Mechanism of Host–Guest Complex Formation and Identification of Intermediates through NMR Titration and Diffusion NMR Spectroscopy

The formation of host–guest (H‐G) complexes between 1,8‐bis[(diethylgallanyl)ethynyl]anthracene (H) and the N‐heterocycles pyridine and pyrimidine (G) was studied in solution using a combination of NMR titration and diffusion NMR experiments. For the latter, diffusion coefficients of potential host–guest structures in solution were compared with those of tailor‐made reference compounds of similar shape (synthesized and characterized by NMR, HRMS, and in part XRD). Highly dynamic behavior was observed in both cases, but with different host–guest species and equilibria. With increasing concentrations of the pyridine guest, the equilibrium H₂?H₂κ¹‐G₁?HG₂ is observed (in the second step a host dimer coordinates one guest molecule); for pyrimidine the equilibrium H₂→H₁κ²‐G₁?HG₂ is observed (the formation of a 1:1 aggregate is the second step).     

Colorimetric and Fluorescent Chemosensors for the Detection of 2,4,6‐Trinitrophenol and Investigation of their Co‐Crystal Structures

A full account of our studies of 2,4,6‐trinitrophenol (TNP) sensing is provided. A series of chemosensors 2 , 3 , 4 , 5 with a variety of aromatic chromophores for specific recognition of TNP has been designed and then realized through the fluorescence “on/off” mechanism. These chemosensors demonstrated highly selective, sensitive, and fluorescent quenching of TNP with remarkable visual changes through the intramolecular charge‐transfer (ICT) process. Their host–guest interactions were investigated by ¹H NMR spectroscopic titrations and their corresponding co‐crystal structures, which showed that the 1:1 host–guest complexes were formed by multiple hydrogen‐bond interactions in solution or in the solid state. The origins of the significant affinity demonstrated during the fluorescence recognition process were further disclosed through DFT calculations of corresponding compounds.     

Theoretical prediction of the host–guest interactions between novel photoresponsive nanorings and C60: A strategy for facile encapsulation and release of fullerene

A series of photoresponsive‐group‐containing nanorings hosts with 12～14 Å in diameter is designed by introducing different number of azo groups as the structural composition units. And the host–guest interactions between fullerene C₆₀ and those nanoring hosts were investigated theoretically at M06‐2X/6‐31G(d)//M06‐L/MIDI! and wB97X‐D/6‐31G(d) levels. Analysis on geometrical characteristics and host–guest binding energies revealed that the designed nanoring molecule (labeled as 7 ) which is composed by seven azo groups and seven phenyls is the most feasible host for encapsulation of C₆₀ guest among all candidates. Moreover, inferring from the simulated UV‐vis‐NIR spectroscopy, the C₆₀ guest could be facilely released from the cavity of the host 7 via configuration transformation between trans‐form and cis‐form of the host under the 563 nm photoirradiation. Additionally, the frontier orbital features, weak interaction regions, infrared, and NMR spectra of the C₆₀@7 host–guest complex have also been investigated theoretically. © 2015 Wiley Periodicals, Inc.     

Inclusion compounds of 2,5‐di­phenyl­hydro­quinone

The crystal structures of three 1:2 inclusion compounds that consist of host mol­ecule 2,5‐di­phenyl­hydro­quinone (C₁₈H₁₄O₂) and the guest mol­ecules 2‐pyridone (C₅H₅NO), 1,3‐di­phenyl‐2‐propen‐1‐one (chalcone, C₁₅H₁₂O) and 1‐(4‐meth­oxy­phenyl)‐3‐phenyl‐2‐propen‐1‐one (4′‐methoxy­chal­cone, C₁₆H₁₄O₂) were determined in order to study the ability of guest mol­ecules in inclusion compounds to undergo photoreaction. All of the crystals were found to be photoresistant. The three inclusion compounds crystallize in triclinic space group . In each case, the host/guest ratio is 1:2, with the host mol­ecules occupying crystallographic centers of symmetry and the guest mol­ecules occupying general positions. The guest mol­ecules in each of the inclusion compounds are linked to the host mol­ecules by hydrogen bonds. In the inclusion compound where the guest mol­ecule is pyridone, the host mol­ecule is disordered so that the hydroxy groups are distributed between two different sites, with occupancies of 0.738 (3) and 0.262 (3). The pyridone mol­ecules form dimers via N—H⋯O hydrogen bonds.     

