Leveraging Coupled Solvatofluorochromism and Fluorescence Quenching in Nitrophenyl-Containing Thiazolothiazoles for Efficient Organic Vapor Sensing

Rapid and ultra-sensitive trace water determination in organic solvents utilizing nitrobenzoxadiazole (NBD)-based fluorescent sensing system

The presence of minute quantities of water in organic solvents can affect the progress of many reactions and cause unnecessary losses and even safety accidents in the chemical industry, especially in the productions process of organic fine chemicals. Therefore, it is necessary to carry out high-performance strategies for trace water detections in commonly used organic solvents. In this work, a fluorescent sensing system based on competitive binding of protons has been developed, demonstrating remarkable responses by UV-vis absorption and fluorescence two-modes toward a trace amount of water in organic solvents including 1,4-dioxane (Diox), tetrahydrofuran (THF), acetonitrile (MeCN), acetone (ACE), dimethylsulfoxide (DMSO) and mixed organic solvents (THF: MeCN=1: 1). The key component of the sensing system is a newly designed fluorophore NBD-PMA, which can be deprotonated to form a dynamic non-luminescent adduct, namely NBD-PMA-F, by an organic fluoride salt tetrabutylammonium fluoride (TBAF). NBD-PMA-F can be reprotonated via using trace water, exhibiting fluorescence turn on of the system. The as-prepared sensing system shows superior sensitivity, low detection limits (v/v, 0.0007 %), quick response speed (≤1.2 s) and good reversibility. Moreover, naked-eye visual rapid detection has also been successfully realized at ambient temperature, which demonstrated their practical applications value for trace water determinations.

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.

Reactive oxygen species-responsive nano-platform with dual-targeting and fluorescent lipid-specific imaging capabilities for the management of atherosclerotic plaques

Atherosclerosis (AS), a pathological cause of cardiovascular disease, results from endothelial injury, local progressive inflammation, and excessive lipid accumulation. AS plaques rich in foam cells are prone to rupture and form thrombus, which can cause life-threatening complications. Therefore, the assessment of atherosclerotic plaque vulnerability and early intervention are crucial in reducing the mortality rates associated with cardiovascular disease. In this work, A fluorescent probe FC-TPA was synthesized, which switches the fluorescence state between protonated and non-protonated, reducing background fluorescence and enhancing imaging signal-to-noise ratio. On this basis, FC-TPA is loaded into cyclodextrin (CD) modified with phosphatidylserine targeting peptide (PTP) and coated with hyaluronic acid (HA) to construct the intelligent responsive diagnostic nanoplatform (HA@PCFT). HA@PCFT effectively targets atherosclerotic plaques, utilizing dual targeting mechanisms. HA binds strongly to CD44, while PTP binds to phosphatidylserine, enabling nanoparticle aggregation at the lesion site. ROS acts as a smart release switch for probes. Both in vitro and in vivo evaluations confirm impressive lipid-specific fluorescence imaging capabilities of HA@PCFT nanoparticles (NPs). The detection of lipid load in atherosclerotic plaque by fluorescence imaging will aid in assessing the vulnerability of atherosclerotic plaque. STATEMENT OF SIGNIFICANCE: Currently, numerous fluorescent probes have been developed for lipid imaging. However, some challenges including inadequate water solubility, nonspecific distribution patterns, and fluorescence background interference, have greatly limited their further applications in vivo. To overcome these limitations, a fluorescent molecule has been designed and synthesized, thoroughly investigating its photophysical properties through both theoretical and experimental approaches. Interestingly, this fluorescent molecule exhibits the reversible fluorescence switching capabilities, mediated by hydrogen bonds, which effectively mitigate background fluorescence interference. Additionally, the fluorescent molecules has been successfully loaded into nanocarriers functionalized with the active targeting abilities, which has significantly improved the solubility of the fluorescent molecules and reduced their nonspecific distribution in vivo for an efficient target imaging in atherosclerosis. This study provides a valuable reference for evaluating the performance of such fluorescent dyes, and offers a promising perspective on the design of the target delivery systems for atherosclerosis.

Achieving Smart Photochromics Using Water-Processable, High-Contrast, Oxygen-Sensing, and Photoactuating Thiazolothiazole-Embedded Polymer Films

Water-soluble dipyridinium thiazolo[5,4-d]thiazole (TTz) compounds are incorporated into inexpensive poly(vinyl alcohol) (PVA)/borax films and exhibit fast (<1 s), high-contrast photochromism, photofluorochromism, and oxygen sensing. Under illumination, the films change from clear/yellow TTz2+ to purple TTz•+ and then blue TTz0. The contrast and speed of the photochromism are dependent on the polymer matrix redox properties and the concentration of TTz2+. The photoreduced films exhibit strong, near-infrared light (1000-1500 nm) absorbances in addition to visible color changes. Spectroscopic ellipsometry was used to establish the complex dielectric function for the TTz2+ and TTz0 states. Incorporating non-photochromic dyes yields yellow-to-green and pink-to-purple photochromism. Additionally, when illuminated, reversible photoactuation occurs, causing mechanical contraction in the TTz-embedded films. The blue film returns to its colorless state via exposure to O2, making the films able to sense oxygen and leak direction for smart packaging. These films show potential for use in self-tinting smart windows, eyeglasses, displays, erasable memory devices, fiber optic communication, and oxygen sensing.

