Patterned monolayers of five-coordinate metalloporphyrins on surfaces have potential application as templates for spatially organizing axially attached functional moieties, but their surface chemistry has been much less studied than that of their four-coordinate analogues. One important difference between the molecular structures of four and five-coordinate metalloporphyrins that could affect monolayer formation and structure is that the latter exhibit pyramidal behavior at the metal center. To probe this question, a series of gallium(III) octaethylporphyrins [Ga(OEP)X, X=Cl, Br, I, OTf, CCPh] has been synthesized. The dependence of the extent of pyramidalization on the nature of the ligand has been studied using density functional theory calculations, and found to lie in the order X = CCPh > halide > OTf. Scanning tunneling microscopy (STM) has been used to observe the propensity of the molecules to self-assemble into two-dimensional arrays on highly oriented pyrolytic graphite (HOPG) at both the solid/air and solid/liquid interfaces. All compounds were observed to form well-ordered arrays at both interfaces with similar pseudo-hexagonal structures and prominent axial-ligand projections, the metrical details of which will be described. Attempts to use these arrays for organizing carbon nanostructures and other functional units will be discussed.

Structures of self-assembled gallium octaethylporphyrin monolayers on HOPG

246th National Meeting (2013)

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