The molecular organization of both components and the degree of miscibility in the different mixed films have been inferred by surface techniques such as π–A isotherms, ellipsometry, reflection spectroscopy, Brewster angle microscopy (BAM), and IR spectroscopy for the LB films, additionally the results have been discussed according to the additivity rule. The equimolecular Ir-dye/DMPA mixture leads to a totally miscible, stable and homogeneous monolayer. Any surplus of DMPA with respect to the 1 : 1 ratio segregates under compression while forming domains. By varying the surface concentration of DMPA in the mixture we demonstrate that the Ir-dye can be confined to certain regions of the 2D patterned structure formed at the air–water interface. The fraction of surface containing the photofunctional complex can be controlled by both the fraction of lipid in the initial co-spread mixture and the surface pressure applied to the film. Finally, the additivity rule has been applied, for the first time to our knowledge, to simulate the ellipsotherms of mixed monolayers.