Solvation effect enabled visualized discrimination of multiple metal ions

Highly efficient detection of environmental residual potentially toxic species is of concern worldwide as their presence in an excessive amount would greatly endanger the health of human beings as well as environmental sustainability. The solvation effect is a critical factor to be considered for understanding chemical reaction progress as well as the photophysical behaviors of substances and thus is promising for visualized detection of metal ions. Herein, by applying 5-amino-1,10-phenanthroline (APT) as the optical probe, a sensing strategy was proposed based on the solvation effect modulated complexation of APT towards different metal ions to achieve the visualized discrimination of four critical ions (Cu(II), Zn(II), Cd(II), and Al(III)). How the crucial intrinsic properties of the solvent (e.g., polarity, solvent free energy, and electrostatic potential) influenced the complexation and the product emission was clarified, and the detection performances were systematically evaluated with detection limits as low as the nM level and good recognition selectivity. Furthermore, a portable sensing chip was developed with potential for highly efficient analysis in complicated scenes; thus, this strategy offers a new insight into determining multiple metal ions or other critical substances upon solvation manipulation.

Highly selective detection of 2,4-dinitrophenol by fluorescent NH2-MIL-125(Ti) via dual-parameter sensing technology

The organic contaminant 2,4-dinitrophenol (2,4-DNP) is widely prevalent and poses significant risks to human health. Although numerous in-depth studies having been reported on the highly sensitive detection of 2,4-DNP, there are still challenges to its selective detection. Here, the fluorescence intensity ratio (I0/I) and emission peak shift (Δλ) were utilized for selective detection of 2,4-DNP by NH2-MIL-125(Ti). Notably, the emission peak of the NH2-MIL-125(Ti) suspension exhibited a remarkable red shift in the presence of 2,4-DNP (Δλ = 26 nm), accompanied by the blue shift or weak red shift of analogs, which provided a solid basis for selective detection of 2,4-DNP. Meanwhile, the I0/I ratio of the NH2-MIL-125(Ti) suspension exhibited a robust linear correlation with 2,4-DNP at the low concentration range (0-70 μM). The interaction of the analyte with NH2-MIL-125(Ti) was revealed to involve intermolecular charge transfer (ICT) and fluorescence resonance energy transfer (FRET) through XPS, FTIR, and UV-vis absorption spectroscopy. Additionally, we achieved the detection of 2,4-DNP using a smartphone by recognizing both the blue (B) values and the luminance (L) values. The obtained results demonstrated that the NH2-MIL-125(Ti) probe based on dual-parameter sensing technology exhibited excellent potential for selectively detecting 2,4-DNP in water environments, thereby offering significant prospects for its application in water quality assessment.

Fluorescent Probes Based on Charge and Proton Transfer for Probing Biomolecular Environment

Fluorescent probes for sensing fundamental properties of biomolecular environment, such as polarity and hydration, help to study assembly of lipids into biomembranes, sensing interactions of biomolecules and imaging physiological state of the cells. Here, we summarize major efforts in the development of probes based on two photophysical mechanisms: (i) an excited-state intramolecular charge transfer (ICT), which is represented by fluorescent solvatochromic dyes that shift their emission band maximum as a function of environment polarity and hydration; (ii) excited-state intramolecular proton transfer (ESIPT), with particular focus on 5-membered cyclic systems, represented by 3-hydroxyflavones, because they exhibit dual emission sensitive to the environment. For both ICT and ESIPT dyes, the design of the probes and their biological applications are summarized. Thus, dyes bearing amphiphilic anchors target lipid membranes and report their lipid organization, while targeting ligands direct them to specific organelles for sensing their local environment. The labels, amino acid and nucleic acid analogues inserted into biomolecules enable monitoring their interactions with membranes, proteins and nucleic acids. While ICT probes are relatively simple and robust environment-sensitive probes, ESIPT probes feature high information content due their dual emission. They constitute a powerful toolbox for addressing multitude of biological questions.

Correlating structure and photophysical properties in thiazolo[5,4-d]thiazole crystal derivatives for use in solid-state photonic and fluorescence-based optical devices

There is a growing demand for new fluorescent small molecule dyes for solid state applications in the photonics and optoelectronics industry. Thiazolo[5,4-d]thiazole (TTz) is an organic heterocycle moiety which has previously shown remarkable properties as a conjugated polymer and in solution-based studies. For TTz-based small molecules to be incorporated in solid-state fluorescence-based optical devices, a thorough elucidation of their structure-photophysical properties needs to be established. Herein, we have studied four TTz-based materials functionalized with alkyl appendages of varying carbon chain lengths. We report the single crystal structures of the TTz derivatives, three of which were previously unknown. The packing modes of the crystals reveal that molecular arrangements are largely governed by a chorus of synergistic intermolecular non-covalent interactions. Three crystals packed in herringbone mode and one crystal packed in slipped stacks proving that alkyl appendages modulate structural organization in TTz-based materials. Steady state and time-resolved photophysical properties of these crystals were studied via diffuse-reflectance, micro-Raman, and photoluminescence spectroscopy. The crystals fluoresce from orange-red to blue spanning through the whole gamut of the visible spectrum. We have established that photophysical properties are a function of crystal packing in symmetrically substituted TTz-based materials. This correlation was then utilized to fabricate crystalline blends. We demonstrate, for the first time, that symmetrically substituted donor-acceptor-donor TTz-based materials can be used for phosphor-converted color-tuning and white-light emission. Given the cost effectiveness, ease of synthesis and now a structure-photophysics correlation, we present a compelling case for the adoption of TTz-based materials in solid-state photonic and fluorescence-based optical devices.