Recent progress in thin film fluorescent probe for organic amine vapour

Molecular design and architectonics towards film-based fluorescent sensing

The past few decades have witnessed encouraging progress in the development of high-performance film-based fluorescent sensors (FFSs) for detecting explosives, illicit drugs, chemical warfare agents (CWAs), and hazardous volatile organic chemicals (VOCs), among others. Several FFSs have transitioned from laboratory research to real-world applications, demonstrating their practical relevance. At the heart of FFS technology lies the sensing films, which play a crucial role in determining the analytes and the resulting signals. The selection of sensing fluorophores and the fabrication strategies employed in film construction are key factors that influence the fluorescence properties, active-layer structures, and overall sensing behaviors of these films. This review examines the progress and innovations in the research field of FFSs over the past two decades, focusing on advancements in fluorophore design and active-layer structural engineering. It underscores popular sensing fluorophore scaffolds and the dynamics of excited state processes. Additionally, it delves into six distinct categories of film fabrication technologies and strategies, providing insights into their advantages and limitations. This review further addresses important considerations such as photostability and substrate effects. Concluding with an overview of the field's challenges and prospects, it sheds light on the potential for further development in this burgeoning area.

Control of Fluorescence of Organic Dyes in the Solid-State by Supramolecular Interactions

Fluorescent organic dyes play an essential role in the creation of new "smart" materials. Fragments and functional groups capable of free rotation around single bonds can significantly change the fluorescent organic dye's electronic structure under analyte effects, phase state transitions, or changes in temperature, pressure, and media polarity. Dependencies between steric and electronic structures become highly important in transition from a solution to a solid-state. Such transitions are accompanied by a significant increase in the dye molecular structure's rigidity due to supramolecular associates' formation such as H-bonding, π···π and dipole-dipole interactions. Among those supramolecular effects, H-bonding interactions, first of all, lead to significant molecular packing changes between loose or rigid structures, thus affecting the fluorescent dye's electronic states' energy and configuration, its fluorescent signal's position and intensity. All the functional groups and heteroatoms that are met in the organic dyes seem to be involved in the control of fluorescence via H-bonding: C-H···N, C-H···π, S = O···H-C, P = O···H, C-H···O, NH···N, C - H···C, C - H···Se, N-H···O, C - H···F, C-F···H. Effects of molecular packing of fluorescent organic dyes are successfully used in developing mechano-, piezo-, thermo- fluorochromes materials for their applications in the optical recording of information, sensors, security items, memory elements, organic light-emitting diodes (OLEDs) technologies.

Resolving Cross-Sensitivity Effect in Fluorescence Quenching for Simultaneously Sensing Oxygen and Ammonia Concentrations by an Optical Dual Gas Sensor

Simultaneous sensing of multiple gases by a single fluorescent-based gas sensor is of utmost importance for practical applications. Such sensing is strongly hindered by cross-sensitivity effects. In this study, we propose a novel analysis method to ameliorate such hindrance. The trial sensor used here was fabricated by coating platinum(II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) and eosin-Y dye molecules on both sides of a filter paper for sensing O₂ and NH₃ gases simultaneously. The fluorescent peak intensities of the dyes can be quenched by the analytes and this phenomenon is used to identify the gas concentrations. Ideally, each dye is only sensitive to one gas species. However, the fluorescent peak related to O₂ sensing is also quenched by NH₃ and vice versa. Such cross-sensitivity strongly hinders gas concentration detection. Therefore, we have studied this cross-sensitivity effect systematically and thus proposed a new analysis method for accurate estimation of gas concentration. Comparing with a traditional method (neglecting cross-sensitivity), this analysis improves O₂-detection error from −11.4% ± 34.3% to 2.0% ± 10.2% in a mixed background of NH₃ and N₂.