Highly Flexible,Tough, and Self‐Healing Supramolecular Polymeric Materials Using Host–Guest Interaction

Flexible, tough, and self‐healable polymeric materials are promising to be a solution to the energy problem by substituting for conventional heavy materials. A fusion of supramolecular chemistry and polymer chemistry is a powerful method to create such intelligent materials. Here, a supramolecular polymeric material using multipoint molecular recognition between cyclodextrin (CD) and hydrophobic guest molecules at polymer side chain is reported. A transparent, flexible, and tough hydrogel (host–guest gel) is formed by a simple preparation procedure. The host–guest gel shows self‐healing property in both wet state and dry state due to reversible nature of host–guest interaction. The practical utility of the host–guest gel as a scratch curable coating is demonstrated.

     

Dendronized tricyanopyrroline‐based chromophores in nonlinear optical active host polymer

We synthesized new nonlinear optical (NLO) chromophores containing a 3,5‐bis(3,5‐bisbenzyloxy‐benzyloxy)‐benzoate dendron. Tricyanopyrroline (TCP)‐based chromophores were designed and prepared by virtue of its strong electron withdrawing property. A soluble polyimide containing 6‐({4‐[2‐(1‐allyl‐4‐cyano‐5‐dicyanomethylene‐2‐oxo‐2,5‐dihydro‐1H‐pyrrol‐3‐yl)‐vinyl]‐phenyl}‐butyl‐amino)‐hexanoyl group in the side chain was also prepared as an NLO active host polymer. A benzoate dendron was tethered at two different binding positions of the chromophore to yield two different guest molecules. Thin‐film composites of these dendronized chromophores dissolved in the NLO active polyimide host were employed to fabricate the electro‐optic (EO) samples. The EO properties of new NLO polyimides containing dendronized chromophores were compared with those of the sample with nondendronized plain chromophores. The effect of a bulky dendron on the EO properties was investigated using an in situ reflection technique. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5064–5076, 2008     

Facile synthesis and electro‐optic activities of new polycarbonates containing tricyanofuran‐based nonlinear optical chromophores

Two series of novel electro‐optic (EO) polycarbonates containing two different kinds of nonlinear optical (NLO) chromophores with tricyanofurane (TCF) electron acceptor have been successfully prepared through the facile polycondensation between diol NLO chromophore and bisphenol A bis(chloroformate). These new polycarbonates which were characterized by ¹H‐NMR and Fourier transform infrared exhibited good solubility in common polar organic solvents. They also showed glass transition temperatures (T_g) in the range of 124–156 °C. The morphology studies indicated that these polycarbonates had good film quality before and after corona poling. The EO coefficients (r₃₃) of two polycarbonates films were up to 45 pm/V (PC‐TCFC‐2) and 75 pm/V (PC‐DFTC‐3) at the wavelength of 1310 nm. Moreover, good temporal stability of the poling‐induced dipole alignment was also achieved, and the resulting poled films of PC‐TCFC‐2 and PC‐DFTC‐3 could retain 90 and 80% of the initial EO activities at 85 °C for more than 500 h, respectively. Both EO activity and temporal stability results were better than the guest–host EO polymers containing the same concentration chromophores, which indicated that such kind of polycarbonates could effectively suppress the intermolecular electrostatic interaction and translate microscopic molecular hyperpolarizability into macroscopic EO activity. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2841–2849.     

