Unsymmetrical diarylethenes as molecular keypad locks with tunable photochromism and fluorescence via Cu2+ and CN− coordinations

A Reversible Fluorescent Chemosensor for the Selective Detection of Cu2+ and CN- ions by Displacement Approach

A novel fluorescence chemosensor BDP (2-(1-(benzothiazol-2-yl)-5-(4-(diphenylamino)phenyl)-4,5-dihydro-1H-pyrazol-3-yl)phenol) has been synthesized and its sensing behavior has been screened towards various cations by absorption, emission and mass spectroscopic techniques. The probe BDP detects Cu2+ ions preferentially over other metal ions, and the resulting BDP-Cu2+ ensemble acts as a secondary sensor for cyanide anion detection over other anions. The fluorescence intensity of the probe BDP is quenched when it comes into contact with Cu2+ ions, but it is increased reversibly when it comes into contact with cyanide anion, according to spectroscopic measurements. Along with this, optical studies indicate that the sensor BDP has capability to sense Cu2+ and CN- ions selectively over other examined competitive ions with the LOD of 2.57×10-8 M and 2.98×10-8 M respectively. The detection limit of Cu2+ ions is lower than the WHO recommended Cu2+ ions concentration (31.5 µM) in drinking water. On the basis of "on-off-on" fluorescence change of the probe BDP upon interaction with Cu2+ and CN- ions, a possible mechanism for this selective sensing behavior was presented and IMPLICATION logic gate was successfully designed. Furthermore, cell imaging investigations were used to investigate the probe BDP's biological applicability.

Detection of cyanide and sulfide ions by different mechanisms using a fluorescent chemical sensor containing a fluorophore and a potential ligand for metal complexes

Here, we present a fluorescent chemical sensor for the simultaneous detection of CN- and S2- ions, which are highly toxic to humans and the environment. When the BPMA-Flu-Cu2+ complex comprising BPMA-Flu, a fluorophore combined with Cu2+, was used, the fluorescence was turned off. However, the fluorescence was turned on again by the addition of CN- and S2- ions. BPMA-Flu is a unique compound containing both a fluorophore and a ligand coordinated to a metal ion. This strategy using the proposed BPMA-Flu-Cu2+-based fluorescent chemical sensor facilitated quantitative analysis of CN- and S2- ions with high selectivity and sensitivity, despite varying detection mechanisms. The detection limit was as low as 290 nM and 74 nM for CN- and S2- ions, respectively. The sensor was selective and excluded other anions at concentrations 10-fold higher than those of CN- and S2- ions. The recovery rates did not exceed 10% of the original values for the detection of CN- ions in rainwater and tap water. These results indicate acceptable accuracy and precision for practical applications.

Future-Oriented Advanced Diarylethene Photoswitches: From Molecular Design to Spontaneous Assembly Systems

Diarylethene (DAE) photoswitch is a new and promising family of photochromic molecules and has shown superior performance as a smart trigger in stimulus-responsive materials. During the past few decades, the DAE family has achieved a leap from simple molecules to functional molecules and developed toward validity as a universal switching building block. In recent years, the introduction of DAE into an assembly system has been an attractive strategy that enables the photochromic behavior of the building blocks to be manifested at the level of the entire system, beyond the DAE unit itself. This assembly-based strategy will bring many unexpected results that promote the design and manufacture of a new generation of advanced materials. Here, recent advances in the design and fabrication of diarylethene as a trigger in materials science, chemistry, and biomedicine are reviewed.

Light and Cation-Driven Optical Switch based on a Stilbene-Appended Terpyridine System for the Design of Molecular-Scale Logic Devices

A molecular system comprising a terpyridine moiety capable of coordinating with different cations and a photoswitchable stilbene unit has been utilized here for the fabrication of multiply configurable logic systems. Incorporation of a substituted stilbene unit into the terpyridine motif generates an intraligand charge-transfer-sensitive module whose absorption and emission spectral properties are highly sensitive to light as well as cations. On the basis of the optical response profile of the receptor in the presence of selected cations as well as light of a specific wavelength, we are able to demonstrate multiple Boolean logic functions such as INHIBIT, IMPLICATION, OR, NOR, and NAND, as well as various combinations of them. Of particular interest, we utilized the present system for the construction of security keypad locks and memory devices by maintaining a proper sequence of the stimuli and monitoring either absorption or emission spectral response at a specific wavelength as the output signal. In addition to various Boolean logic functions, the present system has also the ability to mimic fuzzy logic operations for generating an infinite-valued logic scheme depending on its emission spectral responses upon varying the concentration of cationic (Fe²⁺ and/or Zn²⁺) and anionic (CN^-) inputs.

