Multi‐Stimuli Response of Advanced Functional Spiropyran‐Based Smart Chromic Material: Acid Vapors Sensing Applications

Abstract Advanced functional molecules with multi‐stimuli responsiveness are crucial for multifunctional applications. One unique feature of such smart materials is their chromogenic properties, which provide real‐time indications of absorption changes. Herein, the general strategy for developing spiropyran (SP) based multi‐stimuli responsive material, which responds to solvent polarity, light, and acids, is presented. The advanced functional OH‐substituted SP (SP‐OH) is synthesized via a simple acid‐catalyzed ether hydrolysis reaction and confirmed using spectroscopic techniques. Furthermore, its solvato‐, photo‐ and acido‐chromic studies are investigated. The solvatochromism is examined in various organic solvents (TCM, DCM, DMF, DMSO, and MeOH). The photochromism is studied under 365, 405, and 530 nm light sources and dark conditions. Under 365 and 405 nm light sources, ring‐opening is induced, however, ring‐closing is induced using 530 nm, and darkness. The optimized time for complete ring‐opening is found to be 1 and 5 min for 365 and 405 nm, respectively. For ring‐closing, it is found at 5 and 20 min, corresponding to 530 nm and darkness, respectively. Additionally, free‐standing SP‐OH/PVA composite film is tested for photochromism and acidochromism with acid vapors (HCl, H₂SO₄, HNO₃, HCOOH, and CH₃COOH). Smart responsiveness of SP‐based material to studied stimuli suggests its suitability for multiple stimuli‐induced chromic sensing applications.