Three polymorphs of an inclusion compound of 2,2′‐(disulfanediyl)dibenzoic acid and trimethylamine

Polymorphism is the ability of a solid material to exist in more than one form or crystal structure and this is of interest in the fields of crystal engineering and solid‐state chemistry. 2,2′‐(Disulfanediyl)dibenzoic acid (also called 2,2′‐dithiosalicylic acid, DTSA) is able to form different hydrogen bonds using its carboxyl groups. The central bridging S atoms allow the two terminal arene rings to rotate freely to generate various hydrogen‐bonded linking modes. DTSA can act as a potential host molecule with suitable guest molecules to develop new inclusion compounds. We report here the crystal structures of three new polymorphs of the inclusion compound of DTSA and trimethylamine, namely trimethylazanium 2‐[(2‐carboxyphenyl)disulfanyl]benzoate 2,2′‐(disulfanediyl)dibenzoic acid monosolvate, C₃H₁₀N⁺·C₁₄H₉O₄S₂⁻·C₁₄H₁₀O₄S₂, (1), tetrakis(trimethylazanium) bis{2‐[(2‐carboxyphenyl)disulfanyl]benzoate} 2,2′‐(disulfanediyl)dibenzoate 2,2′‐(disulfanediyl)dibenzoic acid monosolvate, 4C₃H₁₀N⁺·2C₁₄H₉O₄S₂⁻·C₁₄H₈O₄S₂²⁻·C₁₄H₁₀O₄S₂, (2), and trimethylazanium 2‐[(2‐carboxyphenyl)disulfanyl]benzoate, C₃H₁₀N⁺·C₁₄H₉O₄S₂⁻, (3). In the three polymorphs, DTSA utilizes its carboxyl groups to form conventional O—H…O hydrogen bonds to generate different host lattices. The central N atoms of the guest amine molecules accept H atoms from DTSA molecules to give the corresponding cations, which act as counter‐ions to produce the stable crystal structures via N—H…O hydrogen bonding between the host acid and the guest molecule. It is noticeable that although these three compounds are composed of the same components, the final crystal structures are totally different due to the various configurations of the host acid, the number of guest molecules and the inducer (i.e. ancillary experimental acid).     

Host–Guest Interactions of Phosphorescent Molecular Tweezers Based on an Alkynylplatinum(II) Terpyridine System with Polyaromatic Hydrocarbons

Host–guest interactions of a molecular tweezer complex 1 with various planar organic molecules including polyaromatic hydrocarbons (PAHs) were investigated by 1D and 2D ¹H NMR spectroscopy, UV/Vis absorption and emission titration studies. 2D and DOSY NMR spectroscopies support the sandwiched binding mode based on 1:1 host–guest interactions. The binding constants (K_S) of complex 1 for various PAHs were determined by NMR titration studies and the values were found to span up to an order of 10⁴ M ^?1 for coronene to no observable interaction for benzene, indicating that the π‐surface area is important for such host–guest interactions. The substituent effect on the host–guest interaction based on the guest series of 9‐substituted anthracenes was also studied. In general, a stronger interaction was observed for the anthracene guest with electron‐donating groups, although steric and π‐conjugation factors cannot be completely excluded. The photophysical responses of complex 1 upon addition of various PAHs were measured by UV/Vis and emission titration studies. The UV/Vis absorption spectra were found to show a drop in absorbance of the metal‐to‐ligand charge‐transfer (MLCT) and ligand‐to‐ligand charge‐transfer (LLCT) admixture band upon addition of various guest molecules to 1 , whereas the emission behavior was found to change differently depending on the guest molecules, showing emission enhancement and/or quenching. It was found that emission quenching occurred either via energy transfer or electron transfer pathway or both, while emission enhancement was caused by the increase in rigidity of complex 1 as a result of host–guest interaction.     

Host-Guest Interactions between N,N＇-Bis（ferrocenylmethyl- ene）-Diaminobutane and Benzenetetracarboxylic Dianhydride Bridged Bis（β-cyclodextrin）s

A novel water soluble ditopic guest, the quaternary ammonium salt of N,N＇-bis（ferrocenylmethylene）-diaminobutane （1）, and a known water soluble ditopic host, benzenetetracarboxylic dianhydride bridged bis（β-cyclodextrin）s （2）, have been synthesized and characterized. ^1H NMR spectra and cyclic voltammogram （CV） studies revealed the host-guest interactions between them in aqueous solution. The supramolecular interaction also exists in solid state as confirmed by the studies of the solid samples, which were obtained by frozen-drying the solution sampies, using FTIR spectroscopy and differential scanning calorimetry （DSC） techniques. TEM measurement demonstrated that wire-shaped supramolecular aggregates exist in the aqueous solution of the two compounds. The lengths of the aggregates could reach micrometers.     

