Synthesis of "porphyrin-linker-thiol" molecules with diverse linkers for studies of molecular-based information storage

The attachment of redox-active molecules such as porphyrins to an electroac tive surface provides an attractive approach for electrically addressable m olecular-based information storage. Porphyrins are readily attached to a go ld surface;via thiol linkers. The rate of electron transfer between the ele ctroactive surface and the porphyrin is one of the key factors that dictate s suitability for molecular-based memory storage, This rate depends on the type and length of the linker connecting the thiol unit to the porphyrin. W e have developed different routes for the preparation of thiol-derivatized porphyrins with eight different linkers. Two sets of linkers explore the ef fects of linker length and conjugation with one set comprising phenylethyne units and one set comprising alkyl units. One electron-deficient linker ha s four fluorine atoms attached directly to a thiophenyl unit. To facilitate the synthesis of the porphyrins, convenient routes have been developed to a wide range of aldehydes possessing a protected S-acetylthio group. An eff icient synthesis of 1-(S-acetylthio)-4-iodobenzene also has been developed. A set of porphyrins, each bearing one S-acetyl-derivatized linker at one m eso position and mesityl moieties at the three remaining meso positions, ha s been synthesized. Altogether seven new aldehydes, eight free base porphyr ins and eight zinc porphyrins have been prepared. The zinc porphyrins beari ng the different linkers all form self-assembled monolayers (SAMs) on gold via in situ cleavage of the S-acetyl protecting group. The SAM of each porp hyrin is electrochemically robust and exhibits two reversible oxidation wav es.