Review on application of perylene diimide (PDI)-based materials in environment: Pollutant detection and degradation

Environment pollution is getting serious and various poisonous contaminants with chemical durability, biotoxicity and bioaccumulation have been widespreadly discovered in municipal wastewaters and surface water. The detection and removal of pollutants show great significance for the protection of human health and other organisms. Due to its distinctive physical and chemical properties, perylene diimide (PDI) has received widespread attention from different research fields, especially in the area of environment. In this review, a comprehensive summary of the development of PDI-based materials in fluorescence detection and advanced oxidation technology for environment was introduced. Firstly, we chiefly presented the recent progress about the synthesis of PDI and PDI-based nanomaterials. Then, their application in fluorescence detection for environment was presented and categorized, principally including the detection of heavy metal ions, harmful anions and organic contaminants in the environment. In addition, the application of PDI and PDI-based materials in different advanced oxidation technologies for environment, such as photocatalysis, photoelectrocatalysis, Fenton and Fenton-like reaction and persulfate activation, was also summarized. At last, the challenges and future prospects of PDI-based materials in environmental applications were discussed. This review focuses on presenting the practical applications of PDI and PDI-based materials as fluorescent probes or catalysts (especially photocatalysts) in the detection of hazardous substances or catalytic elimination of organic contaminants. The contents are aimed at supplying the researchers with a deeper understanding of PDI and PDI-based materials and encouraging their further development in environmental applications.

Diethylamine fluorescence sensor based on silica hollow sphere photonic crystals

In this study, based on silica hollow sphere photonic crystals (SHSPCs), a simple and selective fluorescence sensor for high-performance diethylamine detection was developed. The sensor does not involve complicated integration of arrays or tedious synthetic work. During the detection, the SHSPCs could significantly enhance the fluorescence intensity of rhodamine 6G (Rh6G), and meanwhile, adsorb some Rh6G on their surface. Due to the competitive adsorption, diethylamine could free the Rh6G which was adsorbed on the surface of the SHSPCs, thus enhancing the fluorescence emission intensity with the increase of Rh6G concentration. The second enhancement of the fluorescence emission enabled the selective detection of diethylamine. It is remarkable that a simple and readily available dye (Rh6G) facilitates the efficient detection of diethylamine. Moreover, the sensor has good interference immunity, stability and reusability.

Perylene Imide-Based Optical Chemosensors for Vapor Detection

Perylene imide (PI) molecules and materials have been extensively studied for optical chemical sensors, particularly those based on fluorescence and colorimetric mode, taking advantage of the unique features of PIs such as structure tunability, good thermal, optical and chemical stability, strong electron affinity, strong visible light absorption and high fluorescence quantum yield. PI-based optical chemosensors have now found broad applications in gas phase detection of chemicals, including explosives, biomarkers of some food and diseases (such as organic amines (alkylamines and aromatic amines)), benzene homologs, organic peroxides, phenols and nitroaromatics, etc. In this review, the recent research on PI-based fluorometric and colorimetric sensors, as well as array technology incorporating multiple sensors, is reviewed along with the discussion of potential applications in environment, health and public safety areas. Specifically, we discuss the molecular design and aggregate architecture of PIs in correlation with the corresponding sensor performances (including sensitivity, selectivity, response time, recovery time, reversibility, etc.). We also provide a perspective summary highlighting the great potential for future development of PIs optical chemosensors, especially in the sensor array format that will largely enhance the detection specificity in complexed environments.

Perylene Diimide-Based Fluorescent and Colorimetric Sensors for Environmental Detection

Perylene tetracarboxylic diimide (PDI) and its derivatives exhibit excellent thermal, chemical and optical stability, strong electron affinity, strong visible-light absorption and unique fluorescence on/off features. The combination of these features makes PDIs ideal molecular frameworks for development in a broad range of sensors for detecting environmental pollutants such as heavy metal ions (e.g., Cu2+, Cd2+, Hg2+, Pd2+, etc.), inorganic anions (e.g., F-, ClO4-, PO4-, etc.), as well as poisonous organic compounds such as nitriles, amines, nitroaromatics, benzene homologues, etc. In this review, we provide a comprehensive overview of the recent advance in research and development of PDI-based fluorescent sensors, as well as related colorimetric and multi-mode sensor systems, for environmental detection in aqueous, organic or mixed solutions. The molecular design of PDIs and structural optimization of the sensor system (regarding both sensitivity and selectivity) in response to varying analytes are discussed in detail. At the end, a perspective summary is provided covering both the key challenges and potential solutions for the future development of PDI-based optical sensors.