Self‐Assembled Tetragonal Prismatic Molecular Cage Highly Selective for Anionic π Guests

The metal‐directed supramolecular synthetic approach has paved the way for the development of functional nanosized molecules. In this work, we report the preparation of the new nanocapsule 3? (CF₃SO₃)₈ with a A₄B₂ tetragonal prismatic geometry, where A corresponds to the dipalladium hexaazamacrocyclic complex Pd‐1 , and B corresponds to the tetraanionic form of palladium 5,10,15,20‐tetrakis(4‐carboxyphenyl)porphyrin ( 2 ). The large void space of the inner cavity and the supramolecular affinity for guest molecules towards porphyrin‐based hosts converts this nanoscale molecular 3D structure into a good candidate for host–guest chemistry. The interaction between this nanocage and different guest molecules has been studied by means of NMR, UV/Vis, ESI‐MS, and DOSY experiments, from which highly selective molecular recognition has been found for anionic, planar‐shaped π guests with association constants (K_a) higher than 10⁹ M ^?1, in front of non‐interacting aromatic neutral or cationic substrates. DFT theoretical calculations provided insights to further understand this strong interaction. Nanocage 3? (CF₃SO₃)₈ can not only strongly host one single molecule of M(dithiolene)₂ complexes (M=Au, Pt, Pd, and Ni), but also can finely tune their optical and redox properties. The very simple synthesis of both the supramolecular cage and the building blocks represents a step forward for the development of polyfunctional supramolecular nanovessels, which offer multiple applications as sensors or nanoreactors.     

A Porphyrin‐Based Discrete Tetragonal Prismatic Cage: Host–Guest Complexation and Its Application in Tuning Liquid‐Crystalline Behavior

The host–guest complexation between a porphyrin‐based 3D tetragonal prism ( H ) and electron‐rich pyrene is investigated. This host–guest molecular recognition is further utilized to suppress the liquid‐crystalline behavior of a nematic molecule ( G ) containing cyanobiphenyl mesogens functionalized with a pyrenyl unit. Furthermore, coronene, with an increased number of π‐electrons, is used as a competitive guest to recover the liquid‐crystalline behavior of G . This supramolecular approach provides a glimpse of the new possibilities to modulate the structures of the mesophases.

     

Inclusion of chlorophenols by 4,4′‐(cyclohexane‐1,1‐diyl)diphenol: structures and kinetics of decomposition

The structures of the inclusion compounds 4,4′‐(cyclohexane‐1,1‐diyl)diphenol–3‐chlorophenol (1/1) and 4,4′‐(cyclohexane‐1,1‐diyl)diphenol–4‐chlorophenol (1/1), both C₁₈H₂₀O₂·C₆H₅ClO, are isostructural with respect to the host molecule and are stabilized by extensive host–host, host–guest and guest–host hydrogen bonding. The packing is characterized by layers of host and guest molecules. The kinetics of thermal decomposition follow the R2 contracting‐area model, kt = [1 − (1 − α)^½], and yield activation energies of 105 (8) and 96 (8) kJ mol⁻¹, respectively.     

Electrospray ionization mass spectrometry studies of cyclodextrin‐carboxylate ion inclusion complexes

