Dual-Stimulus Luminescent Lanthanide Molecular Switch Based on an Unsymmetrical Diarylperfluorocyclopentene

Photoswitchable luminescent lanthanide complexes controlled and interrogated by four orthogonal wavelengths of light

Optical information storage requires careful control of excitation and emission wavelengths in a reversible and orthogonal manner to enable efficient reading, writing, and erasing of information. Photochromic systems, in which a photoswitch is typcially coupled to an emissive organic fluorophore, have much promise in this regard. However, these suffer from considerable spectral overlap between the switch and fluorophore, such that their emissive and photoswitchable properties are not orthogonal. Here, we overcome this limitation by coupling visible/NIR emissive lanthanide complexes with molecular photoswitches, enabling reversible and orthogonal photoswitching with visible light. Crucially, photoswitching does not lead to sensitised emission from the lanthanide, while excitation of the lanthanide does not induce photoswitching, enabling the state of the system to be probed without perturbation of the switch. This opens up the possibility of developing multi-colour read-write methods for information storage using emissive photoswitches.

Monitoring Hierarchical Assembly of Ring-in-Ring and Russian Doll Complexes Based on Carbon Nanoring by Förster Resonance Energy Transfer

We presented the construction of the ring-in-ring and Russian doll complexes on the basis of triptycene-derived carbon nanoring (TP-[12]CPP), which not only acts as a host for pillar[5]arene (P5A) but also serves as an energy donor for building Förster resonance energy transfer (FRET) systems. We also demonstrated that their hierarchical assembly processes could be efficiently monitored in real time using FRET. NMR, UV-vis and fluorescence, and mass spectroscopy analyses confirmed the successful encapsulation of the guests P5A/P5A-An by TP-[12]CPP, facilitated by C-H···π and ···π interactions, resulting in the formation of a distinct ring-in-ring complex with a binding constant of Ka = 2.23 × 104 M-1. The encapsulated P5A/P5A-An can further reverse its role to be a host for binding energy acceptors to form Russian doll complexes, as evidenced by the occurrence of FRET and mass spectroscopy analyses. The apparent binding constant of the Russian doll complexes was up to 3.6 × 104 M-1, thereby suggesting an enhanced synergistic effect. Importantly, the Russian doll complexes exhibited both intriguing one-step and sequential FRET dependent on the subcomponent P5A/P5A-An during hierarchical assembly, reminiscent of the structure and energy transfer of the light-harvesting system presented in purple bacteria.

Tunable Multicolor Lanthanide Supramolecular Assemblies with White Light Emission Confined by Cucurbituril[7]

Macrocyclic confinement-induced supramolecular luminescence materials have important application value in the fields of bio-sensing, cell imaging, and information anti-counterfeiting. Herein, a tunable multicolor lanthanide supramolecular assembly with white light emission is reported, which is constructed by co-assembly of cucurbit[7]uril (CB[7]) encapsulating naphthylimidazolium dicarboxylic acid (G1 )/Ln (Eu3+ /Tb3+ ) complex and carbon quantum dots (CD). Benefiting from the macrocyclic confinement effect of CB[7], the supramolecular assembly not only extends the fluorescence intensity of the lanthanide complex G1 /Tb3+ by 36 times, but also increases the quantum yield by 28 times and the fluorescence lifetime by 12 times. Furthermore, the CB[7]/G1 /Ln assembly can further co-assemble with CD and diarylethene derivatives (DAE) to realize the intelligently-regulated full-color spectrum including white light, which results from the competitive encapsulation of adamantylamine and CB[7], the change of pH, and photochromic DAE. The multi-level logic gate based on lanthanide supramolecular assembly is successfully applied in anti-counterfeiting system and information storage, providing an effective method for the research of new luminescent intelligent materials.

