Unusual Photoreaction of Triquinacene within Self‐Assembled Hosts

Triquinacene is a concave tricyclic hydrocarbon with diverse photoreactivity. In the cavity of an electron‐accepting molecular host, triquinacene was specifically photooxidized at the peripheral allylic position into an alcohol, 1‐hydroxytriquinacene, via guest‐to‐host electron transfer. The unusual reactivity stems from the extremely electron‐deficient triazine panel ligand of the host cage, which allows the cage to function as a good electron acceptor. Thus, self‐assembled coordination cages can serve not only as molecular‐sized reaction vessels but also function electronically as redox media. Dissolved molecular oxygen is indispensable for the photoreaction and immediately traps a photogenerated radical.     

蝶形主体分子的设计、合成及其包结性能的研究

设计、合成了两种蝶形主体分子：2，5－二（三苯甲基）对苯二酚1，2，5－二（二苯甲基）对苯二酚2.1和2可与许多有机小分子形成配位包合物。用IR表征了主体分子1和2 的包结物， 用¹H NMR测定了主客体分子的摩尔比：1•DMF (1：2)，1•DMSO (1:2)，1 •吡啶 （1：2），1•环戊酮 （2：3）和2•DMF 1：2），2•DMSO （1：2），2 •THF （1：1），2•苯甲醛（1：2），2•苯乙酮 （1：2），2•2，5－己二酮 （1：1），2 •N－甲基－2－吡咯烷酮 （1：3）。单晶X-射线衍射分析了包结物2·苯甲醛的晶体结构，在分子间氢键的相互作用下晶体得以稳定。     

Janus‐Like Squaramide‐Based Hosts: Dual Mode of Binding and Conformational Transitions Driven by Ion‐Pair Recognition

New tripodal squaramide‐based hosts have been synthesised and structurally characterised by spectroscopic methods. In 2.5 % (v/v) [D₆]DMSO in CDCl₃, compound 4 formed dimeric assemblies [log K_dim=3.68(8)] as demonstrated by ¹H NMR spectroscopy and UV dilution experiments. AFM and SEM analyses revealed the formation of a network of bundled fibres, which indicates a preferential mechanism for aggregation. These C₃‐symmetric tripodal hosts exhibited two different and mutually exclusive modes of binding, each one easily accessible by simultaneous reorientation of the squaramide groups. In the first, a convergent disposition of the NH squaramide protons allowed the formation of an array of N? H???X^? hydrogen bonds with anions. In the second mode, reorientation of carbonyl squaramide groups allowed multiple C?O???H interactions with ammonium cations. The titration of 4 with different tetraalkylammonium iodides persistently showed the formation of 1:1 complexes, as well as 1:2 and 1:3 complexes. The corresponding stoichiometries and binding affinities of the complexes were evaluated by multi‐regression analysis. The formation of high‐order complexes, supported by ROESY, NOESY and mass spectrometry experiments, has been attributed to the insertion of NR₄I ion pairs between the carbonyl and NH protons of the squaramide groups located in adjacent arms of 4 . The observed effects reflect the induction of significant conformational changes in the hosts, mainly in relation to the relative orientation of the squaramide groups adapting their geometries to incoming ion‐pair complementary substrates. The results presented herein identify and fully describe two different modes of ion‐pair recognition aimed at directing conformational transitions in the host, therefore establishing a base for controlling more elaborate movements of molecular devices through ion‐pair recognition.     

C1‐Linked Spirobifluorene Dimers: Pure Hydrocarbon Hosts for High‐Performance Blue Phosphorescent OLEDs

Reported here are C1‐linked spiro‐bifluorene dimers. A comprehensive study is carried out to analyze the electronic properties of these highly twisted structures. This work shows that the C1‐position enables the design of pure hydrocarbon materials, with a high triplet energy, for hosting blue phosphors in efficient phosphorescent OLEDs (PhOLEDs). To date, this work describes the highest performance of blue PhOLEDs ever reported for pure hydrocarbons (external quantum efficiency of ca. 23 %), thus highlighting the potential of the C1‐spirobifluorene scaffold in organic electronics.     

