A tetrakis(porphyrin) with branched side chains self-assembled to form supramolecular helical polymers both in solution and in the solid state. The helicity of the supramolecular polymers was determined by the chirality of solvent molecules, which permitted the polymer chains to be used in chiral sensing.
A new technique, surface-enhanced infrared absorption (SEIRA) spectroscopy, was used for the structural investigation of lanthanide (Ln) and actinide (An) complexes containing organic ligands. We synthesized thiol derivatives of organic ligands with coordination sites similar to those of 2-[N-methyl-N-hexanethiol-amino]-2-oxoethoxy-[N',N'-diethyl]-acetamide [diglycolamide (DGA)], Cyanex-272, and N,N,N',N'-tetrakis(2-pyridinylmethyl)-1,2-ethanediamine (TPEN), which have been used for separating Ln and An through solvent extraction. These ligands were attached on a gold surface deposited on an Si prism through S-Au covalent bonds; the gold surface enhanced the IR absorption intensity of the ligands. Aqueous solutions of Ln (Eu3+, Gd3+, and Tb3+) and An (Am3+) ions were loaded onto the gold surface to form ion complexes. The IR spectra of the ion complexes were obtained using Fourier transform infrared spectroscopy in the attenuated total reflection mode. In this study, we developed a new sample preparation method for SEIRA spectroscopy that enabled us to obtain the IR spectra of the complexes with a small amount of ion solution (5 µL). This is a significant advantage for the IR measurement of radiotoxic Am3+ complexes. In the IR spectra of DGA, the band attributed to CâO stretching vibrations at â¼1630 cm-1 shifted to a lower wavenumber by â¼20 cm-1 upon complexation with Ln and An ions. Moreover, the amount of the red shift was inversely proportional to the extraction equilibrium constant reported in previous studies on solvent extraction. The coordination ability of DGA toward Ln and An ions could be assessed using the band position of the CâO band. The Cyanex-272- and TPEN-like ligands synthesized in this report also showed noticeable SEIRA signals for Ln and An complexes. This study indicates that SEIRA spectroscopy can be used for the structural investigation of ion complexes and provides a microscopic understanding of selective extraction of Ln and An.
In this report, we describe the self-assembly behavior of neutral platinum complexes in toluene. The platinum complexes were seen to form two different types of assemblies depending on the preparation temperature.
This Review introduces the research directions for the synthesis of supramolecular fullerene polymers. First, the discovery of host-guest complexes of pristine fullerenes is briefly outlined. We focus on progress in supramolecular fullerene polymers directed by the use of calix[5]arene-fullerene interactions, which comprise linear, networked, helical arrays of fullerenes in supramolecular ensembles. The unique self-sorting behavior of right-handed and left-handed helical supramolecular fullerene arrays is discussed. Thereafter, an extensive investigation of the calix[5]arene-fullerene interaction for control over the chain structures of covalent polymers is introduced.
Calixarenes , Fullerenes , Calixarenes/chemistry , Fullerenes/chemistry , Polymers
We describe self-sorting supramolecular polymerization that uses chiral calix[5]arene hosts and a dumbbell-shaped fullerene guest. In a solution containing the racemic host and the guest, the (S)-host and the (R)-host preferably formed their homomeric complexes to form helical supramolecular fullerene polymers in a self-sorting manner. The self-sorting behavior has been studied using diffusion-ordered 1H NMR (DOSY) and circular dichroism (CD) studies. The present findings show that it is possible to accomplish controlled supramolecular polymerization.
In this study, we demonstrated cold gas-phase spectroscopy of chemical intermediates produced in solution. Herein, we combined an electrospray ion source with a T-shaped solution mixer for introducing chemical intermediates in solution into the gas phase. Specifically, the oxidation reaction of 2-(4-nitrophenyl)hydrazinecarboxaldehyde (NHCA) by 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) was initiated by mixing the methanol solutions of NHCA and DDQ in the T-shaped mixer, and the chemical species were injected into the vacuum apparatus for ultraviolet photodissociation (UVPD) spectroscopy. A cationic intermediate was strongly observed at m/z 150 in the mass spectrum, and the UVPD spectrum was observed under cold (â¼10 K) gas-phase conditions. The UVPD spectrum showed a strong, broad absorption at â¼38,000 cm-1, accompanied by a relatively weak component at â¼34,000 cm-1. These spectral patterns can be ascribed to a diazonium cation intermediate, whose existence has been predicted in a previous study. This report indicates that cold gas-phase UV spectroscopy can be a useful method for identifying the structure of chemical intermediates produced in solution.
