Fig. 1. Schematic illustration of the isolated emitter doping into the film for UOP.

a Demonstration of stabilizing molecules by attractive (top) and repulsive (bottom) interactions. b Intermolecular interactions between the emitters and polymer matrix in film. The schematic diagram of hydrogen bonding between the polymer chain and carboxylic group (left) as well as the repulsive interactions between the aromatic hydrogen of the emitter and the hydroxyl hydrogen in polymer (right). Inset: photographs of flexible transparent film with UOP taken under daylight (top), excitation by UV light (middle) and after the removal of the UV excitation (bottom), respectively. c Chemical structures of the emitters.