Aqueous solutions containing simple model aliphatic and alicyclic carboxylic acids (surrogates 1–4) were studied using negative ion electrospray mass spectrometry (ESI‐MS) in the presence and absence of α‐, β‐, and γ‐cyclodextrin. Molecular ions were detected corresponding to the parent carboxylic acids and complexed forms of the carboxylic acids; the latter corresponding to non‐covalent inclusion complexes formed between carboxylic acid and cyclodextrin compounds (e.g., β‐CD, α‐CD, and γ‐CD). The formation of 1:1 non‐covalent inclusion cyclodextrin‐carboxylic complexes and non‐inclusion forms of the cellobiose‐carboxylic acid compounds was also observed. Aqueous solutions of Syncrude‐derived mixtures of aliphatic and alicyclic carboxylic acids (i.e. naphthenic acids; NAs) were similarly studied using ESI‐MS, as outlined above. Molecular ions corresponding to the formation of CD‐NAs inclusion complexes were observed whereas 1:1 non‐inclusion forms of the cellobiose‐NAs complexes were not detected. The ESI‐MS results provide evidence for some measure of inclusion selectivity according to the 'size‐fit' of the host and guest molecules (according to carbon number) and the hydrogen deficiency (z‐series) of the naphthenic acid compounds. The relative abundances of the molecular ions of the CD‐carboxylate anion adducts provide strong support for differing complex stability in aqueous solution. In general, the 1:1 complex stability according to hydrogen deficiency (z‐series) of naphthenic acids may be attributed to the nature of the cavity size of the cyclodextrin host compounds and the relative lipophilicity of the guest. Copyright © 2009 John Wiley & Sons, Ltd.     

Restricted Conformational Flexibility of a Triphenylamine Derivative on the Formation of Host–Guest Complexes with Various Macrocyclic Hosts

Herein, we report the host–guest‐type complex formation between the host molecules cucurbit[7]uril (CB[7]), β‐cyclodextrin (β‐CD), and dibenzo[24]crown‐8 ether (DB24C8) and a newly synthesized triphenylamine (TPA) derivative 1 X₃ as the guest component. The host–guest complex formation was studied in detail by using ¹H NMR, 2D NOESY, UV/Vis fluorescence, and time‐resolved emission spectroscopy. The chloride salt of the TPA derivative was used for recognition studies with CB[7] and β‐CD in an aqueous medium. The restricted internal rotation of the guest molecule on complex formation with either of these two host molecules was reflected in the enhancement of the emission quantum yield and the average excited‐state lifetime for the triphenylamine‐based excited states. Studies with DB24C8 as the host molecule were performed in dichloromethane, a medium that maximizes the noncovalent interaction between the host and guest fragments. The Förster resonance energy transfer (FRET) process involving DB24C8 and 1 (PF₆)₃, as the donor and acceptor fragments, respectively, was established by electrochemical, steady‐state emission, and time‐correlated single‐photon counting studies.     

Determination of enantiomeric excess for organic primary amine compounds by chiral recognition fast-atom bombardment mass spectrometry

Enantiomeric excess (ee) of organic primary amine compounds such as phenylglycine methyl ester hydrochloride (2) has been determined by fast-atom bombardment (FAB) mass spectrometry (NBA matrix). Chiral recognition in host–guest complexation systems between crown ethers [H] and amino acid ester ammonium ions [G] has been extended to the ee determination. The method characteristically uses a 1/1 mixture of a pair of enantiomeric hosts whose enantiomer is isotopically labeled [(RRRR)-1 and (SSSS)-1-d₆]. Chiral recognition of a given guest is simply measured with the given host–pair reagent from the relative peak intensities of the two corresponding diastereomeric host–guest complex ions in I[(H_RRRR · G)⁺]/I[(H_SSSS-d6 · G)⁺ = I_R/I_S-d6, so called IRIS value. The IRIS value varies in a linear fashion with the ee quantitiy of 2 and produces a symmetric linear V-shaped plot, indicating that in the case of a primary amine guest (such as 2) with unknown ee, one can determine the ee by this type of chiral recognition FAB mass spectometry. Further, based on the observed concentration effects on the IRIS values, it is suggested that the present IRIS value reflects the concentration ratio of the diastereomeric complex ions formed in the matrix.     

