Dual-State Emissive Imidazole-Based Photoswitches by Design and Their Use for Data Encryption

Herein, we report the rational design, synthesis, and photophysical characterization of a new family of N-substituted 2,4,5-arylimidazole derivatives that integrate excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT) to achieve reversible photochromism. Solvatochromic studies revealed pronounced shifts in emission (392-457 nm) and large Stokes shifts (4252-7776 cm-1), indicating significant excited-state charge separation driven by the N,N-diethylamino donor group. Lippert-Mataga and time-resolved photoluminescence (TRPL) analysis confirmed the dominant ICT character, particularly for N-aryl derivatives (Δμ = 9.26-9.73 D), which exhibited larger dipole moment changes than N-alkyl derivatives (Δμ = 8.17-8.34 D). Upon UV irradiation (395 nm), reversible E/Z keto photoisomerization was observed both in solution and in the solid state, confirmed by UV-vis, photoluminescence, and infrared spectroscopy. Single crystal X-ray diffraction showed that N-alkyl chain length enhances torsional angles, directly influencing the photoswitching behavior and dual-state emissive properties with quantum yields of Φ = 25% in toluene and Φ = 77% in the solid state for IM-N-Bu. Thermal treatment (80 °C) enabled full reversibility in toluene and poly(methyl methacrylate) (PMMA) films over multiple cycles, which were applied to data encryption, demonstrating their potential in photonic and information security technologies.