Synthesis, characterization, luminescence properties and deciphering the role of a terpyridyl-imidazole based ligand in the dissimilar luminescence sensitization of ternary lanthanide(III) tris-(β-diketonate) complexes

We designed four ternary lanthanide tris-(β-diketonate) complexes of the form [Ln(tta)3(tpy-HImzphen)], where Ln = LaIII, EuIII, SmIII and TbIII; tta = (2-theonyltrifluoroacetonate) and tpy-HImzphen = 2-(4-[2,2':6',2'']terpyridin-4'-yl-phenyl)-1H-phenanthro[9,10-d]imidazole. All the complexes have been thoroughly characterized by standard analytical tools and spectroscopic techniques including single crystal X-ray diffraction. In situ generation of the complexes was also monitored via absorption and emission spectroscopy upon incremental addition of the respective lanthanide precursor {Ln(tta)3(H2O)2} to the dichloromethane solution of the terpyridyl-imidazole ligand. The photophysical behaviors of all the complexes were thoroughly investigated via absorption and both steady-state and time-resolved emission spectroscopic techniques. The emission spectral measurements were carried out at both room temperature and 77 K to understand the deactivation dynamics of the excited states and elucidate the distinctive luminescence responses from the four lanthanide metal ions owing to the introduction of the terpyridyl-based ancillary ligand.

A pillar[5]arene noncovalent assembly boosts a full-color lanthanide supramolecular light switch

A photo-responsive full-color lanthanide supramolecular switch was constructed from a synthetic 2,6-pyridine dicarboxylic acid (DPA)-modified pillar[5]arene (H) complexing with lanthanide ion (Ln3+ = Tb3+ and Eu3+) and dicationic diarylethene derivative (G1) through a noncovalent supramolecular assembly. Benefiting from the strong complexation between DPA and Ln3+ with a 3 : 1 stoichiometric ratio, the supramolecular complex H/Ln3+ presented an emerging lanthanide emission in the aqueous and organic phase. Subsequently, a network supramolecular polymer was formed by H/Ln3+ further encapsulating dicationic G1via the hydrophobic cavity of pillar[5]arene, which greatly contributed to the increased emission intensity and lifetime, and also resulted in the formation of a lanthanide supramolecular light switch. Moreover, full-color luminescence, especially white light emission, was achieved in aqueous (CIE: 0.31, 0.32) and dichloromethane (CIE: 0.31, 0.33) solutions by the adjustment of different ratios of Tb3+ and Eu3+. Notably, the photo-reversible luminescence properties of the assembly were tuned via alternant UV/vis light irradiation due to the conformation-dependent photochromic energy transfer between the lanthanide and the open/closed-ring of diarylethene. Ultimately, the prepared lanthanide supramolecular switch was successfully applied to anti-counterfeiting through the use of intelligent multicolored writing inks, and presents new opportunities for the design of advanced stimuli-responsive on-demand color tuning with lanthanide luminescent materials.

Ytterbium(III) Complex with Photochromic Ruthenium(II) Acetylide Ligand: All Visible Light Photoswitching of NIR Luminescence

We report a ruthenium(II) bisacetylide complex bearing a photochromic dithienylethene (DTE) acetylide arm and a coordinating bipyridyl on the trans acetylide unit. Its coordination with Yb(TTA)₃ centers (TTA = 2-thenoyltrifluoroacetonate) produces a bimetallic complex in which the dithienylethene isomerization is triggered by both ultraviolet (UV) light absorbed by the DTE unit and 450 nm excitation in a transition of the organometallic moiety. The redox behavior arising from the ruthenium(II) bisacetylide system is fully investigated by cyclic voltammetry and spectroelectrochemistry, revealing a lack of stability of the DTE-closed oxidized state preventing effective redox luminescence switching. On the other hand, the photoswitching of ytterbium(III) near-infrared (NIR) emission triggered by the photochromic reaction is fully operational. The electronic structure of this complex in its different states characterized by strong electronic coupling between the DTE and the ruthenium(II)-based moieties leading to metal-assisted photochromic behavior were rationalized with the help of time-dependent density functional theory (TD-DFT) calculations.

Docking rings in a solid: reversible assembling of pseudorotaxanes inside a zirconium metal-organic framework

An unprecedented zirconium metal–organic framework featuring a T-shaped benzimidazole strut was constructed and employed as a sponge-like material for selective absorption of macrocyclic guests. The neutral benzimidazole domain of the as-synthesized framework can be readily protonated and fully converted to benzimidazolium. Mechanical threading of [24]crown-8 ether wheels onto recognition sites to form pseudorotaxanes was evidenced by solution nuclear magnetic resonance, solid-state fluorescence, and infrared spectroscopy. Selective absorption of [24]crown-8 ether rather than its dibenzo counterpart was also observed. Further study reveals that this binding process is reversible and acid–base switchable. The success of docking macrocyclic guests in crystals via host–guest interactions provides an alternative route to complex functional materials with interpenetrated structures.

