Phytoene desaturase (PDS) is a critical functional enzyme in blocking ζ-carotene biosynthesis and is one of the bleaching herbicide targets. At present, norflurazon (NRF) is the only commercial pyridazine herbicide targeting PDS. Therefore, developing new and diverse pyridazine herbicides targeting PDS is urgently required. In this study, diflufenican (BF) was used as the lead compound, and a scaffold-hopping strategy was employed to design and synthesize some pyridazine derivatives based on the action mode of BF and PDS. The preemergence herbicidal activity tests revealed that compound 6-chloro-N-(2,4-difluorophenyl)-3-(3-(trifluoromethyl)phenoxy)pyridazine-4-carboxamide (B1) with 2,4-diF substitution in the benzeneamino ring showed 100% inhibition rates against the roots and stems of Echinochloa crus-galli and Portulaca oleracea at 100 μg/mL, superior to the inhibition rates of BF. Meanwhile, compound B1 demonstrated excellent postemergence herbicidal activity against broadleaf weeds, which was similar to that of BF (inhibition rate of 100%) but superior to that of NRF. This indicated that 6-Cl in the pyridazine ring is the key group for postemergence herbicidal activity. In addition, compound B1 could induce downregulation of PDS gene expression, 15-cis-phytoene accumulation, and Y(II) deficiency and prevent photosynthesis. Therefore, B1 can be considered as a promising candidate for developing high-efficiency PDS inhibitors.

Host-guest recognition-based macrocycle in macrocycle to form “Russian Doll” assemblies remains an interesting topic in supramolecular chemistry. Herein, a macrocycle-in-macrocycle assembly was studied using cucurbit[10]uril (Q[10]) and the smallest cucurbituril-like macrocycle (TD[4]). X-ray crystal structure analysis revealed that TD[4] was encapsulated in the cavity of Q[10] to form a 1:1 complex. Importantly, competitive guest studies suggested that TD[4] had the highest binding constant with the Q[10] host among the guests used, including Q[5], Me8TD[4], and amantadine molecules in water. Our results provided a new cucurbituril-based Russian-doll structure containing both the largest and smallest cavities of the cucurbiturils, which expanded the family of molecular Russian dolls.