Ureido-pyrimidinone (UPy)-appended tris(phenylisoxazolyl)benzenes were synthesized. The UPy moieties of the tris(phenylisoxazolyl)benzenes stably formed self-complementary dimers in solution. The dimers self-assembled to form helically twisted stacking constructs in a process driven by π-π stacking interactions of UPy dimer moieties and dipole-dipole interactions of isoxazole units. Strong association affinity was seen within the stacking constructs compared with the previously reported isoxazole derivatives owing to the auxiliary π-π stacking interaction. Notably, tris(phenylisoxazolyl)benzenes showed an environmentally responsive nature. The absorption bands, emission intensities, and sizes of ensembles depended significantly on the mixing ratio of CHCl3 and methylcyclohexane (MCH). Additionally, sharp on-off switching phenomena were seen in their circular dichroism (CD) and circularly polarized luminescence (CPL) spectra in response to the mixing ratio of CHCl3 and MCH. CD and CPL were activated only at a certain mixing ratio of CHCl3/MCH, thus showing potential for the creation of molecular sensors.
A brand-new self-folding biscavitand was synthesized from a feet-to-feet-connected bisresorcinarene. The X-ray crystal structure of the biscaivtand showed that the two cavities are tightly connected with four butylene linkages. The conformationally coupled two cavities accommodated two cationic guests, showing a homotropic negative cooperativity in nonpolar solvents (toluene and chloroform). A polar tetrahydrofuran solvent weakened the cyclic hydrogen bonding interactions of the biscavitand, which resulted in noncooperative guest binding.
Furans/chemistry , Toluene/chemistry , Hydrogen Bonding , Molecular Conformation , Molecular Structure , Solvents
Since as early as 1867, molecular sensors have been recognized as being intelligent "devices" capable of addressing a variety of issues related to our environment and health (e.g., the detection of toxic pollutants or disease-related biomarkers). In this review, we focus on fluorescence-based sensors that incorporate supramolecular chemistry to achieve a desired sensing outcome. The goal is to provide an illustrative overview, rather than a comprehensive listing of all that has been done in the field. We will thus summarize early work devoted to the development of supramolecular fluorescent sensors and provide an update on recent advances in the area (mostly from 2018 onward). A particular emphasis will be placed on design strategies that may be exploited for analyte sensing and corresponding molecular platforms. Supramolecular approaches considered include, inter alia, binding-based sensing (BBS) and indicator displacement assays (IDAs). Because it has traditionally received less treatment, many of the illustrative examples chosen will involve anion sensing. Finally, this review will also include our perspectives on the future directions of the field.
Neutral platinum complexes that possess chiral triethylene glycol (TEG) moieties were synthesized. The platinum complexes formed helically twisted stacked assemblies in chloroform and toluene, which were studied by 1H NMR, UV/vis spectroscopy, and emission spectroscopy. On the other hand, emissive micellar aggregates were observed in a THF/water mixed solvent. Dynamic light scattering (DLS) experiments revealed that micellar aggregates with a diameter (d) of ≈100 nm emitted strong light, whereas the monomeric form and large aggregates (d > 500 nm) did not show luminescence efficiently. Furthermore, the micellar aggregates were twisted chirally, where the twisted direction was determined by the chirality of the TEG moieties. The assemblies were observed to be solvent responsive, which allows for the modulation of the nanostructure by changing the solvent polarity.
Carbazole-cored phenyl isoxazolyl benzenes possessing chiral moieties were synthesized. The molecules self-assembled to form stacked supramolecular assemblies in an isodesmic fashion in chloroform, whereas the molecules preferably assembled in a cooperative fashion in methylcyclohexane (MCH), which was determined by spectroscopic methods, including UV-vis absorption, fluorescence, and 1H NMR spectroscopy. Clear nucleation and elongation processes were observed in the plot of the degree of aggregation (αagg) against temperature, which allowed us to determine the elongation temperature (Te), the enthalpic gain in the elongation process (ΔHe), the equilibrium constant between nucleation and elongation (Ka), and the degree of polymerization at the elongation temperature ([Nn(Te)]). Circular dichroism (CD) and circularly polarized luminescence (CPL) studies revealed the formation of helically stacked assemblies in solution. Moreover, the majority-rule effect was clearly observed in the solutions of mixtures of (S)- and (R)-1, indicating the chiral amplification behavior of the helically stacked assemblies consisting of (S)- and (R)-1. AFM provided morphological insight into the assemblies on mica, which clearly indicates the formation of polymeric assemblies in the solid state.
To date, supramolecular chemistry techniques have been applied to fullerene polymer synthesis, enabling the development of main-chain fullerene polymers whose primary structure is well regulated, including linear, dendritic, and net-like fullerene arrays. These research achievements have led to an intriguing scientific challenge to create main-chain fullerene polymers with higher structural regulation. Here, we report the fabrication of a helically organized fullerene array based on the supramolecular polymerization of chiral ditopic tetrakiscalix[5]arene hosts and a dumbbell-shaped fullerene. The molecular association between the chiral hosts and the dumbbell-shaped fullerene resulted in sizable supramolecular polymers in solution, with the highest degree of polymerization of more than 32. The achiral dumbbell-shaped fullerene exhibited circular dichroism in the π-π* transition bands arising from the fullerene moieties through supramolecular polymerization. End-capping experiments of the supramolecular helical polymers showed that the chirally twisted conformation of the dumbbell-shaped fullerene was directed by supramolecular polymerization. Finally, the helical morphology of the supramolecular polymer chain was visualized by atomic force microscopy. The successful development of helical main-chain fullerene polymers would break new ground in fullerene chemistry.
