High-Performance Ketone Sensing in Vapor Phase Enabled by o-Carborane-Modified Cyclometalated Alkynyl-Gold(III) Complex-Based Fluorescent Films

Construction of a Long-Range Quantitative Fluorescence Sensor for Multiple Amine Vapors by π···π Aggregates of Carborane

The exploitation of small molecules as fluorescence sensors represents a minimalistic solution toward the sensing of hazardous volatile organic compounds (VOCs). Compared with the conventional aggregation-induced emitting sensors, the carborane (Cb)-based sensors have exhibited multiple advantages and improved quantitative fluorescence (QF) sensing abilities toward the gaseous VOCs. However, in the current Cb-based sensors, the localization of a single responsive site toward VOCs remains less focused, which results in a bias in the trace detection and short-range testing windows. In this work, we synthesized two pyrene-alkynylated carboranes (Py-1 and Py-2) and investigated their photophysical properties in different cases. We found that Py-1 and Py-2 in the films were consistently self-assembled through π···π aggregation of pyrenylethynyl moieties. Theoretical modeling showed that the highly emissive π···π aggregates were thermodynamically stable and their responsive sites toward VOCs were localized on the electron-poor phenyl or fluorenyl groups. As a result, the Py-1 and Py-2 films showed remarkable emission-off sensibilities toward NEt3 vapors via a major route of photoinduced electron transfer. The optimized QF sensor Py-2 showed linear emission-off response toward three types of static amine vapors in long concentration ranges (1.78-90 g/m3 at most), and the limit of detection could be lowered to 99 mg/m3 in the in situ sensing.

Integrated Sensing Platform Validated for the Efficient and On-Site Screening of Amine-Containing Illicit Drugs

Efficient and reliable technologies for the on-site detection of illicit drugs are important in drug-facilitated crime investigations. However, the development of such technologies is challenging. Based on the synthetic optimization, introducing a boron ester functional group to the two furanic indicators endows the stimulus-responsive properties synergistically. The ring-opening reaction of the indicators in the presence of amine-containing illicit drugs generated well-known donor-acceptor Stenhouse adducts, accompanied by strong color changes. A small-size and lightweight laminated sensor was integrated based on the outstanding ratiometric variations of the two active furanic indicators. A prototype platform was fabricated equipped with a circuit control, a mini pump, and a signal processing system. A user-friendly detection and efficient screening of amine-containing illicit drugs, including phenethylamines, amphetamines, cathinones, and tryptamines in the liquid states were conducted. The ratiometric response of the sensor was linear in the concentration range of 2.1-10.6 μg·mL-1 for methamphetamine·HCl and methcathinone ·HCl. The detection limits for the two illicit drugs at the sublevel (ng·mL-1) were found to be 8.4 and 9.0 ng·mL-1, respectively. Double-blind field tests and different illicit drugs were evaluated with good screening capability. Successful trials showed the potential applications of the developed prototype platform for efficient and on-site analytical determination.

Compact device prototype for turn-on fluorescence detection of sarin based on reactive 4,4-diaryloxy-BODIPY derivatives

4,4-Diaryloxy-BODIPYs were presented for fluorescence turn-on detection of sarin in solution media. A compact tubular sensor and a sensing platform prototype were fabricated for in situ detection of real agents and simulants at the sub-mM level.

Fast and Selective Luminescent Sensing by Langmuir-Schaeffer Films Based on Controlled Assembly of Perylene Bisimide Modified with A Cyclometalated AuIII Complex

Condensed films of functional luminophores dominated by the magnitude and dimensionality of the intermolecular interactions play important roles in sensing performance. However, controlling the molecular assembly and regulating photophysical properties remain challenging. In this study, a new luminophore, ortho-PBI-Au, was synthesized by anchoring a cyclometalated alkynyl-gold(III) unit at the ortho-position of perylene bisimide. An unprecedented T-type packing model driven by weak Au-π interaction and Au-H bonds was observed, laying foundation for striking properties of the luminophore. Controlled assembly of ortho-PBI-Au at the air-water interface, realized using the classical Langmuir-Schaeffer technique, afforded the obtained luminescent films with different packing structures. With an optimized film, sensitive, selective, and rapid detection of a hazardous new psychoactive substance, phenylethylamine (PEA), was achieved. The detection limit, response time, and recovery time were <4 ppb, <1 s, and <5 s, respectively, surpassing the performance of the PEA sensors known thus far. The relationship between the characters of films and the sensing performance was systematically examined by grey relational analysis (GRA). The present study suggests that designing novel molecular aggregation with definite adlayer structure is a crucial strategy to enhance the sensing performance, which could be favorable for the film-based fluorescent sensors.

Dual-Mode Optical Sensor Array for Detecting and Identifying Perillaldehyde in Solution Phase and Plant Leaf with Smartphone

Promising techniques for detecting and quantifying active components in the plants and foods have received global concern in smart agriculture. Dual-mode optical assays are becoming more attractive and popular thanks to robust and reliable analysis parameters. We herein unveil a novel turn-on and dual-mode sensor array comprising three kinds of reactive indicators including ring-closed rhodamine-hydrazine, squaraine-hydrazine, and 2,4-dinitrophenylhydrazine for evaluating perillaldehyde. Significant colorimetric and fluorescent changes were triggered through reacting primary amine/hydrazine with the active aldehyde group in perillaldehyde, thus turning on the chromogenic responses of all the indicators. Optimal colorimetric sensing showed good responses to perillaldehyde ranged up to 100 mM in ethanol. Dramatic fluorescence enhancement was also exhibited, illustrating good selectivity as well as high sensitivity (detection limit ∼20.0 μM). Inspired by rapid chemical reactions and distinct optical changes, distinct sensor array strips loaded with the optimal solid-state reactive indicators were developed for evaluating the perillaldehyde content in the perilla frutescence leaves. Smartphone-enabled readout system and digital data processing were further performed for chemometric analysis. A good correlation was obtained and the semiquantitative evaluation of the perillaldehyde content could be achieved within 15 min, possessing the significant features of naked-eye recognition, easy operation, and disposability. To the best of our knowledge, present work demonstrated the use of chromogenic sensing strips to evaluate the active perillaldehyde content in solution and vapor phases for the first time. Taken together, these characteristics also indicate that the present turn-on sensor array has great potential applications in the precise detection and evaluation of perillaldehyde in the forthcoming smart agriculture.

