Substrate-mediated face-on self-assembly of non-amphiphilic phthalocyaninates on solids

Abstract

Herein, we report a novel approach to fabricating condense face-on arrangements of aromatic molecules on hydrophilic solid surfaces. A substrate-mediated condensation method was used to control face-on/edge-on molecular orientation in the monolayers of non-amphiphilic crown-substituted double-decker cerium phthalocyanine on solids. Because of the strong tendency to aromatic stacking, the molecules undergo spontaneous face-on to edge-on switching of the orientation during their transferring onto solids via conventional LB deposition. The edge-on structure of LB-deposited monolayers was confirmed by atomic force microscopy and X-ray wide angle scattering methods. The introduction of potassium ions into the subphase cannot stabilize the face-on structure through coordination with crown groups at the air/water interface; instead, the presence of metal ions promotes the formation of edge-on sandwich-type intermolecular complexes. To overcome these limitations, we applied substrate-mediated condensation of molecules on a surface of mica and potassium-doped quartz glass for fabricating tightly packed face-on assemblies of complexes. The face-on arrangement of phthalocyaninates in such monolayers was confirmed by the AFM and UV–vis spectroscopy together with spectroscopic ellipsometry. Our strategy allows therefore the fabrication of ultrathin coatings with controlled morphology and optical properties from phthalocyaninates and related discotic compounds.