Self-assembly of porphyrins is a fascinating topic, not only for mimicking chlorophyll assemblies in photosynthetic organisms, but also for the potential of creating molecular-level devices. Herein, zinc porphyrin derivatives bearing a meta-pyridyl group at the meso position were prepared and their assemblies studied in chloroform. Among the porphyrins studied, one with a carbamoylpyridyl moiety gave a distinct 1 Hâ NMR spectrum in CDCl3 , which allowed the supramolecular structure in solution to be probed in detail. Ring-current-induced chemical-shift changes in the 1 Hâ NMR spectrum, together with vapor-pressure osmometry and diffusion-ordered NMR spectroscopy, among other evidence, suggested that the porphyrin molecules form a trimer with a triangular cone structure. Incorporation of a directly linked porphyrin-ferrocene dyad with the same assembling properties in the assemblies led to a rare example of a light-harvesting/charge-separation system in which an energy gradient is incorporated and reductive quenching occurs.
Recent decades have seen an increased interest in the preparation of polymers possessing host or guest moieties as the end group, which has enabled new polymeric materials such as self-healable, shape-memory, and stimuli-responsive materials. Such polymers are commonly synthesized by tethering the host or guest moieties to polymers. On the other hand, there are limited reports demonstrating the preparation of host- or guest-appended polymers by directly polymerizing the corresponding host- or guest-appended monomers, which is valuable for easy access to diverse polymers from single molecular species. However, reactive host and/or guest moieties of the monomer interfere with the polymerization reaction. Here, we report that a biscalix[5]arene host-appended molecule can be polymerized with various monomers to form the corresponding host-appended polymers. The host-guest complexation behavior of calix[5]arene-appended polymers with fullerene derivatives was studied by 1H NMR and UV/Vis spectroscopic techniques, which revealed that the long polymer chains did not prevent host-guest complexation even when the fullerene derivative was equipped with a polymer chain. Thus, the present study shows the potential for developing polymers that have various combinations of polymer chains.
The repeating guest units of poly-(R)-2 were selectively encapsulated by the self-assembled capsule poly-1 possessing eight polymer side chains to form the supramolecular graft polymer (poly-1)n â poly-(R)-2. The encapsulation of the guest units was confirmed by 1 Hâ NMR spectroscopy and the DOSY technique. The hydrodynamic radius of the graft polymer structure was greatly increased upon the complexation of poly-1. The supramolecular graft polymer (poly-1)n â poly-(R)-2 was stably formed in the 1:1 host-guest ratio, which increased the glass transition temperature by more than 10 °C compared to that of poly-1. AFM visualized that (poly-1)n â poly-(R)-2 formed the networked structure on mica. The (poly-1)n â poly-(R)-2 gelled in 1,1,2,2-tetrachloroethane, which led to fabrication of distinct viscoelastic materials that demonstrated self-healing behavior in a tensile test.
A dual redox-responsive supramolecular polymer driven by molecular recognition between bisporphyrin (bisPor) and trinitrofluorenone (TNF) has been developed. The supramolecular polymer was degraded into monomers in response to both oxidation and reduction stimuli.
Three carbo[5]helicenes ([5]CHs) containing benzylmaleimide groups displayed columnar stacked organizations, including dislocated, parallel, and alternating (P)- and (M)-helix molecular arrangements in the solid state. The peripheral benzyl groups resulted in very small steric interactions that are responsible for the formation of columnar stacked arrangements in the crystalline state.
Chiral biscalixarenes and a C60-appended polyphenylacetylene have been synthesized. The chiral biscalixarene encapsulated the C60 unit of the phenylpolyacetylene, which induced the preferred helicity of the polyacetylene.
An increased interest in the use of platinum complex based luminescent micelles for imaging biological tissues has emerged in recent years due to their low cytotoxicity, synthetic flexibility, photostability, and high emission efficiency. Here, we report a luminescent micelle that is prepared through the self-assembly of an amphiphilic, neutral Pt(ii) complex with isoxazole moieties in THF/water on account of its aggregation-induced emission (AIE) property.
Dithienogermole derivatives S- and R-1 possessing phenylisoxazoles and chiral side chains were synthesized. The helical assembly of 1 in methylcyclohexane exhibited circularly polarized luminescence (CPL). The CPL signals of the assembly in the elongation regime were inverted with respect to those in the nucleation regime.
