Design and synthesis of novel coumarin compounds for plant hormone controlled release activated by light

This study reported the synthesis of the photoresponsive coumarin series for controlled releases of plant hormones and herbicides. The materials were designed by varying substituted positions of long alkoxy side chains (-OC16H33), introduced to gain adhesive properties on plant leaves, in the coumarin core structure. The target compounds were synthesized via Williamson reaction, Pechmann reaction and esterification, respectively. All chemical structures were characterized by 1H NMR, 13C NMR, FTIR, and mass spectroscopy. In addition, nanoemulsion of these compounds were prepares by using PVA as a stabilizer and as a surfactant. The optimized condition was obtained by using 3 wt% PVA, 1 wt% SDS, and 0.2 wt% of coumarin with a volume ratio of oil-in-water at 75:25. The particle size, wettability and photolysis of nanoformulations were studied. It was found that the obtained nanoemulsion gave high physical stability with average particle diameter about 292-403 nm and expresses good wettability (contact angle 48-57 degree) on Cassia fistula leaf surface. Moreover, the controlled releases of plant hormones and herbicides from photoresponsive compounds were studied by irradiating under the specific wavelength (365 nm) and normal sunlight. Photolysis was monitored by UV-vis absorption and emission. We found that the substituted position of the alkoxy group on coumarin rings and substituted position of the carboxylate linkage on indoles also effected a photolysis rate.