Light-Responsive CNPPV-Conjugated Polymer Nanoherbicide for Controlled Release of Usnic Acid

Abstract

We report a visible-light-activated nanobioherbicide based on the conjugated polymer poly(2,5-di(hexyloxy)cyanoterephthalylidene) (CNPPV) for the controlled delivery of the natural bioherbicide usnic acid (UA). The nanostructures were fabricated by an adapted nanoprecipitation method, yielding spherical nanoparticles with a mean hydrodynamic diameter of 162 ± 76 nm, polydispersity index < 0.25, and encapsulation efficiency > 80%. Photophysical studies demonstrated strong optical absorption and efficient photoresponsiveness under blue-light irradiation (450 nm). Light-triggered release experiments revealed non-Fickian transport behavior characterized by a Super Case II mechanism. The nanobioherbicide exhibited adequate colloidal stability during 90 days of protected storage and showed light-triggered release of UA, inducing a concentration-dependent photoinhibitory response in Lemna minor. This work demonstrates a visible-light-responsive nanoplatform for usnic acid delivery and provides proof-of-concept evidence of its phytotoxic effects in Lemna minor, supporting further investigation of conjugated polymers for agrochemical delivery.