Luminescence Switching Research Articles

Supramolecular hydrogel with luminescence tunablility and responsiveness based on co-doped lanthanide and deoxyguanosine complex

Lanthanide (Ln)-based supramolecular hydrogels are a new category of smart optical materials, which are promising for applications in chemistry sensors, bioimaging agents and light-emitting devices. Herein, we report a supramolecular hydrogel with tunable and responsive luminescence, which is based on the assembly of Ln and deoxyguanosine (dG, one of the units of DNA). ESI-TOF-MS, NMR, FTIR, PXRD and simulation results verify the formation of dG/Ln hydrogels. dG/Tb hydrogel emits strong green luminescence, while dG/Eu hydrogel is nonluminous; when Tb is co-doped into dG/Eu, surprisingly we find that co-doped dG/Tb/Eu hydrogel displays tunable luminescence from green, orange to red by simply regulating the stoichiometric ratio of Tb and Eu. A cascade luminescence resonance energy transfer mechanism (from dG to Tb, and to Eu) is proposed in this co-doped system, which is confirmed by luminescence decay curves and emission spectra. Subsequently, luminescence switch is designed based on reversible responsiveness of hydrogel upon Ag+/L-Cys, temperature and pH stimuli via dynamic supramolecular coordination. Our work provides a new route to construct multicolor functional materials.

Reversible stimulus-responsive coordination polymers mainly involving conversion between the lone-pair–π and cation–π interactions

A new 3-position substituted imidazo[1,2-a]pyridine ligand, 4-(2-chloroimidazo[1,2-a] pyridine-3-carboxamido)phthalic acid (H2L), was conveniently synthesized and acts as a three-connecting T-shaped building block. Based on this ligand, two isostructural coordination polymers, [ML(H2O)] n (M = Zn (1) and Co (2)) with a rare one-dimensional (1D) ladder-like chain structure, were solvothermally synthesized and structurally characterized. There exist hydrogen bond and lone-pair–π interactions between two adjacent ladder chains. Compared to the H2L ligand, coordination polymer 1 reveals a blue-shifted emission stemming from ligand-to-metal charge transfer, meanwhile, coordination polymer 2 presents a dominant antiferromagnetism. Interestingly, the carboxylate anion (COO−) in coordination polymers 1 and 2 could be protonated into carboxylic acid (–COOH), upon exposure to HCl vapor. As a result, coordination polymers 1 and 2 display reversible luminescent switching in the response to acid-base vapor stimuli, which mainly originates from the conversion between lone-pair–π and cation–π interactions mediated by the protonation-deprotonation processes. Such stimulus-responsive conversion between lone-pair–π and cation–π interactions is first reported in coordination polymers, and provides a promising approach to design and construct smart coordination polymer materials.

Optical temperature sensing and luminescent switching properties in Pr/Er‐doped (K0.5Na0.5)NbO3 materials

AbstractFor optical temperature sensing materials, the emission and excitation bands are extremely critical to measure the temperature by fluorescence intensity ratio (FIR) technique. Singly Ln‐doped optical temperature sensing materials exhibit very few emission bands, which greatly constraints their practical applications of FIR technique. Here, the fabricated Pr/Er co‐doped (K0.5Na0.5)NbO3 materials exhibited multi‐color (red‐green) and dual‐mode (downshifting/upconversion) luminescence properties. The temperature sensitivity can be effectively tuned by choosing different emission or excitation bands. The optimized optical temperature sensitivity reached up to 0.0094 K−1, much higher than that of most temperature sensing materials. Besides, the samples also showed excellent luminescence modulation properties based on the photochromic reaction. Under sunlight irradiation, the luminescent switching contrast (ΔRt) of the samples reached more than 60%. These results may provide a guiding role in designing and modulating optical temperature sensing properties for multifunctional materials.