A dual-mode visual detector for toxic hydrazine

Hydrazine (N₂H₄) is one of the commonly used chemical reagents in numerous industries and applications but its toxicity to humans poses a need to develop simple visual detection methods. Herein, we demonstrate a novel dual-mode system to detect and simultaneously consume hydrazine in vapour and solution by using a small photoresponsive molecule that has altered optical response (both colourimetric and fluorescent) after reacting with hydrazine.

A small photoresponsive molecule changes colour from blue to colourless when exposed to hydrazine vapours. It also becomes emissive providing two convenient ways of detecting the presence of this toxic chemical.

Origami paper analytical assay based on metal complex sensor for rapid determination of blood cyanide concentration in fire survivors

Cyanide-based blood poisoning can seriously damage fire victims and cause death if not detected quickly. Previous conventional methods require laboratory equipment, which are expensive and increase the duration of the analysis. Here, a simple origami based microfluidic device was introduced for point of need detection of blood cyanide concentration in people involved in fire. The device is made of four layers of paper. Each layer was in the size of 1 × 1 cm folded on each other. In this work, the blood sample was acidified by trichloroacetic acid to separate cyanide from methaemoglobin in the form of HCN gas. The produced gas released into borate buffer to recover free cyanide ions which interacted with the Pt complex ([Pt(p-MeC₆H₄)₂(phen)]) used as a receptor in this study. Optimized conditions were applied to have a suitable interaction causing the color of the receptor to change from yellow to colorless. The color changes were recorded by a smartphone, and the sensor response was calculated by the routine image analysis software. The assay was capable of determining cyanide ions at different concentrations in the range of 1.0 to 100.0 µmol L⁻¹. The detection limit of these determination was equal to 0.4 µmol L⁻¹. The assay responses were not affected by the interfering species. As a practical analysis, the proposed sensor was applied to determine cyanide ions in the blood sample of 20 studied fire survivors and 10 controls with high accuracy.

Photoluminescent and Chromic Nanomaterials for Anticounterfeiting Technologies: Recent Advances and Future Challenges

Counterfeiting and inverse engineering of security and confidential documents, such as banknotes, passports, national cards, certificates, and valuable products, has significantly been increased, which is a major challenge for governments, companies, and customers. From recent global reports published in 2017, the counterfeiting market was evaluated to be $107.26 billion in 2016 and forecasted to reach $206.57 billion by 2021 at a compound annual growth rate of 14.0%. Development of anticounterfeiting and authentication technologies with multilevel securities is a powerful solution to overcome this challenge. Stimuli-chromic (photochromic, hydrochromic, and thermochromic) and photoluminescent (fluorescent and phosphorescent) compounds are the most significant and applicable materials for development of complex anticounterfeiting inks with a high-security level and fast authentication. Highly efficient anticounterfeiting and authentication technologies have been developed to reach high security and efficiency. Applicable materials for anticounterfeiting applications are generally based on photochromic and photoluminescent compounds, for which hydrochromic and thermochromic materials have extensively been used in recent decades. A wide range of materials, such as organic and inorganic metal complexes, polymer nanoparticles, quantum dots, polymer dots, carbon dots, upconverting nanoparticles, and supramolecular structures, could display all of these phenomena depending on their physical and chemical characteristics. The polymeric anticounterfeiting inks have recently received significant attention because of their high stability for printing on confidential documents. In addition, the printing technologies including hand-writing, stamping, inkjet printing, screen printing, and anticounterfeiting labels are discussed for introduction of the most efficient methods for application of different anticounterfeiting inks. This review would help scientists to design and develop the most applicable encryption, authentication, and anticounterfeiting technologies with high security, fast detection, and potential applications in security marking and information encryption on various substrates.

