Site-selective reversible Diels–Alder reaction between a biphenylene-based polyarene and a semiconductor surface

Abstract

Understanding the mechanisms involved in the covalent attachment of organic molecules to surfaces is a major challenge for nanotechnology and surface science. On the basis of classical organic chemistry mechanistic considerations, key issues such as selectivity and reactivity of the organic adsorbates could be rationalized and exploited for the design of molecular-scale circuits and devices. Here we use tris(benzocyclobutadieno)triphenylene, a singular Y-shaped hydrocarbon containing antiaromatic cyclobutadienoid rings, as a molecular probe to study the reaction of polycyclic conjugated molecules with atomic scale moieties, dangling-bond (DB) dimers on a hydrogen-passivated Ge(001):H surface. By combining molecular design, synthesis, scanning tunneling microscopy and spectroscopy (STM/STS) and computational modeling, we show that the attachment involves a concerted [4+2] cycloaddition reaction that is completely site-selective and fully reversible. This selectivity, governed by the bond alternation induced by the presence of the cyclobutadienoid rings, allows for the control of the orientation of the molecules with respect to the surface DB-patterning. We also demonstrate that by judicious modification of the electronic levels of the polycyclic benzenoid through substituents, the reaction barrier height can be modified. Finally, we show that after deliberate tip-induced covalent bond cleavage, adsorbed molecules can be used to fine tune the electronic states of the DB dimer. This power to engineer deliberately the bonding configuration and electronic properties opens new perspectives for creating prototypical nanoscale circuitry.

Covalent attachment of chitosan to graphene via click chemistry for superior antibacterial activity

“…In fact, the presence of the D mode is generally used to monitor the covalent bonds formed in graphene and widely accepted. 30 These spectroscopic features shown herein fully demonstrate that we successfully modified graphene via a click reaction, and the result of the corresponding reaction should be the aryl groups connected to the graphene sheets via s-bonds.…”

Extended iron phthalocyanine islands self-assembled on a Ge(001):H surface

“…This allows us to draw the conclusion that the FePc molecules recorded in Figure 6a were immobilized by DBDs. It is worth noting that the preferred localization of polycyclic molecules on DBDs on Ge(001):H has already been reported for starphenes [25,30,34] and tribiphyenylenes [35].…”

“…Interestingly, the recorded islands partly extend over several hundreds of nanometers, crossing several terrace steps without losing integrity, as shown in Supporting Information File 1, Figure S7. Taking into account the above atomic-scale defects and our previous experiments with other organic molecules [35], we may expect that single FePc molecules on the surface are trapped at surface defects, although the formation of molecular islands hints at a sufficient mobility of the molecules on the Ge(001):H surface. In a previously reported case of starphenes on Ge(001):H, the molecules passivated all DBDs when a sufficient amount of molecules was deposited onto the surface [34].…”

“…In such a way, different atomic nanostructures could be fabricated in a controllable manner; artificial molecules [32] or surface logic gates [33] could act as examples. Further, such nanostructures may be applied in hybrid systems to couple organic molecules with the underlying surface in a controlled way [34,35], or even provide pivot points for nanoscale rotors [30]. It is also worth mentioning that bringing into practice newly designed nanoscale circuits might be beneficial especially on Ge or Si surfaces, since those semiconductors are at the foundations of traditional electronics.…”

o-Silylaryl Triflates: A Journey of Kobayashi Aryne Precursors

“…More exciting applications on this Pd-catalyzed cyclotrimerization protocol were reported by different research groups, and the structural complexity of the corresponding triphenylene-based products has been significantly enhanced (Scheme ). In 2004, Pérez, Vollhardt, and co-workers employed biphenylynes to assemble C 3 -symmetric trimers 15-8 , which was later found to reversibly and selectively add onto a semiconductor surface via Diels–Alder reaction . Both substituted 2,3-triphenylynes and 2,3-naphthalynes were able to trimerize to furnish the corresponding 15-9 and 15-10 , respectively.…”