A very sensitive and highly selective organic selector in CNTs composite chemiresistive for efficient differentiation of organic amine vapours

With the call for the IoE (Internet of Everything), stable and efficient electric noses/tongues have become the most critical part of the sensor network. Identifying target gases efficiently and rapidly at ambient air becomes a focus on sensor research. We designed a chemiresistive sensor based on a composite of a specific selector and single-walled carbon nanotubes (SWNTs) for the detection and differentiation of organic amine vapours in air (25 ℃, 55% RH). The synergetic combination of F4-TCNQ (2,3,5,6-Tetrafluoro-7,7',8,8'-tetracyanoquinodimethane) and SWCNTs could modulate the electrical properties of sensor leading to the enhancement of response up to ppb-level for primary amine vapor detection. Different from traditional chemiresistive sensor, this sensing materials exhibit unique differences in response to different types of amines thought different mechanisms. We have proven the practical possibilities through the detection of the simulated complexed environmental atmosphere in industrial production. Furthermore, we explored the working mechanism of high-performance sensors, which could provide theoretical guidance for sensor design for more commercial applications. This study provided a simple, convenient, and highly efficient practical method for organic amine detection at ambient air for real-life applications.

Bromine-Substituted Fluorene: Molecular Structure, Br-Br Interactions, Room-Temperature Phosphorescence, and Tricolor Triboluminescence

Organic tribophosphorescence materials are rarely reported and the introduction of Br atoms may be a practical way to design such materials. Here four bromine-substituted fluorene-based derivatives are presented and BrFlu-CBr, having fluorescence-phosphorescence dual-emission induced not only by UV light but also by mechanical stimulus, manifests the highest phosphorescence efficiency of 4.56 % upon photoirradiation. During the grinding process, three different triboluminescent spectra were identified. Upon introduction of a mechanical stimulus, the triboluminescence emission is cyan, whereas after an extended period it changed to blue. After removing the mechanical stimulus, green-white phosphorescent emission was observed. Careful research on single-crystal structures and theoretical calculations demonstrate that strong Br⋅⋅⋅Br interactions are vital to facilitate spin-orbit coupling and promote intersystem crossing, thus generating the unique properties.

Multiple Stimuli-Responsive Fluorescent Sensor from Citric Acid and 1-(2-Aminoethyl)piperazine

Multiresponsive fluorescent supramolecular materials are quite interesting, for they combine the multiresponsiveness of supramolecules and the high sensitivity of fluorescent materials. Different from the multiresponsive supramolecular materials based on host-guest interactions, in this report, a supramolecular ionic network was fabricated by 1-(2-aminoethyl)piperazine and citric acids via ionic interactions. Despite the fact that there are no conventional chromophores, the obtained supramolecular ionic material can emit strong fluorescence. Most interestingly, the thin film of this supramolecular ionic material can change its fluorescent intensity in response to four external stimuli, including humidity, triethylamine, acetic acid, and temperature. Beneficial to the supramolecular ionic structure, this multiresponsive fluorescent sensor is self-healable. It is found that a new route has been opened to prepare the multiresponsive fluorescent sensors.

Ratiometric Luminescent Detection of Organic Amines Due to the Induced Lactam-Lactim Tautomerization of Organic Linker in a Metal-Organic Framework

Here we demonstrate that a fluorescent benzothiadiazole (BTD)-conjugated terphenyldicarboxylate (TPDC) linker (denoted as H₂-ostpdc) has been hybridized by a quinoxaline-2,3-(1H,4H)-dione (QD) moiety possessing lactam-lactim tautomerism, which was further integrated into a robust and porous UiO-68 type zirconium metal-organic framework (MOF UiO-68-osdm) by utilizing the mixed two dicarboxylate struts with the same ligand lengths. The resultant MOF UiO-68-osdm can work as a ratiometric luminescent sensor for visual and selective detection of alkyl amines. Furthermore, it can discriminate secondary alkylamines from other type amine species.

Fluorescent sensing arrays for cations and anions

A review of fluorescent sensing arrays for anions and cations, highlighting promising strategies and directions for future research.

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.

Selective fluorescence detection of anilines and Fe3+ ions by two lanthanide metal–organic frameworks

Two isostructural lanthanide metal–organic frameworks [Ln₂(TDC)₃(CH₃OH)₂·(CH₃OH)] (Ln = Eu, 1; Tb, 2, TDC = 2,5-thiophenedicarboxylic acid) were successfully synthesized.