Circularly Polarized Luminescence in Nanoassemblies: Generation, Amplification, and Application

Currently, the development of circularly polarized luminescent (CPL) materials has drawn extensive attention due to the numerous potential applications in optical data storage, displays, backlights in 3D displays, and so on. While the fabrication of CPL-active materials generally requires chiral luminescent molecules, the introduction of the "self-assembly" concept offers a new perspective in obtaining the CPL-active materials. Following this approach, various self-assembled materials, including organic-, inorganic-, and hybrid systems can be endowed with CPL properties. Benefiting from the advantages of self-assembly, not only chiral molecules, but also achiral species, as well as inorganic nanoparticles have potential to be self-assembled into chiral nanoassemblies showing CPL activity. In addition, the dissymmetry factor, an important parameter of CPL materials, can be enhanced through various pathways of self-assembly. Here, the present status and progress of self-assembled nanomaterials with CPL activity are reviewed. An overview of the key factors in regulating chiral emission materials at the supramolecular level will largely boost their application in multidisciplinary fields.

Homogeneous DNA-only keypad locks enable one-pot assay of multi-inputs

Homogeneous DNA-only keypad locks were built with multi-stranded scalable junction substrates and a series of double-stranded eliminators to differentially process correctly- and wrongly-added DNA inputs, respectively. Unlike conventional strategies that employed solid-phase platforms, one-pot assay of multiple DNA inputs was achieved, showing merits in fabricating complicated information security systems.

An unprecedented polyhydroxycarboxylic acid ligand bridged multi-EuIII incorporated tellurotungstate and its luminescence properties

The first polyhydroxycarboxylic acid ligand bridged multi-EuIII-incorporated tellurotungstate K14H10[Eu4(H2O)4W6(H2glu)4O12(B-α-TeW9O33)4]·60H2O (H6glu = d-gluconic acid) (1) was synthesized via an organic ligand-driven self-assembly strategy. The polyhydroxycarboxylic acid ligand bridged tetrameric polyoxoanion [Eu4(H2O)4W6(H2glu)4O12(B-α-TeW9O33)4]24- in 1 can be viewed as an aggregation of four trivacant Keggin [B-α-TeW9O33]8- fragments and an innovative heterometallic [Eu4(H2O)4W6(H2glu)4O12]8+ cluster, in which four high-coordinate polyhydroxy flexible H2glu4- ligands chelate W and Eu centers through carboxyl and hydroxyl groups, giving rise to a heterometallic cluster. The hexagonal packing of the tetrameric polyoxoanions in 1 along the c axis provides excellent porous channels, which greatly increases the specific surface area of the whole framework and may be of benefit for fluorescence sensing in aqueous solution. 1 can function as a "turn-off" luminescence sensor to detect Cu2+ ions in aqueous solution. The limit of detection (LOD) of the 1-sensor is 8.82 × 10-6 mM, which is the lowest among the reported polyoxometalate-based fluorescence sensors. As for the Cu2+-quenching system, it can function as an "off-on" sensor to detect cysteine in an aqueous system, affording a LOD of 1.75 × 10-4 mM. This work opens up an avenue to broaden the applications of polyoxometalate-based materials in the optical intelligence detection field.

A novel imidazole derived colorimetric and fluorometric chemosensor for bifunctional detection of copper (II) and sulphide ions in environmental water samples

Herein, a novel "ON-OFF" colorimetric and fluorometric chemosensor; 1N-allyl-2-(2, 5-dimethoxyphenyl)-4, 5-diphenyl-1H-imidazole (ADPPI), was constructed for sequential determination of Cu²⁺ and S^2- ions in aqueous media. The interaction between chemosensor ADPPI and different metal cations was investigated using UV-VIS and fluorimetric spectroscopy. ADPPI showed a favorable and good interaction with Cu²⁺ ions producing blue colored solution peaked at 610 nm with blue fluorescence at λ_em. = 447 nm. The produced complex between Cu²⁺ ions and ADPPI can be used as a cascade probe for detection of S^2- ions. The detection limits (LODs) were 1.01 nM and 1.25 μM for Cu²⁺ and S^2- ions, respectively (the lowest between the family of colorimetric and fluorometric chemosensors). To further increase the applicability of the proposed method, Cu²⁺ and S^2- ions concentrations were measured in environmental water samples.

