A new kind of naphthalimide-based organogelator, TN, was designed and synthesized. The intramolecular guanylation of TN promoted by Hg2+ or Ag+ in both solution and gel state was studied through several approaches including FL, UV-visible, NMR, FT-IR and SEM experiments. TN could selectively sense Hg2+ and Ag+ ions with obvious fluorescence quenching and color changes from yellow to colorless among test ions in the solution state. Interestingly, the S-gel of TN could be used to selectively discriminate Hg2+ from Ag+via phase and morphology changes. Hg2+ ions triggered the gel-to-gel transition with morphology changes of the TN S-gel from nanofibrils to porous sheet structure, together with fluorescence quenching. In contrast, the gel collapsed in the presence of Ag+ ions, which was comprised of short and disordered fiber structure. To the best of the authors’ knowledge, this is the first example of gels selectively sensing Hg2+ or Ag+via a reaction approach.

A sugar functionalized naphthalimide derivative (H1) self-assembles into supramolecular nanotubes (25 nm pore diameter) by the reaction of 4-N-ethylaminenaphthalimide-N-propinyl and delta-gluconolactone in refluxed ethanol. The suspension of the tube assembly in water can directly form hydrogels when triggered by sonication, without change in morphology or molecular aggregates in the pH range of 5–8. Modified with aminocarproic acid, H2 with more hydrogen bonding sites can form pH tolerant hydrogels in the widest range of pH values from 1–14 accelerated by sonication. The gelation mechanism was studied in detail. To the best of our knowledge, this is the first paradigm wherein hydrogels were constructed from naphthalimide derivatives. Finally, the potential of the hydrogel as a drug delivery and release system for hydrophilic medicine was explored.

A naphthalimide-based fluorescent gelator (N1) 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 n-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 N1 decreased during the gelation process in a linear relationship with the sonication time. The S-gel of N1 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 N1 resulted in a dramatic enhancement of the fluorescence intensity, accompanied by a gel-to-sol transition. On the contrary, when the S-gel of N1 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 N1 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 N1 via hydrogen-bonding and charge-transfer interactions, maintaining the gel state. As potential applications, testing strips of N1 were prepared to detect aniline.Keywords: amine sensor; fluorescence; naphthalimide; organogel; supramolecular chemistry; ultrasound;

A new kind of terpyridine-based Ca2+ sensor TS was designed and studied based on the internal charge transfer (ICT). In the diluted solution state, TS sensed Ca2+ and Mg2+ ions among test ions via an “off–on” approach as seen from fluorescence spectra of test ions. Moreover, TS was able to form stable fluorescent gels in organic solvents accelerated by ultrasound, indicating the ultrasound responsive properties of TS molecules. The S-gel of TS could be successfully used to selectively recognize Ca2+ through fluorescent emission color and morphological changes, which was different from that of the solution state. It was predicated that the competition between the self-assembly of TS molecules and the host–guest interaction of TS with Ca2+ or Mg2+ was responsible for the sensing properties. To the best of our knowledge, this is the first example that organogels could selectively sense Ca2+ ions.

Two sugar functionalized naphthalimide derivatives (S1, S2) self-assembled into organogels by a heating–cooling process or triggered by ultrasound. The gelation properties in organic solvents were examined by several experiments including UV-vis, fluorescence, FT-IR spectra and SEM, XRD techniques. It was deduced that minor changes in the terminal group had great impact on the gelation and ultrasound responsive properties. Moreover, ultrasound triggered the formation of a yellow emissive gel (S1, with lifetimes in the range of ns) that was readily doped with Eu3+ in situ affording luminescent gels with red emission color (with lifetimes in the range of μs), which expressed efficient energy transfer from the S1 assembly to Eu3+ ion. It was presented that the efficient energy transfer only happened in the ordered fibrous aggregates of S1, whereas, the ET process was not observed in the solution state, indicating the phase control on the ET process. Such findings would pave a new way for the construction of novel rare earth based luminescent materials.

•Two new kinds of dual-channel naphthalimide-based chemsensors were synthesized.•L1 and L2 could sense flouride anion in NIR region with dramatic color changes.•L2 could sense flouride anion with dramatically quenched flourescence in NIR region.Two new kinds of dual-channel naphthalimide-based chemsensors for selective detection of fluoride anion was designed and synthesized. Upon the addition of F−, they displayed dramatic color changes from orange to blue, together with drastically quenched fluorescence, through hydrogen bonding interactions. The maximum absorption wavelength was red-shifted for over 100 nm to the near-infrared region (NIR region). In addition, L1 showed high selectivity toward fluoride ion among test anions such as F−, AcO−, Cl−, Br− and I−, and the maximum fluorescent region was also at the NIR region.

A new kind of fluorescein-based chemosensor L toward anions was designed and synthesized. The chemosensor L could selectively sense F− and AcO− among test anions, which was accompanied by the “off–on” fluorescence enhancement and “colorless-to-yellow” color changes. The anion bonding ability of L was checked by UV–vis, FL, and 1HNMR titration experiments. Notably, the compound L could detect F− in 30 % aqueous solution (DMSO: Water = 7:3, v: v) with 0.36 ppm sensitivity through selectively fluorescence enhancement by cooperative interaction of “ring-open” reaction and hydrogen bonding.

