On-Surface Molecular Recognition Driven by Chalcogen Bonding

Abstract

Chalcogen bonding interactions (ChBIs) have been widely employed to create ordered noncovalent assemblies in solids and liquids. Yet, their ability to engineer molecular self-assembly on surfaces has not been demonstrated. Here, we report the first demonstration of on-surface molecular recognition solely governed by ChBIs. Scanning tunneling microscopy and ab initio calculations reveal that a pyrenyl derivative can undergo noncovalent chiral dimerization on the Au(111) surface through double Ch···N interactions involving Te- or Se-containing chalcogenazolo pyridine motifs. In contrast, reference chalcogenazole counterparts lacking the pyridyl moiety fail to form regular self-assemblies on Au, resulting in disordered assemblies.

Figure 1

Schematic representations of the first examples of noncovalent molecular self-assembly at surfaces, respectively driven by (A) hydrogen bonds, (B) metal coordination bonds, (C) dipole–dipole interactions, (D) halogen bonds, and (E) ChBIs investigated in this work.

Figure 2

(A) STM image of (CGP-Te)₂ dimers on Au(111). The herringbone reconstruction of the Au substrate is also visible. In the rectangles, the 3-fold equivalent dimer orientations are highlighted. Tunneling current (I_t) = 300 pA; tunneling bias (V_t) = 1.000 V; T = 11 K. The top-right-corner inset shows two enantiomers; I_t = 250 pA; V_t = 0.500 V. (B) Experimental (I_t = 300 pA; V_t= 0.630 V; T = 11 K) and (C) simulated (V_t = 0.630 V) STM image of an individual dimer. In the simulated image, the chemical structure of the monomer is also overlaid to display the strong Te-centered signal. (D) STM image of self-assembled (CGP-Se)₂ dimers on Au(111). I_t = 300 pA; V_t = 0.800 V; T = 8.5 K. (E) STM image of an individual dimer. I_t = 150 pA; V_t = 0.100 V; T = 8.5 K. (F) STM image of the reference tellurazole molecules deposited on Au(111). Kinetic aggregates of various shapes and sizes can be observed. I_t = 400 pA; V_t = 1.000 V; T = 11 K. (G) Detail of a molecular assembly. I_t = 400 pA; V_t = 1.000 V; T = 11 K. Scale bars: 5 nm in (A), (D), and (F); 0.5 nm in (B), (C), (E), and (G); and 2 nm in the inset of (A).

Figure 3

From top to bottom: BRSTM image (constant height, V_t = 5 mV, T = 8.7 K) and DFT relaxed geometrical model of the individual (CGP-Te)₂ and (CGP-Se)₂ dimers.

Figure 4

DFT analysis of ChBIs in a (CGP-Te)₂ dimer. (A, B) Gas phase and adsorption geometries (side view). The tilt angle of the chalcogenazole moiety with respect to the pyrene unit is shown. (C, D) Electrostatic potential (in au) superimposed on a charge density isosurface (ρ = 0.025 au). Atomic charges Q are reported for Te and N. (E, F) Molecular graph showing bond paths (dotted lines), bond critical points in red, and ring critical points in green. For clarity, bond paths between the dimer and substrate are not shown, except for Te···Au and N···Au. (G, H) Reduced density gradient (on the 0.5 au isosurface) showing the noncovalent ChBIs; blue and red regions indicate attractive and repulsive interactions, respectively; the dashed circles highlight the attractive interaction at the bond critical point between Te and N atoms.