Engineering diformyl diaryldipyrromethane into a molecular keypad lock

A diaryldipyrromethane-based acyclic system acts as a photolabile sequential chemosensor for both anions and cations via ESIDPT and deprotonation, which is engineered into a fluorescent molecular keypad lock system.

Novel Diarylethene-Based Fluorescent Switching for the Detection of Al3+ and Construction of Logic Circuit

A novel photochromic diarylethene was synthesized successfully containing a phthalazine unit. Its multistate fluorescence switching properties were investigated by stimulating with UV/vis lights and Al3+/EDTA. The synthesized diarylethene displayed excellent selectivity to Al3+ with a distinct fluorescence change, revealing that it could be used as a sensor for fluorescence identification of Al3+, and a logic circuit was constructed by utilizing this diarylethene molecular platform. Moreover, it also exhibited a high accuracy for the determination of Al3+ in practical water samples.

Anion Sensing by Novel Triarylboranes Containing Boraanthracene: DFT Functional Assessment, Selective Interactions, and Mechanism Demonstration

Analytical methods often involve expensive instrumentation and tedious sample pretreatment for an analyte detection. Being toxic and detrimental to human health, sensing of cyanide (CN-), fluoride (F-), chloride (Cl-), bromide (Br-), nitrate (NO3 -), acetate (CH3COO-), and bisulfate (HSO4 -) is performed by a boron-based molecular receptor, N,N,N,3,5-pentamethyl-4-{2-thia-9-boratricyclo[8.4.0.03,8]tetradeca-1(10),3(8),4,6,11,13-hexaen-9-yl}anili-nium (1), and the three newly designed receptors from it. Thermodynamics, electronic structure, and photophysical properties are computed by employing density functional theory (DFT) and time-dependent density functional theory (TD-DFT) to explore selective sensing of these anions and its mechanism. Free-energy changes (ΔG) and binding energies (ΔE) suggest that among these anions, only binding of CN- and F- is thermodynamically feasible with a very strong binding affinity with the receptors. Boron atoms containing positive natural charges act as the electrophilic centers to bind the anions involving a 2p-2p orbital overlap resulting in charge transfer. In the receptor-analyte complexes with CN- and F-, fluorescence is quenched due to the intramolecular charge transfer transitions (π-π* transitions in the case of the receptors lead to fluorescence), internal conversion, and associated configurational changes. Among the six tested functionals, CAM-B3LYP/6-31G(d) is found to be the most accurate one. The designed receptors are better fluorescent probes for F- and CN-, demonstrating their importance for the practical utility.

Development of three ways molecular logic gate based on water soluble phenazine fluorescent 'selective ion' sensor

New hydrophilic fluorescent selective ion sensor based on phenazine and phthalazine moieties, 1,1'-(phenazine-2,3-diyl)-bis(3-(1,4-dihydroxyphthalazin-6-yl)urea) (1), has been designed, synthesized and characterized. Interestingly, sensor 1 exhibits prominent "turn-on" and "turn-off" fluorogenic signaling at 580 nm towards Fe²⁺ & AcO^- and Sr²⁺ & Cu²⁺, respectively. The fluorescence titration experiments shed light on the nature of the interaction between 1 and guest molecules (Fe²⁺, Sr²⁺, Cu²⁺ and AcO^-), which divulge that 1 is flexible enough to orient itself according to the size of the guest molecule. Water mediated excited-state intramolecular proton transfer (ESIPT) and photo-induced electron transfer (PET) mechanisms are responsible for the dual behavior of 1, which binds with guest molecules in 1:1 stoichiometry. Based on the significant duplex fluorescence response of 1, a molecular logic gate keypad lock with sixteen "on" passwords for a storage system has been developed.

A novel near-infrared ratiometric fluorescent probe for cyanide and its bioimaging applications

A new near-infrared ratiometric type fluorescent probe was prepared. 3-formyl BODIPY derivatives without substituent group in the 2, 6-position was obtained through DDQ oxidation reaction. Furthermore, it reacted with indole salt to produce probe. This probe bears indolium group as the recognition site and the 3-formyl-BODIPY as fluorophore. The specific detection of cyanide was conducted the nucleophilic attack of cyanide toward the indolium group of the probe, breaking the intramolecular charge transfer (ICT) effect and generating a ratio change in the fluorescence signal. The probe has high selectivity and sensitivity for cyanide. Moreover, cell experiments indicated this probe was benign to HepG-2 cells, and has the potential application in imaging CN^- in living HepG-2 cells.