A T-shaped ligand was designed as struts for building a zirconium metal–organic framework. Acid–base switchable docking and releasing a 24-membered crown ether inside crystals was successfully accomplished via post-synthetic modification.

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.

Crown Ether-Based Supramolecular Polymers: From Synthesis to Self-Assembly

Supramolecular polymers not only possess many advantages of traditional polymers, but also have many unique characteristics. Supramolecular polymers can be constructed by self-assembly of various noncovalent interactions. Host-guest interaction, as one important type of noncovalent interactions, has been widely applied to construct supramolecular polymers. From the perspective of classification of the recognition system motifs, host-guest recognition motifs mainly include crown ether, cyclodextrin, calixarene, cucurbituril, and pillararene-based host-guest recognition pairs. Crown ethers, as the first-generation macrocyclic hosts, have played a very important part in the development of supramolecular chemistry. Due to the easy modification of crown ethers, various crown ether derivatives have been prepared by attaching some functional groups to the edges of crown ethers, which endowed them with some interesting properties and made them ideal candidates for the fabrication of supramolecular polymers. This review gives a review of the preparation of crown ether-based supramolecular polymers (CSPs) and summarizes crown ether-based recognition pairs, organization methods, topological structures, stimuli-responsiveness, and functional characteristics.

Luminescent lanthanide-macrocycle supramolecular assembly

A series of macrocyclic compounds, including crown ether, cyclodextrin, cucurbituril and pillararene, bound to various specific organic/inorganic/biological guest molecules and ions through various non-covalent interactions, can not only make a single system multifunctional but also endow the system with intelligence, especially for luminescent materials. Due to their excellent luminescence properties, such as long-lived excited states, sharp linear emission bands and large Stokes shift, lanthanides have shown great advantages in luminescence, and have been more and more applied in the design of advanced functional luminescent materials. Based on reported research, we summarize the progress of lanthanide luminescent materials based on different macrocyclic compounds from ion or molecule recognition to functional nano-supramolecular assembly of the lanthanide-macrocycle supramolecular system including photo-reaction mediated switch of lanthanide luminescent molecules, multicolor luminescence, ion detection and cell imaging of rare-earth up-conversion of macrocyclic supramolecular assembly. Finally, we put forward the prospects of future development of lanthanide luminescent macrocyclic supramolecular materials.

Luminescence switch based on the acid/base induced reversibility of covalent bonds in lanthanide(III) complexes

We report an exceptional example of Tb(III) luminescence switching using a reversible covalent bond. The antenna and quencher moieties attached to a ligand of a Tb(III) complex undergo acid/base-driven exchange based on the reversible formation of a hemiaminal ether structure to achieve on-off regulation of luminescence.

Structure Determination of Europium Complexes in Solution Using Crystal-Field Splitting of the Narrow f-f Emission Lines

Nine nona-coordinated Eu(III) complexes (1-9) studied here have three unsymmetric β-diketonate ligands and one chiral Ph-Pybox ligand, which can produce eight possible coordination isomers, depending on the position of the three unsymmetric β-diketonate ligands. Substituents on the β-diketonate ligands cause a rational structural rearrangement upon crystallization. Substituents with higher polarity, including -CN, -F, -Cl, -Br, -OMe, and -OEt, employ intercomplex hydrogen bonding to generate an association complex through structural rearrangement upon crystallization. Substituents with lower polarity, including -CF3, -SMe, and -Me, cause the most energetically favorable isomer to crystallize directly from solution. These two crystal structures exhibit well-resolved f-f emission lines with characteristic Stark splitting structures. This work revealed that the configuration of the Eu(III) complexes in solution can be determined by systematic comparison of their Stark splitting structures to those obtained from the solid phase using density functional theory (DFT)-based predictions combined with circular dichroism data.

