Haonan Peng

A novel picric acid film sensor via combination of the surface enrichment effect of chitosan films and the aggregation-induced emission effect of siloles

A novel fluorescent film was fabricated by doping the aggregates of hexaphenylsilole (HPS) into a chitosan film. It was demonstrated that the fluorescence emission of the film is stable, sensitive and highly selective to the presence of picric acid (PA). The detection limit for PA is about 2.1 × 10−8 mol/L. Introduction of 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), nitrobenzene (NB), phenol, benzene, toluene, methanol, ethanol, and zinc nitrate (Zn(NO3)2) had little effect upon the fluorescence emission of the film. The selectivity of the film was attributed to the specific electrostatic association effect of the protonated substrate film to picrate anion and the screening effect of the film to the interferents. The network structure of the substrate film is also favourable for the stabilization of the fluorescence emission of the hybrid film, by preventing the further aggregation of silole aggregates. Fluorescence lifetime measurements revealed that the quenching is static in nature. Furthermore, the quenching process is fully reversible. Considering the simplicity of the preparation and the outstanding performance of the hybrid film, it is anticipated that it could be developed into a real-life PA sensor.

An Ultrasensitive Fluorescent Sensing Nanofilm for Organic Amines Based on Cholesterol‐Modified Perylene Bisimide

A stable, ultrasensitive, and fully reversible fluorescent sensing film for organic amines has been fabricated by assembling cholesterol (Chol)-derived perylene bisimide on a glass plate surface. The compound exhibits excellent film formation properties and forms well-defined nanofibers, as evidenced by SEM and AFM measurements. It has been revealed that besides the molecular structure of the specially designed perylene derivative, the existence of nanofibers in the film is another key factor to endow the film with superior sensing ability for organic amines, including aniline. The detection limit of the amine is ca. 150.0 ppt in the vapor phase and at room temperature. Furthermore, the sensing process is free of interference from common organic solvents, nitroaromatics, and particularly phenols, which makes the film a potential candidate to be used in lung cancer diagnoses and related applications.

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.

Dynamic Covalent Chemistry-based Sensing: Pyrenyl Derivatives of Phenylboronic Acid for Saccharide and Formaldehyde.

We synthesized two specially designed pyrenyl (Py) derivatives of phenylboronic acid, PSNB1 and PSNB2, of which PSNB2 self-assemble to form dynamic aggregate in methanol-water mixture (1:99, v/v) via intermolecular H-bonding and pi-pi stacking. Interestingly, the dynamic aggregate shows smart response to presence of fructose (F) as evidenced by fluorescence color change from green to blue. More interestingly, the fluorescence emission of the resulted PSNB2-F changes from blue to green with the addition of formaldehyde (FA). The reason behind is formation of a PSNB2-F dimer via FA cross-linking. Based upon the reactions as found, sensitive and fast sensing of F and FA in water was realized, of which the experimental DLs could be significantly lower than 10 μM for both analytes, and the response times are less than 1 min. It is believed that not only the materials as created may have the potential to find real-life applications but also the strategy as developed can be adopted to develop other dynamic materials.

New solvatochromic probes: performance enhancement via regulation of excited state structures

A new fluorescent conjugate (PNBD) with a structure of D-π-A was designed and synthesized, where the donor (D), the acceptor (A) and the bridge (π) are naphthalyl, dicyanovinyl and phenylethynyl-phenylethynyl, respectively. To improve the solubility of the conjugate, two long alkyl chains were introduced as substituents of the central aromatic ring. Spectroscopic studies demonstrated that PNBD is a strongly solvatochromic probe which is characterized by a large molar absorption coefficient (>32 000 cm-1 M-1), long wavelength absorption (>410 nm), large solvatochromic emission range (470-650 nm), high photochemical stability, and good solubility in common organic solvents. The fluorescent quantum yield of PNBD is limited in some polar solvents due to dual emission, a phenomenon ascribed to radiative decay from a higher excited singlet state. To eliminate dual emission, a covalently bound dimer (BPNBD) of PNBD characterized by weak vibronic coupling, was designed and synthesized. The dimer constituents are linked by a single bond between the naphthalyl moieties of the two PNBD monomers. As expected, BPNBD maintains almost all the strong points of the monomer, exhibits a substantial increase in fluorescence quantum yield, and eliminates dual emission by facilitating efficient internal conversion. Importantly, the use of PNBD and BPNBD in concert provides unprecedented discrimination among solvents of similar structures, such as (CH2Cl2, CHCl3, CCl4), (ethyl ether, THF, dioxane), or (methanol, ethanol, n-propanol, n-butanol, n-pentanol, n-hexanol, n-heptanol, n-octanol, n-decanol), allowing rapid and selective visual identification.

Fabrication and humidity sensing performance studies of a fluorescent film based on a cholesteryl derivative of perylene bisimide.

A fluorescent film based on a cholesteryl derivative of perylene bisimide (PTCDI-co-CholDEA) was fabricated via utilization of an electrostatic spinning technique on a glass plate surface. SEM studies revealed that the film was characterized by fibrous network structure. It is the structure and the chemical composition that make the fluorescence emission of the film sensitive to the variation of local environmental humidity. The sensitivity of the sensing is 0.1497 (×10(4)a.u. of the intensity)/1% RH, of which RH is the abbreviation of relative humidity. The maximum quenching efficiency of the film is 55.4% when humidity reaches 97% RH. Furthermore, the sensing process is fully reversible, and presence of other commonly found liquids shows little effect to the monitoring process.

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.