Synergism in multicomponent self-propagating molecular assemblies

Multicomponent self-propagating molecular assemblies (SPMAs) have been generated from an organic chromo-phore, a redox-active polypyridyl complex, and PdCl₂. The structure of the multicomponent SPMA is not a linear combination of two assemblies generated with a single molecular constituent. Surface-confined assemblies formed from only the organic chromophore and PdCl₂ are known to follow linear growth, whereas the combination of polypyridyl complexes and PdCl₂ results in exponential growth. The present study demonstrates that an iterative deposition of both molecular building blocks with PdCl₂ results in an exponentially growing assembly. The nature of the assembly mechanism is dictated by the polypyridyl complex and overrides the linear growth process of the organic component. Relatively smooth, multicomponent SPMAs have been obtained with a thickness of ∼20 nm on silicon, glass, and indium-tin oxide (ITO) coated glass. Detailed information of the structure and of the surface-assembly chemistry were obtained using transmission optical (UV/Vis) spectroscopy, ellipsometry, atomic force microscopy (AFM), synchrotron X-ray reflectivity (XRR), and electrochemistry.