Applicability of DFT functionals for evaluating the first hyperpolarizability of phenol blue in solution

Area of Science:

• Computational chemistry
• Quantum chemistry
• Nonlinear optics

Background:

• Phenol blue (PB) exhibits interesting electronic properties.
• Solvent effects significantly influence molecular behavior.
• Accurate calculation of electronic hyperpolarizability (β) is crucial for materials science.

Purpose of the Study:

• To investigate the first electronic hyperpolarizability (β) of phenol blue (PB) in various solvents.
• To explore the relationship between β and solvent dielectric constants.
• To assess the performance of different density functional theory (DFT) functionals.

Main Methods:

• Density Functional Theory (DFT) calculations.
• Møller-Plesset second-order perturbation theory (MP2) for reference.
• Average solvent electrostatic configuration/free energy gradient method for geometry optimization.
• Quantum mechanics/molecular mechanics (QM/MM) methodology.

Main Results:

• The LC-BLYP functional best describes static and dynamic β values.
• β increases with diminishing bond length alternation (BLA), peaking at intermediate BLA.
• The difference between ground- and excited-state dipole moments (Δμ) impacts β in solution.

Conclusions:

• A clear relationship exists between PB's first hyperpolarizability and BLA in solution.
• Solvent polarity and Δμ significantly modulate β.
• Results align with experimental observations.