A novel diarylethene-based fluorescent “turn-on” sensor for the selective detection of Mg2+

A new photochromic diarylethene derivative with a 4-methylphenol unit has been designed and synthesized. It displayed distinct photochromism and fluorescent ‘‘turn on’’ features to Mg²⁺ in acetonitrile solution. With the addition of Mg²⁺, there was an obvious increase of fluorescent emission intensity at 552 nm, accompanied by a clear change of fluorescent color from dark purple to green. Meantime, the 1 : 1 stoichiometry between the derivative and Mg²⁺ was verified by Job's plot and HRMS. Furthermore, the sensor was successfully applied in the detection of Mg²⁺ in practical samples. Moreover, based on the multiple-responsive fluorescence switching behaviors, it also could be used to construct a molecular logic circuit with UV/vis lights and Mg²⁺/EDTA as input signals and the emission at 552 nm as the output signal.

A new photochromic diarylethene derivative with a 4-methylphenol unit has been designed and synthesized.

Water-Soluble Perylene Diimide for Highly Sensitive and Repeatable Metal Ion Detection with Novel Logic Gate Operation

In this paper, we report a synthesised water soluble perylene derivative, N,N′-di(2-aspartic acid)-perylene-3,4,9,10-tetracarboxylic diimide (PASP), for highly sensitive and repeatable detection of copper (Cu2+) and aluminium ions (Al3+) and novel logic gate operation. In the presence of metal ions, a dramatic decrease in PASP optical intensity was induced based on the strong interaction between terminal carboxy groups and the metal ions. Detection limits of 0.22 and 0.24μM were respectively obtained at physiological pH. The signals could be recovered upon the addition of ethylenediaminetetraacetate (EDTA) and P2O74−, which competed for Cu2+ and Al3+ in the PASP-CuII and PASP-AlIII systems and induced their dissociation as secondary sensors for anions. At least four detection cycles were performed with a high recovery efficiency. Based on these phenomena, a novel three-level logic gate (OR-IMP-OR) was performed for smart signal readout with metal ions (Cu2+ and Al3+) and anions (EDTA and P2O74−) as input signals, and the relative change of optical intensity of PASP as output signal. Furthermore, the prepared PASP molecule also responded sensitively to Cu2+ and Al3+ in 10% diluted serum medium.

A turn-on fluorescence sensor for the highly selective detection of Al3+ based on diarylethene and its application on test strips

A novel fluorescent sensor, 1O, based on photochromic diarylethene with a 2-hydroxybenzhydrazide unit was designed and synthesized and can be used to recognize Al³⁺ in methanol (2.0 × 10⁻⁵ mol L⁻¹).

The light-controlling of temperature-responsivity in stimuli-responsive polymers

Light-controlling of phase separation in temperature-responsive polymer solutions by using light-responsive materials for reversible controlling physical and chemical properties of the media with an out-of-system stimulus with tunable intensity.

A BODIPY derivative for colorimetric fluorescence sensing of Hg2+, Pb2+ and Cu2+ ions and its application in logic gates

A BODIPY-based colorimetric and fluorescent chemosensor 1 anchored with dipyridylamino (DPA) receptor has been designed, synthesized and characterized. It exhibited a simultaneous sensitive recognition for Cu²⁺, Hg²⁺ and Pb²⁺ ions. With the addition of these three kinds of metal ions into 1 in CH₃CN, its initial absorption maximum displayed obvious blue shifts, and the color changes of the solution could be clearly observed by naked eyes. Besides, the fluorescence intensity was significantly enhanced accompanied with the appearance of new emission peaks at 587 nm for Pb²⁺ and Hg²⁺ ions and 545 nm for Cu²⁺ ions. These results were attributed to the π-deconjugation between N-pyridyl and the BODIPY group due to the binding of metal ions with the BODIPY and DPA groups. Based on the sensing behaviors of 1, three logic gates (OR, INHIBT and combinational logic gate) were constructed correspondingly.

