Multicomponent monolayer architectures at the solid-liquid interface: towards controlled space-confined properties and reactivity of functional building blocks.

TLDR: Various recent results based on novel approaches for the self-assembly of multicomponent 2D nanostructures at the solid–liquid interface and their characterization on the submolecular scale by in situ STM studies are highlighted.

Abstract: Achieving full, nanometer-scale control over the positioning and organization of molecules into monolayers at surfaces represents a major challenge, with potential interest in the field of fabrication of multifunctional nanodevices. Bottom-up approaches successfully exploit the self-assembly of molecules to generate preprogrammed structures and patterns on such a scale. In this context, scanning tunneling microsACHTUNGTRENNUNGcopy (STM) is a tool of choice to characterize the molecular packing on solid surfaces and unravel dynamic processes such as organic monolayer formation, in particular at the solid–liquid interface. 10] While the formation of single-component self-assembled monolayers and their characterization by STM has been thoroughly reported for more than a decade, only recently have interesting studies on multicomponent two-dimensional (2D) architectures been proposed. In this contribution we highlight various recent results based on novel approaches for the self-assembly of multicomponent 2D nanostructures at the solid–liquid interface and their characterization on the submolecular scale by in situ STM studies. The controlled formation of ordered multicomponent nanostructures with a periodic structural motif is not trivial as most binary mixtures are prone to undergo phase segregation or to form randomly mixed domains. Ordered bior multicomponent nanostructures can be formed by a subtle interplay between intramolecular, intermolecular, and interfacial interactions, and in particular by combining principles of supramolecular chemistry and interfacial chemistry. An important role is played by the solvent, not only in view of its different interactions with the molecules, but also in light of the possibility to coadsorb at surfaces. For example, De Feyter and co-workers observed the coadsorption of solvent (1-octanol) molecules within a monoACHTUNGTRENNUNGlayer of an isophtalic acid derivative (the “studied” molecule) on highly oriented pyrolytic graphite (HOPG). They showed the exchange dynamics between 1-octanol solvent molecules and the isophtalic acid proceeds at the monolayer domain boundaries, leading to a rearrangement of a large part of the monolayer within a domain in a cooperative manner (see details in Ref. [14]). Such a result is in line with the findings of Padowitz and co-workers, who employed thioether molecules coadsorbed within an alkane monolayer as tracers to follow the rate of exchange (adsorption–desorption processes) and the specific molecular processes at grain boundaries. Recently, a few STM studies reported the construction of mixed donor–acceptor monolayers by applying a solution containing the two molecular systems to crystalline solid surfaces such as HOPG. In a seminal work, Rabe and coworkers studied the monolayer formation of a donor–acceptor model system, namely isophtalic acid and pyrazine derivatives, forming hydrogen-bonded 2D networks on graphite, and compared the structure with a 3D crystalline [*] Dr. P. Samor Istituto per la Sintesi Organica e la Fotoreattivit Consiglio Nazionale delle Ricerche (C.N.R.) via Gobetti 101, 40129 Bologna (Italy) Fax: (+39)051-6399844 E-mail: samori@isof.cnr.it