Reversible Photochromic System Based on Rhodamine B Salicylaldehyde Hydrazone Metal Complex

A fluorescent light-up probe based on AIE and ESIPT processes for β-galactosidase activity detection and visualization in living cells

A novel fluorescent probe SA-βGal is reported here with light-up response to β-galactosidase. SA-βGal possesses the β-galactopyranoside group to react with β-galactosidase and releases the fluorescent salicylaldehyde azine with both aggregation induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT) characteristics. The linear fluorescent response enables the in vitro quantification of β-galactosidase activity in a range of 0-0.1 U mL^-1 with a detection limit of 0.014 U mL^-1. The probe exhibits significant advantages, such as no self-quenching at high concentrations, a large Stokes shift (190 nm) and high specificity to β-galactosidase with an excellent light-up ratio of 820 fold. Moreover, thanks to its good retention in living cells, the application of SA-βGal for the imaging of cellular β-galactosidase was also achieved with high contrast.

A Novel Mechanochromic and Photochromic Polymer Film: When Rhodamine Joins Polyurethane

A rhodamine-based molecule, Rh-OH, is synthesized. Rh-OH exhibits a reversible mechanochromic luminescent character but a passivating response to UV light. An elastomeric polymer film based on polyurethane with embedded Rh-OH is prepared via a polycondensation reaction. The film shows mechanochromic and photochromic properties with reversible color change, which originates from the isomerization of the Rh-OH molecule from a twisted spirolactam in the ring-closed form to a planarized zwitterionic structure in the ring-open state.

Crystal Violet Lactone Salicylaldehyde Hydrazone Zn(II) Complex: a Reversible Photochromic Material both in Solution and in Solid Matrix

Crystal violet lactone (CVL) is a classic halochromic dye which has been widely used as chromogenic reagent in thermochromic and piezochromic systems. In this work, a very first example of CVL-based reversible photochromic compound was developed, which showed distinct color change upon UV-visible light irradiation both in solution and in solid matrix. Moreover, metal complex of CVL salicylaldehyde hydrozone was facilely synthesized, exhibiting reversible photochromic properties with good fatigue resistance. It was served as promising solid material for photo-patterning.

Sonochemical Synthesis of Hydrophilic Drug Loaded Multifunctional Bovine Serum Albumin Nanocapsules

A facile sonochemical approach is designed to fabricate protein nanocapsules for hydrophilic drugs (HDs), and HD-loaded multifunctional bovine serum albumin (BSA) nanocapsules (MBNCs) have been prepared for the first time. The as-synthesized HD-loaded MBNCs have a satisfying size range and an excellent magnetic responsive ability. Moreover, high-dose hydrophilic drugs could be loaded into the MBNCs. As carriers, HD-loaded MBNCs also show attractive redox-responsive controlled release ability for hydrophilic drugs and could be internalized selectively by the tumor cells through the folate-mediated endocytosis.

Aggregation-induced emission and aggregation-promoted photochromism of bis(diphenylmethylene)dihydroacenes

Reported herein is a new class of pure polycyclic hydrocarbon molecules, designed through a novel aggregation-induced emission (AIE) strategy, with unexpected photochromic properties. The restriction of intramolecular motion was found as a comprehensive mechanism for the AIE effect. The photochromism mechanism study revealed that the photocyclization reaction of cis-stilbene, the molecular conformation in the single crystal and the tetracene backbone should contribute to the unique photo behavior. In particular, the fast responsive, photo-reversible and thermo-irreversible photochromic effect facilitated in the solid state opens a new field of aggregation-promoted photochromism.

Crystal structure of aqua-[(E)-N'-(5-bromo-2-oxido-benzyl-idene-κO)benzohydrazidato-κ(2) O,N']dioxidomolybdenum(VI) di-methyl-formamide monosolvate

The title compound, [Mo(C14H9BrN2O2)O2(H2O)]·C3H7NO, has a distorted octa-hedral geometry around the Mo atom, with the two terminal oxide groups lying cis to each other. The two aromatic rings present in the mol-ecule are almost coplanar, forming a dihedral angle of 1.4 (2)°. The five-membered ring involving the metal atom is puckered, with an amplitude Q = 0.358 (2) Å and ϕ = 204.1 (6)°. In the crystal, pairs of inversion-related mol-ecules are linked by O-H⋯N hydrogen bonds. An O-H⋯O hydrogen bond connects the water ligand to the di-methyl-formamide solvent mol-ecule. The crystal packing also features π-π [centroid-centroid distance of 3.688 (2) Å] and C-H⋯O inter-actions.

Flexible self-supporting nanofibers thin films showing reversible photochromic fluorescence

Highly sensitive stimuli-responsive fluorescent films play an important role in smart sensors and readable optical devices. However, systems involving light-driven fluorescence changes are still limited compared with photochromic materials that simply change color upon photostimulation. Herein, by incorporation of stilbene-based molecules into a poly(vinyl alcohol) host, we have developed new flexible self-supporting nanofiber films that exhibited fast and obvious photochromic fluorescence (PCF). The reversible transfer between two fluorescent states can be easily recycled. Fluorescence microscopy and atomic force microscopy images supplied in situ evidence of changes in fluorescence and surface morphology, respectively. Density functional theoretical calculations showed that the PCF can be attributed to photoisomerization of the stilbene-based molecules. Therefore, based on the combination of experimental and theoretical studies, this work not only supplies new stilbene-based systems with light-induced fluorescence change, but also gives detailed understanding on the photoisomerization and PCF processes of the nanofibers systems. We anticipate that these PCF films can be applied in erasable memory devices and antiforgery materials, and that our strategy may be extended to other systems to fabricate multistimuli-responsive fluorescent materials.

