Formation of one-dimensional (1D) ASA chains at 300 Okay
Thermally deposited 2Br-DEB molecules spontaneously assembled on Ag(111) at about 150 Okay (Fig. 2a). A person 2Br-DEB molecule seems as a four-lobed motif within the STM picture (marked in crimson in Fig. 2b) the place two brighter lobes are attributed to be the hooked up Br atoms and the opposite two darker ones, terminal alkynyl teams, as proven by the superimposed molecular constructions in Fig. 2b. Every meeting area is dominantly fashioned by molecules of the identical adsorption chirality, whereas these of reverse adsorption chirality (marked in blue in Fig. 2b) often seem as chiral defects.
2Br-DEB monomers on Ag(111). a Massive space (Scanning circumstances: Bias = 200 mV, suggestions present = 170 pA, imaging temperature = 77 Okay) and b high-resolution (−400 mV, 70pA, 77 Okay) STM photographs of the molecular meeting fashioned by 2Br-DEB monomers on Ag(111). Molecules of reverse adsorption chirality are marked in crimson and blue in b, respectively. Scale bars: a 10 nm, b 1 nm
The pattern was subsequently annealed at 300 Okay for eight h so as to set up the response equilibrium. In consequence, the Ag(111) substrate was coated by stripe-shaped molecular islands (Fig. 3a) which lengthen alongside equal < 1(bar 1)zero > instructions (white dashed arrows). Excessive-resolution STM picture (Fig. 3b) identifies alternately organized elliptic (blue dashed circles) and round (grey dots) protrusions alongside the extending route of the stripe-shaped island (white dashed arrow). Sequential tip manipulations of the protrusions in a stripe-shaped island alongside the instructions marked by the yellow arrows in Fig. 3d, e resulted within the bending of the molecular wires as a complete (Fig. 3d–f), indicating that the stripe-shaped islands are fashioned by parallelly mendacity molecular chains which lengthen alongside the < 1(bar 1)zero > instructions of Ag(111). Due to this fact, the protrusions within the chains are held collectively by robust chemical bonds and adjoining chains, by comparatively weaker forces.
1D ASA chains fashioned at 300 Okay. a STM picture of stripe-shaped islands fashioned on Ag(111) after annealing of the pattern at 300 Okay for eight h (200 mV, 170pA, 77 Okay). Inset: STM picture of the periphery of a stripe-shaped island (60 mV, 180 pA, 77 Okay). Some indifferent Br atoms are representatively marked by the white arrows. b Excessive-resolution STM picture of the ASA chains with their structural fashions superimposed (60 mV, 180 pA, 77 Okay). Molecules with two, one and 0 Br atoms hooked up are correspondingly highlighted with the crimson, blue and cyan dashed circles. Ag atoms are marked by the grey dots. The interactions between adjoining chains are marked by the yellow dashed traces. The inter-molecular distance of the ASA chain is marked by the blue arrow. The chain-segment fashioned by fully debrominated molecules is highlighted by the white dashed rectangle. The extending instructions of the islands are marked by the white dashed arrows in a and b. The equal < 1(bar 1)zero > instructions of Ag(111) are marked by white arrows in a and b. c Optimized molecular fashions of the ASA chains (prime) and correspondingly simulated STM picture at 100 mV (backside). Coloration code: grey: C, white (small): H, white (massive): substrate Ag, blue: adatom Ag. d-f Sequential lateral tip manipulations of the ASA chains alongside the instructions marked by yellow arrows (200 mV, 100pA, four.2 Okay). Scale bars: a 20 nm, Inset: 1 nm, b, c 1 nm, d–f 2 nm
Based mostly on the experimental details, a structural mannequin for the stripe-shaped islands is proposed and superimposed in Fig. 3b. On this mannequin, the parallelly mendacity chains are the ASA merchandise generated by the metalation response between the terminal alkynyl teams in 2Br-DEB and cell Ag adatoms. Theoretical calculations (see Supplementary Strategies for particulars) yield a bonding vitality of −2.52 eV for the C–Ag bond within the chain, which is robust sufficient to outlive the tip manipulations (Fig. 3d–f)29,32. The elliptic protrusions are as a result of molecular moieties and the round ones, Ag atoms. Three varieties of elliptic protrusions in several sizes might be distinguishable, as marked by crimson, blue and cyan dashed circles in Fig. 3b. These protrusions are assigned because the molecular moieties with two, one and 0 Br atoms hooked up, and correspondingly denoted as 2Br-DEB, Br-DEB and DEB. The appearances of Br-DEB and DEB counsel concurrent molecular debromination and the ASA formation. The indifferent Br atoms seem as dim dots on the island periphery, as marked by the white arrows within the inset of Fig. 3a. The proposed mannequin is additional supported by the settlement between the measured distance between two adjoining elliptic protrusions in a sequence (1.20±zero.05 nm, as marked by the blue arrow in Fig. 3b) and the optimized inter-molecular distance in an ASA dimer fashioned by 2Br-DEB molecules (1.22 nm, Supplementary Fig. 1a). Furthermore, the DFT-based STM simulation of the parallelly mendacity ASA chains fashioned by the DEB molecules is proven in Fig. 3c, depicting the identical options because the experimentally noticed chain-segments fashioned by fully debrominated molecules, as highlighted by the white dashed rectangle in Fig. 3b. Due to this fact, the stripe-shaped islands achieved at 300 Okay are assemblies of the parallelly mendacity ASA chains fashioned by partially debrominated 2Br-DEB molecules and Ag atoms. The formation of the ASA species by the reactions of the precursors possessing each halogen atoms and terminal alkynyl teams on Ag(111) below related experimental circumstances have additionally been reported in earlier works27,28,29,33,34. The driving power for the secure parallel meeting of the ASA chains is meant to be the engaging interactions between the electron-rich alkynyl π-bonds and the σ-hole of the Br-substituent which possesses constructive electrostatic potential35,36, as marked by the yellow dashed traces between the ASA chains in Fig. 3b.