Photoresponsive supramolecular coordination polyelectrolyte as smart anticounterfeiting inks

While photoluminescence printing is a widely applied anticounterfeiting technique, there are still challenges in developing new generation anticounterfeiting materials with high security. Here we report the construction of a photoresponsive supramolecular coordination polyelectrolyte (SCP) through hierarchical self-assembly of lanthanide ion, bis-ligand and diarylethene unit, driven by metal-ligand coordination and ionic interaction. Owing to the conformation-dependent photochromic fluorescence resonance energy transfer between the lanthanide donor and diarylethene acceptor, the ring-closure/ring-opening isomerization of the diarylethene unit leads to a photoreversible luminescence on/off switch in the SCP. The SCP is then utilized as security ink to print various patterns, through which photoreversible multiple information patterns with visible/invisible transformations are realized by simply alternating the irradiation with UV and visible light. This work demonstrates the possibility of developing a new class of smart anticounterfeiting materials, which could be operated in a noninvasive manner with a higher level of security.

Protein-Activatable Diarylethene Monomer as a Smart Trigger of Noninvasive Control Over Reversible Generation of Singlet Oxygen: A Facile, Switchable, Theranostic Strategy for Photodynamic-Immunotherapy

The development of activatable photosensitizers to allow for the reversible control of singlet oxygen (¹O₂) production for photodynamic therapy (PDT) faces great challenges. Fortunately, the flourishing field of supramolecular biotechnology provides more effective strategies for activatable PDT systems. Here, we developed a new reversible PDT on a switch that controls the ¹O₂ generation of self-assembled albumin nanotheranostics in vitro and in vivo. A new molecular design principle of aggregation-induced self-quenching photochromism and albumin on-photoswitching was demonstrated using a new asymmetric, synthetic diarylethene moiety DIA. The photosensitizer porphyrin and DIA were incorporated as building blocks in a glutaraldehyde-induced covalent albumin cross-linking nanoplatform, HSA-DIA-porphyrin nanoparticles (NPs). More importantly, the excellent photoswitching property of DIA enables the resultant nanoplatform to act as a facile, switchable strategy for photodynamic-immunotherapy.

Building a quadruple stimuli-responsive supramolecular gel based on a supra-amphiphilic metallogelator

A supramolecular gel was fabricated based on a novel supra-amphiphilic metallogelator, and it showed quadruple stimuli-responsive properties.

Photo-modulated wide-spectrum chromism in Eu3+ and Eu3+/Tb3+ photochromic coordination polymer gels: application in decoding secret information

Photo-switching emission of photochromic materials has paramount importance in the field of optoelectronics. Here, we report synthesis and characterization of a dithienylethene (DTE) based photochromic low molecular weight gelator (LMWG) and self-assembly with lanthanide (Eu3+ and Tb3+) ions to form a photochromic coordination polymer gel (pcCPG). Based on DTE ring opening and closing, the TPY-DTE gel shuttles from pale-yellow coloured TPY-DTE-O to dark blue coloured TPY-DTE-C and vice versa upon irradiating with UV and visible light, respectively, and both the photoisomers show distinct optical properties. Furthermore, integration of Eu3+ and Tb3+ lanthanides with TPY-DTE resulted in red and green emissive Eu-pcCPG (Q.Y. = 18.7% for the open state) and Tb-pcCPG (Q.Y. = 23.4% for the open state), respectively. The photoisomers of Eu-pcCPG exhibit photo-switchable spherical to fibrous reversible morphology transformation. Importantly, an excellent spectral overlap of the Eu3+ centred emission and absorption of DTE in the closed form offered photo-switchable emission properties in Eu-pcCPG based on pcFRET (energy transfer efficiency >94%). Further, owing to the high processability and photo-switchable emission, the Eu-pcCPG has been utilized as invisible security ink for protecting confidential information. Interestingly, mixed Eu3+/Tb3+ pcCPG exhibited photo-modulated multi-spectrum chromism reversibly where the colour changes from yellow, blue, and red to green and vice versa under suitable light irradiation.

Metal-directed synthesis of quadruple-stranded helical Eu(III) molecular switch: a significant improvement in photocyclization quantum yield

The self-assembly of a quadruple-stranded Eu(iii) helicate induces the conformation transformation of a DAE-based photochromic ligand from parallel to antiparallel, which brings a significant improvement in the photocyclization quantum yield (Φo-c) as compared with the free ligand. Furthermore, the photocontrolled open- and closed-rings of the ligand realized a reversible modulation toward Eu3+ center emission.

