All‐Lignin Colloidal Particles Enable Structural Color and Photothermal Conversion

The scope of mimicking the optical control of natural systems is gradually expanding from color perception to functional applications such as photothermal conversion. However, photonic structures-including colloidal amorphous arrays and amorphous plasmonic arrays-are mostly derived from metals and inorganic materials, so far there have been no reports made of organic components. Here, a method for creating all-organic colloidal lignin particles (CLPs) enable structural color and photothermal conversion is reported. The intermolecular and intramolecular interactions facilitate lignin aggregation to form stable particles. By tailoring the particle size of CLPs, distinct near-infrared optical behaviors and photothermal efficiencies are achieved. Multiscale simulations reveal that smaller CLPs exhibit blueshifted structural color, stronger π-π stacking, and molecular conjugation, while concurrently enhancing Mie scattering and local electromagnetic field confinement at the mesoscale. The synergistic coupling of enhanced π-conjugation and photonic field effects enables efficient photothermal conversion. This work provides mechanistic insights into photothermal conversion in organic photonic materials and informs the rational design of sustainable functional colloidal amorphous arrays.