We demonstrate that molecular gradients on organic monolayers are formed by preferential binding of ruthenium complexes from solutions also containing an equimolar amount of isostructural osmium complexes. The monolayer consists of a nanometer-thick assembly of 1,3,5-tris(4-pyridylethenyl)benzene (TPEB) covalently attached to a silicon- or metal-oxide surface. The molecular gradient of ruthenium and osmium complexes is orthogonal to the surface plane. This gradient propagates throughout the molecular assembly with thicknesses over 30 nanometers. Using other monolayers consisting of closely related organic molecules or metal complexes results in the formation of molecular assemblies having an equimolar distribution of ruthenium and osmium complexes. Spectroscopic and computational studies revealed that the geometry of the complexes and the electronic properties of their ligands are nearly identical. The isostructural osmium and ruthenium complexes are packed differently in crysrals grown from solution. The different packing behavior, combined with the organic monolayer, significantly contributes to the observed differences in chemical composition on the surface.
ASJC Scopus subject areas
- Colloid and Surface Chemistry