A label-free luminescent light switching system for miRNA detection based on two color quantum dots

In this study, we report a novel switchable fluorescent nanobiosensor for detection of miRNA. The sensor consists of green-emitting and orange-emitting CdTe QDs exhibiting emission spectra at 525 and 599 nm respectively, under excitation wavelength of 360 nm. Following the addition of miRNA targets to the DNA probes and heteroduplex formation of the hybrid, Green fluorescence CdTe QDs were aggregated and quenched by the DNA/miRNA hybrid via strong interactions at their metal centers. Then, with the addition of orange emitting QDs causes the fluorescence energy transfer to occur and was introduced as a ratiometric approach for miR-155 detection. The relative fluorescence intensity ratio was directly proportional to the concentration of miR-155 from 20 to 100 pM and the detection limit was determined at 14.0 pM. The novel nanobiosensor is “light-on”, rapid, and convenient while it does not require modification or separation procedures and can be applied for the detection of miRNAs in cell lysis with satisfactory results.

Switchable Luminescence of New Compounds Based on Imidazoles and Azomethines

The spectral and luminescent properties of compounds A3–SA, A4–o–SA, and A4–o–K have been studied, whose structures include moieties of triphenylimidazole A3, tetraphenylimidazole A4, and hydroxyazomethines salicylideneaniline SA and coumarin-substituted azomethine K. Due to electronic conjugation of moieties, the compound A3–SA exhibits switchable luminescence only in alcohol solutions, whereas independent behavior of the moieties is observed in the case of linking of these luminophores by an oxygen bridge and luminescence switching by changing the excitation wavelength is possible both in solutions and polymeric media.

Luminescent molecular switches based on dicationic P-doped polycyclic aromatic hydrocarbons

We report the efficient synthesis cationic P-doped Polycyclic Aromatic Hydrocarbons showing electrofluorochromic properties.

A pH-regulated ratiometric luminescence Eu-MOF for rapid detection of toxic mycotoxin in moldy sugarcane

pH-Regulated ratiometric luminescence switching from red to blue for rapid detection of 3-nitropropionic acid (3-NPA).

A stable nanoscaled Zr-MOF for the detection of toxic mycotoxin through a pH-modulated ratiometric luminescent switch.

A stable nanoscaled single-excitation ratiometric luminescent pH sensor (MPDB-PCN) over a broad pH range from 2.5 to 8.6 is fabricated through post-synthetic modification of PCN-224 with naphthalimide-derived molecules. Due to the rapid, sensitive and linear response to pH, MPDB-PCN is capable of detecting 3-nitropropionic acid (3-NPA), an acid neurotoxin in food safety, with a low detection limit of 15 μM in sugarcane juice.

Unveiling the Relationship between Energy Transfer and the Triplet Energy Level by Tuning Diarylethene within Europium(III) Complexes.

Luminescence performance and photoisomerization control of sensitized energy transfer in a series of Eu(acac)3De complexes that contain photochromic diarylethene (De) as the ligand are studied by theoretical methods. Both the open-ring and closed-ring isomers exhibit a consistent coordination mode between the EuIII ion and De. An unneglected weak interaction originating from electrostatic attraction is found in the region of the coordinate bond Eu-N. The open-ring isomer has higher triplet energy levels than 5D1 and 5D0 of the EuIII ion, which facilitates forward energy transfer from De to the EuIII ion. The closed-ring isomer, for the extended conjugated system formed in cyclization, has a much lower triplet energy level than 5D0 of the EuIII ion. The energy-gap deficit makes energy transfer unavailable. By utilization of this phenomenon, regulation of energy transfer and reversible on/off luminescence switching of the europium(III) complex can be achieved. The forward and backward energy-transfer rates in different channels are also calculated for the series of complexes. A statistics diagram is obtained to exhibit the change trend of energy-transfer rates in the forward and backward directions as a function of the triplet energy level, which indicates the contribution of different channels to energy transfer in each level region and figures out that the optimal triplet energy level should be in the range of 21740-19532 cm-1.

Dual Light and Redox Control of NIR Luminescence with Complementary Photochromic and Organometallic Antennae.

With the help of a judicious association between dithienylethene (DTE) units, an ytterbium ion, and a ruthenium carbon-rich complex, we describe (i) the efficient (on/off) switching of pure NIR luminescence with a photochromic unit absorbing in the UV range and (ii) the association of electrochemical and photochemical control of this NIR emission in a single system with nondestructive readout.

