Simulating the Energy Capture Process in Push-Pull Norbornadiene-Quadricyclane Photoswitches

Area of Science:

• Photochemistry
• Molecular Solar Thermal Energy Storage (MOST)
• Computational Chemistry

Background:

• Norbornadiene-quadricyclane (NBD-QC) isomer pairs are key for MOST.
• The mechanism of their photoinduced [2+2] cycloaddition is not fully understood, especially for push-pull substituted derivatives.
• Push-pull substitution is crucial for achieving efficient photoisomerization quantum yields.

Purpose of the Study:

• To computationally investigate the photochemistry of NBD-QC switches with push-pull substitution.
• To elucidate the mechanism and kinetics of the photoinduced cycloaddition reaction.
• To determine the reaction time scale and quantum yield.

Main Methods:

• Static calculations to determine excited state structures and potential energy surfaces.
• Nonadiabatic molecular dynamics (NAMD) simulations.
• Analysis of ground- and excited-state potential energy landscapes.

Main Results:

• Detailed picture of the energy capture process provided.
• Photoinduced cycloaddition initiates in the bright excited state.
• Ring closing in a model compound occurs on a ~150 fs timescale.
• Identified as one of the fastest known photoisomerization reactions.

Conclusions:

• Push-pull substituted NBD-QC systems exhibit ultrafast photoisomerization.
• The computational approach provides critical insights into the MOST mechanism.
• These findings advance the development of efficient molecular solar thermal energy storage systems.