Fine‐Tuning of Saponification‐Triggered Gelation by Strategic Modification of Peripheral Substituents: Gelation Regulators

Abstract

A pioneering approach towards controlling the efficiency of saponification assisted gelation in ethyl ester based Zn -complexes have been described. Using four new ester containing bis-salen Zn complexes (C1-C4) involving different para-azo phenyl substituted ligands it has been clearly shown that gelation efficiency is greatly influenced by the electronic effects of the substituents (-H (C1), -CH (C2), -NO (C3), and -OCH (C4)). Morphological, photophysical, and rheological investigations corroborated the experimental observations well and established that gelation efficiency was enhanced with electron-withdrawing characteristics of substituents (C4<C2<C1<C3). This conclusion was also supported by DFT studies.

Acquiring preferred mode of aggregation through positional antagonism for saponification triggered gelation

“…However, C4 did not undergo proper gelation (reported efficiency for C1–C4 was C3 > C1 > C2 > C4 ). 19 This discrepancy has been attributed to the dissimilarity between C4 and B , which was nothing but the occupancy of –OCH 3 . In B , –OCH 3 is present at 5-phenyldiazenyl substituted o -vanillin that contains imine-linked isophthalate ring while C4 had –OCH 3 as a para -azo-phenyl ( p -a-p) substituted moiety.…”

“…18 Further, efficiency toward gelation for this class of gelators was also compared using four para -azophenyl-substituted Zn II -complexes ( C1–C4 ). These complexes differ only in having a dissimilar functional group at a fixed position called fn ; –H ( C1 ), –CH 3 ( C2 ), –NO 2 ( C3 ), and –OCH 3 ( C4 ), 19 which demonstrated substituent-mediated tuning for this type of gelation. Noticeably, it signified that this type of metallogels can simply be obtained by saponification through Zn II -complexes based on diethyl-5-aminoisophthalate-derived Schiff bases.…”