Frontispiece: Circularly Polarized Luminescence Switching in Small Organic Molecules

The circularly polarized luminescence (CPL) switching is of great interest for applications in security technologies and sensing devices. Small organic molecules (SOMs) show several advantages over metal complexes, supramolecular assemblies, and polymers. Therefore, the recent progress on the CPL switching in SOMs is here reviewed. The results are summarized based on the strategies used to tune the factors that influence the emission properties, and thus, to realize CPL switching. For more details see the Minireview by J.-L. Ma, Q. Peng, and C.-H. Zhao on page 15441 ff.

Expanding the Toolbox for Label-Free Enzyme Assays: A Dinuclear Platinum(II) Complex/DNA Ensemble with Switchable Near-IR Emission.

Switchable luminescent bioprobes whose emission can be turned on as a function of specific enzymatic activity are emerging as important tools in chemical biology. We report a promising platform for the development of label-free and continuous enzymatic assays in high-throughput mode based on the reversible solvent-induced self-assembly of a neutral dinuclear Pt(II) complex. To demonstrate the utility of this strategy, the switchable luminescence of a dinuclear Pt(II) complex was utilized in developing an experimentally simple, fast (10 min), low cost, and label-free turn-on luminescence assay for the endonuclease enzyme DNAse I. The complex displays a near-IR (NIR) aggregation-induced emission at 785 nm in aqueous solution that is completely quenched upon binding to G-quadruplex DNA from the human c-myc oncogene. Luminescence is restored upon DNA degradation elicited by exposure to DNAse I. Correlation between near-IR luminescence intensity and DNAse I concentration in human serum samples allows for fast and label-free detection of DNAse I down to 0.002 U/mL. The Pt(II) complex/DNA assembly is also effective for identification of DNAse I inhibitors, and assays can be performed in multiwell plates compatible with high-throughput screening. The combination of sensitivity, speed, convenience, and cost render this method superior to all other reported luminescence-based DNAse I assays. The versatile response of the Pt(II) complex to DNA structures promises broad potential applications in developing real-time and label-free assays for other nucleases as well as enzymes that regulate DNA topology.

Multiresponsive Supramolecular Luminescent Hydrogels Based on a Nucleoside/Lanthanide Complex.

Supramolecular luminescent hydrogels based on natural molecules have shown high potential for a variety of applications because of unique optical properties and biocompatibility, particularly serving as advanced biomaterials for bioimaging, biosensing, cell engineering, and so forth. A lanthanide complex-based system provides a promising way to prepare supramolecular luminescent hydrogels. Herein, we realize the creation of a luminescent hydrogel assembled from lanthanides and nucleosides. Nucleosides, the essential components of nucleic acids, functioning as the ligands, successfully chelate with lanthanides and form complexes in water. The complexes subsequently serve as building-blocks to form supramolecular hydrogels, which exhibit characteristic luminescent emission of lanthanides. The coordination modes and forming mechanism are studied by electrospray ionization time-of-flight mass spectrometry, matrix-assisted laser desorption/ionization time of flight mass spectrometry, 1H NMR spectroscopy, and Fourier transform infrared spectroscopy; the corresponding molecular simulations are presented, and macro-/micro-morphologies, mechanical properties, and luminescent performances of hydrogels are systemically studied. Remarkably, these luminescent hydrogels show fluorochromic properties in response to external stimuli, including pH, temperature, anions, and cations, which are thus adopted to design smart luminescent switches and detect specific species such as Cu2+. Our work provides a feasible strategy to prepare stimuli-responsive luminescent hydrogels, reveals the diverse potential of nucleoside-based hydrogels, and exhibits a novel pathway for the preparation of smart optical materials.