Statistical evaluation revealed that the ASA construction was the dominant response product at 300 Okay, whereas the ASP or PSP species had been barely noticed. Almost 100% of the terminal alkynyl teams within the molecules had been dehydrogenated and bonded to the Ag atoms at this stage. Along with the intermolecular response between the terminal alkynyl teams, intramolecular debromination additionally came about at 300 Okay. Nonetheless, in distinction to the whole conversion of the terminal alkynyl teams, about 53% Br atoms within the 2Br-DEB molecules had been indifferent on the response equilibrium (Fig. 4a). The dominant debromination product was Br-DEB moieties with a yield of about 83%, whereas 2Br-DEB and DEB moieties occupied 6 and 11%, respectively (Fig. 4a). The comparatively weak chain–chain and chain–substrate interactions, as confirmed by the above-mentioned tip-manipulations of the ASA chains, counsel that the debromination websites within the molecular moieties be passivated by H atoms26,27. DFT calculations additionally exclude the opportunity of the unpassivated chains, based on the numerous distinction within the simulated STM picture of the unpassivated chains (Supplementary Fig. 2) and their experimental counterpart. The H atoms are proposed to be originated from both the residual gasoline in vacuum or the dehydrogenation of the terminal alkynyl teams. Due to this fact, the 2Br-DEB molecules reacted on Ag(111) at 300 Okay to type the ASA chains primarily composed of the Br-DEB moieties. Two terminal alkynyl teams within the 2Br-DEB molecule had been concerned within the formation of the ASA nodes, and one Br atom was indifferent and the debromination web site coupled with an H atom. Step one response is termed as Step 1 in Fig. 4b.
Stepwise activation of Br-substituents and dissymmetric response of 2Br-DEB. a Statistical outcomes of the debromination yield and debromination price within the 1D chains and 2D networks. b Schematic illustration of stepwise activation and dissymmetric response of 2Br-DEB on Ag(111)
Formation of 2D binodal organometallic community at elevated temperatures
Additional thermal remedy of the pattern at 320–450 Okay gave rise to a outstanding transformation of the densely packed 1D section into ordered 2D networks with hexagonal pores (Fig. 5a and Supplementary Fig. three). The unit cell parameters of the 2D construction had been measured as m = n = three.89 ± zero.03 nm and θ = 60±1°. Excessive-resolution STM picture (Fig. 5b) identifies a posh porous community. Every hexagonal pore consists of six triangular clusters (white dashed triangles) and 6 round protrusions (mild blue dots, denoted as kind I) positioned in between two adjoining triangular clusters. Contained in the triangular clusters, there seem six protrusions, of which the interior three (darkish blue dots, denoted as kind II) are round and comparatively brighter, and the outer three (crimson dots, denoted as kind III) are elliptic and comparatively darker.
