Lingyun Wei

Solution STM images of porphyrins on HOPG reveal that subtle differences in molecular structure dramatically alter packing geometry

Solution STM images are reported for free-base octaethylporphyrin (H2OEP) and the Cu(II) and Zn(II) chelates (CuOEP and ZnOEP) on HOPG in 1,2-dichlorobenzene solution under ambient conditions. H2OEP and CuOEP each form a quasi-square lattice, whereas ZnOEP forms a quasi-hexagonal lattice on the surface. The binary mixture of any two of the porphyrins forms a well-ordered two-layer structure on the HOPG surface, with one species occupying the bridge sites of the array of the other species. All of the mixed adlayers exhibit a quasi-hexagonal lattice with a higher packing density than the single-component adlayers. Collectively, these observations indicate that the structure of the adlayers is controlled by a complex interplay of substrate-molecule and molecule-molecule interactions.

Multistate molecular information storage using S-acetylthio-derivatized dyads of triple-decker sandwich coordination compounds

An approach toward molecular information storage employs redox-active molecules attached to an electroactive surface. The chief advantages of such molecular capacitors include higher charge density and more versatile synthetic design than is afforded by typical semiconductor charge-storage materials. An architecture containing two triple-decker sandwich coordination complexes and an S-acetylthiomethyl-terminated tether has been designed for multibit storage. Each triple decker is composed of two phthalocyanines, one porphyrin, and two europium atoms. The oxidation potentials of each triple decker are tuned through the use of different substituents on the phthalocyanines (t-butyl, methyl, H) and porphyrins (pentyl, p-tolyl). Interleaving of the four cationic oxidation states of each triple decker potentially affords eight distinct oxidation states. Two dyads were examined in solution and in self-assembled monolayers (SAMs) on a Au surface. One dyad exhibited eight distinct states in solution and in the SAM, thus constituting a molecular octal counter. The potentials ranged from −0.1-+1.3 V in solution and +0.1-+1.6 V in the SAM. Taken together, this approach provides a viable means of achieving multibit information storage at relatively low potential.