Meso-Substituted BODIPYs as supramolecular building blocks of ordered Langmuir–Blodgett films: structural and morphological characterization

Abstract

Two crystalline meso-substituted BODIPYs were investigated as supramolecular building blocks of Langmuir–Blodgett (LB) thin films. These sorts of thin films are formed by the transfer of a Langmuir monolayer film of organized amphiphilic molecules onto a solid substrate. In the present contribution, we exploited the capacity of the featured BODIPYs to produce ordered supramolecular self-assemblies through hydrogen-bonding and π-stacking to pre-organize and to control their assembly as LB thin films. Electronic absorption and fluorescence emission of the meso-substituted BODIPYs in solution, LB films, and in solid state were studied. The morphology and structure of the LB films were examined by scanning electron microscopy and atomic force microscopy. The structural differences between both BODIPYs have no marked influence on the absorption and fluorescence emission properties in solution. In contrast, absorption properties in solid state (solid samples and LB thin films) depend on the structural nature of the dyes with the appearance of red-shifted bands, which could be an indicator of the presence of aggregates. The supramolecular information contained in the BODIPYs was reflected on the surface characteristics of the featured LB thin films. Both produced homogeneous and uniform films with the presence of some microcrystals, as the number of transferred monolayers increased. These results broaden the capacity of the Langmuir–Blodgett technique to produce ordered and self-assembled thin films of functional small organic molecules (such as BODIPYs) as components of different optoelectronic devices.