PAH/PAH(CF₃ )_n Donor/Acceptor Charge-Transfer Complexes in Solution and in Solid-State Co-Crystals

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Organic Electronics

Background:

• Charge-transfer (CT) complexes are crucial in organic electronics and materials science.
• Polycyclic aromatic hydrocarbons (PAHs) are versatile building blocks for functional materials.
• Understanding donor/acceptor interactions is key to designing novel materials with tailored electronic properties.

Purpose of the Study:

• To investigate novel donor/acceptor (D/A) charge-transfer complexes using polycyclic aromatic hydrocarbon (PAH) donors and perfluorinated PAH (PAH(CF3)n) acceptors.
• To explore the structural and electronic properties of these CT complexes in solution, solid-state, and through computational analysis.
• To provide new insights into controlling D/A interactions and the formation of CT co-crystals.

Main Methods:

• Synthesis and characterization of six PAH(CF3)n acceptors and four PAH donors.
• X-ray crystallography to determine the co-crystal structures and stoichiometries (1/1, 1/2, 2/1).
• UV-Vis spectroscopy to measure charge-transfer bands and computational studies to analyze electronic properties.

Main Results:

• Seven co-crystal X-ray structures were obtained, showing hexagonal arrays of mixed π-stacks.
• All nine D/A combinations exhibited charge-transfer bands in solution between 467 and 600 nm.
• A linear correlation was found between charge-transfer energy and the difference between donor ionization energy and acceptor electron affinity (E(λmax) vs. [IE - EA]) with a slope of 0.72±0.03 eV/eV.

Conclusions:

• This work presents the first detailed study of CT complexes with PAH(CF3)n acceptors.
• The results offer new perspectives on controlling D/A interactions and the structural organization of CT co-crystals.
• The study challenges the common assumption of a unity slope in E(λmax) vs. [IE - EA] plots, suggesting a need for re-evaluation in certain systems.