Fluorogenic conjugated polymer fibers from amphiphilic diacetylene supramolecules

Self-Assembly of Alkylamido Isophthalic Acids toward the Design of a Supergelator: Phase-Selective Gelation and Dye Adsorption

A new series of 5-alkylamido isophthalic acid (ISA) derivatives with varying single and twin alkyl chain lengths were designed and synthesized as potential supramolecular organogelators. 5-alkylamido ISAs with linear or branched alkyl tail-groups of different lengths were effective gelators for low polarity solvents. In particular, among the presented series, a derivative with a branched, 24 carbon atom tail-group behaves as a “supergelator” with up to twenty organic solvents forming gels that are highly stable over time. The gelation behavior was analyzed using Hansen solubility parameters, and the thermal stability and viscoelastic properties of select gels were characterized. Microscopy, spectroscopy, powder X-ray diffraction, and computer modeling studies were consistent with a hierarchical self-assembly process involving the formation of cyclic H-bonded hexamers via the ISA carboxylic acid groups, which stack into elementary fibers stabilized by H-bonding of the amide linker groups and π–π stacking of the aromatic groups. These new nanomaterials exhibited potential for the phase-selective gelation of oil from oil–water mixtures and dye uptake from contaminated water. The work expands upon the design and synthesis of supramolecular self-assembled nanomaterials and their application in water purification/remediation.

Fabrication of Helical Nanoribbon Polydiacetylene via Supramolecular Gelation: Circularly Polarized Luminescence and Novel Diagnostic Chiroptical Signals for Sensing

Four kinds of commercially available diacetylene (DA) monomers with different chain length, diacetylene positions were fabricated into the organogels via mixing with a chaperone gelator, an amphiphilic l-histidine ester derivative LHC18 that can help the nongelator to form gels. Upon photo irradiation with a 254 nm UV light, the white gels underwent topochemical reaction and turned into red or blue gels, depending on the DA monomer structures. Through the gel formation, the molecular chirality of LHC18 can be transferred to the polydiacetylene (PDA) and helical nanoribbon structures were obtained. The blue gels showed a clear response to stimuli such as pH variation, heating, mechanical force and organic solvents, and turned into red gels. Interestingly, the blue gel showed strong supramolecular chirality, which could be turned off or changed into red phase CD signals. Such changes in chiroptical signals depended on the external heating and various organic solvents. In the case of heating, the blue gel changed into red one, which showed both strong CD signals and circularly polarized luminescence. In the case of organic solvents, although all the tested solvents made the blue gel to red, only some of them could keep the CD signals, thus providing additional sensing capacity of the PDA system. So far, the blue-to-red color change and the "fluorescence on" was widely used as colorimetric and fluorogenic diagnostic signals for PDA, here we showed an additional chiroptical diagnostic signal for a more precise sensing by using the helical PDA.

Stimuli-Responsive Matrix-Assisted Colorimetric Water Indicator of Polydiacetylene Nanofibers

An alternative signal transduction mechanism of polydiacetylene (PDA) sensors is devised by combining stimuli-responsive polymer hydrogel as a matrix and PDA sensory materials as a signal-generating component. We hypothesized that volumetric expansion of the polymer hydrogel matrix by means of external stimuli can impose stress on the imbedded PDA materials, generating a sensory signal. PDA assembly as a sensory component was ionically linked with the alginate hydrogel in order to transfer the volumetric expansion force of alginate hydrogel efficiently to the sensory PDA molecules. Under the same swelling ratio of alginate hydrogel, alginate gel having embedded 1-dimensional thin PDA nanofibers (∼20 nm diameter) presented a sharp color change while 0-dimensional PDA liposome did not give any sensory signal when it was integrated in alginate gel. The results implied that dimensionality is an important design factor to realize stimuli-responsive matrix-driven colorimetric PDA sensory systems; more effective contact points between 1-dimensional PDA nanofibers and the alginate matrix much more effectively transfer the external stress exerted by the volumetric expansion force, and thin PDA nanofibers respond more sensitively to the stress.

Polydiacetylenes: supramolecular smart materials with a structural hierarchy for sensing, imaging and display applications

While a large variety of conjugated polymers exist, polydiacetylenes (PDAs) remain a major research area among scientists due to their interesting optical, spectral, electronic, and structural properties. Heavily reviewed in regards to their stimuli responsive properties, much is known about the assortment of sensing and detection capabilities of PDAs. In this article, we look more upon the structural diversities of polydiacetylenes that have been achieved in recent years, particularly from a hierarchical perspective of 1, 2, and 3-dimensional configurations. In addition, we examine how these different dimensional arrangements of PDAs have heralded clear applications in several key areas. Successful integration of these stimuli-responsive "smart" materials into various geometries has required researchers to have a comprehensive understanding of both the fabrication and synthesis processes, as well as the signalling mechanism for the optical, fluorogenic or spectral transitions. The on-going discovery of new PDA formulations continues to provide interesting structural manifestations such as liposomes, tubes, fibres, organic/inorganic incorporated hybrids and composite structures. By highlighting some of the recent conceptual and technological developments, we hope to provide a measure of the current pace in new PDA derivative development as core components in efficient sensor, imaging and display systems.