An Efficient PCM Scheme for ESA Oscillator Strengths within the Unrelaxed TD-DFT Approximation

Area of Science:

• Computational Chemistry
• Theoretical Chemistry
• Physical Chemistry

Background:

• Excited-state absorption (ESA) is crucial for understanding photophysical processes.
• Accurate computation of ESA properties in solution remains challenging.
• Existing methods often neglect solvent effects or use simplified models.

Purpose of the Study:

• To propose and validate a time-dependent density functional theory (TD-DFT) protocol for computing unrelaxed excited-state absorption (ESA) oscillator strengths in solution.
• To incorporate both linear-response and state-specific solvent effects using the cLR² scheme within the PCM framework.
• To analyze the impact of two solvation regimes (fast and slow) on ESA properties.

Main Methods:

• Formulation of a TD-DFT protocol within the Polarizable Continuum Model (PCM) framework.
• Inclusion of linear-response and state-specific solvent effects via the cLR² scheme.
• Application of the protocol in two regimes: fast (no solvent relaxation) and slow (solvent relaxation allowed).

Main Results:

• Solvent effects predominantly shift oscillator strengths through variations in transition dipole moments.
• The magnitude of solvent effects is system- and state-dependent.
• Comparison with experimental ESA spectra shows improvement over in vacuo calculations, correctly identifying intense ESA regions.

Conclusions:

• The proposed TD-DFT protocol offers a significant improvement for calculating ESA properties in solution.
• The two solvation regimes (fast and slow) can yield distinct effects on ESA transition properties.
• While the protocol shows promise, distinguishing between the fast and slow regimes for specific systems remains an area for further investigation.