Congdi Shang

Functionality-Oriented Derivatization of Naphthalene Diimide: A Molecular Gel Strategy-Based Fluorescent Film for Aniline Vapor Detection

Modification of naphthalene diimide (NDI) resulted in a photochemically stable, fluorescent 3,4,5-tris(dodecyloxy)benzamide derivative of NDI (TDBNDI), and introduction of the long alkyl chains endowed the compound with good compatibility with commonly found organic solvents and in particular superior self-assembly in the solution state. Further studies revealed that TDBNDI forms gels with nine of the 18 solvents tested at a concentration of 2.0% (w/v), and the critical gelation concentrations of five of the eight gels are lower than 1.0% (w/v), indicating the high efficiency of the compound as a low-molecular mass gelator (LMMG). Transmission electron microscopy, scanning electron microscopy, and confocal laser scanning microscopy studies revealed the networked fibrillar structure of the TDBNDI/methylcyclohexane (MCH) gel. On the basis of these findings, a fluorescent film was developed via simple spin-coating of the TDBNDI/MCH gel on a glass substrate surface. Fluorescence behavior and sensing performance studies demonstrated that this film is photochemically stable, and sensitive and selective to the presence of aniline vapor. Notably, the response is instantaneous, and the sensing process is fully and quickly reversible. This case study demonstrates that derivatization of photochemically stable fluorophores into LMMGs is a good strategy for developing high-performance fluorescent sensing films.

Calix[4]arene‐Based Dynamic Covalent Gels: Marriage of Robustness, Responsiveness, and Self‐Healing

Herein, the report on a new class of self-healing and pH/temperature responsive mixed solvent (ethanol and water) gels shows unusual mechanical properties to resist slicing, sustain high compression, and withstand stretching as evidenced by the cutting breaking stress, the fracture compressive stress, and the stretching ratio of one of the gels as obtained can reach or exceed 26.4 MPa, 9.2 MPa, and ≈5 times, respectively. The gels are designed by introducing dynamic covalent bond, acylhydrazone, which is believed to combine the merits of conventional chemical bonds and those of supramolecular interactions. Specifically, a hydrazide-modified calix[4]arene derivative and linear benzaldehyde-terminated poly(ethylene glycol)s are synthesized and used as reactive components to build gel networks. Interestingly, acid-degradable hydrogel can be obtained via natural drying of the mixed solvent gel first and then swelling in pure water.

Dynamic Chemistry-Based Sensing: A Molecular System for Detection of Saccharide, Formaldehyde, and the Silver Ion

Development of artificial complex molecular systems is of great importance in understanding complexity in natural processes and for achieving new functionalities. One of the strategies is to create them via optimized utilization of noncovalent interactions and dynamic covalent bonds. We report here on a new complex molecular system, which was constructed by integrating the multiple interactions containing a dynamic covalent interaction between 1,2-diol and boronic acid, a coordination interaction between the silver ion and pyridyl, and an easy accessible reaction between secondary amine and formaldehyde. By employing the three dynamic interactions, a pyrene (Py) labeled fluorophore, PPB, was designed and synthesized. The compound reacts with fructose (F), a monosaccharide, in aqueous phase and produces a fluorescent adduct, PPB-F, which can be further used as a sensing platform for formaldehyde (FA) and the silver ion. The respective dynamic interactions are accompanied with color changes due to the reversible switching between Py-monomer emission and excimer emission. The respective experimental detection limits (DLs) for the three analytes are much lower than 0.2 mM, 0.1 mM, and 2.5 μM, respectively. The presence of relevant compounds or ions shows little effect upon the sensing. No doubt, the results as presented show that the integration of supramolecular interactions including dynamic covalent bonds can be employed as a general strategy to develop new functional molecular systems or materials.

Non-contact identification and differentiation of illicit drugs using fluorescent films

Sensitive and rapid identification of illicit drugs in a non-contact mode remains a challenge for years. Here we report three film-based fluorescent sensors showing unprecedented sensitivity, selectivity, and response speed to the existence of six widely abused illicit drugs, including methamphetamine (MAPA), ecstasy, magu, caffeine, phenobarbital (PB), and ketamine in vapor phase. Importantly, for these drugs, the sensing can be successfully performed after 5.0 × 105, 4.0 × 105, 2.0 × 105, 1.0 × 105, 4.0 × 104, and 2.0 × 102 times dilution of their saturated vapor with air at room temperature, respectively. Also, presence of odorous substances (toiletries, fruits, dirty clothes, etc.), water, and amido-bond-containing organic compounds (typical organic amines, legal drugs, and different amino acids) shows little effect upon the sensing. More importantly, discrimination and identification of them can be realized by using the sensors in an array way. Based upon the discoveries, a conceptual, two-sensor based detector is developed, and non-contact detection of the drugs is realized.Sensitive and rapid identification of illicit drugs in a non-contact mode remains a challenge. Here, the authors report three film-based fluorescent sensors showing remarkable sensitivity, selectivity and response speed to six widely abused illicit drugs in vapor phase.

Detection of gaseous amines with a fluorescent film based on a perylene bisimide-functionalized copolymer

A fluorescent film sensor based on a perylene bisimide (PBI)-functionalized copolymer for the fast and selective detection of aniline vapor has been fabricated. In this work, the common H-aggregation of the PBI units was obviously hindered by using numerous hydroxy-ethyl side chains as a spatial scaffold. Sensing performance studies demonstrated that the fluorescence of the film was instantaneously quenched by ppb-level volatile amines with excellent reversibility and reproducibility. The response time for aniline vapor was found to be less than 1 s. The high surface area and porosity of the silica gel substrate and hydrogen bonding interactions may assist the high sensitivity and fast response of the film towards aniline. Furthermore, the massive amount of fluorescence intensity data of the sensing film when exposed to low concentrations and a continuous flow of amine vapors were collected in a home-made sensing platform. In addition, the response feature investigates using the kinetic sorption and desorption information shows the promising potential of the film in real applications. This work has expanded the applications of PBI-based materials in the fluorescent sensing of toxic compounds, particularly amine vapors.

Highly Sensitive and Discriminative Detection of BTEX in the Vapor Phase: A Film-Based Fluorescent Approach

BTEX (benzene, toluene, ethylbenzene, o-xylene, m-xylene, and p-xylene) represents a group of volatile organic compounds (VOCs) and constitutes a great threat to human health. However, sensitive, selective, and speedy detection of them on-site and in the vapor phase remains a challenge for years. Herein, we report a film-based fluorescent approach and a conceptual sensor, which shows unprecedented sensitivity, speed, and reversibility to the aromatic hydrocarbons in the vapor phase. In the studies, pentiptycene was employed to produce a nonplanar perylene bisimide (PBI) derivative, P-PBI. The compound was further utilized to fabricate the film. The novelty of the design is the combination of capillary condensation and solvent effect, which is expected to enrich the analytes from vapor phase and shows outputs at the same time. Importantly, the film permits instant response (∼3 s) and real-time identification (<1 min) of benzene and toluene from other aromatic hydrocarbons. The experimental detection limits (DLs) of the six analytes are lower than 9.2, 2.7, 1.9, 0.2, 0.4, and 0.4 ppm, which with the exception of benzene, are significantly lower than the NIOSH recommended long-term exposure limits. More importantly, the film is photochemically stable, and more than 300 repetitive tests showed no observable bleaching. In addition, the sensing is fully reversible. The superior performance of the film device is in support of the assumption that the combination of capillary condensation and solvation effect would constitute an effective way to design high-performance fluorescent films, especially for challenging chemical inert and photoelectronically inactive VOCs.