Photochromic properties and crystal structure of 3,3′-(perfluorocyclopent-1-ene-1,2-diyl)bis(5-(4-(azidomethyl)phenyl)-2-methylthiophene), C29H20F6N6S2

C29H20F6N6S2, monclinic, C2/c (no. 15), a = 26.2504(11) Å, b = 8.6981(4) Å, c = 13.3064(6) Å, β = 107.659(2)°, V = 2895.1(2) Å3, Z = 4, R gt(F) = 0.0436, wR ref(F 2) = 0.1314, T = 296(2) K.

Lanthanide-Containing Rotaxanes, Catenanes, and Knots

The valuable luminescence, magnetic, and catalytic properties of lanthanide cations are beginning to be exploited in conjunction with structurally exotic mechanically interlocked molecules (MIMs) such as rotaxanes, catenanes and knots. This Minireview provides an account of this rapidly developing research area commencing with the use of lanthanides in extended MIM-containing frameworks. Then, attention turns to discrete lanthanide-containing pseudorotaxanes, followed by fully interlocked rotaxanes, catenanes and knots - where lanthanides have not only been incorporated into MIM architectures but have also been used to template formation of the interlocked structure. Particular focus is paid to examples where the lanthanide MIMs have been put to useful applications, in what is still a relatively youthful avenue of research in both lanthanide coordination chemistry and the chemistry of mechanically interlocked molecules.

Efficient luminescence control in dithienylethene functionalized cyclen macrocyclic lanthanide complexes

We report the synthesis of an original ligand scaffold based on a dimethyl-cyclen platform Medo2pa with two dithienylethene units attached to each picolinate arm and the corresponding yttrium(iii), europium(iii) and ytterbium(iii) complexes.

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 Eu^III 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 Eu^III ion, which facilitates forward energy transfer from De to the Eu^III ion. The closed-ring isomer, for the extended conjugated system formed in cyclization, has a much lower triplet energy level than ⁵D₀ of the Eu^III 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.

Structure and photochromic properties of a novel diarylethene containing a 9-fluorenone hydrazone Schiff base moiety

A novel diarylethene containing a 9-fluorenone hydrazone Schiff base moiety is designed and synthesized. The structure is characterized by single-crystal diffraction analysis and it shows excellent photochromism in the single crystalline phase. Moreover, the diarylethene product shows relatively high fluorescence modulation efficiency and good fatigue resistance.

Photoresponsive Luminescent Polymeric Hydrogels for Reversible Information Encryption and Decryption

Conventional luminescent information is usually visible under either ambient or UV light, hampering their potential application in smart confidential information protection. In order to address this challenge, herein, light-triggered luminescence ON-OFF switchable hybrid hydrogels are successfully constructed through in situ copolymerization of acrylamide, lanthanide complex, and diarylethene photochromic unit. The open-close behavior of the diarylethene ring in the polymer could be controlled by UV and visible light irradiation, where the close form of the ring features fluorescence resonance energy transfer with the lanthanide complex. The hydrogel-based blocks with tunable emission colors are then employed to construct 3D information codes, which can be read out under a 254 nm UV lamp. The exposure to 300 nm UV light leads to the luminescence quenching of the hydrogels, thus erasing the encoded information. Under visible light (>450 nm) irradiation, the luminescence is recovered to make the confidential information readable again. Thus, by simply alternating the exposure to UV and visible lights, the luminescence signals could become invisible and visible reversibly, allowing for reversible multiple information encryption and decryption.

Loading Photochromic Molecules into a Luminescent Metal-Organic Framework for Information Anticounterfeiting

Stimuli-responsive photoluminescent materials have attracted considerable attention owing to their potential applications in security protection because the information recorded directly in materials with static luminescent outputs are usually visible under either ambient or UV light. Herein, we realize reversible information anticounterfeiting by loading a photoswitchable diarylethene derivative into a lanthanide metal-organic framework (MOF). Light triggers the open- and closed-form isomerization of the diarylethene unit, which respectively regulates the inactivation and activation of the photochromic FRET process between the diarylethene acceptor and lanthanide donor, resulting in reversible luminescence on-off switching of the lanthanide emitting center in the MOF host. This photoresponsive host-guest system allows for reversible multiple information pattern visible/invisible transformation by simply alternating the exposure to UV and visible light.

