Synthesis and properties of coumarin-derived organogelators

Synthesis and characterization of coumarin containing fluorescent sugar based gelators

Carbohydrate based self-assembling systems containing coumarin functional groups are interesting class of materials. The unique fluorescence properties can be useful for many practical applications especially as biological probes. Coumarin containing low molecular weight gelators are especially interesting compounds with great potentials for new advanced molecular systems with multiple functions. We have synthesized and characterized a series of eleven coumarin based glucose and glucosamine derivatives. The structures of these compounds are based on the existing good performing supramolecular gelators through rational designs. These include three coumarin derivatives linked to anomeric positons of per-acetylated D-glucose and D-glucosamine via 1,2,3-triazole linkage , and eight4,6-benzylidene acetal protected D-glucosamine derivatives with various coumarin moieties attached to the C-2 positions through several different linkers. The gelation properties and fluorescence properties of these novel coumarin derivatives are studied and several self-assembling coumarin derivatives are also molecular gelators, which may have wide range of applications.

Adjustability and Versatility of Molecular Packing Patterns in Asymmetric Coumarin Liquid Crystals Supramolecular Helical Column Structures

Coumarin asymmetric multi-chain liquid crystals (LCs) were synthesized using click reaction, with coumarin core and 1,2,3-triazole dendritic wings on both sides. The properties of these LCs and the resulting gels were investigated using polarized optical microscopy (POM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and scanning electron microscopy (SEM). These polycatenars demonstrate the ability to self-assemble into columnar LCs phases, exhibiting p4 mm symmetry in their bulk states. In DMF solvent, ether compounds yield gels with notably more ordered, spherical flower-like morphologies, while ester compounds produce gels that are less ordered and exhibit a nanosphere morphology. The findings indicate that the polarities of both the linkages and the solvents play a critical role in the formation of supramolecular nanostructures. Interestingly, the 2 was proved as promising imaging probe for latent fingerprints (LFPs) and fluorescent fingerprints images were obtained with high-resolution, which showed potential practical application for LFPs detection. Additionally, LCs compounds are used as dopants to modify the poly(3,4-ethylenedioxythiophene):polystyrene (PEDOT:PSS) injection layer of Organic silicone-based heterojunction solar cells (HSCs). Finally, Density functional theory (DFT) calculations are performed to theoretically study such as geometric structure, frontier molecular orbitals, molecular electrostatic potential, and dipole moment.

Stimuli responsive dynamic transformations in supramolecular gels

Supramolecular gels are formed by the self-assembly of small molecules under the influence of various non-covalent interactions. As the interactions are individually weak and reversible, it is possible to perturb the gels easily, which in turn enables fine tuning of their properties. Synthetic supramolecular gels are kinetically trapped and usually do not show time variable changes in material properties after formation. However, such materials potentially become switchable when exposed to external stimuli like temperature, pH, light, enzyme, redox, and chemical analytes resulting in reconfiguration of gel matrix into a different type of network. Such transformations allow gel-to-gel transitions while the changes in the molecular aggregation result in alteration of physical and chemical properties of the gel with time. Here, we discuss various methods that have been used to achieve gel-to-gel transitions by modifying a pre-formed gel material through external perturbation. We also describe methods that allow time-dependent autonomous switching of gels into different networks enabling synthesis of next generation functional materials. Dynamic modification of gels allows construction of an array of supramolecular gels with various properties from a single material which eventually extend the limit of applications of the gels. In some cases, gel-to-gel transitions lead to materials that cannot be accessed directly. Finally, we point out the necessity and possibility of further exploration of the field.

Structure–property relationship of novel supramolecular gels based on coumarins

LMWGs based on coumarins could form supramolecular gels with unusual mechanical properties explained by its interactions at theoretical level.

A coumarin embedded highly sensitive nitric oxide fluorescent sensor: kinetic assay and bio-imaging applications

Fluorescence spectroscopy is a significant bio-analytical technique for specific detection of nitric oxide (NO) and for broadcasting the in vitro and in vivo biological activities of this gasotransmitter. Herein, a benzo-coumarin embedded smart molecular probe (BCM) is employed for NO sensing through detailed fluorescence studies in purely aqueous medium. All the spectroscopic analysis and literature reports clearly validate the mechanistic insight of this sensing strategy i.e., the initial formation of 1,2,3,4-oxatriazole on treatment of the probe with NO which finally converted to its carboxylic acid derivative. This oxatriazole formation results in a drastic enhancement in fluoroscence intensity due to the photoinduced electron transfer (PET) effect. The kinetic investigation unveils the second and first-order dependency on [NO] and [BCM] respectively. The very low detection limit (16 nM), high fluorescence enhancement (123 fold) in aqueous medium and good formation constant (Kf = (4.33 ± 0.48) × 104 M-1) along with pH invariability, non-cytotoxicity, biocompatibility and cell permeability make this probe a very effective one for tracking NO intracellularly.

Gels with sense: supramolecular materials that respond to heat, light and sound

Advances in the field of supramolecular chemistry have made it possible, in many situations, to reliably engineer soft materials to address a specific technological problem. Particularly exciting are "smart" gels that undergo reversible physical changes on exposure to remote, non-invasive environmental stimuli. This review explores the development of gels which are transformed by heat, light and ultrasound, as well as other mechanical inputs, applied voltages and magnetic fields. Focusing on small-molecule gelators, but with reference to organic polymers and metal-organic systems, we examine how the structures of gelator assemblies influence the physical and chemical mechanisms leading to thermo-, photo- and mechano-switchable behaviour. In addition, we evaluate how the unique and versatile properties of smart materials may be exploited in a wide range of applications, including catalysis, crystal growth, ion sensing, drug delivery, data storage and biomaterial replacement.

Photoresponsive gelators

We review the different approaches that have been used to form low molecular weight gels that respond to light.