Luminescent Polymers from Natural Polyphenols via Phenol-Yne Click Polymerization

Natural polyphenols, recognized for their versatile chemical reactivity and sustainability, were utilized in the synthesis of poly(vinyl ether)s via phenol-yne click polymerization. This study focused on reactions between various natural polyphenols (including resveratrol, baicalein, gallic acid, and ellagic acid) and diyne esters, yielding fluorescent poly(vinyl ether)s (P1–P4) with tunable emission properties. Through systematic optimization of polymerization parameters, including monomer stoichiometry, reaction time, and temperature, substantial improvements in product yields (up to 89%) and weight-average molecular weights (up to 10300 g/mol) were achieved. Structural analyses confirmed that enol ether linkages were predominantly formed through anti-Markovnikov addition pathways. The resulting polymers exhibited remarkable spectral tunability, with emission wavelengths shifting from 448 nm (blue light, P3), through 504–516 nm (green light, P2 and P1), to 589 nm (orange light, P4). All polymers displayed notable red-shifted emission relative to their polyphenol precursors. Further investigation indicated that the tunable fluorescence of P1–P4 primarily originated from extended π-conjugation along the polyphenol-based polymer backbone, mediated by enol ether linkages, with minimal contribution from intermolecular interactions. This conclusion was supported by density functional theory (DFT) calculations and visualization of localized orbital locator (LOL-π) isosurfaces. Leveraging these optical properties, the polymers were successfully incorporated into multicolor (light-emitting diode) LED devices by blending with poly(vinyl alcohol) (PVA) matrices, resulting in emissions ranging from blue to orange.