Crystal structure and photochromic properties of a novel photochromic perfluordiarylethene containing a triazole bridged pyridine group moiety, C24H18F6N4S2

C24H18F6N4S2, monclinic, P21/c (no. 14), a = 19.0525(18) Å, b = 8.5569(9) Å, c = 15.3792(15) Å, β = 97.241(2)°, V = 2487.3(4) Å3, Z = 4, R gt(F) = 0.0513, wR ref(F 2) = 0.1425, T = 296(2) K.

Crystal structure and photochromic properties of 1-(2-methyl-5-phenyl-3-thienyl)-2-{2-methyl-5-[4-(9-fluorenone hydrazone)-phenyl]-3-thienyl}perfluorocyclopentene, C41H26F6N2S2

C41H26F6N2S2, triclinic, P1̄ (no. 2), a = 11.7525(12) Å, b = 12.2430(12) Å, c = 13.4210(13) Å, α = 84.914(1)°, β = 66.860(1)°, γ = 82.543(1)°, V = 1759.2(3) Å3, Z = 2, R gt(F) = 0.0459, wR ref(F 2) = 0.1268, T = 296(2) K.

An ensemble of Zn2+ with a rhodamine B-3-allylsalicylaldehyde hydrazone as novel photosensitive material: Photochromism, photopatterning, photoprinting and molecular logic gates

An ensemble of Zn²⁺ with Rhodamine B-3-allylsalicylaldehyde hydrazone (1-Zn²⁺), has been synthesized and fully characterized using spectroscopic techniques. A solution of 1-Zn²⁺ in THF, displays color changes from light yellow to pink color in the presence UV light (λ, 405 nm). The process is reversible and owes to keto-enol tautomerism which allows the opening of spirolactam ring of rhodamine in the presence of UV light. It is corroborated by the appearance of a new peak at λ_max = 554 nm. The ensemble, 1-Zn²⁺ embedded in the matrix of silica gel, displays photo patterning phenomena initiated by the conventional light sources including sunlight. It also displays photoprinting property with a laser pen (λ 405 nm) and has been displayed by a videography. The module 1-Zn²⁺ meets real challenges through a simple synthetic route, fast response, and as a binary data storage system with non-destructive optical identity.

Threading-gated photochromism in [2]pseudorotaxanes

Rigid, Y-shaped imidazole compounds containing the bis(thienyl)ethene moiety were designed and synthesized. The 4,5-bis(benzothienyl)-2-phenylimidazolium cations were then used as axles for [2]pseudorotaxane formation with 24-membered crown ether wheels. It was demonstrated using 1H NMR spectroscopy, UV-Vis absorption and emission spectroscopies that this host-guest interaction results in significant changes in the photochromic properties of the imidazolium axles. This is a rare example of gated photochromism, which exploits the recognition event of an interpenetrated molecular system to tune the photochromic properties in one of the components.

Multistimuli-Responsive and Photocontrolled Supramolecular Luminescent Gels Constructed by Anthracene-Bridged Bis(dibenzo-24-crown-8) with Secondary Ammonium Salt Polymer

A novel multistimuli-responsive and photcontrolled supramolecular luminescent gel is fabricated from anthracene-bridged bis(dibenzo-24-crown-8) (1) and secondary ammonium salt-functionalized graft polymer (3). X-ray crystallographic analysis reveals that the dibenzo-24-crown-8 (DB24C8) ring is located at the opposite site of 1, which will greatly hinder the mutual intermolecular π-π stacking between anthracene groups. By taking advantage of the controllable binding of 1 with 3, the unique gel-sol transition could occur under different temperatures, pH, and competitive guest bindings. Benefiting from the photo-oxygenation of anthracene, the luminescence behavior of the supramolecular gel could be switched off and on under UV light (365 nm) and heating treatment, which provides a new approach for constructing photocontrolled supramolecular luminescent gel.

