A Compact All-Carbon Tripodal Tether Affords High Coverage of Porphyrins on Silicon Surfaces

Redox-active molecules designed to give high charge density on electroactive surfaces are essential for applications in molecular information storage. To achieve a small molecular footprint and thereby high surface charge density, a compound consisting of a triallyl tripod attached via a p-phenylene unit to a porphyrin (1) has been synthesized. The zinc chelate of 1 (Zn-1) was attached to Si(100). Electrochemical measurements indicate that the molecular footprint (75 A) in the monolayer is only ∼50% larger than the minimum achievable, indicating high surface coverage. IR spectroscopy indicates that the bands due to the ν(CC) (1638 cm-1) and γ(CH) (915 cm-1) vibrations present in the solid sample (KBr pellet) are absent from the spectra of the monolayers of Zn-1, consistent with saturation of the double bond in each of the three legs of the tripod upon the hydrosilylation process accompanying attachment. Comparison of the relative intensities of the in-plane (998 cm-1) versus out-of-plane (797 cm-1) porphy...