Visualization and monitoring of damaging-healing processes of polymers by AIEgen-loaded multifunctional microcapsules

Polymeric materials play an essential and ubiquitous role in modern societies, but they are inevitably damaged during service, which can lead to compromised performance or even direct failure. The sensitive detection and dynamic monitoring of the health states of polymers is thus crucial to increase their reliability, safety, and lifetime. Herein, a facile fluorescence-based approach that can achieve the nondestructive, on-site, real-time, full-field, and sensitive visualization and monitoring of damaging-healing processes of polymers is demonstrated. By embedding novel UV-blocking microcapsules containing a diisocyanate solution of aggregation-induced emission luminogens (AIEgens) into a polymer matrix, the damaged regions of the composite show turn-on fluorescence and dual signal changes in both fluorescence intensity and fluorescence color can be observed during the healing processes. The invisible information of the static health states and dynamic healing processes can be directly and semi-quantitatively visualized by naked eyes based on the collective effects of AIE and twisted intramolecular charge transfer. In addition to the autonomous damage-reporting, self-healing, and health indication functionalities, the microcapsule-embedded polymeric coatings possess excellent photo- and water-protection capabilities, which are appealing to various practical applications.

A Flexible Chemosensor Based on Colorimetric and Fluorescent Dual Modes for Rapid and Sensitive Detection of Hypochlorite Anion

A flexible chemosensor has been developed based on colorimetric and fluorescent dual modes using tetraphenylethylene-centered tetraaniline (TPE4A) for rapid and sensitive detection of hypochlorite anion. The fluorescent probe TPE4A exhibits a unique aggregation-induced emission (AIE) character which is proved by a blue shift of the fluorescent peak from 544 to 474 nm with the water equivalents increasing. With the addition of hypochlorite in solution, the absorbance of the probe changes and the responding fluorescence color can be observed to change from light green to purple. The detection limit of hypochlorite is 1.80 × 10−4 M in solution, and the visual detection limit is 1.27 µg/cm2 with the naked eye for the flexible paper-based chemosensor. The proposed flexible chemosensors show a good selectivity and sensitivity which has great potential for effective detection of hypochlorite anions without any spectroscopic instrumentation.

A confined carbon dot-based self-calibrated fluorescence probe for visible and high-sensitivity moisture readouts

Excellent luminescent materials are essential for high-performance fluorescent nanosensors. Here, a new-type self-calibrated humidity sensor has been established through monitoring the fluorescent color change of carbon dots (CDs) confined in sodium hydroxide (CDs@NaOH). The CDs are prepared by a facile and rapid microwave assisted heating method using citric acid, urea, and NaOH as precursors. The confinement effect from NaOH has reduced the nonradiative transition and suppressed the aggregation-induced quenching of the CDs in solid. Compared with other sensors based on CD fluorescent visualization, the sensor has good linearity and wide humidity detection range from 6.9% to 95.4%. With the increased relative humidity, the fluorescence color of the sensor change from green to blue. The proposed sensing mechanism is due to the breaking and reforming of hydrogen bonds and proton transfer occurring at the CD-NaOH matrix interfaces. This finding suggests a potential role for the spatial confinement effect and may provide an avenue for developing highly sensitive humidity readouts.

Exploiting deep learning for predictable carbon dot design

This work developed a multi-layer deep convolution neural network (DCNN) model for predicting the optical properties of carbon dots (CDs), including spectral properties and fluorescence color under ultraviolet irradiation.

Dynamic tuning of metal–ligand coordination through water molecules to induce multicolor fluorescence variations for humidity monitoring and anti-counterfeiting applications

We proposed a simple and effective strategy to construct a luminescent ratiometric RH sensor that can exhibit fluorescence color changes from blue to yellow upon increasing the RH.

Mechanoresponsive Elastomers Made with Excimer-Forming Telechelics

Mechanoresponsive luminescent (MRL) elastomers, which change their fluorescence color or intensity upon deformation, can facilitate simple strain detection through optical signals. Several polymers have been endowed with MRL properties by blending them with excimer-forming dyes, whose assembly and emission color are affected by deformation of the blended materials. However, access to elastic MRL polyurethanes based on this approach has proven difficult and usually requires the covalent incorporation of such dyes in high concentration. Here, we show that much simpler access to MRL elastomers is possible by blending thermoplastic polyurethane elastomers with a small weight fraction of a telechelic sensor macromolecule carrying two excimer-forming oligo(p-phenylene vinylene) dyes at the termini. While the mechanical properties of the two polyurethanes, which were selected because of their dissimilar mechanical behaviors, remain unchanged, the additive imparts these materials with MRL characteristics. Notably, the reliable and reversible detection of strains as low as 5% is possible. The highly sensitive mechanochromic response mirrors the deformation and relaxation processes occurring in these model polyurethanes and enabled a detailed analysis of the processes underlying the shape-memory properties in one of the polyurethanes, in which such behavior was imparted by a crystallizable soft segment.

Fluorescence Fluoride Ion Sensor Utilizing Desilylation of N-Silylated 9- Aminoanthracene

N,N-Bis(trimethylsilyl)-9-aminoanthracene (Si9AA) was synthesized by deprotonation of 9-aminoanthracne (9AA) with n-BuLi followed by the addition of trimethylsilyl chloride (TMSCl). Under ultraviolet, Si9AA showed blue fluorescence originated from the anthracene skeleton due to orthogonal relation between anthracene skeleton and bis(trimethylsilyl)amino group, which was determined by X-ray crystallographic analysis, while 9AA, in which conjugation exists between the anthracene and the amino group, showed green fluorescence. In a THF solution, Si9AA was converted to 9AA by desilylation of bis(trimethylsilyl)amino group with fluoride ion, which was contained in tetrabutylammonium fluoride (TBAF) or KF-18-crown-6 complex, resulting in fluorescence color change from blue to green. Si9AA was found to utilize as a sensor to detect fluoride ion in THF solution or on a thin layer chromatography (TLC) via the fluorescence color change without any metals, regarding a metal free fluorescence fluoride sensor in green chemistry.