Methodological keys for accurate pKa* simulations.

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Photochemistry

Background:

• Photoacids exhibit enhanced proton donation in excited states, crucial for materials science.
• Experimental determination of excited-state dissociation constants (pKa*) is difficult due to short excited-state lifetimes.

Purpose of the Study:

• To establish reliable protocols for calculating photoacid excited-state dissociation constants (pKa*) using advanced computational methods.
• To compare different theoretical approaches within the PCM-TD-DFT formalism for accuracy.

Main Methods:

• Utilized the Polarizable Continuum Model Time-Dependent Density Functional Theory (PCM-TD-DFT) formalism.
• Implemented both corrected linear response (cLR) and state-specific (SS) approaches.
• Compared equilibrium (eq) and non-equilibrium (neq) solvent models.

Main Results:

• The state-specific TD-DFT formalism, combined with the Born-Haber cycle (eq limit) or Föster cycle (neq limit), yields results consistent with experimental data.
• Non-equilibrium solvent models with the Föster cycle and absorption energies showed good agreement.
• The study validated specific PCM-TD-DFT protocols for pKa* calculations.

Conclusions:

• Developed and validated robust computational protocols for determining photoacid pKa* values.
• The SS-TD-DFT method provides a reliable pathway for understanding photoacid behavior.
• Findings facilitate the design of novel photoacid-based materials.