Imaging on-surface hierarchical assembly of chiral supramolecular networks

Abstract

The bottom-up assembly of chiral structures usually relies on a cascade of molecular recognition interactions. A thorough description of these complex stereochemical mechanisms requires the capability of imaging multilevel coordination in real-time. Here we report the first direct observation of hierarchical expression of supramolecular chirality at work, for 10,10 0 -dibromo-9,9 0 -bianthryl (DBBA) on Cu(111). Molecular recognition first steers the growth of chiral organometallic chains and then leads to the formation of enantiopure islands. The structure of the networks was determined by noncontact atomic force microscopy (nc-AFM), while high-speed scanning tunnelling microscopy (STM) revealed details of the assembly mechanisms at the ms time-scale. The direct observation of the chirality transfer pathways allowed us to evaluate the enantioselectivity of the interchain coupling.

Synthesis of armchair graphene nanoribbons from the 10,10′-dibromo-9,9′-bianthracene molecules on Ag(111): the role of organometallic intermediates

“…3(a) and (b) . In agreement with other STM studies 15 , 34 – 37 , 58 , 61 ,the bright protrusions, which appear in the STM image on both sides of the chain axis, are associated with the upward-pointing lobes of the anthracene subunits, constituting the DBBA molecule. On Ag(111) these bright protrusions form an “armchair” pattern (highlighted by the white line shown in the inset in Fig.…”

“…Figure 3(a) and (b) show STM images of DBBA on Ag(111) after annealing to 120 °C and, for comparison, “molecular chains” formed by DBBA on Cu(111) at RT, respectively. According to our previous STM experiments 34 , 58 , recently supported by extensive studies by means of nc-AFM and high-speed STM 61 , DBBA molecules form OM chains on Cu(111) at RT. These chains are composed of fully debrominated DBBA molecules linked via the Cu atom.…”

“…These chains are composed of fully debrominated DBBA molecules linked via the Cu atom. Individual chains tend to assemble into OM islands 61 . Similar regions of “chain-like” structures are clearly visible on Ag(111).…”

“…3(c) and (d) together with the characteristic distances. According to the model for the OM chain on Cu(111) 34 , 58 , 61 , each of the DBBA radicals in the chain is bridged between two metal adatoms and the anthracene lobes are tilted in an alternating fashion with respect to each other. Similar structures are suggested for the OM chains on Ag(111), but in order to produce the “armchair” pattern observed in the STM images, the two anthracene lobes located next to each other on the same side of the chain’s axis should be tilted in the same direction.…”

“…These intermediate structures are composed of molecular units linked through the C–M–C bonds 41 – 47 , 50 – 53 , 60 . In particular, OM chains were observed on Cu(111) surface after deposition of DBBA molecules at room temperature (RT) followed by a complete debromination of DBBA 34 , 58 , 61 . Nevertheless, to date the role of OM intermediates in the formation of 7-AGNRs on Ag(111) from DBBA precursors has not been studied explicitly.…”