Four caltrop-shaped molecules that might be useful as surface-bound electric field-driven molecular motors have been synthesized. The caltrops are comprised of a pair of electron donor-acceptor arms and a tripod base. The molecular arms are based on a carbazole or oligo(phenylene ethynylene) core with a strong net dipole. The tripod base uses a silicon atom as its core. The legs of the tripod bear sulfur-tipped bonding units, as acetyl-protected benzylic thiols, for bonding to a gold surface. The geometry of the tripod base allows the caltrop to project upward from a metallic surface after self-assembly. Ellipsometric studies show that self-assembled monolayers of the caltrops are formed on Au surfaces with molecular thicknesses consistent with the desired upright-shaft arrangement. As a result, the zwitterionic molecular arms might be controllable when electric fields are applied around the caltrops, thereby constituting field-driven motors.

Aryl molecules were covalently grafted to hydride-passivated Si(100) surfaces (Si-H) by the in situ conversion of aryldiethyltriazenes into aryldiazonium salts using 2% HF, followed by spontaneous surface grafting of the aryl species to the silicon surface. Major advances are as follows: first, reactive diazonium species need not be isolated, and second, by using aqueous HF as the triazene-to-diazonium conversion promoter, the entire process can be carried out in air since any Si-oxide is continuously converted to the Si-H species. Molecular layers from a monolayer to 200 nm thick could be formed depending on the reaction conditions used. In one case where the molecule bore an R-triazene and ω-aniline (6), after grafting of the molecular layer onto Si-H via the triazene, the remaining aniline moiety was converted into a diazonium salt in situ with NOBF 4 and then permitted to react with functionalized single-walled carbon nanotubes (SWNTs), thereby covalently attaching nanotubes to the silicon surface using the aryl molecular layer as a tethering unit.

Organic triazene compounds are stable precursors to diazonium salts for functionalizing single-wall carbon nanotubes (SWNTs) in aqueous media. This method is particularly useful when a target molecule has functionality that will not tolerate diazotization conditions. We illustrate this by detailing the synthesis of a biotin-containing triazene followed by reaction with SWNTs.

[structure: see text] A series of building blocks for the synthesis of oligo(phenylene vinylene)s (OPVs) and hybrid oligomers were prepared, and alternating Heck coupling and Horner-Wadswoth-Emmons (HWE) reactions were used to couple the building blocks. Model studies were carried out to optimize the reaction strategies. The products were made to bear aryl diazonium functionalities that allow them to be used as surface grafting moieties in hybrid silicon/molecule assemblies. A library of OPV and hybrid oligomer tetramers was synthesized using fluorous mixture synthesis (FMS). The fluorous tags, which are secondary amines bearing different numbers of fluorine atoms, were synthesized and used as phase tags in mixture synthesis. The tags and substrates were anchored together by triazene linkages. The mixture synthesis was monitored by analytical HPLC on a fluorous column, and isolation of final OPV and hybrid oligomer tetramers was achieved by preparative HPLC. At the end of the FMS, after demixing, the tagged products were detagged by cleaving the triazene linkage and generating a series of aryl diazonium compounds. The fluorous tags could be recovered and reused. The NMR spectra of the 1-aryl-3,3-dialkyltriazenes are discussed.