Synthesis, Morphology, and Sensory Applications of Multifunctional Rod–Coil–Coil Triblock Copolymers and Their Electrospun Nanofibers

We report the synthesis, morphology, and applications of conjugated rod–coil–coil triblock copolymers, polyfluorene<i>-block-</i>poly­(<i>N</i>-isopropylacrylamide)<i>-block</i>-poly­(N-methylolacrylamide) (<b>PF</b><b>-</b><i><b>b</b></i><b>-</b><b>PNIPAAm</b><i><b>-b-</b></i><b>PNMA</b>), prepared by atom transfer radical polymerization first and followed by click coupling reaction. The blocks of PF, PNIPAAm, and PNMA were designed for fluorescent probing, hydrophilic thermo-responsive and chemically cross-linking, respectively. In the following, the electrospun (ES) nanofibers of PF-<i>b</i>-PNIPAAm-<i>b</i>-PNMA were prepared in pure water using a single-capillary spinneret. The SAXS and TEM results suggested the lamellar structure of the <b>PF</b><b>-</b><i><b>b</b></i><b>-</b><b>PNIPAAm</b><b>-</b><i><b>b</b></i><b>-</b><b>PNMA</b> along the fiber axis. These obtained nanofibers showed outstanding wettability and dimension stability in the aqueous solution, and resulted in a reversible on/off transition on photoluminescence as the temperatures varied. Furthermore, the high surface/volume ratio of the ES nanofibers efficiently enhanced the temperature-sensitivity and responsive speed compared to those of the drop-cast film. The results indicated that the ES nanofibers of the conjugated rod–coil block copolymers would have potential applications for multifunctional sensory devices

Soft Poly(butyl acrylate) Side Chains toward Intrinsically Stretchable Polymeric Semiconductors for Field-Effect Transistor Applications

Poly­(butyl acrylate) (PBA) side chain equipped isoindigo-bithiophene (II2T) conjugated polymers have been designed and synthesized for stretchable electronic applications. The PBA segment possesses low glass transition temperature and high softness, offering a great opportunity to improve the mechanical property of semiconducting polymer thin films that typically contain lots of rigid conjugated rings. Polymers with 0, 5, 10, 20 and 100% of PBA side chains, named <b>PII2T</b>, <b>PII2T-PBA5</b>, <b>PII2T-PBA10</b>, <b>PII2T-PBA20</b>, and <b>PII2T-PBA100</b>, were explored, and their polymer properties, surface morphology, electrical characteristics, and strain-dependent performance were investigated systematically. The series polymers showed a charge carrier mobility of 0.06–0.8 cm² V^–1 s^–1 with an on/off current ratio over 10⁵ dependent on different amounts of PBA chains as probed using a top-contact transistor device. Moreover, we can still achieve a mobility higher than 0.2 cm² V^–1 s^–1 even if 10% of PBA side chains were added (i.e., <b>PII2T-PBA10</b>). Such <b>PII2T-PBA</b> polymers, more attractive, exhibited superior thin film ductility with a low tensile modulus down to 0.12 GPa (<b>PII2T-PBA20</b>) due to the soft PBA side chain. The more PBA segment was incroporated, the lower modulus was reached. The mobility performance, at the same time, remained approximately 0.08 cm² V^–1 s^–1 based on <b>PII2T-PBA10</b> films even under a 60% strain and could be simultaneously operated over 400 stretching/releasing cycles without significant electrical degradations. The above results suggest that the rational design of soft PBA side chains provides a great potential for next-generation soft and wearable electronic applications

Novel Highly Selective and Reversible Chemosensors Based on Dual-Ratiometric Fluorescent Electrospun Nanofibers with pH- and Fe³⁺-Modulated Multicolor Fluorescence Emission

Novel dual-ratiometric fluorescent electrospun (ES) nanofibers featuring high sensitivity for pH and ferric ion (Fe³⁺) were prepared using binary blends of poly­(2-hydroxyethyl methacrylate<i>-<i>co</i>-N</i>-methylolacrylamide<i>-<i>co</i>-</i>nitrobenzoxadiazolyl derivative) (poly­(HEMA<i>-<i>co</i>-</i>NMA<i>-<i>co</i>-</i>NBD)) and a spirolactam rhodamine derivative (SRhBOH) by employing a single-capillary spinneret. The HEMA, NMA, and NBD moieties were designed to exhibit hydrophilic properties, chemical cross-linking, and fluorescence (fluorescence resonance energy transfer (FRET) donor), respectively. The fluorescence emission of SRhBOH was highly selective for pH and Fe³⁺; when SRhBOH detected acidic media and Fe³⁺, the spirocyclic form of SRhBOH, which is nonfluorescent, was transformed into the opened cyclic form and exhibited strong fluorescence emission. The emission colors of ES nanofibers in acidic or Fe³⁺ aqueous solutions changed from green to red because of FRET from NBD (donor) to SRhBOH (acceptor). The off/on switching of the FRET process was modulated by adjusting the SRhBOH blending ratio, pH, and Fe³⁺ concentration. Poly­(HEMA<i>-<i>co</i>-</i>NMA<i>-<i>co</i>-</i>NBD) ES fibers blended with 20% SRhBOH showed high sensitivity in sensing Fe³⁺ and pH because of the substantial 57 nm red shift in emission as well as substantial reversible dual photoluminescence. The prepared FRET-based dual-ratiometric fluorescent ES nanofibrous membranes can be used as “naked eye” sensors and have potential for application in multifunctional environment sensing devices

Water-Resistant Efficient Stretchable Perovskite-Embedded Fiber Membranes for Light-Emitting Diodes

Cesium lead halide perovskite nanocrystals (NCs) with excellent intrinsic properties have been employed universally in optoelectronic applications but undergo hydrolysis even when exposed to atmospheric moisture. In the present study, composite CsPbX₃ (X = Cl, Br, and I) perovskite NCs were encapsulated with stretchable (poly­(styrene-butadiene-styrene); SBS) fibers by electrospinning to prepare water-resistant hybrid membranes as multicolor optical active layers. Brightly luminescent and color-tunable hydrophobic fiber membranes (FMs) with perovskite NCs were maintained for longer than 1 h in water. A unique remote FMs packaging approach was used in high-brightness perovskite light-emitting diodes (PeLEDs) for the first time