Coaxial Carbon/MnO2 Hollow Nanofibers as Sulfur Hosts for High‐Performance Lithium‐Sulfur Batteries

Lithium‐sulfur (Li‐S) batteries have recently attracted a large amount of attention as promising candidates for next‐generation high‐power energy storage devices because of their high theoretical capacity and energy density. However, the shuttle effect of polysulfides and poor conductivity of sulfur are still vital issues that constrain their specific capacity and cyclic stability. Here, we design coaxial MnO₂‐graphitic carbon hollow nanofibers as sulfur hosts for high‐performance lithium‐sulfur batteries. The hollow C/MnO₂ coaxial nanofibers are synthesized via electrospinning and carbonization of the carbon nanofibers (CNFs), followed by an in situ redox reaction to grow MnO₂ nanosheets on the surface of CNFs. The inner graphitic carbon layer not only maintains intimate contact with sulfur and outer MnO₂ shell to significantly increase the overall electrical conductivity but also acts as a protective layer to prevent dissolution of polysulfides. The outer MnO₂ nanosheets restrain the shuttle effect greatly through chemisorption and redox reaction. Therefore, the robust S@C/MnO₂ nanofiber cathode delivers an extraordinary rate capability and excellent cycling stability with a capacity decay rate of 0.044 and 0.051 % per cycle after 1000 cycles at 1.0 C and 2.0 C, respectively. Our present work brings forward a new facile and efficient strategy for the functionalization of inorganic metal oxide on graphitic carbons as sulfur hosts for high performance Li‐S batteries.     

Calix[4]arene‐Functionalised Silver Nanoparticles as Hosts for Pyridinium‐Loaded Gold Nanoparticles as Guests

A series of lipophilic gold nanoparticles (AuNPs) circa 5 nm in diameter and having a mixed organic layer consisting of 1‐dodecanethiol and 1‐(11‐mercaptoundecyl) pyridinium bromide was synthesised by reacting tetraoctylammonium bromide stabilised AuNPs in toluene with different mixtures of the two thiolate ligands. A bidentate ω‐alkylthiolate calix[4]arene derivative was instead used as a functional protecting layer on AgNPs of approximately 3 nm. The functionalised nanoparticles were characterised by transmission electron microscopy (TEM), and by UV/Vis and X‐ray photoelectron spectroscopy (XPS). Recognition of the pyridinium moieties loaded on the AuNPs by the calix[4]arene units immobilised on the AgNPs was demonstrated in solution of weakly polar solvents by UV/Vis titrations and DLS measurements. The extent of Au‐AgNPs aggregation, shown through the low‐energy shift of their surface plasmon bands (SPB), was strongly dependent on the loading of the pyridinium moieties present in the organic layer of the AuNPs. Extensive aggregation between dodecanethiol‐capped AuNPs and the Ag calix[4]arene‐functionalised NPs was also promoted by the action of a simple N‐octyl pyridinium difunctional supramolecular linker. This linker can interdigitate through its long fatty tail in the organic layer of the dodecanethiol‐capped AuNPs, and simultaneously interact through its pyridinium moiety with the calix[4]arene units at the surface of the modified AgNPs.     

Efficient Self‐Assembly of Di‐, Tri‐, Tetra‐, and Hexavalent Hosts with Predefined Geometries for the Investigation of Multivalency

Coordination‐driven self‐assembly of differently shaped di‐ to hexavalent crown‐ether host molecules is described. A series of [21]crown‐7‐ and [24]crown‐8‐substituted bipyridine and terpyridine ligands was synthetized in a “toolbox” approach. Subsequent coordination to 3d transition metal and ruthenium(II) ions provides an easy and fast access to host assemblies with variable valency and pre‐defined orientations of the crown‐ether moieties. Preliminary isothermal calorimetry (ITC) titrations provided promising results, which indicated the host complexes under study to be suitable for the future investigation of multivalent and cooperative binding. The hosts described herein will also be suitable for the construction of various multiply threaded mechanically interlocked molecules.     

Miscibility and Alignment Effects of Mixed Monolayer Cyanobiphenyl Liquid‐Crystal‐Capped Gold Nanoparticles in Nematic Cyanobiphenyl Liquid Crystal Hosts

Against the rule: Liquid crystal hosts ( 5CB and 8CB ) are doped with different thiol decorated gold nanoparticles (see figure). The “simple” hexanethiol and dodecanethiol capped nanoparticles ( Au1 and Au2 ) are more compatible to the nematic cyanobiphenyl liquid crystals than nanoparticles capped simultaneously with alkylthiols and a nematic cyanobiphenyl thiol ( Au3 and Au4 ).

