Cucurbit[n]urils, the pumpkin shaped macrocyclic host molecules possessing a hydrophobic cavity and two identical carbonyl portals, have drawn a lot of attention in recent years due to their high‐affinity yet dynamic molecular recognition properties in water. The reversible and stimuli‐responsive nature of their host‐guest complexes imparts “smart” features leading to materials with intriguing optical, mechanical and morphological properties. In this review, we focus on the design of cucurbituril based luminescent materials in aqueous media as well in solid or film state. The design principles of fluorescent complexes, small assemblies as well as supramolecular polymers along with their stimuli‐responsive properties and applications in diverse areas such as optoelectronic devices, light harvesting, anti‐counterfeiting and information technology, cell imaging, etc are highlighted with selected examples from recent literature. We also discuss examples of room temperature phosphorescent materials derived from purely organic luminogens in the presence of cucurbiturils.
Bisimidazolium receptors, tagged with chromophoric pyrene at one end and linked to an n-alkyl chain at the other, underwent self-assembly in aqueous media depending on the length of the alkyl segment. The amphiphilic derivatives having n-decyl or longer chains, formed nano-assemblies with cyanic–green emission resulting from the stacked pyrene chromophores in the aggregates. The presence of positive surface charges on the multivalent aggregates led to ATP binding which was accompanied by a significant increase in the excimeric emission intensity. This provided a convenient way of monitoring ATP binding in a “turn-on” mode and an efficient detection of ATP was achieved in aqueous buffer and also in buffer containing 150 mM NaCl at physiological pH value. Furthermore, the multivalent aggregates demonstrated a significant selectivity in ATP detection over ADP, AMP and pyrophosphate.
Signal transduction is essential for the survival of living organisms, because it allows them to respond to the changes in external environments. In artificial systems, signal transduction has been exploited for the highly sensitive detection of analytes. Herein, a remarkable signal transduction, upon ATP binding, in the multivalent fibrillar nanoaggregates of anthracene conjugated imidazolium receptors is reported. The aggregates of one particular amphiphilic receptor sensed ATP in high pm concentrations with one ATP molecule essentially quenching the emission of thousands of receptors. A cooperative merging of the multivalent binding and signal transduction led to this superquenching and translated to an outstanding enhancement of more than a millionfold in the sensitivity of ATP detection by the nanoaggregates; in comparison to the “molecular” imidazolium receptors. Furthermore, an exceptional selectivity to ATP over other nucleotides was demonstrated.
Natural light-harvesting complexes collect energy from sunlight and transfer it to the reaction center through a cascade of energy and electron transfer steps. Artificial lightharvesting systems functioning in aqueous media mimic natural photosynthetic systems. However, their design remains a challenging task as closely packed antenna chromophores often undergo severe self-quenching. Herein, we report luminescent coassemblies between cationic pyrene-appended imidazolium amphiphiles and two anionic biopolymeric scaffolds, heparin and DNA in aqueous media. These co-assemblies served as excellent platforms for constructing artificial light-harvesting systems as upon co-embedding of multiple external dyes, highly efficient single-step and cascade energy transfer was observed from the pyrene donors to the acceptor dyes. Most notably, the efficiency of the energy transfer process was possible to modulate by employing multiple stimuli such as pH and temperature, and this resulted in the generation of multi-color luminescent materials in solution and film states, and they were also exploited in ratiometric temperature sensing. Their stimuli-responsive luminescence in the solid state was found to be advantageous for encryption studies.
Heparin,
an anionic biomacromolecule, is routinely used as an anticoagulant
during medical surgery to prevent blood clot formation and in the
treatment of several heart, lung, and circulatory disorders having
a higher risk of blood clotting. We herein report supramolecular polymeric
nanoassemblies of cationic pyrene-tagged bis-imidazolium amphiphiles
for heparin detection with high sensitivity and selectivity in aqueous
buffer, plasma, and serum media. The nano-assemblies exhibited cyan-green
excimeric emission in aqueous media, and their multivalent array of
positive surface charges allowed them to form co-assemblies with heparin,
resulting in significantly enhanced emission. This provided a convenient
method for heparin detection in buffer at nanomolar concentrations,
and most notably, a ratiometric fluorescence response was obtained
even in highly competitive 100% human serum and 100% human plasma
in a clinically relevant concentration range. Moreover, using the
heparin-based luminescent co-assemblies, protamine sulfate, a clinically
administered antidote to heparin, was also detected in 100% human
serum and 100% human plasma at sub-micromolar concentrations.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.