2D binodal organometallic community fashioned at elevated temperatures. a STM picture of the 2D community fashioned by 2Br-DEB on Ag(111) after annealing of the pattern at 330 Okay (80 mV, 190pA, four.2 Okay). The unit cell is marked by the white parallelogram. The chirality of the triangular cluster is marked by the curved arrow. b Excessive-resolution STM picture of the 2D community (640 mV, 30pA, four.2 Okay). The equal < 1(bar 1)zero > instructions of Ag(111) are marked by white arrows in a and b. c Fixed-height STM picture of the 2D community obtained by a Br-modified tip (500 mV, 100pA, four.2 Okay). The molecular construction of the 2D community is superimposed. The distances between totally different protrusions are highlighted by the crimson arrows and marked with a, b and c, respectively. d Simulated STM picture at 500 mV of the 2D community based on the optimized fashions as superimposed. e dI/dV spectra acquired on a Ag atom in an ASA node (mild blue), a Ag atom in an ASP node (darkish blue), a molecular moiety (crimson) and the substrate in a hexagonal pore (grey). Unique knowledge and smoothed outcomes are introduced by the dots and the traces, respectively. Fixed-height dI/dV mappings acquired at biases of f 1.5 V, g 2.zero V and h 2.5 V. Scale bars: a 5 nm, b–d, f–h 1 nm
To uncover the fragile 2D community fashioned by 2Br-DEB, constant-height imaging with a Br-modified tip was performed. The resulted STM picture displayed in Fig. 5c exhibits that the protrusions of sorts I and II (mild and darkish blue dots) seem in related brightness and are a lot brighter than those of kind III (crimson dots), indicative of their totally different chemical nature. The dramatic distinction in distinction of the three varieties of protrusions means that the 2D community be a bi-component construction. Provided that the on-surface response solely entails the molecules and the silver substrate, one can conclude that the bi-component community is a metal-organic hybrid construction consisting of the molecular moieties and Ag adatoms. The protrusions of sorts I and II are recognized because the Ag atoms as a result of their smaller measurement and better brightness31 and the kind III protrusions, the molecular moieties. To determine how the molecules and Ag atoms are bonded within the community, spacings between the molecular moieties within the community (crimson arrows a and b in Fig. 5c) had been measured to be a = 1.23±zero.04 nm and b = zero.98±zero.05 nm. These values are in good settlement with the optimized inter-molecular distances of the ASA (1.22 nm, Supplementary Fig. 1a) and ASP (zero.97 nm, Supplementary Fig. 1b) dimers, supporting the judgment that the ASA and ASP nodes are fashioned by the molecular moieties and Ag atoms. This conclusion additionally finds help within the areas of the Ag atoms in between the molecules: The Ag atom between the molecules separated by a spacing of a sits in the best center of two neighboring molecules, which agrees with the state of affairs in an ASA node. The Ag atom between the molecules at a spacing of b locates removed from one of many molecules at a distance of c = zero.61±zero.03 nm (marked by the crimson arrow in Fig. 5c) which agrees properly with the optimized separation between the molecule middle and the Ag atom bonded by way of an alkynyl group in an ASP dimer (zero.61 nm, Supplementary Fig. 1b). Accordingly, a molecular mannequin with an organometallic spine of the 2D community is proposed, as proven in Fig. 5c. On this mannequin, two varieties of organometallic nodes are embedded within the community: the triangular cluster is fashioned by the ASP nodes between three molecules, and the adjoining triangular clusters are linked by the ASA nodes. DFT-based STM simulation of the hexagonal community at numerous biases, as proven in Fig. 5d and Supplementary Fig. 4b primarily based on the structural mannequin in Fig. 5c, is in glorious settlement with the experimental observations in Fig. 5b and Supplementary Fig. 4a. Such comparisons between the experimental and theoretical outcomes additional verify the proposed construction for the 2D community. Different structural fashions with totally different chemical linking methods between the 2Br-DEB molecules, together with organometallic and covalent connections, had been additionally taken into consideration (Supplementary Fig. 5). Nonetheless, none of them agrees in dimensions with the experimental measurements (see Supplementary Dialogue for particulars). The dim dots randomly distributed across the spine of the community as seen in Fig. 5a–c are recognized as indifferent Br atoms as a result of they’re susceptible to be moved by the STM tip (Supplementary Fig. 6).
To seek out additional experimental help for the proposed mannequin of the 2D community, tunneling spectra (dI/dV) experiments had been carried out. As depicted in Fig. 5e, the acquired dI/dV spectra on the Ag atoms (mild and darkish blue curves in Fig. 5e) and molecular moieties (crimson curve) present totally different traits: The formers exhibit small shoulder options at round 1.5 V, whereas the latter shows no characteristic at 1.5 V and the next depth of dI/dV above 2.zero V is as an alternative observed. The constant-height dI/dV mappings obtained at totally different biases (Fig. 5f–h) intuitively present the distinction within the dI/dV spectra for the molecular moieties and Ag atoms. At 1.5 V (Fig. 5f), the Ag atoms (darkish and lightweight blue dots) are resolved extra clearly than the molecular moieties (dashed crimson circles). Quite the opposite, the dI/dV mapping at 2.5 V (Fig. 5h) exhibits that the molecular moieties (crimson dots) are clearly seen however the Ag atoms (dashed mild and darkish blue circles) are hardly seen. The dI/dV mapping at 2.zero V (Fig. 5g) exhibits intermediate options of the mappings at 1.5 V and a pair of.5 V. In consequence, the dI/dV measurements present additional proof that the 2D community is a metal-organic hybrid construction, and reveal totally different areas of the Ag atoms and molecular moieties within the 2D community.
