Spatiotemporal Release of Singlet Oxygen in Low Molecular Weight Organo-Gels Upon Thermal or Photochemical External Stimuli.

The first example of a material capable of spatiotemporal catch and release of singlet oxygen (1O2) in gel phase is presented. Several low molecular weight organogelators based around an oxotriphenylhexanoate (OTHO) core are developed and optimized with regard to; their gelation properties, and ability of releasing 1O2 upon thermal and/or photochemical external stimuli, in both gel phase and solution. Remarkably, reversible phase transitioning between the gel and solution phase are also demonstrated. Taken together two complementary modes of releasing 1O2, one thermally controlled over time, and one rapid release by means of photochemical stimuli is disclosed. These findings represent the first phase reversible system where function and aggregation properties can be controlled independently, and thus pave the way for novel applications in material sciences as well as in life sciences.

Amine-rich Nickel(II)-Xerogel as a Highly Active Bifunctional Metallo-organo Catalyst for Aqueous Knoevenagel Condensation and Solvent-free CO2 Cycloaddition.

Metallogels formed from supramolecular interactions of low-molecular-weight gelators (LMWGs) combine the qualities of heterogeneous catalysts and offer the advantages of multifunctionality owing to the facile installation of desired task-specific moieties on the surface and along the channels of the gels. We discuss the applications of a triazole-based Ni(II) gel-derived xerogel (NiXero) having a high density of Ni(II)-nodes and appended primary amines as a recyclable heterogeneous catalyst for Knoevenagel condensation of aldehyde and malononitrile in water and the solvent-free cycloaddition of CO2 to form a series of cyclic carbonates with near-quantitative conversion of the respective epoxides, with low catalyst loading (0.59 mol %), high catalyst stability, and recyclability. The structural advantages of NiXero, due to the concurrent presence of bifunctional Lewis acid-base sites on the channels, open Ni(II) nodes, Ntriazole, pendant -NH2 and its chemical stability, are conducive to the cooperative heterogeneous catalytic activity under mild conditions. This work emphasizes the effective amalgamation of metals with purpose-built ligand systems for the construction of metallogels and their utility as heterogeneous catalysts for desired organic transformations.

Exploring amine-rich supramolecular silver(I) metallogels for autonomous self-healing and as catalysts for a three component coupling reaction.

A series of Ag(I) supramolecular organo-aqueous gels have been synthesized in the presence of an amine-rich triazole ligand as a gelator. Judicious choice of the triazole derivative and counter anion allows a desired spatial orientation of the pendant amine functionality to accentuate the gelation ability and autonomous self-healability via hydrogen bonding. In addition, the hydrogen bond donors, i.e. pendant -NH2 groups, offer a critical proximity of counter anions to the Lewis acidic Ag(I) and the reactants for promoting a three component coupling reaction of an aldehyde, a terminal alkyne and an amine, giving expedient access to propargyl amines, with remarkable functional group tolerance for both aromatic and aliphatic aldehydes, and aryl acetylenes. Experiments substantiate the pivotal role of counter anions and H-bonding interactions in the observed preference for propargylamines over the diacetylene by-product. Our catalyst is robust, bench-stable, and recyclable, and demonstrates a catalytic efficiency comparable to or better than those of reported systems. The catalyst was found equally effective for the gram-scale synthesis of propargylamines. Our approach lies at the intersection of metal-based, H-bond-mediated counter anion-tuned catalysis, evincing a potential for the development of purpose-built supramolecular gels for desired catalytic applications in the future.

Multistimuli-Responsive Self-Healable and Moldable Nickel(II)-Based Gels for Reversible Gas Adsorption and Palladium Sequestration via Gel-to-Gel Transformation.

We report the in situ formation of Ni-based supramolecular organogel and organic-aqueous gels using amine appended triazole ligand, having varying morphology and rheological properties. These gels are self-healable and moldable or injectable respectively depending on the absence or presence of water in the gelation medium. Our studies reveal that the formation and rupture of hydrogen bonds assisted by the solvent movement is responsible for the self-healing nature of the gels. The porous structure of the gel has been observed from the migration of dye molecules on the self-healed gel. In addition, the gels show dual function of reversible adsorption of toxic gases and sequestration of heavy metal ions, especially palladium via  gel-to-gel transformation. It is imperative to stress that such transformation is extremely rare for small molecule based metallogels. The dynamic nature of Ni-Ntriazole interactions has been utilized in achieving the reversible gas/vapor responsive behavior of the metallogels, which could be suitable in developing colorimetric probes for the detection of toxic gases and heavy metal ions. Such multifunctional gels are exceptional in contemporary literature and are expected to find utility in fabricating smart multistimuli-responsive gel-based materials in the future.