Molecularly Engineered Ultralow‐Loss Soft Polymers for Deformable Printed Photonics

Achieving ultralow optical loss, broadband transparency, and mechanical softness within a single polymer network remains a long‐standing challenge for soft photonics. Here, we report a molecularly engineered class of UV‐curable thiol‐ene‐aromatic polymers that reconciles optical performance with mechanical compliance. By combining thiol crosslinkers with aromatic acrylates to form a low‐absorption network and introducing a phenyl‐bearing comonomer to mitigate near‐infrared vibrational overtone absorption while tuning elasticity and printability, the optimized A50 formulation exhibits ultralow optical attenuation of ∼0.004 dB cm − 1 , together with broadband transparency from 310 to 1100 nm and transmittance exceeding 90% above 380 nm at millimeter‐scale thicknesses. The same formulation remains mechanically compliant and supports high‐fidelity freeform UV‐based 3D printing, while exhibiting high thermal stability (onset ≈333°C). Leveraging this combination of optical and mechanical properties, we demonstrate deformable waveguides and bioinspired optomechanical devices capable of robust, multichannel optical sensing under repeated low‐force interactions and compliant manipulation. This work establishes a molecular design strategy for creating soft polymers with ultralow optical loss, providing a materials platform for next‐generation soft photonic interfaces and adaptive robotic systems.