Ultrafast Electronic Relaxation in Aqueous [Fe(bpy)₃]²⁺: A Surface Hopping Study

Area of Science:

• Computational Chemistry
• Photochemistry
• Inorganic Chemistry

Background:

• [Fe(bpy)3]2+ is a key photosensitizer with complex electronic relaxation dynamics.
• Understanding ultrafast relaxation pathways is crucial for its applications.

Purpose of the Study:

• To elucidate the electronic relaxation dynamics of [Fe(bpy)3]2+ in aqueous solution.
• To simulate the relaxation from photoexcited singlet metal-to-ligand charge-transfer (MLCT) states to metastable quintet metal-centered (MC) states.

Main Methods:

• Trajectory surface hopping simulations were employed.
• A previously developed model electronic Hamiltonian for MLCT and MC states of [Fe(bpy)3]2+ was used.

Main Results:

• Most simulated trajectories showed sequential relaxation via triplet MC states.
• A direct pathway from MLCT to quintet MC states was also observed.
• Population transfer to the singlet MC ground state was minimal, with quintet MC state population exceeding 96%.

Conclusions:

• The simulations accurately reproduce experimental observations of high quantum efficiency.
• Triplet MC states play a significant role in the relaxation pathway.
• The dominant population of quintet MC states is confirmed.