Achieving selective photochemistry on a metal surface by tuning the aromatic core

Area of Science:

• Surface Science
• Photochemistry
• Organic Synthesis

Background:

• On-surface photochemistry offers precise control over reactions, avoiding defects from thermal methods.
• Ullmann coupling is a key reaction for studying on-surface mechanisms and control.
• The influence of aromatic cores on photoinduced C-Br bond activation during Ullmann coupling is not well understood.

Purpose of the Study:

• Investigate how distinct aromatic cores in dibromo precursors affect photoinduced Ullmann coupling on Au(111).
• Elucidate the mechanism of photoinduced C-Br bond cleavage.
• Establish structure-reactivity relationships for light-controlled on-surface synthesis.

Main Methods:

• Experimental investigation of photoinduced Ullmann coupling using three dibromo precursors with varying aromatic cores on Au(111).
• Irradiation using 405 nm and 532 nm light sources.
• Time-dependent density functional theory (TD-DFT) calculations to model charge transfer and potential energy surfaces for C-Br bond dissociation.

Main Results:

• The three molecular precursors exhibited significantly different photoreactivities under irradiation.
• TD-DFT calculations indicated a photoinduced surface-to-molecule charge-transfer process.
• A direct correlation was found between the molecular aromatic core and the photo-selectivity of C-Br bond cleavage.

Conclusions:

• The aromatic core of molecular precursors plays a crucial role in governing photoinduced C-Br activation during on-surface Ullmann coupling.
• Mechanistic insights into light-controlled on-surface synthesis were provided.
• Design principles for developing light-responsive precursors for targeted carbon nanostructure synthesis were established.