Are azobenzenophanes rotation-restricted?

Area of Science:

• Photochemistry
• Computational Chemistry
• Molecular Dynamics

Background:

• Azobenzene derivatives are crucial in photochromic materials.
• Understanding their photoisomerization dynamics is key for designing advanced functional molecules.
• Semiclassical methods offer a balance between accuracy and computational cost for complex systems.

Purpose of the Study:

• To simulate the photoisomerization dynamics of an azobenzenophane molecule.
• To investigate the roles of different electronic excitations (n-->pi* and pi-->pi*) in the reaction pathway.
• To compare simulation results with experimental time-resolved fluorescence data.

Main Methods:

• Utilized a semiclassical surface hopping approach.
• Employed a semiempirical reparametrized quantum mechanics/molecular mechanics (QM/MM) Hamiltonian.
• Treated one azobenzene chromophore with quantum mechanics and the other with molecular mechanics.

Main Results:

• The photoisomerization reaction primarily proceeds via rotation around the N=N double bond.
• Simulated excited state relaxation dynamics showed qualitative agreement with experimental observations.
• Both n-->pi* and pi-->pi* excitations were considered in the simulations.

Conclusions:

• The study provides insights into the mechanism of azobenzene photoisomerization at a molecular level.
• The QM/MM approach effectively captures the essential dynamics of the system.
• The results support the validity of the employed simulation methodology for studying similar photoactive molecules.