Preparation of Macrometallocycle and Selective Sensor for Copper Ion

Two bis-imidazolium salts 1,8-bis[2'-(N-R-imidazoliumyl)acetylamino]naphthalene chloride (L1H4·Cl2: R = Et; L2H4·Cl2: R = nBu), as well as their four NHC metal complexes [L1H2Ag]Cl (1), [L1Ni] (2), [L2Ni] (3) and [L1H2Hg(HgCl4)] (4) have been synthesized. In each of the cationic moieties of complexes 1 or 4, there is a groove-like 14-membered macrometallocycle, and each macrometallocycle is consisted of one biscarbene ligand L1H2 and one metal ion (silver(I) ion for 1 and mercury(II) ion for 4). Three 6-membered cycles are contained in each molecule of complexes 2 or 3. Additionally, the selective recognition of macrometallocycle 1 for Cu2+ was studied with the methods of fluorescence and ultraviolet spectroscopy, 1H NMR titrations, MS and IR spectra. The experimental results display macrometallocycle 1 can discriminate Cu2+ from other cations effectively.

A Photoswitchable Colorimetric Sensor for Fluoride Based on a Dithienylethene Unit

A novel dithienylethene amide-based photoswitchable anion receptor was synthesised by amidation of 4,4′-(cyclopent-1-ene-1,2-diyl) bis(5-methylthiophene-2-carboxylic acid) with 4-nitroaniline in 56% yield under mild conditions; its structure was confirmed by NMR, MS and elemental analysis. Investigation of its photochromic properties indicated that 4,4′-(cyclopent-1-ene-1,2-diyl)bis[5-methyl-N-(4-nitrophenyl) thiophene-2-carboxamide] had good reversibility and excellent fatigue resistance upon irradiation with UV or visible light and can serve as a colorimetric sensor for fluoride, resulting in a significant change in the absorption spectrum.

A novel fluorescence "turn-on" sensor based on a photochromic diarylethene for the selective detection of Al(III)

A novel photochromic diarylethene with a triazole-containing 2-(2'-phenoxymethyl)-benzothiazole group has been synthesized via "click" reaction. The diarylethene exhibited good photochromism and photoswitchable fluorescence. Its fluorescence emission intensity was enhanced 7-fold by acids, accompanied by the red-shift of emission peak from 526nm to 566nm and the concomitant color change from dark to bright flavogreen. The diarylethene selectively formed a 1:1 metal complex with Al³⁺, resulting in a "turn-on" fluorescence signal. The complexation - reaction between Al³⁺ and the diarylethene is reversible with the binding constant of 2.73×10³Lmol^-1. The limit of detection (LOD) of Al³⁺ was determined to be 5.94×10^-8molL^-1. Based on this unimolecular platform, a logic circuit was fabricated using the fluorescence emission intensity at 572nm as the output and the combined stimuli of Al³⁺/EDTA and UV/Vis as the inputs.

Molecules for security measures: from keypad locks to advanced communication protocols

The idea of using molecules in the context of information security has sparked the interest of researchers from many scientific disciplines. This is clearly manifested in the diversity of the molecular platforms and the analytical techniques used for this purpose, some of which we highlight in this Tutorial Review. Moreover, those molecular systems can be used to emulate a broad spectrum of security measures. For a long time, molecular keypad locks enjoyed a clear preference and the review starts off with a description of how these devices developed. In the last few years, however, the field has evolved into something larger. Examples include more complex authentication protocols (multi-factor authentication and one-time passwords), the recognition of erroneous procedures in data transmission (parity devices), as well as steganographic and cryptographic protection.

Divalent Pseudorotaxane with Polarized Plug-Socket and Padlock Functions

A dual-pore structured host composed of one 24-crown-8 and one 34-crown-10, and a "U"-shaped guest consisting of two different recognition units, one dibenzylammonium and one viologen, were synthesized and bound 1:1 into a divalent pseudorotaxane P1. P1 can mimic the inserting and pulling out functions of a polarized plug-socket system under solvent driven stimulus and can also realize the locking and unlocking actions of a padlock under pH stimulus.

