Ultrafast and Coherent Dynamics in a Solvent Switchable "Pink Box" Perylene Diimide Dimer

Area of Science:

• Organic molecular photonics
• Supramolecular chemistry
• Photovoltaic devices

Background:

• Perylene diimide (PDI) aggregates are crucial for organic electronics.
• Understanding their excited-state dynamics is vital but challenging due to architecture-dependent coupling.
• A macrocyclic PDI dimer allows solvent-controlled tuning of excitonic coupling without synthesis.

Purpose of the Study:

• To investigate solvent-dependent excited-state dynamics in a macrocyclic PDI dimer.
• To correlate conformational changes with excitonic coupling strengths.
• To elucidate the mechanisms of excimer formation and vibronic coupling.

Main Methods:

• Coherent multidimensional spectroscopy (2D electronic spectroscopy).
• Computational modeling (Density Functional Theory - DFT).
• Analysis of low-frequency Raman active modes and 2D electronic "beatmaps".

Main Results:

• Solvent-induced conformational changes modulate interchromophoric coupling.
• Strongly coupled conformers form an excimer within 300 fs.
• Low-frequency modes characteristic of exciton coupling were identified and assigned.
• Time-dependent frequencies during excimer formation were observed.
• Vibronic coupling effects beyond the displaced harmonic oscillator model were detected.

Conclusions:

• Solvent engineering offers a viable strategy to control supramolecular structure and photophysical properties of PDI dimers.
• Ultrafast excimer formation and complex vibronic coupling govern the excited-state dynamics.
• Coherent multidimensional spectroscopy provides detailed insights into exciton-vibrational interactions in molecular aggregates.