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Partial Switching in Anil Crystals: Impact on the Second-Order Nonlinear Optical Properties
Noah Deveaux1, François Mairesse1, Benoît Champagne1
1Laboratory of Theoretical Chemistry, Namur Institute of Structured Matter, University of Namur, Rue de Bruxelles 61, Namur 5000, Belgium.
The Journal of Physical Chemistry Letters
|November 20, 2025
Summary
This study explores how partial switching affects optical properties in photochromic crystals using TD-DFT. Results show linear and non-linear optical responses depend on the keto/enol ratio, validating the calculation method.
Area of Science:
- Materials Science
- Computational Chemistry
- Optics
Background:
- Photochromic crystals exhibit tunable optical properties through reversible structural changes.
- Understanding the relationship between molecular switching and macroscopic optical response is crucial for material design.
Purpose of the Study:
- To investigate the influence of partial photochromic switching on linear and second-order nonlinear optical (NLO) properties.
- To assess the impact of keto/enol distribution on optical responses in anil crystals.
- To validate the reliability of TD-DFT calculations for predicting NLO contrasts in solid-state systems.
Main Methods:
- Time-dependent density functional theory (TD-DFT) calculations were employed.
- A periodic boundary conditions approach was used for anil crystals 4A and 4P.
- Calculations assessed optical properties as a function of keto/enol (K/E) distribution.
Main Results:
- Ground-state energies and linear susceptibilities showed additive behavior with K/E ratio.
- Band gaps exhibited system-specific trends: additive in 4A, modulated by switching in 4P.
- Second-harmonic generation (SHG) tensors showed additive and nonadditive characteristics, with 4P's dominant components near-linear evolution.
Conclusions:
- The study provides insights into the additive and nonadditive contributions to NLO properties in photochromic systems.
- The crystalline orbital TD-DFT approach is reliable for predicting NLO contrasts in solid-state photochromic materials.
- Results support the tunability of optical properties based on the K/E ratio.
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