| Abstract
| - We report the preparation of two novel H2[pz(An;B4-n)] porphyrazines (pzs) which were designedto position themselves quite differently when attached to a surface: one to form a standard self-assembledmonolayer (SAM) roughly perpendicular to a surface, the other to lie horizontally along a surface. As theformer, we synthesized a pz, 1, where one pyrrole group is functionalized with two thioethers terminatedin mercaptides (SR, R = (CH2)3CONH(CH2)2S−), each protected as a disulfide, and −S−Me is attachedto the other pyrrole sites; the latter is a pz, 2, with dialkoxybenzo groups fused to two trans-pyrroles of thepz ring, and SR groups are attached to the other pair of pyrroles. Nanostructures of 1 and 2 were successfullypatterned on gold surfaces via dip-pen nanolithography, and the predicted molecular orientation of theresulting structures was confirmed by topographic AFM images. The two pzs exhibit similar reductionpotentials in solution. Both show large shifts in potential upon surface binding, with the magnitude of theshift depending on the proximity/orientation of the pz to the surface. The first reduction potential of the“vertically” aligned 1 shifts by ca. +430 mV when incorporated in a binary pz/hexanethiol SAM, while thatfor 2, which lies flat, shifts by ca. +800 mV; the potential thus shifts by ca. +370 mV upon taking a givenpz that stands atop a two-legged insulating “standoff” in a traditional SAM and “laying it down”. We suggestthese observed effects can be explained by image-charge energetics, and this is supported by a simplemodel.
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