Real-space Imaging of the Multiple Halogen Bonds by Ultrahigh-resolution Scanning Probe Microscopy

Abstract

Understanding the physical origin of STM/AFM image contrast is of significance for not only promoting surface characterization techniques, but also probing surface nanostructures with the atomic/sub-molecular resolution. Herein, we demonstrate the real-space imaging of halogen bonds acquired by non-contact atomic force microscopy (nc-AFM)/bond-resolution scanning tunneling microscopy (BR-STM) with functional CO-tip, and study the image contrast origin of halogen bonds. The presence of bright line features is associated to the specific site where halogen bond forms, which is experimentally evidenced to be contributed by both CO-tip bending and electron density exchange. Three distinct types of halogen bonds are observed, which origin from the noncovalent interactions of Br-atoms with positive potential H-atom, neutral potential Br-atom and negative potential N-atom, respectively. Our work shows that nc-AFM and BR-STM can directly image halogen bonds and can be used to unambiguously discriminate their bonding 2 features. This work demonstrates the potential use of this technique to image other non-covalent intermolecular bonds and to understand complex supramolecular assemblies at the sub-molecular level.

Excited State Dynamics in Dual-Defects Modified Graphitic Carbon Nitride

“…7,8 Recently, a metalfree, π-conjugated semiconductor photocatalyst, graphitic carbon nitride (g-C 3 N 4 ), has gained immense popularity due to its excellent physicochemical properties, nontoxicity, high stability, suitable electronic band structure, low cost, and easy synthesis. 9 It is a visible-light-driven photocatalyst that has the capacity to utilize the broad solar spectrum effectively. 10,11 Structurally, it is similar to honeycomb graphite with layer stacking of a two-dimensional (2D) conjugated framework, attracted by van der Waals forces.…”

Properties and Stabilities of Cyclic and Open Chains of Halogen Bonds

“…It might be noted finally that very recent ultra-high-resolution scanning probe microscopic images 25 have verified the pinwheel shape of the halogen-bonded cyclic tetramer of 2,7,13,18tetrabromodibenzo [a,c]dibenzo [5,6:7,8]-quinoxalino[2,3-i]phenazine on the Au(111) surface.…”

Visualization and Comprehension of Electronic and Topographic Contrasts on Cooperatively Switched Diarylethene-Bridged Ditopic Ligand

“…STM is a powerful technique which probes the local electron density of states (DOS) [55,56,[59][60][61]76] as well as the correlated surface topographic information [40,43,[52][53][54]77]. The electron DOS contrast is a complex interplay between the electronic structures of the surface-supported adsorbent (the molecules in our case) and the STM tips [78]. In the STM constant-current mode, the tunneling current depends exponentially on the distance between the two electrodes as well as on the electron DOS from both sides of the tunneling junction, i.e., the tip and the sample [40,43,[52][53][54]77,79].…”