Multistimuli-responsive organogels based on hydrazide and azobenzene derivatives

The behaviors of organogels of gelators containing hydrazide and azobenzene units connected via different flexible central spacers, 1-[4-(4'-methoxylphenylazo) phenoxy]-n-[(N-(4-nitrobenzoyl)-N'( benzoyl-4'-oxy) hydrazine)] alkane (En, n = 5, 6, 10) have been studied. The length and parity of the central flexible spacer play crucial roles in the gelation. E6 and E10 could form a stable organogel in DMF, and the critical gelation concentration of E10 is higher than that of E6, but no gelation is observed for compound E5. Xerogels of E6 and E10 from DMF exhibited fibrous aggregates. The organogels showed a photoinduced gel-to-precipitate transition under the irradiation by UV light irradiation, which was attributed to the photoisomerization of azobenzene. The trans-cis isomerization in gels further caused the morphological change from fibrous to globular aggregates. In addition, the organogel exhibited multiple stimuli-responsive behaviors upon exposure to stimuli such as temperature, anions and pH.