Theoretical study of the benzene excimer using time-dependent density functional theory

Area of Science:

• Computational Chemistry
• Physical Chemistry
• Quantum Chemistry

Background:

• Excited states of aromatic molecules like benzene are crucial for understanding photochemical reactions.
• Benzene excimers, transient species formed by two excited benzene molecules, play a role in photophysics.
• Accurate theoretical models are needed to predict the behavior and stability of these excimers.

Purpose of the Study:

• To theoretically characterize the potential energy surfaces of singlet benzene excimer states.
• To investigate the energetic stability and structural parameters of the benzene excimer.
• To evaluate the accuracy of time-dependent density functional theory (TD-DFT) for modeling aromatic excimers.

Main Methods:

• Utilized time-dependent density functional theory (TD-DFT) for electronic structure calculations.
• Performed computations along intermolecular translational coordinates (parallel and perpendicular).
• Examined the effects of in-plane rotation, out-of-plane rotation, and slipped-parallel translation at the minimum energy distance.

Main Results:

• The lowest excited state for parallel translation is bound, with a minimum at 3.15 angstroms and a binding energy of 0.46 eV.
• Perpendicular translation was found to be a repulsive state.
• Deviations from D6h geometry and slipped-parallel translations destabilize the excimer, with dissociation barriers of 0.50-0.61 eV.
• Calculated energetics show semiquantitative agreement with experimental values.

Conclusions:

• TD-DFT provides a reasonably accurate method for characterizing the potential energy surfaces and energetics of aromatic excimers.
• The study elucidates the binding and stability of the singlet benzene excimer.
• Findings support the utility of TD-DFT in predicting the behavior of excited aromatic systems.