Polarizable H‐Bond Concept in Aromatic Poly(thiourea)s: Unprecedented High Refractive Index, Transmittance, and Degradability at Force to Enhance Lighting Efficiency

Abstract Developing transparent and highly refractive environmentally friendly polymers has not been realized yet toward sustainable optoelectronics. This work describes poly(thiourea)s ( PTU s) design following a new “polarizable group synergy” concept, combining highly polarizable hydrogen bonding groups and aromatic‐based spacers to form densely packed and high‐refractive‐index polymer networks. Specifically, PTUs containing m‐ and p ‐phenylene spacers exhibit an easy synthesis, high thermostability ( T _g = 159 °C), visible transparency (>92 %T at 1 µm‐film), ultra‐high refractive index ( n _D = 1.81) based on the random H‐bonding arrays with a high packing constant ( K _p = 0.738), and straightforward preparation of flexible films via solvent‐based techniques. Capitalizing on these assets, PTU ‐films are integrated into benchmark graphene‐based lighting device architectures based on the light‐emitting electrochemical cells (LECs) concept. A joint optical modeling and experimental validation confirm the increase in external quantum efficiency expected by the enhanced light out‐coupling of PTU ‐films. Finally, PTU s are efficiently depolymerized to low molecular weight compounds by simply adding diamines under heating, following the dynamic covalent bond exchange between thiourea moieties. Overall, this work highlights the PTU family as new promising materials with a unique polarizable H‐bond design to meet efficient and sustainable thin‐film lighting devices.