•Two new cholesterol-based compounds O1 and O2 were designed and synthesized.•O2 could form opaque gel in 1,4-dioxane with red color.•The gel could selectively response to fluoride ions with color and phase changes.In this paper, two new cholesterol-based compounds O1 and O2 were designed and synthesized. The compound O2 could selectively gel in 1,4-dioxane with porous ribbon structure. The aggregation mode of O2 molecules were characterized by SEM, IR, UV–vis and XRD experiments. Interestingly, the gel of O2 was also fluoride-responsive. The addition of TBAF on the gel surface would trigger the gel–sol transition, and the collapse time could be controlled by amount of fluoride ions. The response process was also accompanied by dramatic color changes from orange to purple. From the NMR titration experiments, it was deduced that the hydrogen bonding competition between the anion-receptor and self-assembly of the receptor played an important role for the gel–sol transition.

•A new kind of fluorescein-based ion sensor was synthesized.•The sensor could be a good probe for Ca2 + and Mg2 + determination.•Two-step binding events were observed in the sensing process.In the present work, a new kind of fluorescein-based chemosensor L was designed and synthesized to selectively recognize Ca 2+ or Mg 2+ over other competing ions. The chemosensor showed “off–on” fluorescent and color changes upon the addition of Ca2 + and Mg2 +. The dynamic binding events with the formation of 1:1(L/M) and 1:2(L/M) complexes were examined. The cation-driven conformation changes of L were understood and proposed rationally by the UV–vis, FL, and 1HNMR titrations. By this allosteric effect, Ca2 + and Mg2 + could be selectively recognized with the 1:2 stoichiometry by fluorescent changes, which were different from other known reports on chemosensors that the host-cation complexion was exploited for controlling chromophore interaction as the model of signaling.

In this paper, a new p-nitrophenylhydrozine-based anion receptor 1 containing cholesterol group had been designed and synthesized. It could selectively recognize fluoride among different anions tested with color changes from pale yellow to red for visual detection. Simultaneously, it could gel in cyclohexane, and the gel was also fluoride-responsive. When treated with TBAF (tetra-n-butylammonium fluoride), the gel could undergo gel–sol transition accompanied by color, morphology and surface changes. The binding mechanism had been investigated by UV–vis and 1HNMR (proton nuclear magnetic resonance spectra) titrations. From SEM (scanning electron microscope), SAXS (small-angle X-ray scattering), IR (Infrared Spectroscopy) and CA (contact angle) experiments, it was indicated that the addition of F− could destroy the molecule assembly of host 1 in the gel state, thus resulting in the gel-to-sol transition due to the binding site competition effect. To the best of our knowledge, this was the simplest fluoride-responsive organogel with high selectivity.Highlights► A novel kind receptor for selective recognition of fluoride had been designed. ► Its organogel was also fluoride-responsive. ► This is the simplest fluoride-responsive organogel with high selectivity.

A new kind of naphthalimide-based organogelator, TN, was designed and synthesized. The intramolecular guanylation of TN promoted by Hg2+ or Ag+ in both solution and gel state was studied through several approaches including FL, UV-visible, NMR, FT-IR and SEM experiments. TN could selectively sense Hg2+ and Ag+ ions with obvious fluorescence quenching and color changes from yellow to colorless among test ions in the solution state. Interestingly, the S-gel of TN could be used to selectively discriminate Hg2+ from Ag+via phase and morphology changes. Hg2+ ions triggered the gel-to-gel transition with morphology changes of the TN S-gel from nanofibrils to porous sheet structure, together with fluorescence quenching. In contrast, the gel collapsed in the presence of Ag+ ions, which was comprised of short and disordered fiber structure. To the best of the authors’ knowledge, this is the first example of gels selectively sensing Hg2+ or Ag+via a reaction approach.

The facile tuning of the fluorescent properties of organogels is highly desirable for optical switches, light-emitting diodes, chemosensors and bioprobes. The design of organic molecules with multiple emission colors but only one molecular platform remains challenging. Herein, a new cholesterol-based organogelator N1 containing D–A pairs (salicylaldehyde and naphthalimide units) was designed. We successfully obtained multiple solvent-tuned emission colors in both the solution and gel states using a unimolecular platform. Moreover, the effects of the solvent on the gel morphology, rheology and anion-responsive properties were studied. Finally, we showed that the gel in benzene displayed reversible thermochromic properties with changes in emission color from yellow-green to red. Several experiments suggested that a short-distance and ordered array of the D–A pairs facilitated the efficient intermolecular electron transfer of the fluorophores.

A sugar functionalized naphthalimide derivative (H1) self-assembles into supramolecular nanotubes (25 nm pore diameter) by the reaction of 4-N-ethylaminenaphthalimide-N-propinyl and delta-gluconolactone in refluxed ethanol. The suspension of the tube assembly in water can directly form hydrogels when triggered by sonication, without change in morphology or molecular aggregates in the pH range of 5–8. Modified with aminocarproic acid, H2 with more hydrogen bonding sites can form pH tolerant hydrogels in the widest range of pH values from 1–14 accelerated by sonication. The gelation mechanism was studied in detail. To the best of our knowledge, this is the first paradigm wherein hydrogels were constructed from naphthalimide derivatives. Finally, the potential of the hydrogel as a drug delivery and release system for hydrophilic medicine was explored.