     

Functional Molecular Flasks: New Properties and Reactions within Discrete,Self‐Assembled Hosts

Insider dealing : Self‐assembled hosts applied as “molecular flasks” can alter and control the reactivity and properties of molecules encapsulated within their well‐defined, confined spaces. A variety of functional hosts of differing sizes, shapes, and utility have been prepared by using the facile and modular concepts of self‐assembly.

     

Chiral Supramolecular Switches Based on (R)‐Binaphthalene–Bipyridinium Guests and Cucurbituril Hosts

We designed and synthesized the three molecular tweezers 1 a – c ⁴⁺ containing an electron acceptor 4,4′‐bipyridinium (BPY²⁺) unit in each of the two arms and an (R)‐2,2′‐dioxy‐1,1′‐binaphthyl (BIN) unit that plays the role of chiral centre and the hinge of the structure. Each BPY²⁺ unit is connected to the BIN hinge by an alkyl chain formed by two‐ ( 1 a ⁴⁺), four‐ ( 1 b ⁴⁺), or six‐CH₂ ( 1 c ⁴⁺) groups. The behavior of 1 a – c ⁴⁺ upon chemical or photochemical reduction in the absence and in the presence of cucurbit[8]uril (CB[8]) or cucurbit[7]uril (CB[7]) as macrocyclic hosts for the bipyridinium units has been studied in aqueous solution. A detailed analysis of the UV/Vis absorption and circular dichroism (CD) spectra shows that the helicity of the BIN unit can be reversibly modulated by reduction of the BPY²⁺ units, or by association with cucurbiturils. Upon reduction of 1 a – c ⁴⁺ compounds, the formed BPY^{+ .} units undergo intramolecular dimerization with a concomitant change in the BIN dihedral angle, which depends on the length of the alkyl spacers. The alkyl linkers also play an important role in association to cucurbiturils. Compound 1 a ⁴⁺, because of its short carbon chain, associates to the bulky CB[8] in a 1:1 ratio, whereas in the case of the smaller host compound CB[7] a 1:2 complex is obtained. Compounds 1 b ⁴⁺ and 1 c ⁴⁺, which have longer linkers, associate to two cucurbiturils regardless of their sizes. In all cases, association with CB[8] causes an increase of the BIN dihedral angle, whereas the formation of CB[7] complexes causes an angle decrease. Reduction of the CB[8] complexes results in an enhancement of the BPY^{+ .} dimerization with respect to free 1 a – c ⁴⁺ and causes a noticeable decrease of the BIN dihedral angle, because the BPY^{+ .} units of the two arms have to enter into the same macrocycle. The dimer formation in the CB[8] complexes characterized by a 1:2 ratio implies the release of one macrocycle showing that the binding stoichiometry of these host–guest complexes can be switched from 1:2 to 1:1 by changing the redox state of the guest. When the reduction is performed on the CB[7] complexes, dimer formation is totally inhibited, as expected because the CB[7] cavity cannot host two BPY^{+ .} units.     

Voltammetric Characterization of Redox‐Inactive Guest Binding to LnIII[15‐Metallacrown‐5] Hosts Based on Competition with a Redox Probe

A novel competitive binding assay was implemented to monitor the binding of a redox inactive substrate to a redox inactive metallacrown host based on its competition with ferrocene carboxylate (FcC^?) using cyclic voltammetry (CV). First, the binding of FcC^? to Ln^III[15‐MC‐5] (LnMC) hosts was characterized by cyclic voltammetry. It was shown that the voltammetric half wave potentials, E_1/2, shifted to more positive potentials upon the addition of LnMC. The explicit dependence of E_1/2 with the concentration of LnMC was used to determine the association constants for the complex. The FcC^? binding strength decreased with larger central lanthanide metals in the LnMC hosts, and substantially weaker binding was observed with La^III. X‐ray crystallography revealed that the hydrophobic host cavity incompletely encapsulated FcC^? when the guest was bound to the nine‐coordinate La^III, suggesting the LnMC’s ligand side chains play a substantial role in guest recognition. With knowledge of the MC‐FcC^? solution thermodynamics, the binding affinity of a redox inactive guest was then assessed. Addition of sodium benzoate to a LnMC and FcC^? mixture resulted in E_1/2 shifting back to the value observed for FcC^? in the absence of LnMC. The association constants between benzoate and LnMC’s were calculated via the competitive binding approach. Comparison with literature values suggests this novel assay is a viable method for determining association constants for host–guest systems that exhibit the proper electrochemical behavior. Notably, this CV competitive binding approach does not require the preparation of a modified electrode or a tethered guest, and thus can be generalized to a number of host–guest systems.     

