π-Stacking-Dependent Vibronic Couplings Drive Excited-State Dynamics in Perylenediimide Assemblies

Area of Science:

• Physical Chemistry
• Spectroscopy
• Materials Science

Background:

• Vibronic coupling, the interplay of electronic and nuclear motion, is crucial for photoinduced reactions.
• Experimental studies on model systems are limited, hindering a deep understanding of vibronic coupling's impact on excited-state dynamics.

Purpose of the Study:

• To experimentally investigate the role of vibronic coherences in perylenediimide (PDI) slip stacks.
• To elucidate how specific vibronic couplings influence excimer formation and mixed-state generation in PDI aggregates.

Main Methods:

• Utilized two-dimensional electronic spectroscopy (2DES) to excite and probe vibronic coherences.
• Employed quantum beatmaps to analyze Fourier amplitude oscillations and identify species signatures (Frenkel exciton, ionic, excimer).

Main Results:

• Identified a low-frequency vibrational mode in short-axis slip stacks associated with excimer formation, showing longer survival and a phase shift compared to monomers.
• Discovered that low-frequency modes coupled to a high-frequency coordinate of the Frenkel exciton state are key for mixed-state generation in long-axis slip stacks.

Conclusions:

• Experimentally demonstrated the complex and varied roles of vibronic couplings in tightly packed PDI multimers.
• Provided new insights into the mechanisms governing photoinduced processes like energy and charge transfer in molecular aggregates.