Smart Stimulation Response of a Pyrene-Based Lanthanide(III) MOF: Fluorescence Enhancement to HX (F and Cl) or R-COOH and Artificial Applicable Film on HCl Vapor Sensing

Toxic acids produced by industries are major hazards to the environment and human health, and luminescent pyrene-based crystalline metal-organic frameworks (MOFs) demonstrate promising performance in the detection of toxic acids. Herein, two novel isostructural 3D porous lanthanide MOFs, H3O·[Ln3(TBAPy)2(μ2-H2O)2(OH)2]·2DMA·2Diox·6.5H2O (Ln = Pr (1) and Ce (2); H4TBAPy (1,3,6,8-tetrakis(p-benzoic acid)pyrene); and DMA: N,N-dimethylacetamide) were synthesized, which showed alb topology. Based on the protonation and hydrogen bond mechanism, complex 1 could be used as a fluorescence recognition sensor for HX (X = F, Cl, Br, and I) acid solutions with different luminescence behaviors. It is worth noting that complex 1 exhibited high sensitivity in the fluorescence enhancement sensing of hydrofluoric acid, oxalic acid, and trichloroacetic acid. In particular, complex 1 had a low limit of detection (LOD) for OA (0.1 μM) and was applied to real monitoring of orange fruit samples. In addition, the PVA@1 film could selectively, sensitively, and quantitatively respond to hydrochloric acid (HCl) vapor through fluorescent quenching; due to its protonation and adsorption capacity, the LOD was 0.18 ppm. Therefore, the portable optical device, the PVA@1 film, can detect HCl gas in trace amounts, achieving the ultimate goal of real-time and rapid detection, which has potential application value for industrial production safety.

Improved Analytical Performance of an Amphiphilic Probe upon Protein Encapsulation: Spectroscopic Investigation along with Computational Rationalization

An easily synthesizable pyrene-based amphiphilic probe (Pybpa) has been developed, which exhibited no responses with metal ions in the pure aqueous medium despite possessing a metal ion-chelating bispicolyl unit. We believe that spontaneous aggregation of Pybpa in aqueous medium makes the ion binding unit not accessible to the metal ions. However, the sensitivity and selectivity of Pybpa toward Zn²⁺ ions drastically improve in the presence of serum albumin protein, HSA. The differences in the microenvironment inside the protein cavity, in terms of local polarity, and conformational rigidity might be attributing factors for that. The mechanistic investigations also suggest that there might be the involvement of polar amino acid residues that take part in coordination with Zn²⁺ ions. Pybpa shows no detectable spectroscopic changes with Zn²⁺ ions in aqueous medium in the absence of HSA. However, it can effectively recognize Zn²⁺ ions in the protein-bound form. Moreover, the photophysical behavior of Pybpa and its zinc complex have been investigated with DFT and docking studies. Noteworthy, such an unusual sensing aspect of Zn²⁺ exclusively in the protein-bound state and particularly in aqueous medium is truly rare and innovative.

Rapid Identification of Bacteria by Membrane-Responsive Aggregation of a Pyrene Derivative

An imidazolium-derived pyrene aggregation was developed to rapidly identify and quantify different bacteria species. When the nonemissive aggregates bound to the anionic bacteria surface, the sensor disassembled to turn on significant fluorescence. At the same time, ratiometric signals between pyrene monomer and excimer emission were controlled by different interactions with various bacteria surfaces. The resulted different fluorescent emission profiles then were obtained as fingerprints for various bacterial species. By converting emission profiles directly into output signals of two channels, fluorescence increase and ratiometric change, a two-dimensional analysis map was generated for bacteria identification. We demonstrated that our sensor rapidly identified 10 species of bacteria and 14 clinical isolated multidrug-resistant bacteria, and we determined their staining properties (Gram-positive or Gram-negative).

Water Dispersible Few-Layer Graphene Stabilized by a Novel Pyrene Derivative at Micromolar Concentration

The search for graphene or few-layer graphene production methods that are simple, allow mass production, and yield good quality material continues to provoke intense investigation. The present work contributes to this investigation through the study of the aqueous exfoliation of four types of graphene sources, which are namely graphite and graphite nanoflakes with different morphologies and geographical origins. The exfoliation was achieved in an aqueous solution of a soluble pyrene derivative that was synthesized to achieve maximum interaction with the graphene surface at low concentration (5 × 10⁻⁵ M). The yield of bilayer and few-layer graphene obtained was quantified by Raman spectroscopic analysis, and the adsorption of the pyrene derivative on the graphene surface was studied by thermogravimetric analysis and X-ray diffraction. The whole procedure was rationalized with the help of molecular modeling.

Pyrene Derivative Emitting Red or near-Infrared Light with Monomer/Excimer Conversion and Its Application to Ratiometric Detection of Hypochlorite

Fluorescent sensors are attractive and versatile tools for both chemical sensing and biological imaging. Herein, a novel pyrene derivative fluorophore, Py-Cy, possessing the monomer/excimer conversion feature, was synthesized; and the design rationale for this fluorophore is combination of extending conjugation length and incorporating donor-π-acceptor structure. The positively charged Py-Cy shows quite good water solubility and exhibits absorption in the visible-light range, and its monomer and excimer emit red light and near-infrared light respectively, which is extremely beneficial for biosensing or bioimaging. To explore the potential utilization of this new fluorophore, we choose hypochlorite as a model analyte, which can break the double bond in the molecular structure, thereby generating the water-insoluble pyrenecarboxaldehyde; this process correspondingly leads to fluorescence changes and thus affords the ratiometric fluorescent detection of hypochlorite in real samples and cell imaging. The approach offers new insights for designing other fluorophores which emit red or near-infrared light and for devising technically simple ratiometric fluorescent sensors.