Direct polymerization of tyrosine conjugates into melanin-like polymers for efficient protection of photosensitive pesticides

Melanin-inspired materials are being increasingly utilized across diverse areas, with their unique light absorption properties playing a decisive role in multiple domains. However, constrained by the structural complexity, effective strategies for controlling their light absorption properties remain limited, which mainly focus on modulating intramolecular conjugation through molecular doping. Nevertheless, these strategies have hit a bottleneck in regulating the light absorption properties due to constraints in doping levels and the oversight of the critical potential for modulating intermolecular conjugation. In this work, we proposed a modular and facile method to prepare a series of melanin-like polymers with excellent ultraviolet (UV) absorption properties through the direct polymerization of tyrosine-oligo(ethylene glycol) (OEG) conjugates. Detailed structural analysis revealed that the introduction of OEG chains into the resulting polymers could disrupt the intramolecular conjugations by inhibiting the oxidation and cyclization of phenolic units and simultaneously restricting the intermolecular conjugations through steric hindrance that prevented tight packing of the oligomers. These synergistic effects significantly increased the energy bandgap of the polymers, effectively suppressing the redshift in their absorption spectra and ultimately enhancing the UV absorption. These melanin-like polymers with boosted UV absorption capabilities demonstrated excellent performance in the efficient protection of photosensitive pesticides.