Columnar aggregates of crown ether substituted phthalocyanines perpendicularly anchored on a surface via a selective binding site

Abstract

The purpose of this work is to anchor perpendicularly to a surface the aggregates obtained by complexation of crown-ether substituted lutetium bisphthalocyanine, [(15 C 5)4 Pc ]2 Lu , in the presence of KSCN . In order to orientate these aggregates perpendicularly to the substrate, silica surface is grafted with an unsymmetrical lutetium bisphthalocyanine substituted, on one macrocycle by four crown ether subunits, and on the other one with four lateral chains terminated by a carboxylic group. The latter compound is used as a selective binding site to anchor pillar-like aggregates formed in solution. The aggregates were characterized in a mixture of chloroformic based solution by UV-visible and light scattering experiments and gave evidence for the formation of rod-like particles in the presence of excess of KSCN . Then, the aggregates were deposited on surfaces and their morphologies were studied by atomic force microscopy (AFM). In the case of substrates having non-specific binding sites such as silica and functionalized silica with 3-trimethoxy-propylaminosilane, rods were observed lying parallel on the surface. In the case of the substrate grafted with the selective binding site, single columns of these supramolecular assemblies perpendicular to the surface have been observed by AFM.