Monolayer and aggregate formation of a modified phthalocyanine on mica determined by a delicate balance of surface interactions

An ordered layer of a phthalocyanine modified with ether tails can be formed on muscovite mica if removed from solution and dried. This ordered layer forms on potassium terminated as well as on sodium terminated mica, but not on a hydronium terminated surface. The molecules lie flat on the surface, as shown by AFM and X-ray diffraction, giving a layer thickness of approximately 1 nm. In solution, however, no in-plane ordering exists. The material is attracted to the substrate surface but instead of ordering, it aggregates in a liquid-like mobile fashion. This is likely caused by the fact that the water present in solution has a stronger interaction with the potassium ions on the mica surface than with the ether tails of the phthalocyanine.