Controlled Photophysical Behaviors between Dibenzo-24-crown-8 Bearing Terpyridine Moiety and Fullerene-Containing Ammonium Salt

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.

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.

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.

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 ferrocene∩europium assembly showing phototriggered anticancer activity and fluorescent modality imaging

Two macrocyclic ferrocenophanes containing a coumarin fluorophore, Se₂N[7]ferrocenophane (fc1), and Se₄N₂[7,7]ferrocenophane (fc2), construct an assembly of fc1-H⁺ClO₄[Eu(C₁₀H₂₁COO)₂(H₂O)₂(ClO₄)] (fc1∩Eu) and fc2-2H⁺{ClO₄[Eu(C₁₀H₂₁COO)₂(H₂O)₂(ClO₄)]}₂ (fc2∩Eu) via a N-HO hydrogen bond and a coordinate bond between Eu^III and ClO₄^-. In fc1∩Eu, UV light irradiation triggers non-covalent bond cleavage to release a ferrocenium and Eu^II complex, accompanying chromism and luminescence signals. Investigations through the steady-state UV-vis absorption, fluorescence, time-resolved fluorescence, femtosecond transient absorption spectra and electrochemical characterization elucidate a stepwise mechanism: firstly, an effective electron transfer occurs from a ferrocene unit to the singlet state of a coumarin unit; the following proton-coupled electron transfer (PCET) reduces Eu^III and results in a non-covalent interaction cleavage. Further in vitro exploration of fc1∩Eu in HepG2 cells demonstrated phototriggered integrated cell cytotoxicity and fluorescent modality imaging.

Acid/base-controllable fluorescent molecular switches based on cryptands and basic N-heteroaromatics

Two kinds of fluorescent BMP32C10-based cryptands 1 and 2 have been developed. Cryptand 1 contains a binaphthol group, while cryptand 2 bears a coumarin group in their third arms. Based on this design, novel self-assemblies constructed from cryptand 1 or 2 and basic N-heteroaromatic guests 3-6 were successfully obtained. Moreover, the threading/dethreading processes of the host-guest complexes could be well switched by the alternate addition of acid/base, and accompanied by concurrent changes in fluorescence.

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.

A pH-responsive fluorescent [5]pseudorotaxane formed by self-assembly of cationic water-soluble pillar[5]arenes and a tetraphenylethene derivative

The formation of a pH-responsive fluorescent [5]pseudorotaxane by self-assembly of cationic water-soluble pillar[5]arenes and a tetraphenylethene derivative was reported.

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.

Aggregation-induced emission behavior of a pH-controlled molecular shuttle based on a tetraphenylethene moiety

A TPE-based molecular shuttle having amide and amine units has been synthesized. The shuttling motion of the macrocycle component can adjust its AIE behaviour.

Photophysical investigations on supramolecular fullerene/phthalocyanine charge transfer interactions in solution

The photophysical features of non-covalently linked fullerenes C60 and C70 with a designed free-base phthalocyanine, namely, 2,3,9,10,16,17,23,24-octakis-(octyloxy)-29H,31H-phthalocyanine (1) have been investigated employing various spectroscopic tools like UV-vis absorption spectrophotometry, steady state and time resolved fluorescence along with proton NMR measurements in toluene. The ground state interaction between fullerenes and 1 is nicely demonstrated with the appearance of well defined charge transfer absorption bands in the visible region of the electronic spectra. Steady state fluorescence experiment reveals efficient quenching of the excited singlet state of 1 in presence of both C60 and C70. The average values of binding constants for the non-covalent complexes of C60 and C70 with 1 are determined to be ~18,150 and ~32,000 dm(3) mol(-1), respectively. The magnitude of K suggests that 1 preferentially binds C70 in comparison to C60 although average value of selectivity in binding is measured to be low (~1.75). Time resolved emission measurements establish photoinduced energy transfer from the excited singlet state of 1 to fullerene in toluene. Measurements of free energy of electron transfer and free energy of radical ion-pair formation elicit that C70/1 complex is stabilized more in comparison to C60/1 complex regarding generation of charge-separated state. Proton NMR studies provide very good support in favor of effective ground state complexation between fullerenes and 1. Semi empirical theoretical calculations on fullerene/1 systems in vacuo substantiate the stronger binding between C70 and 1 in comparison to C60/1 system in terms of heat of formation value of the respective complexes, and determine the orientation of bound guest (here C70) towards the plane of 1 during complexation.

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.

The marriage of terpyridines and inorganic nanoparticles: synthetic aspects, characterization techniques, and potential applications

The utilization of supramolecular chemistry, i.e., metal-to-ligand coordination, in the field of nanotechnology is evaluated with respect to 2,2':6',2″-terpyridine, as tridentate metal binding site. Stabilization as well as directed self-assembly of nanometer-sized materials into ordered arrays are the most widely studied targets of current research. Moreover, energy- and/or electron-transfer processes are enabled when redox-active terpyridine complexes are bound to (semi)conducting species (e.g., fullerenes, polyoxometalates)-thus, applications in nanoelectronics and catalysis are currently arising from these hybrid materials. Progress made in these fields, resulting from the marriage of terpyridines (as well as their metal complexes) and nanostructures, is summarized in this Review Article.