From Spiropyran to a Circadian-Responsive Photochromic Supramolecular System for Sustainable Crop Protection: Enhanced Photostability, Biofilm Disintegration, and Foliar Adhesion.

Abstract

Biofilms establish protective sanctuaries that shield resident bacteria, facilitating resistance. Despite extensive efforts, current chemicals for biofilm eradication remain insufficient, with the reliance on single-structure antimicrobials further exacerbating resistance. Photoisomerizable spiropyran derivatives reversibly transition between conformational states, alternately exerting antimicrobial activity against pathogens and potentially mitigating resistance. However, the biofilm-eradicating potential of spiropyran derivatives remains unverified, while their application is hindered by limited fatigue resistance, suboptimal foliar affinity, and reliance on UV-induced isomerization, all of which are incompatible with sustainable agriculture. Herein, we present a supramolecular strategy to fabricate SpA6(MC)⊂CB[8], a self-assembled complex of the spiropyran derivative SpA6 and cucurbit[8]uril, offering day-night cycle isomerization, enhanced photostability, potent biofilm disruption, improved foliar adhesion, and high antibacterial activity. Notably, neither ambient light nor darkness attenuates its potency, enabling persistent antibacterial activity across diverse molecular configurations. In vivo studies demonstrate its superior dual protective/curative efficacy (54.73%/49.60%) at 200 µg mL-1 against bacterial leaf blight, surpassing thiazole copper (37.63%/33.58%) and bismerthiazol (31.20%/25.59%) without compromising safety, while extended indications reveal its enhanced efficacy (78.99%/63.50%) against citrus canker, outperforming thiazole copper (59.50%/41.42%). This work establishes a paradigm for developing light-responsive supramolecular agrochemicals that combine structural dynamism with enhanced functionality, offering sustainable solutions against plant pathogens.