Synthesis and luminescence properties of salicylaldehyde isonicotinoyl hydrazone derivatives and their europium complexes

Four novel salicylaldehyde isonicotinoyl hydrazone derivatives and their corresponding europium ion complexes were synthesized and characterized, while the luminescence properties and the fluorescence quantum yields of the target complexes were investigated. The results indicated that the ligands favored energy transfers to the emitting energy level of europium ion, and four target europium complexes showed the characteristic luminescence of central europium ion. Besides the luminescence intensity of the complex with methoxy group, which possessed the highest fluorescence quantum yield (0.522), was stronger than that of other complexes. Furthermore, the electrochemical properties of the target complexes were further investigated by cyclic voltammetry, the results indicated that the highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy levels and the oxidation potential of the complexes with electron donating group increased, however, that of the complexes with accepting electron group decreased.

Single Probe for Imaging and Biosensing of pH, Cu(2+) Ions, and pH/Cu(2+) in Live Cells with Ratiometric Fluorescence Signals

It is very essential to disentangle the complicated inter-relationship between pH and Cu in the signal transduction and homeostasis. To this end, reporters that can display distinct signals to pH and Cu are highly valuable. Unfortunately, there is still no report on the development of biosensors that can simultaneously respond to pH and Cu(2+), to the best of our knowledge. In this work, we developed a single fluorescent probe, AuNC@FITC@DEAC (AuNC, gold cluster; FITC, fluorescein isothiocyanate; DEAC, 7-diethylaminocoumarin-3-carboxylic acid), for biosensing of pH, Cu(2+), and pH/Cu(2+) with different ratiometric fluorescent signals. First, 2,2',2″-(2,2',2″-nitrilotris(ethane-2,1-diyl)tris((pyridin-2-yl-methyl)azanediyl))triethanethiol (TPAASH) was designed for specific recognition of Cu(2+), as well as for organic ligand to synthesize fluorescent AuNCs. Then, pH-sensitive molecule, FITC emitting at 518 nm, and inner reference molecule, DEAC with emission peak at 472 nm, were simultaneously conjugated on the surface of AuNCs emitting at 722 nm, thus, constructing a single fluorescent probe, AuNC@FITC@DEAC, to sensing pH, Cu(2+), and pH/Cu(2+) excited by 405 nm light. The developed probe exhibited high selectivity and accuracy for independent determination of pH and Cu(2+) against reactive oxygen species (ROS), other metal ions, amino acids, and even copper-containing proteins. The AuNC-based inorganic-organic probe with good cell-permeability and high biocompatibility was eventually applied in monitoring both pH and Cu(2+) and in understanding the interplaying roles of Cu(2+) and pH in live cells by ratiometric multicolor fluorescent imaging.

Tunable solid-state fluorescent materials for supramolecular encryption

Tunable solid-state fluorescent materials are ideal for applications in security printing technologies. A document possesses a high level of security if its encrypted information can be authenticated without being decoded, while also being resistant to counterfeiting. Herein, we describe a heterorotaxane with tunable solid-state fluorescent emissions enabled through reversible manipulation of its aggregation by supramolecular encapsulation. The dynamic nature of this fluorescent material is based on a complex set of equilibria, whose fluorescence output depends non-linearly on the chemical inputs and the composition of the paper. By applying this system in fluorescent security inks, the information encoded in polychromic images can be protected in such a way that it is close to impossible to reverse engineer, as well as being easy to verify. This system constitutes a unique application of responsive complex equilibria in the form of a cryptographic algorithm that protects valuable information printed using tunable solid-state fluorescent materials.

Solid-state fluorescent materials show promise for potential applications in security and anti-counterfeiting technologies. Here, the authors report a heterorotaxane which has found application in security inks with highly tunable solid-state fluorescence through supramolecular encapsulation.

Dynamic behavior of molecular switches in crystal under pressure and its reflection on tactile sensing

Molecular switches have attracted increasing interest in the past decades, due to their broad applications in data storage, optical gating, smart windows, and so on. However, up till now, most of the molecular switches are operated in solutions or polymer blends with the stimuli of light, heat, and electric fields. Herein, we demonstrate the first pressure-controllable molecular switch of a benzo[1,3]oxazine OX-1 in crystal. Distinct from the light-triggered tautomerization between two optical states, applying hydrostatic pressure on the OX-1 crystal results in large-scale and continuous states across the whole visible light range (from ∼430 to ∼700 nm), which has not been achieved with other stimuli. Based on detailed and systematic control experiments and theoretical calculation, the preliminary requirements and mechanism of pressure-dependent tautomerization are fully discussed. The contributions of molecular tautomerization to the large-scale optical modulation are also stressed. Finally, the importance of studying pressure-responsive materials on understanding tactile sensing is also discussed and a possible mechanotransduction mode is proposed.

A photoresponsive glycosidase mimic

Azobenzene-3,3'-dicarboxylic acid exists in photoisomerizable (E) and (Z)-forms. Deprotonation of the carboxylic acid groups from the (E)-form occurs simultaneously, whereas in the (Z)-form it occurs in a stepwise fashion. The mono anionic form of the (Z)-isomer acts as a glycosidase mimic that proceeds through a general acid-general base catalytic mechanism. This is the first example of a photoresponsive glycosidase mimic.