Preparation and characterization of non-aromatic ether self-assemblies on a HOPG surface

Abstract

On-surface self-assemblies of aromatic organic molecules have been widely investigated, but the characterization of analogous self-assemblies consisting of fully sp3-hybridized molecules remains challenging. The possible on-surface orientations of alkyl molecules not exclusively comprised of long alkyl chains are difficult to distinguish because of their inherently low symmetry and non-planar nature. Here, we present a detailed study of diamondoid ethers, structurally rigid and fully saturated molecules, which form uniform 2D monolayers on a highly oriented pyrolytic graphite (HOPG) surface. Using scanning tunneling microscopy (STM), various computational tools, and X-ray structural analysis, we identified the most favorable on-surface orientations of these rigid ethers and accounted for the forces driving the self-organization process. The influence of the oxygen atom and London dispersion interactions were found to be responsible for the formation of the observed highly ordered 2D ether assemblies. Our findings provide insight into the on-surface properties and behavior of non-aromatic organic compounds and broaden our understanding of the phenomena characteristic of monolayers consisting of non-planar molecules.

Diamondoid ether clusters in helium nanodroplets

“…As part of our investigation of covalent diamondoid assemblies consisting of two or more diamondoid cages connected with a heteroatom linker, we recently prepared a series of diamondoid ether derivatives. 29,33 We explored on-surface assemblies and capability of monolayer formation in a 2D environment and demonstrated the importance of LD interactions acting in such supramolecular systems. Some ether derivatives 34 were previously studied at HND conditions but as they were not as bulky as diamondoid ethers, they could not engage in numerous intermolecular C–H bond contacts that would produce a strong additive LD effect.…”

Sustainable Synthesis of Diamondoid Ethers by High-Temperature Ball Milling

“…This reduction in the reaction efficiency when 1a is used instead of 4a may be due to a difference in the carbocation stability since the diamantane framework produces a more stable carbocation than the adamantane cage. 70,73 To compare ball milling with conventional synthesis (neat or solution-based) of diamondoid ethers, we also performed the synthesis of ethers 1, 2, and 4 following our previously reported procedure, 43 as well as the synthesis of ethers 3, 5, and 6 that were described for the first time in this work (note that we also reported characterization of ether 3 in the mentioned previous work where we obtained it as a byproduct). Some smaller diamondoid derivatives typically tend to sublimate even at slightly elevated temperatures which then prevents their interaction with other components of the However, condensing 4a with diamantan-4-ol yielded 16% of ether 6 after heating in DMF for 24 h at approximately 153 °C.…”

“…All four crystal packings are dominated by weak dispersion interactions between the cages, similar to diamondoid ethers 1, 2, and 4 reported earlier (Figure S20). 43 The main objective of this work was to develop a sustainable synthetic methodology for preparing tertiary diamondoid ethers which could serve as stable and rigid blocks in nanomaterial design. From the thermal input point of view, the mechanochemical synthesis of diamondoid ethers requires higher temperatures compared to conventional synthesis.…”

“…68 Corresponding methanesulfonates were prepared according to our recently published procedure. 43 Milling reactions were performed with InSolido Technologies IST 636 vibratory ball mill using 10 mL Teflon jars placed inside a larger aluminum container. Temperature-controlled ball milling was achieved with an external 75 W band heater and a PID controller according to the previously published procedure.…”

“…We recently reported on the synthesis and spontaneous self-assembly of ethers 1, 2, and 4 on the highly oriented pyrolytic graphite (HOPG) surface, shedding light on the importance of London dispersion interactions for on-surface supramolecular systems of this type. 43 However, synthesizing cage ethers that consist of two directly connected diamondoid subunits remains challenging. Diamondoid cages are quite bulky, and larger diamondoid composites often suffer from limited solubility in common organic solvents and are challenging to purify by alternative methods like sublimation.…”