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.