DFT Insights on Ligand Photodissociation Pathways in Ruthenium-Terpyridine Complexes: ³MLCT- or ³MC-Triggered?

Area of Science:

• Inorganic Chemistry
• Photochemistry
• Computational Chemistry

Background:

• Ruthenium-terpyridine complexes are crucial in photochemistry.
• Understanding acetonitrile photodissociation mechanisms is key for catalyst design.

Purpose of the Study:

• To computationally elucidate the acetonitrile photodissociation mechanism in Ru-terpyridine PACT complexes.
• To investigate the role of ligand structure in influencing photodissociation pathways and quantum yields.

Main Methods:

• Density Functional Theory (DFT) calculations were employed.
• Relaxed scans were performed to explore reaction pathways.
• Transition states for acetonitrile loss were located.

Main Results:

• An atypical dissociative triplet metal-to-ligand charge transfer (3MLCT) state, dominated by terpyridine distortion, was identified.
• Photosubstitution can occur without a canonical elongated Ru-ACN bond.
• The relative energies of dissociation and internal conversion barriers rationalize experimental photodissociation quantum yields.
• Both 3MLCT- and 3MC-mediated pathways for acetonitrile loss are plausible and competitive.
• Sterically tuned terpyridine ligands can influence the 3MLCT-3MC conversion, offering a strategy for tuning photosubstitution.

Conclusions:

• The mechanism of acetonitrile photodissociation in these complexes involves a distorted excited state.
• Ligand design, particularly steric tuning of terpyridine derivatives, can control photosubstitution efficiency.
• This work provides insights for designing novel photosensitive ruthenium complexes.