σ Interference: Through-Space and Through-Bond Dichotomy

Area of Science:

• Quantum chemistry
• Molecular electronics
• Condensed matter physics

Background:

• Orbital interactions are classified as through-space (TS) and through-bond (TB).
• Understanding these interactions is crucial for molecular properties and electron transport.
• Quantum interference, specifically σ interference, is a key phenomenon in σ systems.

Purpose of the Study:

• To elucidate the origin of σ interference in electron transport.
• To investigate the roles of TS and TB interactions in σ interference.
• To analyze the influence of molecular conformation on σ interference.

Main Methods:

• Electron transport calculations using density functional theory and nonequilibrium Green's function methods.
• Fragment molecular orbital (FMO) analysis to study TS and TB interactions.
• Chemical graph theory analysis (ladder C model) to explore topological origins.

Main Results:

• Destructive σ interference was confirmed in the syn and gauche conformers of ethylenediamine.
• TB interactions dictate frontier orbital distribution and energy alignment.
• Changes in TS interactions, driven by dihedral angles, modulate the energy gap and enable σ interference in specific conformers.

Conclusions:

• σ interference arises from the interplay between TS and TB interactions.
• Vicinal interactions, sensitive to dihedral angles, critically determine the occurrence of σ interference.
• These findings provide insights for designing molecular systems leveraging σ interference.