Masuma Khatun, Pranesh Chowdhury, Bipasha Saha, Mahasweta Nandi, Ashok Mandi, Arindam Ray, Keya Ghosh, Gourab Kanti Das
Advanced reversible photochromism in the dual phases (solid and liquid phases of the same material) is vital for practical device integration. In this study, a nonphotochromic Schiff base ligand, rhodamine B-3,5-di tert -butylsalicylaldehyde hydrazone (L-2), and its Zn complex (L-2-Zn Complex) are synthesized to achieve dual-phase photochromism. Job’s plot (1:1 stoichiometry), isosbestic point (progress of the reaction), ESI-MS (mass of the product), and Benesi–Hildebrand analysis (binding constant = 4.81 × 10 4 M –1 ) confirm the complex formation. The complex exhibits a reversible color change from pale greenish-yellow to deep purple-pink under UV light (photoconversion) and reverts in the dark (photoreversion) or upon heating (thermoreversion), both in solution and on solid support. Poloxamer-407 acts as the most efficient solid support through the formation of a SCM (soft coordination microenvironment). The SCM is a significant strategy for a solid-state photochromic system. The polymer-supported dual-phase photochromic material becomes easy processable, quicker responsive, better fatigue durable, and multiwavelength (UV + vis) excitable (i.e., dual mode photochromism, DMP). Thus, it makes a significant advancement over single-phase metal-guided photochromism. UV–vis spectra reveal an absorption band at 553 nm due to photocoloration. The initial (pale greenish-yellow) form emits a strong emission at 526 nm (greenish-yellow), while the final (purple pink) form exhibits weak split bands at 522 and 580 nm. Both photoconversion and thermoreversion follow first-order kinetics with a rate constant of 1.04 × 10 –3 s –1 and 3.49 × 10 –4 s –1 at 20 °C, respectively. Thermal bleaching accelerates with increasing temperature and becomes optimum at 50 °C. Spectrokinetic, thermodynamic, and DFT analyses confirm a unique dual-phase metal-guided photochromic system with potential for advanced optical applications in photopatterning and photoinking.