Preprogrammed 2D folding of conformationally flexible oligoamides: foldamers with multiple turn elements.

Controlling the molecular conformation of oligomers on surfaces through noncovalent interactions symbolizes an important approach in the bottom-up patterning of surfaces with nanoscale precision. Here we report on the design, synthesis, and scanning tunneling microscopy (STM) investigation of linear oligoamides adsorbed at the liquid-solid interface. A new class of extended foldamers comprising as many as four turn elements based on a structural design "rule" adapted from a mimic foldamer was successfully synthesized. The self-assembly of these progressively complex oligomeric structures was scrutinized at the liquid-solid interface by employing STM. Submolecularly resolved STM images of foldamers reveal characteristic in-plane folding and self-assembly behavior of these conformationally flexible molecules. The complexity of the supramolecular architectures increases with increasing number of turn elements. The dissimilarity in the adsorption behavior of different foldamers is discussed qualitatively in light of enthalpic and entropic factors. The modular construction of these oligomeric foldamers with integrated functionalities provides a simple, efficient, and versatile approach to surface patterning with molecular precision.

Controlling the position of functional groups at the liquid/solid interface: impact of molecular symmetry and chirality.

With the aim of controlling the position of functional groups in a substrate-supported monolayer, a new family of functionalized linear alkyl chains was designed and synthesized, aided by molecular mechanics and dynamics simulations of its two-dimensional self-assembly on graphite. The self-assembly of these amino functionalized diamides at the liquid/solid interface was investigated with scanning tunneling microscopy. Intermolecular hydrogen-bonding interactions involving amides, combined with the effect of molecular symmetry and chirality, were found to guide the self-assembly. Control of the relative position and orientation of the amine groups was achieved, in the case of enantiopure compounds. Interestingly, racemates led to both racemic conglomerate and solid solution formation, with a concomitant loss of positional and orientational control of the amino groups as a result.

Molecular patterning at a liquid/solid interface: the foldamer approach.

Molecular patterning has received a lot of attention in the past decade; however, the functionalization of these surface-confined 2D patterns on the nanoscale level remains a challenge. Assembling 2D patterns from oligomeric foldamers turns out to be an interesting approach to accomplishing the controlled positioning of functional elements. We designed a family of peptidomimetic foldamers bearing a 2D turn element folding at the liquid/solid interface. The turning element was developed while studying derivatives with one turning unit. Furthermore, folding was found to be induced by the confinement of the surface. This achievement paves the way for the design of foldamers with multiple turns, providing a higher versatility in the functionalization of nanopatterns.