Revisiting the benzene excimer using [2,2] paracyclophane model system: Experiment and theory

Area of Science:

• Photochemistry
• Quantum Chemistry
• Spectroscopy

Background:

• [2,2]-paracyclophane (PCP) serves as a model for benzene dimer excimer formation due to its constrained structure.
• Understanding PCP excited states is crucial for modeling excimer dynamics.

Purpose of the Study:

• To perform high-level calculations of PCP excited states.
• To explain experimental transient absorption spectral evolution of PCP.
• To elucidate the electronic structure dynamics of the PCP excimer.

Main Methods:

• High-level quantum chemical calculations of excited states.
• Ultrafast pump-probe spectroscopy on oriented single crystals.
• Broadband 8 fs pump transient absorption spectroscopy.

Main Results:

• Calculations explain the main features of transient absorption spectral evolution.
• The brightest excimer transition is polarized along the inter-fragment axis.
• Weaker transitions of Rydberg character are observed.
• Time-resolved modulations of excimer absorption were observed.

Conclusions:

• The study provides a detailed picture of PCP excimer electronic structure evolution.
• The constrained geometry of PCP simplifies the study of inter-ring distance effects.
• Theory and experiment combined offer insights into molecular dynamics.