Orthogonal stimuli-responsiveness in benzene-bridged bis-spiropyran covalently embedded silicone elastomers: mechano-induced red versus photo-induced green chromism

Compounds exhibiting multi-stimulus responsive behavior, exemplified by spiropyran, have demonstrated many potential and practical applications. However, current research primarily focuses on single-spiro systems, where the uniform open-ring state and color render effective differentiation of stimuli sources challenging. In this work, a novel benzene-bridged bis-spiropyran compound has been designed and synthesized, which is covalently bonded to a silicone matrix. This system exhibits orthogonal chromatic responses to mechanical force and ultraviolet (UV) light: mechanical force stimulation only activates one of the spiro-ring units within the benzene-bridged bis-spiropyran, resulting in a red colorimetric response (λ ∼ 515 nm), while UV light irradiation induces the cooperative opening of both spiro rings, generating a green colorimetric response (λ ∼ 645 nm). The red-green colorimetric transition exhibits a high contrast (Δλ > 130 nm) and rapid reversibility. Notably, the dual-stimulus orthogonal behavior of mechanical force-induced single-ring opening versus UV light-induced dual-ring activation reported herein stands in stark contrast to the phenomenon of simultaneous opening of dual spiro-rings induced by mechanical force observed in current studies. The covalent integration of the bis-spiropyran with silicone presents a controllable multi-stimulus responsive platform, providing a novel approach for stimulus recognition in complex environments and demonstrating significant potential in programmable smart sensing and dynamic display technologies.