A Reversible Luminescent Lanthanide Switch Based on a Dibenzo[24]-Crown-8−Dipicolinic Acid Conjugate

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.

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.

A turn-on luminescence probe for highly selective detection of an anthrax biomarker

Highly selective detection of Bacillus anthrax spores has attracted worldwide attention because Bacillus anthrax spores not only are harmful to the health of human beings and animals, but also can be used as biological warfare agents. Here, we report a simple platform by mixing EuCl₃ ·6H₂ O and sodium polyacrylate in aqueous solution and further investigate its luminescence response towards Bacillus anthrax biomarker dipicolinic acid (DPA) as a turn-on luminescence probe. Importantly, our probe has good sensitivity, lower detection limit, excellent selectivity as well as great anti-interference ability due to the great luminescence enhancement of Eu³⁺ . Moreover, a test paper is constructed to realize the purpose of portable detection. These results indicate that our probe is an excellent candidate for sensing DPA.

Molecular and Electronic Structure, and Hydrolytic Reactivity of a Samarium(II) Crown Ether Complex

The reaction of SmI₂ with dibenzo-30-crown-10 (DB30C10), followed by metathesis with [Bu₄N][BPh₄], allows for the isolation of [Sm^II(DB30C10)][BPh₄]₂ as bright-red crystals in good yield. Exposure of [Sm(DB30C10)]²⁺ to solvents containing trace water results in the conversion to the dinuclear Sm^III complex, Sm₂(DB30C10)(OH)₂I₄. Structural analysis of both complexes shows substantial rearrangement of the crown ether from a folded, Pac-Man form with Sm^II to a twisted conformation with Sm^III. The optical properties of [Sm^II(DB30C10)][BPh₄]₂ exhibit a strong temperature dependence and change from broad-band absorption features indicative of domination by 5d states to fine features characteristic of 4f → 4f transitions at low temperatures. Examination of the electronic structure of these complexes via ab initio wave function calculations (SO-CASSCF) shows that the ground state of Sm^II in [Sm^II(DB30C10)]²⁺ is a 4f⁶ state with low-lying 4f⁵5d¹ states, where the latter states have been lowered in energy by ∼12 000 cm^-1 with respect to the free ion. The decacoordination of the Sm^II cation by the crown ether is responsible for this alteration in the energies of the excited state and demonstrates the ability to tune the electronic structure of Sm^II.

A Photoinduced Reversible Phase Transition in a Dipeptide Supramolecular Assembly

Tunable supramolecular assembly has found various applications in biomedicine, molecular catalysis, optoelectronics, and nanofabrication. Unlike traditional covalent conjugation, non-covalent introduction of a photoswitchable moiety enables reversible photomodulation of non-photosensitive dipeptide supramolecular assembly. Under light illumination, a long-lived photoacid generator releases a proton and mediates the dissociation of dipeptide-based organogel, thereby resulting in sol formation. Under darkness, the photoswitchable moiety entraps a proton, resulting in gel regeneration. Furthermore, accompanying the isothermal recycled gel-sol transition in a spatially controlled manner, renewable patterns are spontaneously fabricated. This new concept of light-controlled phase transition of amino acid-based supramolecular assemblies will open up the possibility of wide applications.

Tunable Luminescent Lanthanide Supramolecular Assembly Based on Photoreaction of Anthracene

Lanthanide luminescence materials generally show great superiority in light-emitting materials, gaining increasingly exploration in the design of advanced functional materials. Herein, we prepared a supramolecular assembly via the coordination of a host molecule (1) and dilanthanide metal. Compound 1 possesses a 9,10-diphenylanthracene (ant) core with photosensitivity and terminal terpyridine (tpy), containing two-arm dibenzo-24-crown-8. The assembly could exhibit excellent lanthanide luminescence after undergoing a photoreaction from anthracene unit in 1. Significantly, the luminescence of the assembly could be reversibly switched on and off through a regulable photoreaction upon light irradiation or heating. The multiple functional behavior combined with the ease of assembly reveals that this photo/thermo-controlled lanthanide luminescence supramolecular polymer design method offers a convenient pathway for future engineering of multi-stimuli-responsive materials.

Reversibly Photoswitchable Supramolecular Assembly and Its Application as a Photoerasable Fluorescent Ink

A photoswitchable supramolecular assembly can efficiently and reversibly switch on/off the luminescence of the [Ru(bpy)3]2+ center upon irradiation by light with different wavelengths in solution and the solid state. The assembly possesses reversible photoisomerization and a high Förster resonance energy transfer efficiency, and when used as an ink it can be reversibly and repeatedly erased and recovered by altering the wavelength of irradiation light.

Lanthanide-directed synthesis of luminescent self-assembly supramolecular structures and mechanically bonded systems from acyclic coordinating organic ligands

Herein some examples of the use of lanthanide ions (f-metal ions) to direct the synthesis of luminescent self-assembly systems (architectures) will be discussed. This area of lanthanide supramolecular chemistry is fast growing, thanks to the unique physical (magnetic and luminescent) and coordination properties of the lanthanides, which are often transferred to the resulting supermolecule. The emphasis herein will be on systems that are luminescent, and hence, generated by using either visibly emitting ions (such as Eu(III), Tb(III) and Sm(III)) or near infrared emitting ions (like Nd(III), Yb(III) and Er(III)), formed through the use of templating chemistry, by employing structurally simple ligands, possessing oxygen and nitrogen coordinating moieties. As the lanthanides have high coordination requirements, their use often allows for the formation of coordination compounds and supramolecular systems such as bundles, grids, helicates and interlocked molecules that are not synthetically accessible through the use of other commonly used templating ions such as transition metal ions. Hence, the use of the rare-earth metal ions can lead to the formation of unique and stable species in both solution and in the solid state, as well as functional and responsive structures.

Photo-responsive pseudorotaxanes and assemblies

Optical responses for understanding the dynamic conformational change(s) in solution during the stimuli responsive complexation and decomplexation process(es) in a supramolecular assembly.

Fluorescence responsive conjugated poly(tetraphenylethene) and its morphological transition from micelle to vesicle

A crown ether-functionalized poly(tetraphenylethene) (AP-TPE) is synthesized and the rotation of the TPE group is successfully restricted, leading to a stepwise enhanced fluorescence accompanied by a morphological transition from micellar to vesicular.

Exploiting lanthanide luminescence in supramolecular assemblies

We review herein significant and recent work focused on the incorporation of luminescent lanthanides into switchable, supramolecular and surface bound assemblies.

Switchable V-type [2]pseudorotaxanes

A V-type molecule comprising a 2-[2-[4-(dimethylamino)phenyl]ethenyl]pyridinium cyanine branch and a p-aminophenoxy ethyl side arm was synthesized and can form quite different [2]pseudorotaxanes with cucurbit[7]uril (CB[7]) as a model thread in aqueous solution. The CB[7] ring can be switched reversibly from the cyanine branch to the aminophenoxy ethyl side arm by protonation of the aniline group, and the color of the solution was changed from orange red to yellow.