It’s noteworthy that the moieties related by the ASP nodes consisting of the triangular clusters prepare in a chiral method, as marked by the curved arrows in Fig. 5a and Supplementary Fig. 7a. The ordered association of the triangular clusters of the identical chirality offers rise to chiral domains of the 2D networks. Iso-energetically, domains of the 2D networks with an reverse chirality must also seem, which was certainly experimentally noticed (Supplementary Fig. 7).
Statistically, over 99% of the molecules within the 2D community have misplaced each Br atoms, resulting in a debromination price of almost 100% (Fig. 4a). This implies the activation of the second Br-substituents within the molecules in the course of the second step. In the meantime, the yields of the intermolecular response merchandise, i.e., the ASA, ASP and PSP nodes, within the 2D construction had been correspondingly about 34%, 65 and 1%. These values are much like the perfect ones calculated from the right mannequin of the 2D community, i.e., 33% for ASA, 67% for ASP and none for PSP. The slight discrepancy between experiment and mannequin stems from the defects in co-existence with the ordered hexagonal networks (Supplementary Fig. eight). The numerous enhance within the yield of the ASP node within the 2D construction in contrast with that within the 1D section signifies the involvement of the Br-substituted websites activated within the second step within the intermolecular metalation reactions. As a consequence, about 89% molecular species within the 2D community are the molecular moieties whose terminal alkynyl teams and certainly one of its Br-substituted websites are concerned within the intermolecular organometallic bonding.
The transformation from the 1D section to the 2D construction entails the dissociation of the C–Ag bonds within the ASA nodes that type the 1D chains, the diffusive rearrangement of the resulted molecular moieties, and the reformation of the organometallic bonds within the ASP and ASA nodes. The driving power for these processes lies within the metalation of the Br-substituted websites within the 2Br-DEB molecules triggered at elevated temperatures. This response requires the involvement of a second 2Br-DEB molecule to type a stabilized intermolecular organometallic product, which may solely be fulfilled by the structural transformation of the 1D section. Upon activation, the debromination websites could take part in metalation response with both the terminal alkynyl teams or the debromination websites in different molecular moieties, forming the ASP or PSP nodes, respectively. Nonetheless, solely the ASP nodes had been discovered within the ordered 2D remaining product. This extremely selective formation of the ASP species may very well be defined by a spectacular match between the 2D community spine and the substrate lattice, as observed by high-resolution STM imaging with a modified tip (Fig. 6a). As proven within the STM picture (Fig. 6a), the indifferent Br atoms (blue crosses) had been positioned on the hole websites of the substrate, in accordance with beforehand reported end result that Br atoms preferentially adsorb on the hole websites on Ag(111) at a low protection37. The so-achieved Ag(111) floor lattice is overlaid on the STM picture in Fig. 6a. As well as, the molecular fashions of the 2D nanostructure are superimposed in Fig. 6a to make clear the spine construction of the community imaged with a modified STM tip. A comparability of the substrate lattice and the community construction instantly manifests the floor areas of the Ag atoms within the community: All Ag atoms within the ASP nodes are positioned on the hole websites of the substrate and people within the ASA nodes, at bridge websites. The molecular moieties are related by the Ag atoms positioned at both hole or bridge websites. In consequence, the sides of the hexagonal pores within the 2D community run roughly alongside the < 1(bar 1)zero > instructions of the Ag(111) substrate, as proven by the molecular fashions in Fig. 6b. The outstanding match between the spine construction of the 2D community and the Ag(111) lattice invokes a robust adlayer–substrate interplay which stabilizes the 2D floor nanostructure19,38. Due to this fact, the hexagonal 2D community during which all of the Br-substituted websites activated within the second step are concerned within the ASP nodes survives as the one remaining product with an vitality desire. As a comparability, the state of affairs the place all of the reactive debromination websites are engaged within the PSP nodes was additionally thought-about (Supplementary Fig. 9). Nonetheless, the resulted mannequin exhibits a poor match with the substrate lattice (see Supplementary Dialogue for particulars), implying much less stabilization impact of the substrate to this construction, which can presumably clarify its absence. The conversion from the 1D construction to the 2D community is schematically illustrated as Step 2 in Fig. 4b.
Matching relationship between the 2D community and the Ag(111) substrate. a Excessive-resolution STM picture of the 2D community acquired with a modified tip (380 mV, 110pA, 77 Okay). Molecular fashions and substrate lattice are superimposed. Some indifferent Br atoms are highlighted by the blue crosses. Scale bar: 1 nm. b Molecular fashions of the 2D community on the substrate
The 2D community might survive 450 Okay annealing (Supplementary Fig. 10a), indicative of its excessive thermal stability. At increased temperatures, e.g., about 530 Okay, the organometallic community decomposed and fewer ordered covalent constructions had been fashioned (Supplementary Fig. 10b).