Light-Programmable Morphology in Photothermal Polyurethanes Based on Stenhouse Salt as Photothermal Agent

Spatially controlled photothermal heating has enabled multiple advances in soft robotics, adaptive structures, and information encoding, but most implementations require multistep processing to localize photothermal additives. Here we report semicrystalline thermoplastic polyurethanes with backbone-integrated Stenhouse salt chromophores that enable single-step, micron-scale photopatterning and spatially selective photothermal heating (ΔT ≈ 15 °C) while retaining host mechanical performance (E ≈ 300 MPa; σ_y ≈ 12 MPa). A triflic acid-catalyzed step-growth synthesis tolerates the ionic Stenhouse salt diol, providing scalable, one-pot access to functional semicrystalline polyurethanes. White-light irradiation through a photomask is shown to trigger an irreversible cyclopentenone-forming rearrangement that permanently photobleaches exposed regions while preserving photothermal activity in masked areas. Subsequent green-light illumination heats the colored domains above the melting transition, while bleached regions remain below it, creating coexisting amorphous and semicrystalline zones within a single film. This light-addressable control over local crystallinity yields photothermal materials with spatially programmed mechanics, including sequential yielding, without additive redistribution.