Study on electrochromic-fluorescence switching performance of film based on silicomolybdotungstate and silica nanoparticles doped with negative charged dye

We developed a novel way to construct the multifunctional composite films with luminescence and redox properties in this study. Firstly, the luminescent molecule HOPTS (8-hydroxypyene-1,3,6-trisulfonic acid trisodium salt) was incorporated into the silica spheres to form the green emission silica materials, HOPTS@SiO2, that were characterized by SEM (scanning electron microscope), FTIR (fourier transform infrared spectroscopy) and luminescence spectroscopy to verify their structure, morphology and property. And then the luminescent silica materials were functionalized by APTES (3-aminopropyltriethoxysilane) to form the positively charged surface, HOPTS@SiO2-APTES+. Afterwards, the composite luminescent films containing HOPTS@SiO2-APTES+ and SiMoW (SiMoW10O398−) were constructed by the layer-by-layer (LBL) assembly method immediately. The films were characterized by fluorescence spectroscopy, UV-vis spectroscopy, CV (cyclic voltammetry), XPS (X-ray photoelectron spectroscopy) and AFM (atomic force microscopy) to confirm their composition, morphology and property. Finaly, the reversible electrochemical photoluminescent switch performance of the composite luminescent films was investigated by in situ spectroelectrochemical system. The results indicated that thus-prepared composite films, [(PEI/SiMoW)5/(HOPTS@SiO2-APTES+/SiMoW)25/(PEI/SiMoW)20], displayed stable luminescence switching performance and wide voltage range as well as favourable stability and reversibility.

Reversible Redox Switching of Concurrent Luminescence and Visual Color Change Based on Lanthanide Metallogel.

The development of reversible redox supramolecular gels capable of concurrent luminescence switch and visible color change with the facile redox process has always been an intriguing challenge. A redox-responsive supramolecular lanthanide metallogel with strong luminescence and yellow color is obtained via coordination interaction between 3,5-dinitrosalicylic acid (DNSA) and europium (Eu3+). Upon the addition of TiO2 to the prepared gel (DNSA/Eu3+ gel), the oxidation process of the gel (DNSA/Eu3+/TiO2 gel) can be easily achieved by UV irradiation. The DNSA/Eu3+/TiO2 gel exhibits a concurrent reversible "on-off" luminescence and color change in response to redox stimuli. The DNSA/Eu3+/TiO2 gel shows a concurrent quench of luminescence and a color change from yellow to red when the gel was stimulated by the reductant. Upon UV irradiation, the luminescence and color of the reduced DNSA/Eu3+/TiO2 gel restored to its initial state due to the strong oxidation ability of hydroxyl radicals derived from photocatalytic oxidation of TiO2. The results of UV-vis and mass spectroscopy indicated that the reversible redox responsiveness of DNSA/Eu3+/TiO2 gel depends on the reversible oxidation-reduction reactions of DNSA. Moreover, DNSA/Eu3+/TiO2 gel remains stable because the morphology of the gel had no change during the redox process. Exemplarily, the application of DNSA/Eu3+/TiO2 gels to achieve luminescent patterning was investigated. The results demonstrated that the prepared metallogel has potential applications in the fields of writable materials, anticounterfeiting, sensors, and others.

A [2]Rotaxane-Based Circularly Polarized Luminescence Switch.

A rotaxane-based molecular shuttle has been synthesized in which the switching of the position of a fluorescent macrocycle on the thread turns “on” or “off” the circularly polarized luminescence (CPL) of the system while maintaining similar fluorescence profiles and quantum yields in both states. The chiroptical activity relies on the chiral information transfer from an ammonium salt incorporating d- or l-phenylalanine residues as chiral stereogenic covalent units to an otherwise achiral crown ether macrocycle bearing a luminescent 2,2′-bipyrene unit when they interact through hydrogen bonding. Each enantiomeric thread induces CPL responses of opposite signs on the macrocycle. Upon addition of base, the switching of the position of the macrocycle to a triazolium group disables the chiral information transfer to the macrocycle, switching “off” the CPL response. The in situ switching upon several acid/base cycles is also demonstrated.

