Bis(phosphine imide)s: easily tunable organic electron donors

Area of Science:

• Inorganic Chemistry
• Electrochemistry
• Spectroscopy
• Computational Chemistry

Background:

• Bis(phosphine imide)s are a class of compounds with interesting electronic properties.
• Understanding their electrochemical behavior is crucial for designing new materials.
• Previous studies have explored related phosphorus-nitrogen compounds.

Purpose of the Study:

• To investigate the electrochemical, structural, and spectroscopic properties of p-phenylenebis(phosphine imide)s and N,N'-4,4'-biphenylene(bis(triphenyl)phosphine imide).
• To determine how modifications to substituents and aromatic linkers affect their oxidation potentials and electronic communication.
• To elucidate the nature of the oxidized species formed.

Main Methods:

• Electrochemical techniques (cyclic voltammetry) were used to determine oxidation potentials.
• UV-visible-Near-Infrared (NIR) spectroscopy was employed to study the electronic transitions.
• Density Functional Theory (DFT) calculations were performed to model the electronic structure.

Main Results:

• p-Phenylenebis(phosphine imide)s (1a-d) exhibit two reversible single-electron oxidations with tunable potentials based on phosphorus substituents.
• Oxidation leads to delocalized radical cations and quinonoidal dications, with significant electronic coupling (Hab ~1.1 eV).
• N,N'-4,4'-biphenylene(bis(triphenyl)phosphine imide) (3) also forms radical cationic and dicationic species, but with weaker electronic communication (Hab ~0.63 eV) and distinct NIR absorptions.

Conclusions:

• The electronic properties of bis(phosphine imide)s can be systematically tuned by altering substituents and aromatic linkers.
• The compounds form stable delocalized radical cations and quinonoidal dications upon oxidation.
• The aromatic linker plays a critical role in mediating electronic communication between the phosphine imide units.