Fluorescence On/Off Switching in Nanoparticles Consisting of Two Types of Diarylethenes

Single- and double-component nanoparticles consisting of two types of diarylethenes, 1,2-bis(3-methyl-5-phenyl-2-thienyl)perfluorocyclopentene (1a) and 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene (2a), were fabricated by a reprecipitation method. Nanoparticles consisting of 1a exhibited orange or green fluorescence depending on the fabrication condition and did not undergo any photocyclization reaction. On the other hand, nanoparticles consisting of 2a underwent photoreversible photochromic reactions upon alternating irradiation with ultraviolet and visible light. Nanoparticles consisting of 1a and 2a exhibited fluorescence on/off switching with rapid switching speed and high on/off contrast, accompanying the photochromic reactions of 2a. The dependence of fluorescence on/off switching properties on Förster distance and molar fraction was observed and quantitatively evaluated by a simplified model.

A theoretical study on anion sensing mechanism of multi-phosphonium triarylboranes: intramolecular charge transfer and configurational changes

The binding selectivity and recognition mechanism of a series of mono-, di- and triphosphonium substituted triarylboranes: (4-(dimesitylboryl)-3,5-dimethylphenyl)phosphonium ([Mes₂BAr^P]⁺, 1), 1,1'-mesitylboranediylbis(3,5-dimethylphenyl)phosphonium ([MesBAr^P₂]²⁺, 2) and 1,1',1''-boranetriyltris(3,5-dimethylphenyl)phosphonium ([BAr^P₃]³⁺, 3) where Ar^P = 4-(H₃P)-2,6-Me₂-C₆H₂, for various anions has been investigated by employing density functional theory (DFT) and time dependent-density functional theory (TD-DFT) methods. Natural population analysis indicates the electrophilic nature of the boron centers in 1-3 for the nucleophilic addition of anions. The calculated free energy changes (ΔG) reveal that out of CN^-, F^-, Cl^-, Br^-, NO₃^-, CH₃COO^- and HSO₄^- only the binding of CN^- and F^- with 1, 2 and 3 is thermodynamically feasible. In addition, the calculated binding energies reflect that CN^- shows lesser binding affinity than F^- with 1, 2 and 3. Frontier molecular orbital (FMO) analysis reveals that the first excited states (S₁) of 1-3 are the local excited states with a π → π* transition, whereas the third excited state (S₃), fifth excited state (S₅), fourth excited state (S₄) and fourth excited states (S₄) of [Mes₂BAr^P]⁺F (1F, the fluoro form of 1), [MesBAr^P₂]²⁺F (2F, the fluoro form of 2), [Mes₂BAr^P]⁺CN (1CN, the cyano form of 1) and [MesBAr^P₂]²⁺CN (2CN, the cyano form of 2), respectively, are charge separation states found to be responsible for the intramolecular charge transfer (ICT) process. The partial configuration changes and ICT induce fluorescence quenching in 1F, 2F, 1CN and 2CN synergistically after an internal conversion (IC) from their respective S₃, S₅, S₄ and S₄ to S₁.

A highly selective fluorescence “turn-on” sensor for Ca2+ based on diarylethene with a triazozoyl hydrazine unit

A new photochromic diarylethene derivative with a triazozoyl hydrazine unit has been designed and synthesized.

Single sensor for multiple analytes in different optical channel: Applying for multi-ion response modulation

A Schiff-base, (2,4-di-tert-butyl-6-((2-hydroxyphenyl-imino)-methyl)phenol) (L), has been improved to function as a simultaneous multi-ion probe in different optical channel. The probe changes from colorless to orangish upon being deprotonated by F^-, while the presence of Al³⁺ significantly enhances the fluorescence of the probe due to the inhibition of CN isomerization, cation-induced inhibition of excited-state intramolecular proton transfer (ESIPT), and chelation enhanced fluorescence (CHEF). Dual-channel "off-on" switching behavior resulted from the sequential input of F^- and Al³⁺, reflecting the balance of independent reactions of Al³⁺ and F^- with L and with one another. This sensing phenomenon realizes transformation between multiple states and beautifully mimics a "Write-Read-Erase-Read" logic circuit with two feedback loops.