Assessing the Dynamics of Hemithioindigo-Based Photoswitches Using Multistate Molecular Mechanics

Area of Science:

• Computational chemistry
• Photochemistry
• Molecular dynamics

Background:

• Hemithioindigo photoswitches are crucial in molecular devices.
• Understanding their photoisomerization mechanism is key for applications.
• Accurate modeling of excited states and solvent effects is computationally challenging.

Purpose of the Study:

• To develop an efficient multistate molecular mechanics model for hemithioindigo photoswitches.
• To investigate the explicit solvent effects on the Z-E isomerization from the triplet state.
• To gain mechanistic understanding of the photoisomerization process.

Main Methods:

• Multistate molecular mechanics (MSMM) model development.
• Nanosecond-scale molecular dynamics (MD) simulations.
• Statistical sampling of thousands of trajectories.
• Committor analysis for mechanistic elucidation.

Main Results:

• The MSMM model achieves near quantum mechanical accuracy with high computational efficiency.
• Explicit solvent effects on Z-E switching energetics and kinetics were elucidated.
• Isomerization ratios and vibrational relaxation times were directly assessed.
• Key descriptors governing the Z-E isomerization were identified via committor analysis.

Conclusions:

• The developed MSMM model enables efficient and accurate simulations of photoswitch behavior.
• Solvent plays a significant role in the energetics and kinetics of hemithioindigo photoisomerization.
• This work provides a powerful computational tool for designing and understanding photoswitch systems.