Solid-State Photochromism of Schiff Bases

Schiff bases, defined by the imine linkage between an amine and an aldehyde or ketone, have emerged as versatile molecular switches in the solid state. Photochromism in these materials involves reversible light-induced colour changes driven by structural reorganisation such as enol–keto tautomerism or cis–trans isomerisation. In the crystalline phase, the rigidity of the lattice, hydrogen-bonding networks and π–π stacking interactions all modulate the efficiency, fatigue resistance and kinetics of the photochromic response. Fine-tuning substituents on the aromatic rings can control molecular planarity, intramolecular hydrogen bonding strength and the propensity for aggregation-induced phenomena. As a result, researchers have demonstrated that crystal engineering—through choice of substituents, co-crystallisation or host matrices—offers a route to optimise switching wavelengths, achieve bistability at ambient conditions and integrate these compounds into optoelectronic devices, sensors for environmental monitoring and data-storage media. Advances in spectroscopic, diffraction and computational methods now allow a detailed understanding of how solid-state packing and intermolecular forces govern photochromic performance, opening pathways for rational design of robust, reversible chromic materials.

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Solid-State Photochromism of Schiff Bases publication trend

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Technical terms

Photochromism: Reversible transformation between two molecular states with different absorption spectra induced by light.

Schiff base: An organic compound featuring a C=N imine bond formed by condensation of a primary amine with a carbonyl compound.

Enol–keto tautomerism: Equilibrium between isomeric forms differing by proton transfer, one bearing an OH and a C=C bond and the other a C=O and CH bond.

Polymorphism: The phenomenon whereby a solid material can adopt more than one crystal structure with distinct packing arrangements.

Aggregation-induced emission: Enhancement of fluorescence emission when molecules form aggregates, often due to restricted intramolecular motion.

References

1. Unraveling the Effects of Co-Crystallization on the UV/Vis Absorption Spectra of an N-Salicylideneaniline Derivative. A Computational RI-CC2 Investigation. Molecules (2020).
2. Aggregation-Induced Emission Enhancement and Solid-State Photoswitching of Crystalline Carbazole N‑Salicylidene Anilines. ACS Omega (2024).
3. Synthesis and structures of three isoxazole-containing Schiff bases. Acta Crystallographica Section C: Structural Chemistry (2020).
4. Selected solid-state behaviour of three di-tert-butyl-substituted N-salicylideneaniline derivatives: temperature-induced phase transitions and chromic behaviour. Acta Crystallographica Section C: Structural Chemistry (2021).