Molecular Nuances Governing the Self-Assembly of 1,3:2,4-Dibenzylidene-d-sorbitol

Abstract

1,3:2,4-Dibenzylidene-d-sorbitol (DBS) is the gold-standard for low-molecular-weight organogelators (LMOGs). DBS gels a wide array of solvents, as illustrated by the large Hansen sphere representing gels (2δ_d = 33.5 MPa^1/2, δ_p = 7.5 MPa^1/2, and δ_h = 8.7 MPa^1/2; radius = 11.2 MPa^1/2). Derivatives of DBS have been synthesized to isolate and determine molecular features essential for organogelation. In this work, π-π stacking and hydrogen bonding are the major noncovalent interactions examined. The importance of π-π stacking was studied using 1,3:2,4 dicyclohexanecarboxylidene-d-sorbitol (DCHS), which eliminates possible π-π stacking while still conserving the other structural aspects of DBS. The replacement of the benzyl groups with cyclohexyl groups led to a very a poor gelator; only one of the several solvents examined, carbon tetrachloride, formed a gel. 1,3:2,4-Diethylidene-d-sorbitol (DES), another DBS analogue incapable of π-π stacking but with very different polarity, gelated a large Hansen space (2δ_d = 34.0 MPa^1/2, δ_p = 10.9 MPa^1/2, and δ_h = 10.8 MPa^1/2; radius = 9.2 MPa^1/2). DES gels solvents with higher δ_p and δ_h values than DBS. To assess the role of hydrogen bonding, DBS was acetalated (A-DBS), and it was found that the Hansen space gelated by A-DBS shifted to less polar solvents with higher hydrogen-bonding Hansen solubility parameters (HSPs) (2δ_d = 33.8 MPa^1/2, δ_p = 6.3 MPa^1/2, and δ_h = 9.6 MPa^1/2; radius = 11.1 MPa^1/2) than for DBS. These systematic structural modifications are the first step in exploring how specific intermolecular features alter aspects of Hansen space corresponding to positive gelation outcomes.