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Summary
This summary is machine-generated.

This study generalizes a time-dependent method for calculating intersystem crossing (ISC) rates, extending beyond the Condon approximation. The new approach accurately predicts ISC rates for various molecules, including rhodamine A, offering new insights into triplet formation pathways.

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Area of Science:

  • Theoretical Chemistry
  • Quantum Chemistry
  • Spectroscopy

Background:

  • Intersystem crossing (ISC) is crucial for photophysical processes.
  • The Condon approximation limits ISC rate calculations for certain electronic transitions.
  • El-Sayed rules identify transitions forbidden under the Condon approximation.

Purpose of the Study:

  • Generalize a time-dependent method for calculating ISC rates.
  • Extend the method beyond the Condon approximation to include vibronic effects.
  • Provide accurate theoretical predictions for ISC rates and triplet formation.

Main Methods:

  • Time-dependent method for ISC rate calculation.
  • Extension beyond the Condon approximation using linear dependence of spin-orbit matrix elements on nuclear coordinates.
  • Generating function formalism and multi-mode harmonic oscillator approximation.
  • Inclusion of finite-temperature effects with Boltzmann population.

Main Results:

  • Developed a generalized method for calculating ISC rates, incorporating vibronic contributions.
  • Achieved excellent agreement with literature data for xanthone, thioxanthone, thionine, and free-base porphyrin.
  • Computed vibronic one-photon spectra for free-base porphyrin and free-base chlorin.
  • Quantitatively determined triplet formation rates in rhodamine A for the first time, identifying the S1↝ T2 channel as dominant.

Conclusions:

  • The generalized method accurately calculates ISC rates, even for transitions forbidden by the Condon approximation.
  • The approach provides valuable theoretical insights into photophysical processes and triplet state formation.
  • This work offers a robust theoretical framework for studying ISC in complex molecules.