Origin of Stabilization of Ligand-Centered Mixed Valence Ruthenium Azopyridine Complexes: DFT Insights for...

Area of Science:

• Materials Science
• Computational Chemistry
• Condensed Matter Physics

Background:

• Redox-driven conductance changes are key for molecular memristive devices used in neuromorphic computing.
• The fundamental mechanisms of conductance switching in these systems remain incompletely understood.

Purpose of the Study:

• To investigate charge disproportionation (CD) processes and interfragment charge transfer (IFCT) in [Ru^IIL₂](PF₆)₂ molecular systems.
• To elucidate the roles of temperature and volumetric expansion in facilitating electron transfer and counterion movement for enhanced conductivity.

Main Methods:

• Utilized a combination of *ab initio* molecular dynamics simulation (AIMD), time-dependent density functional theory (TD-DFT), and density functional theory (DFT).
• Analyzed density of states and performed constrained DFT calculations to understand electronic transitions and state stabilization.
• Emulated molecular films using periodic DFT and AIMD simulations to observe charge separation and counterion mobility.

Main Results:

• Unpaired electrons and azo (N═N) groups are critical for low-energy electronic transitions and transport between molecular fragments.
• Electron localization on azo ligands leads to reduced HOMO-LUMO gaps and enhanced conductivity, with minimal change at Ru centers.
• Stabilization of asymmetric states correlates with significant charge separation (∼0.33 e) and increased counterion mobility (>0.7 Å displacement).

Conclusions:

• Azo groups are pivotal in facilitating IFCT and electron redistribution, stabilizing asymmetric states in redox-driven molecular systems.
• Findings provide crucial insights into the mechanisms of redox-driven memristive behavior.
• The study has significant implications for the design and development of next-generation neuromorphic technologies.