Structure−Function Studies of Modular Aromatics That Form Molecular Organogels

Abstract

Three urea-based aromatics 1-3, each with distinct steric and electronic characteristics, have been synthesized and their ability to undergo hierarchical assembly and gel organic solvents investigated. We have found that compound 1 promotes the sol-gel phase transition in primary alcohols (from CH3OH to C10H21OH; CGC < 15 mg/mL), while 2 and 3 do not. IR spectroscopy, X-ray powder diffraction (XRPD), and transmission electron microscopy (TEM) measurements show that 1 organizes into "cylinders" in primary alcohols, using three-centered hydrogen bonds and pi-pi aromatic interactions. The cylinders further organize into pairs through interdigitation of the methyl groups of the adjacent aromatic rings. Importantly, the lateral packing of the cylinders is enhanced as the bulk solvent polarity increases providing a mechanism for controlling the material's morphology via the solvophobic effect. Molecular mechanics (Amber) and semiempirical (AM1) calculations suggested similar conformational behavior but distinct electronic properties of 1-3. Thus, pi-deficient 2 without the methyl groups and pi-rich 3 without aromatic nitrogen fail to promote the sol-gel phase transition in alcohols due to their inability to undergo effective hierarchical assembly, which is necessary for the formation of a 3D fibrillar network. In addition, we have found that the ultrasonication of a supersaturated solution of 1 is necessary for the gelation. Presumably, a fast exchange of the aggregates of 1 is assisted with sonic waves to allow for the effective and "error free" assembly wherein an entangled net of fibers capable of encapsulating solvent molecules is formed.

Aggregation-induced blue shift of fluorescence emission due to suppression of TICT in a phenothiazine-based organogel

“…Low-molecular-weight gelators (LMWGs) have recently excited enormous interest from colloid chemists due to their unique supramolecular architectures and potential applications in optoelectronic devices, sensors, template synthesis, drug delivery, and biomimetics systems [1][2][3][4][5]. In general, the gels are colloidal matter in which the solvents are trapped in the network structures formed by a small quantity of gelators.…”

Self-assembly of fluorescent diimidazolium salts: tailor properties of the aggregates changing alkyl chain features

“…Indeed, signicantly higher C on were calculated for 44 Many reports have underlined that factor different from solvent polarity and viscosity, like size and shape of molecules can be crucial in determining self-assembly processes. 45,46 Consequently, to take in consideration geometrical features of solvents, we used DFT optimized geometries and Amber atomic radii, recently determined studying self-assembly processes of some phenyleneethynylene diimidazolium salts. 6 In particular, the ratio of the smallest to the largest molecular dimension (m/M) gives information about the shape of solvent molecule.…”

Ultrasound-induced modulations of tetrapeptide hierarchical 1-D self-assembly and underlying molecular structures via sonocrystallization

“…Another example was firstly described by Naota et al regarding organogelation by a pallado-macrocycle [5]. This was then extended to new peptide-based palladocomplexes [6], cyclotriveratrylenes [7], urea-derivatives [8][9][10], cholesterol-derivatives [11], glutamic dendrons [12], N-FMOCamino acids [13], and dual-component systems [14]. In these cases, ultrasound was thought to be capable of triggering change of molecular conformations, which results in a different packing of molecules and formation of 3-D networks of nanofibers regarding organogelation.…”