Demonstrations of Photochemical Reactions Using Methylene Blue and Ascorbic Acid

Abstract Photochemical processes are important in nature and technology but can be difficult for students to conceptualize and visualize. In this study, a visible-light-responsive photochromic system comprising methylene blue (MB+) and ascorbic acid (AsA) is used for classroom demonstrations of photochemical reactions. The aqueous system operates at room temperature and exhibits repeatable, reversible coloration under 405 nm blue–violet light, followed by spontaneous decolorization. Four core demonstrations and one optional extension are presented: (1) basic color change, (2) two-dimensional pattern formation, (3) effects of light wavelength and shielding, (4) effects of chemical conditions, and (5) visualization of solution flow using transient photogenerated color.