Visual Recognition of Aliphatic and Aromatic Amines Using a Fluorescent Gel: Application of a Sonication-Triggered Organogel

A naphthalimide-based fluorescent gelator (<b>N1</b>) containing an alkenyl group has been designed and characterized. This material is able to gelate alcohols via a precipitate-to-gel transformation when triggered with ultrasound for less than 2 min (S-gel). The gelation process in <i>n</i>-propanol was studied by means of absorption, fluorescence, and IR spectra, scanning electron microscopy (SEM) images, and X-ray diffraction patterns. The fluorescence intensity of <b>N1</b> decreased during the gelation process in a linear relationship with the sonication time. The S-gel of <b>N1</b> could be used to sense aliphatic and aromatic amines by measuring the change in the signal output. For example, the addition of propylamine to the S-gel of <b>N1</b> resulted in a dramatic enhancement of the fluorescence intensity, accompanied by a gel-to-sol transition. On the contrary, when the S-gel of <b>N1</b> was treated with aromatic amines such as aniline, fluorescence was quenched and there was no gel collapse. The sensing mechanisms were studied by ¹H NMR, small-angle X-ray scattering, SEM and spectroscopic experiments. It is proposed that isomerization of the alkenyl group of <b>N1</b> from the trans to cis form occurs when the S-gel is treated with propylamine, resulting in a gel–sol transition. However, the aromatic aniline molecules prefer to insert into the gel networks of <b>N1</b> via hydrogen-bonding and charge-transfer interactions, maintaining the gel state. As potential applications, testing strips of <b>N1</b> were prepared to detect aniline

Cyclodextrin-Assisted Two-Component Sonogel for Visual Humidity Sensing

In this work, two naphthalimide-based compounds, <b>1a</b> and <b>1b</b>, have been designed and synthesized. Both compounds can form stable two-component gels in <i>n</i>-propanol or <i>n</i>-butanol upon addition of α-cyclodextrin (α-CD) followed by sonication at room temperature. Interestingly, the <b>1a</b>/α-CD gel is thixotropic and very sensitive to water. Addition of a small amount of water induces rapid gel collapse, allowing further development of the gel as a visual relative humidity sensor. Specificity of the sensor has been confirmed using several approaches, such as scanning electron microscopy and fluorescence, Fourier transform infrared, and ¹H NMR spectroscopy experiments. The results show that α-CD acts as a junction for the assembly of <b>1a</b> or <b>1b</b> through hydrogen bonding between hydroxyl and amide groups. Upon addition of water, α-CD interacts with the adamantane group of <b>1a</b> via an incomplete host–guest encapsulation, resulting in the dissociation of the hydrogen-bonding-assisted two-component assembly, accompanied by gel collapse

Intrinsically Coupled 3D nGs@CNTs Frameworks as Anode Materials for Lithium-Ion Batteries

Acquiring high-quality integrated nanographene sheets (nGs) and mitigating their self-aggregation are highly essential to achieving their full potential in energy related applications. The insertion of enthetic spacers into nGs layers can relieve the stacking problems but always results in a change in the intrinsic properties of the nGs and/or the introduction of complexity at the interfaces. In this work, a facile and scalable strategy is used to construct highly integrated, intrinsically coupled, N, S-doped 3D nanographene sheets trapped within carbon nanotubes (nGs@CNTs) through a modified counterion intercalation. The as-obtained nGs@CNTs are composed of two building blocks, in which large amounts of integrated unzipped nanoscale graphene sheets are tightly attached to the intact inner walls of the CNTs. The remaining CNTs serve as inherent spacers to prevent the self-stacking of nGs. Benefiting from the permanent and robust column bracing frameworks, the resultant 3D aerogels are expected to act as effective electrode materials for lithium-ion batteries with superior cyclic performance, delivering a reversible capacity as high as 1089 mAh g^–1 at a current density of 2 A g^–1 even after 300 cycles. The good lithium-ion storage performance is attributed to the hierarchical porous feature, the intrinsically unstacked bridged structure, and the synergistic effects between the N and S. This promising strategy represents a new concept for mitigating the self-aggregation of nGs by using autologous spacers

Large Red-Shifted Fluorescent Emission via Intermolecular π–π Stacking in 4‑Ethynyl-1,8-naphthalimide-Based Supramolecular Assemblies

Two low molecular weight gelators containing 4-ethynyl-1,8-naphthalimide groups with large conjugated structure via different length of alkyl chains were synthesized and fully characterized. The gelation properties, structural character, and fluorescence of the gels were investigated via methods of scanning electron microscopy, X-ray diffraction, and spectral studies. The gelators have high fluorescence quantum yields in both solution and solid state. Interestingly, the wavelength of the fluorescent emission in the reversible sol–gel transition process of the gels has a large red-shift of 80 nm in DMF, which is extremely sparse for 1,8-naphthalimide derivatives in the literature. The intermolecular π–π stacking between naphthalimide is suggested to be the main driving force for the gel formation and fluorescent variation by means of temperature-dependent ¹H NMR study and theoretical calculation

A Highly Sensitive Ratiometric Fluorescent Probe for the Detection of Cytoplasmic and Nuclear Hydrogen Peroxide

As a marker for oxidative stress and a second messenger in signal transduction, hydrogen peroxide (H₂O₂) plays an important role in living systems. It is thus critical to monitor the changes in H₂O₂ in cells and tissues. Here, we developed a highly sensitive and versatile ratiometric H₂O₂ fluorescent probe (<b>NP1</b>) based on 1,8-naphthalimide and boric acid ester. In response to H₂O₂, the ratio of its fluorescent intensities at 555 and 403 nm changed 1020-fold within 200 min. The detecting limit of <b>NP1</b> toward H₂O₂ is estimated as 0.17 μM. It was capable of imaging endogenous H₂O₂ generated in live RAW 264.7 macrophages as a cellular inflammation response, and especially, it was able to detect H₂O₂ produced as a signaling molecule in A431 human epidermoid carcinoma cells through stimulation by epidermal growth factor. This probe contains an azide group and thus has the potential to be linked to various molecules via the click reaction. After binding to a Nuclear Localization Signal peptide, the peptide-based combination probe (<b>pep-NP1</b>) was successfully targeted to nuclei and was capable of ratiometrically detecting nuclear H₂O₂ in living cells. These results indicated that <b>NP1</b> was a highly sensitive ratiometric H₂O₂ dye with promising biological applications