Acridan‐Grafted Poly(biphenyl germanium) with High Triplet Energy,Low Polarizability,and an External Heavy‐Atom Effect for Highly Efficient Sky‐Blue TADF Electroluminescence

We propose the novel σ–π conjugated polymer poly(biphenyl germanium) grafted with two electron‐donating acridan moieties on the Ge atom for use as the host material in a polymer light‐emitting diode (PLED) with the sky‐blue‐emitting thermally activated delayed fluorescence (TADF) material DMAC‐TRZ as the guest. Its high triplet energy (E_T) of 2.86 eV is significantly higher than those of conventional π–π conjugated polymers (E_T=2.65 eV as the limit) and this guest emitter (E_T=2.77 eV). The TADF emitter emits bluer emission than in other host materials owing to the low orientation polarizability of the germanium‐based polymer host. The Ge atom also provides an external heavy‐atom effect, which increases the rate of reverse intersystem crossing in this TADF guest, so that more triplet excitons are harvested for light emission. The sky‐blue TADF electroluminescence with this host/guest pair gave a record‐high external quantum efficiency of 24.1 % at maximum and 22.8 % at 500 cd m^?2.     

Double targeting of tumours with pyrenyl-modified dendrimers encapsulated in an arene-ruthenium metallaprism

The self‐assembly of 2,4,6‐tris(pyridin‐4‐yl)‐1,3,5‐triazine (tpt) triangular panels with p‐cymene–ruthenium building blocks and 5,8‐dioxido‐1,4‐naphthoquinonato (donq) bridges, in the presence of pyrenyl‐containing dendrimers of different generations (P₀, P₁ and P₂), affords the triangular prismatic host–guest compounds [P_n?Ru₆(p‐cymene)₆(tpt)₂(donq)₃]⁶⁺ ([P_n? 1 ]⁶⁺). The host–guest nature of these systems, with the pyrenyl moiety being encapsulated in the hydrophobic cavity of the cage and the dendritic functional group pointing outwards, was confirmed by NMR spectroscopy (¹H, 2D and DOSY). The host–guest properties of these systems were studied in solution by NMR and UV/Vis spectroscopic methods, allowing the determination of their affinity constants (K_a). Moreover, the ability of these water‐soluble host–guest systems to carry the pyrenyl‐containing dendrimers into cancer cells was evaluated on human ovarian cancer cells. The host–guest systems are all more cytotoxic than the empty cage [ 1 ][CF₃SO₃]₆ (IC₅₀≈4 μM ), with the most active compound, [P₀? 1 ][CF₃SO₃]₆, being an order of magnitude more cytotoxic.     

Rattling in the Quadruple Perovskite CuCu3V4O12

Of particular interest is a peculiar motion of guest atoms or ions confined to nanospace in cage compounds, called rattling. While rattling provides unexplored physical properties through the guest–host interactions, it has only been observed in a very limited class of materials. Herein, we introduce an A‐site‐ordered quadruple perovskite, CuCu₃V₄O₁₂, as a new family of cage compounds. This novel AA′₃B₄O₁₂‐type perovskite has been obtained by a high‐pressure synthesis technique and structurally characterized to have cubic Im$\bar 3$ symmetry with an ionic model of Cu²⁺Cu²⁺₃V⁴⁺₄O₁₂. The thermal displacement parameter of the A‐site Cu²⁺ ion is as large as U_iso≈0.045 Ų at 300 K, indicating its large‐amplitude thermal oscillations in the oversized icosahedral cages. Remarkably, the presence of localized phonon modes associated with rattling of the A‐site Cu²⁺ ion manifests itself in the low‐temperature specific heat data. This work sheds new light on the structure–property relations in perovskites.     

Circularly Polarized Luminescence of Achiral Metal–Organic Colloids and Guest Molecules in a Vortex Field

Recently, scientists have reported a range of chiral fluorescence materials or chiral composites that can emit circularly polarized luminescence. Herein, two achiral metal–organic colloidal solutions were studied, showing active circularly polarized luminescence, which is observed in vortex stirring. The absolute values for g_lum are 0.05 and 0.03 and the plus or minus sign of g_lum depends on the colloidal structure and stirring direction, which make the property easy to manipulate. Further, the host–guest interaction study suggests both electrostatic interactions and coordination bonding may influence the chiroptical property from the colloidal solution to the guest molecule. Rhodamine 6G and its carboxylic acid derivative exhibit good quantum yields and acceptable g_lum values in the colloidal solution.