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

Abstract

A substituent mediated change in the mode of aggregation during saponification triggered transformation of two ester-containing Zn^II-complexes (A–B) into metallogels (MG_A–MG_B) has been presented. Structures of A and B have been inspired by reported complexes 1 and C4, which exhibited gelation via the saponification triggered method. A consists of an additional –OCH₃ group compared to 1, while B and C4 are structural isomers, i.e., identical except one positionally altered –OCH₃. During gelation, 1 and C4 exhibited ‘J-aggregation’, but herein, in similar conditions, A and B significantly acquire ‘H-aggregation’, leading to the formation of metallogels. This discrepancy has been addressed for the first time, which signified that gelators with isomeric dissimilarity acquired different modes of aggregation toward gelation. A distinguishing role of particular substituents has been revealed for a suitable mode of aggregation for this class of gelation, which is designated as ‘positional antagonism’. This has been susbtantiated by UV-vis, fluorescence, and ¹H-NMR spectroscopy as well as AFM, SEM, rheological, and DFT studies.