Greatness in Simplicity: Efficient Red Room-Temperature Phosphorescence from Simple Halogenated Maleimides with a 2D Layered Structure

Herein, two maleimide derivatives substituted by Br (DBM) and I (DIM) with a two-dimensional (2D) layered structure are found to have highly efficient red room-temperature phosphorescence (RTP) at 660 nm in solid state, which is independent of their morphology (crystal, powder, and film). The red RTP of DBM and DIM is closely related to the synergism of n_π-ct-π* transitions and the 2D halogen-bonded network. Interestingly, the red RTP can be excited by visible light of 500 nm, which should be ascribed to the forbidden absorption from the ground state to the triplet state activated in the layered halogen-bonded framework. Due to the rich intermolecular interactions in the rigid layered structure, the red RTP of DBM is very stable under water or external force stimulation. Notably, Hg(II) and Cd(II) ions in a pure aqueous solution result in an opposite change in the RTP intensity of the DBM film. The detection limit of Hg(II) ion is as low as 2.5 × 10^-5 nM, lesser than all reported values. The above results not only provide a new idea for the design of simple and efficient red RTP materials but also make it possible to develop solid-state phosphorescent probes for toxic heavy metal ions in environmental sewage with high sensitivity and selectivity.

Self-Assembly of Amphiphilic BODIPY Derivatives on Micropatterned Ionic Liquid Surfaces for Fluorescent Films with Excellent Stability and Sensing Performance

Fluorescent films have been widely recognized as one of the most powerful tools for trace analyte detection. However, their use has been limited due to the poor photochemical stability of fluorophores at a gas-solid interface and inefficient film mass transfer. Herein, novel fluorescent films were developed through self-assembly of amphiphilic BODIPY derivatives on micropatterned ionic liquid surfaces. Unlike solid-state films, the obtained monolayer films exhibit excellent photochemical stability, similar to that of a solution. Moreover, the interfacial assembly of amphiphilic fluorophores can avoid gas diffusion inside the microdroplets, significantly improving the sensing performance. The 1/1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF₄) monolayer exhibits high sensitivity, high selectivity, and a fast response to detect diethylchlorophosphate (DCP) vapor. The detection limit was 226 ppt, with a response time to DCP of 2.0 s. Importantly, the 1/[BMIM]BF₄ monolayer can be reused for at least 50 cycles with no obvious signal fading. This study is expected to benefit the development of new strategies for designing fluorescence sensing films and lay a solid foundation for the fabrication of multifunctional sensing devices with excellent photochemical stability and sensing performance.

Aggregation-induced emission (AIE): emerging technology based on aggregate science

Functional materials serve as the basic elements for the evolution of technology. Aggregation-induced emission (AIE), as one of the top 10 emerging technologies in chemistry, is a scientific concept coined by Tang, et al. in 2001 and refers to a photophysical phenomenon with enhanced emission at the aggregate level compared to molecular states. AIE-active materials generally present new properties and performance that are absent in the molecular state, providing endless possibilities for the development of technological applications. Tremendous achievements based on AIE research have been made in theoretical exploration, material development and practical applications. In this review, AIE-active materials with triggered luminescence of circularly polarized luminescence, aggregation-induced delayed fluorescence, room-temperature phosphorescence, and clusterization-triggered emission at the aggregate level are introduced. Moreover, high-tech applications in optoelectronic devices, responsive systems, sensing and monitoring, and imaging and therapy are briefly summarized and discussed. It is expected that this review will serve as a source of inspiration for innovation in AIE research and aggregate science.

Flexible and Transparent Oligothiophene-o-Carborane-Containing Hybrid Films for Nonlinear Optical Limiting Based on Efficient Two-Photon Absorption

Structure-property relationship for fluorophores with favorable nonlinear optical (NLO) properties are promising topics in organic chemistry and material science. Herein, a series of terthiophene-o-carborane dyads and triads covalently linked with different end-capping styles were readily synthesized and comprehensively investigated. Quantitative values of the crystal and packing structures, photophysical parameters including aggregation-induced emission (AIE) and two-photon absorption (2PA) were provided. Significant impact of carborane unit for introducing the AIE characteristic has been investigated in contrast to the parent oligothiophene. All the obtained fluorophores exhibit maximum absorption around 370 nm in THF and emit bright reddish photoluminscence with absolute fluorescence quantum yields above 16% in solid states. Intramolecular charge communication between oligothiophene and carborane plays important roles in the related NLO properties. These results are supported well by the time-dependent DFT theoretical calculations. Effective 2PA cross sections (δ_2PA = 95-355 GM@650 nm) and transition dipole moments of the derivatives are variable for different end-capping styles. Their potential applications as optical limiting materials based on the 2PA mechanism in solutions and doped PDMS films were further evaluated. Taken together, this work provides an understanding of their structure-property relationship, and flexible PDMS films as outstanding candidates for practical applications in optical limiting.