Photosensitivity in the uncatalyzed CHD–bromate Belousov–Zhabotinsky reaction revealed by ESR spin trapping

Abstract

Photo-addressable chemical oscillators convert light into time-resolved chemical and electrical outputs. We show that the uncatalyzed 1,4-cyclohexanedione–bromate BZ (CHD–BZ) reaction is light responsive via a radical generated pathway. The ESR spin trap (DMPO) reveals an atypical nitroxide pattern (β-H ≈ 0.3 mT) consistent with acid-promoted DMPO ring opening; ESR intensity follows the bromide oscillation. A brief visible pulse reproducibly increases [Br⁻] and amplifies the nitroxide signal ∼3 times. Substitution of CHD to 1,4-hydroquinone reproduces light-only features, and raises Br⁻ intensity, supporting a photoactivated, radical-mediated route involving the H₂Q/ semiquinone couple. CHD–BZ serves as a photosensor with phase or ESR-amplitude readouts.