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Ultrafast intersystem crossing (ISC) in rhenium complexes is driven by spin-vibronic coupling, not just heavy atom effects. This study reveals how nuclear motion influences ISC rates, crucial for understanding photochemistry.

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Area of Science:

  • Photophysics and Photochemistry
  • Quantum Chemistry
  • Spectroscopy

Background:

  • Ultrafast intersystem crossing (ISC) is vital in transition metal complex photophysics and photochemistry.
  • Investigating these femtosecond processes requires advanced experimental and theoretical tools.
  • Multimode molecular dynamics beyond the Born-Oppenheimer approximation is challenging for large, metal-containing molecules.

Purpose of the Study:

  • To elucidate the role of spin-vibronic coupling in ultrafast ISC mechanisms in rhenium(I) complexes.
  • To develop theoretical models for simulating complex excited-state dynamics.
  • To correlate nuclear motion with ISC rates in [Re(X)(CO)3(bpy)] systems.

Main Methods:

  • Development of a model Hamiltonian incorporating vibronic and spin-orbit (SO) coupling.
  • Application of the linear vibronic coupling (LVC) approximation with harmonic potentials.
  • Simulation of ultrafast dynamics using multiconfiguration time-dependent Hartree (MCTDH) wavepacket propagation based on DFT and TD-DFT data.

Main Results:

  • Spin-vibronic coupling significantly influences ultrafast ISC in [Re(Br)(CO)3(bpy)], contrary to simple heavy atom effects.
  • Singlet excited-state lifetimes increase from Cl to Br to I complexes, correlating with the Re-X stretching mode.
  • A model successfully simulates 11 electronic excited states, including vibronic and SO coupling effects.

Conclusions:

  • Nuclear motion, specifically the Re-X stretching mode, plays a critical role in modulating ISC rates.
  • The developed theoretical framework provides insights into ultrafast dynamics in transition metal complexes.
  • This work bridges time-resolved experiments and quantum dynamical simulations for understanding photophysical processes.