Revisiting acene dimers: A comprehensive theoretical study of a less explored conformer

Area of Science:

• Physical chemistry
• Computational chemistry
• Spectroscopy

Background:

• Acenes are polycyclic aromatic hydrocarbons with potential applications in organic electronics.
• Understanding acene dimer structures is crucial for predicting their solid-state properties and assembly behavior.
• Previous studies have explored various acene derivatives, but a systematic investigation of their dimer structures and interactions is needed.

Purpose of the Study:

• To determine the lowest energy structures of naphthalene, anthracene, tetracene, and pentacene dimers.
• To investigate the nature of intermolecular interactions within these dimers.
• To correlate computational findings with experimental spectroscopic data for solution assembly insights.

Main Methods:

• Density Functional Theory (DFT) calculations using B3LYP-D3(BJ)/def2-TZVP level of theory.
• High-level coupled-cluster calculations (PNO-LCCSD(T)-F12) for validation.
• Symmetry-Adapted Perturbation Theory (SAPT) for interaction analysis.
• Experimental UV-Vis absorption and fluorescence spectroscopy.

Main Results:

• The C2 symmetric X-shaped dimer structure was identified as the lowest energy minimum for all studied acenes.
• Slipped-stacked and cross-shaped dimer configurations were found to be higher in energy.
• SAPT analysis revealed the dominant contributions of dispersion and induction forces to the dimer stability.
• Experimental UV-Vis spectra showed good agreement with computed spectra, supporting the proposed dimer structures and assembly.

Conclusions:

• Acene dimers preferentially adopt an X-shaped conformation in the gas phase.
• The computational and experimental data provide a comprehensive understanding of acene dimer formation and stability.
• This study offers valuable insights into the self-assembly of acenes in solution, relevant for materials science applications.