N-Heterocyclic Carbene vs. Thiophene - Chiral Adsorption and Unidirectional Rotation on Au(111)

Area of Science:

• Surface Science
• Organic Chemistry
• Nanotechnology

Background:

• N-Heterocyclic carbenes (NHCs) are crucial ligands for surface functionalization.
• Predicting and controlling NHC adsorption geometry on metal surfaces, particularly gold, remains challenging.
• The role of gold adatoms in NHC surface binding is not fully understood.

Purpose of the Study:

• To investigate the adsorption behavior and surface mobility of two benzimidazole-based NHC derivatives on Au(111).
• To elucidate the role of substituents (thiophene vs. bromine) in dictating NHC-surface interactions and motion.
• To explore the formation and dynamics of NHC-gold adatom complexes.

Main Methods:

• Low-temperature scanning tunneling microscopy (STM) for atomic-scale imaging and manipulation.
• Voltage pulsing and inelastic electron tunneling for inducing molecular motion.
• Density functional theory (DFT) calculations and image simulations for theoretical analysis.

Main Results:

• Both NHC derivatives adsorb in a planar configuration and exhibit chirality on the Au(111) surface.
• Complexes formed between NHCs and gold adatoms were observed.
• The thiophene-substituted NHC derivative demonstrated controlled, unidirectional 60° rotation around the sulfur atom upon voltage pulsing, influenced by chirality and pulse location.
• The bromine-substituted NHC derivative exhibited lateral movement on the surface.

Conclusions:

• NHC adsorption and binding to gold adatoms can be precisely controlled.
• Molecular substituents significantly influence the motion and binding dynamics of NHCs on gold surfaces.
• This study provides insights into the controlled manipulation of molecules on surfaces via NHC-gold adatom interactions.