Photo-responsive cyclodextrin/anthracene/Eu3+ supramolecular assembly for a tunable photochromic multicolor cell label and fluorescent ink

A photo-responsive supramolecular assembly was successfully constructed through the stoichiometric 2 : 1 non-covalent association of two 4-(anthracen-2-yl)pyridine-2,6-dicarboxylic acid (1) units in one γ-cyclodextrin (γ-CD) cavity, followed by the subsequent coordination polymerization of the γ-CD·1 2 (1 2 = two 1) inclusion complex with Eu(iii). Interestingly, owing to the photodimerization behavior of anthracene units and the excellent luminescence properties of Eu(iii), the Eu3+⊂γ-CD·1 2 system showed multicolor fluorescence emission from cyan to red by irradiation for 0-16 minutes. Moreover, white light emission with CIE coordinates (0.32 and 0.36) was achieved at 4 min. Importantly, white light-containing multicolor emission could be obtained in water, solid films and living cells. Especially, the Eu3+⊂γ-CD·1 2 system could tag living cells with marvelous white fluorescence and display no obvious cytotoxicity. Thus, this supramolecular assembly offers a new pathway in the fields of tunable photochromic fluorescent ink and cell labelling.

Ammonia-Responsive Luminescence of Ln3+-β-diketonate Complex Encapsulated within Zeolite Y

Assembling Ln³⁺(HPBA_n) (Ln = Eu or Tb, HPBA = N-(2-pyridinyl)benzoylacetamide) in the cavities of zeolite Y (ZY) via the “ship-in-a-bottle” strategy leads to the formation of novel luminescent composite, Ln(HPBA_n)@ZY, whose luminescence can be easily modulated by ammonia on the basis of the energy level variation of HPBA after deprotonation process. Additionally the bimetallic complex doping sample, Eu_0.5Tb_0.5(HPBA_n)@ZY, show great potential as self-referencing luminescent sensor for detecting low ammonia concentration of 10⁻¹²–0.25 wt%.

A Self-Assembled ATP Probe for Melanoma Cell Imaging

In this investigation, a new terpyridine metal complex was developed as a probe for selective detection of ATP and imaging of melanoma cells. The probe takes advantage of the ability of the metal complex to be transformed to its imaging competent turn-on state through assembly with ATP.

Photoswitchable phthalocyanine-assembled nanoparticles for controlled “double-lock” photodynamic therapy

A new nanoparticle platform,NanoAzoPcS, is created by co-assembly of phthalocyanine and azobenzene amphiphiles, which can be used to gain precise control of PDT simply by regulating the stoichiometric ratio of the components and using light irradiation.

Light-controlled efficient photoluminescence based on an europium β-diketonate complex with single-crystal-to-single-crystal [2+2] cycloaddition

An europium β-diketonate complex is first reported with enhanced luminescence by single-crystal-to-single-crystal [2+2] cycloaddition, which is useful for security photo.

Photocontrolled morphological conversion and chiral transfer of a snowflake-like supramolecular assembly based on azobenzene-bridged bis(dibenzo-24-crown-8) and a cholesterol derivative

A snowflake-like supramolecular clockwise-helical assembly was fabricated via the host–guest interaction, while a snowflake-like supramolecular non-helical assembly can be obtained upon UV-irradiation.

Structure and photochromism of 1-[2-methyl-5-phenyl-3-thienyl]-2-[2-methyl-5-(4-chlorophenyl)-3-thienyl]3,3,4,4,5,5-hexafluorocyclopent-1-ene, C27H16ClF6S2

C27H16ClF6S2, monclinic, P21/c (no. 14), a = 24.1193(5) Å, b = 9.2419(2) Å, c = 10.8343(2) Å, β = 96.1260(10)°, V = 2401.26(8) Å3, Z = 4, Rgt(F) = 0.0292, wRref(F2) = 0.0878, T = 100(2) K.

Hierarchical Emergence and Dynamic Control of Chirality in a Photoresponsive Dinuclear Complex

Chiroptical photoswitches are of interest from a viewpoint of applications in advanced information technologies. We report dynamic on-off photoswitching of circularly polarized luminescence (CPL) in a binuclear europium complex system. Two coordination units are arranged closely in a chiral fashion by a photoresponsive ligand with a one-handed helical structure. The chirality in the helical scaffold is hierarchically transferred to the chirality in nine-coordinate complex sites. The chiral close arrangement of complex units induces the enrichment of a specific chiral coordination structure in the nine-coordinate europium sites. The chiral arrangement of complex units is switched in conjunction with the photoinduced helix-nonhelix structural change in the photoresponsive framework, demonstrating on-off switching of CPL with high contrast.