A D-A-D’ type organic molecule with persistent phosphorescence exhibiting dual-mode mechanochromism

In this contribution, we report a new pure organic molecule ODBTCZ achieves fluorescence-RTP-DF triple emissions and dual-mode mechanochromism. ODBTCZ has an asymmetric D-A-D’ structure with dibenzothiophene and carbazole as the donor and benzophenone as the acceptor. ODBTCZ shows remarkable solvatochromism in different organic solvent due to the intramolecular charge transfer (ICT) effect. Interestingly, crystals of ODBTCZ manifest multiple emissions of prompt fluorescence, delayed fluorescence and persistent phosphorescence at room temperature, which is quite rarely reported in pure organic molecules. The delayed fluorescence is not TADF verified by temperature-dependent experiments. The RTP has a long lifetime of ~410 ms. Crystallographic analysis and TD-DFT calculation are conducted to elucidate the persistent phosphorescence. The enhanced intermolecular interactions highly constrain the motion of ODBTCZ in the crystal, impeding the quenching of oxygen and heat. A kind of dimer with enhanced parallel molecular packing acts more effectively to prompt ISC processes which further generates RTP and DF, due to the larger transition dipole moment and closer energy level between S1 and Tn. The unique triple-emission property endows ODBTCZ with dual-mode mechanochromism, namely fluorescence redshift and phosphorescence/DF on-off switch. This study is expected to contribute to develop stimuli-responsive luminescent switch with persistent RTP and lay the foundation for its wide applications.

Circularly Polarized Luminescence Switching in Small Organic Molecules.

The circularly polarized luminescence (CPL) switching is of significant interest for applications in security technologies and sensing devices. Small organic molecules (SOMs) show several advantages over metal complexes, supramolecular assemblies, and polymers. Therefore, the recent progress on the CPL switching in SOMs is here reviewed. The results are summarized based on the strategies used to tune factors that influence the emission properties, and thus, to realize CPL switching. The strategies that have been adopted include promoting the excimer formation of fluorescent units, changing the conformation of fluorophores, tuning the electronic structure of the π-skeleton/substituent, and modulating the intramolecular charge-transfer dynamics.

Photochromic and photocontrolled luminescence properties of two metal-organic frameworks constructed from a naphthalene diimide derivative

Naphthalene diimides (NDIs), a class of organic dyes with high photochemical activity and strong luminescent characteristics, have attracted considerable interest because of their photoinduced electron transfer to form stable radical anions in the presence of electron donors upon irradiation. In this paper, two novel metal–organic frameworks constructed from NDIs chromophoric and aromatic dicarboxylic acids, [Zn2(DPMNI)(NCA)2·0.5DMF] (1), [Zn(DPMNI)(PTA)·DMF] (2), (H2NCA = 1,4-naphthalenedicarboxylic acid, H2PTA = p-phthalic acid, DPMNI = N,N′-bis(4-pyridylmethyl)-1,4,5,8-naphthalene diimide, DMF = N,N′-dimethylformamide), have been synthesized and characterized systematically. Because of the presence of electron-deficient NDI moieties, they exhibit reversible naked photochromic properties upon irradiation and photocontrolled luminescence due to the generation of NDI radicals. The carboxylate groups as electron donors play a key role in the photoinduced electron-transfer process, and the lone pair–π interaction is a preferred pathway to support photoinduced electron transfer from our work. This study has not only convincingly corroborated the relationship between the photoresponsive rate and non-covalent interactions, but also provided a feasible idea to design novel luminescence switching materials.

Alkyl chain-dependent ESIPT luminescent switches of phenothazine derivatives in response to force

The response of organic materials to mechanical force has attracted significant attention because of its potential applications. Organic molecules with excited state intramolecular proton transfer (ESIPT) luminescence and responsive properties to force are rarely explored. Herein, three phenothiazine derivatives with ESIPT luminescence were synthesized and the influence of alkyl chain on their mechanochromic behaviors was investigated. The results indicate that their fluorescence spectra exhibited large bathochromic shift in polar solvents, meaning intramolecular charge transfer inherent characteristic. Moreover, the compounds with shorter alkyl chain possessed longer emission wavelength in pristine solids. All three compounds exhibited reversible mechanochromism and shifted their fluorescence band to lower energy region. XRD investigations suggested that mechanochromic process was accompanied with the phase transition between crystalline and amorphous states. Furthermore, fluorescence spectral shift values are dependent on alkyl chain length. The compound with ethyl group exhibited the smallest spectral shift (20 nm), whereas the compound with octyl group had the largest shift (31 nm). Solvent fuming and thermal annealing could promote fluorescence recovery. C2PAHN required high temperatures, and C8PAHN recovered its fluorescence at low temperatures, indicating that an alkyl chain length may regulate thermal recovery.