Convergent Modulation of Singlet and Triplet Excited States of Phosphine‐Oxide Hosts through the Management of Molecular Structure and Functional‐Group Linkages for Low‐Voltage‐Driven Electrophosphorescence

The controllable tuning of the excited states in a series of phosphine‐oxide hosts ( DPExPOCzn ) was realized through introducing carbazolyl and diphenylphosphine‐oxide (DPPO) moieties to adjust the frontier molecular orbitals, molecular rigidity, and the location of the triplet excited states by suppressing the intramolecular interplay of the combined multi‐insulating and meso linkage. On increasing the number of substituents, simultaneous lowering of the first singlet energy levels (S₁) and raising of the first triplet energy levels (T₁, about 3.0 eV) were achieved. The former change was mainly due to the contribution of the carbazolyl group to the HOMOs and the extended conjugation. The latter change was due to an enhanced molecular rigidity and the shift of the T₁ states from the diphenylether group to the carbazolyl moieties. This kind of convergent modulation of excited states not only facilitates the exothermic energy transfer to the dopants in phosphorescent organic light‐emitting diodes (PHOLEDs), but also realizes the fine‐tuning of electrical properties to achieve the balanced carrier injection and transportation in the emitting layers. As the result, the favorable performance of blue‐light‐emitting PHOLEDs was demonstrated, including much‐lower driving voltages of 2.6 V for onset and 3.0 V at 100 cd m^?2, as well as a remarkably improved E.Q.E. of 12.6 %.     

Redox‐Active M8L6 Cubic Hosts with Tetraphenylethylene Faces Encapsulate Organic Dyes for Light‐Driven H2 Production

The design of artificial systems that mimic highly evolved and finely tuned natural enzymes is a promising subject of intensive research. The assembly of O‐symmetric cubic structures with an Fe₈L₆ formula was reported through the direct combination of a C₄‐symmetric tetraphenylethylene‐based ligand with a C₃‐symmetric tris(bipyridine)iron node. The robust metal–organic cubes are rich in π‐electron density and provide favorable interactions with planar polycyclic aromatic hydrocarbons. Within the confined space of the host, the aromatic hydrocarbons molecules are forced closer to the redox active host, and the photoinduced electron transfer (PET) is modified into a pseudo‐intramolecular pathway. These iron vertices within the cubes exhibit suitable redox potential for electrochemical reduction of protons and the well‐modified PET is further tailored to create artificial systems for light‐driven hydrogen evolution from water through the encapsulation of fluorescein dyes. Control experiments based on a mononuclear compound resembling the iron corner of the octahedron suggest an enzymatic dynamic behavior. The new, well‐elucidated reaction pathways and the increased molarity of the reaction within the confined space render these supramolecular systems superior to other relevant systems.     

Modulating the Optoelectronic Properties of Large,Conjugated, High‐Energy Gap,Quaternary Phosphine Oxide Hosts: Impact of the Triplet‐Excited‐State Location

The purposeful modulation of the optoelectronic properties was realised on the basis of a series of the large, conjugated, phosphine oxide hosts 9,9‐bis‐{4′‐[2‐(diphenylphosphinoyl)phenoxy]biphenyl‐4‐yl}‐9H‐fluorene (DDPESPOF), 9,9‐bis‐{3′‐(diphenylphosphinoyl)‐4′‐[2‐(diphenylphosphinoyl)phenoxy]biphenyl‐4‐yl}‐9H‐fluorene (DDPEPOF), 9‐[4′‐(9‐{4′‐[2‐(diphenylphosphoryl)phenoxy]biphenyl‐4‐yl}‐9H‐fluoren‐9‐yl)biphenyl‐4‐yl]‐9H‐carbazole (DPESPOFPhCz) and 9‐[4′‐(9‐{3′‐(diphenylphosphoryl)‐4′‐[2‐(diphenylphosphoryl)phenoxy]biphenyl‐4‐yl}‐9H‐fluoren‐9‐yl)biphenyl‐4‐yl]‐9H‐carbazole (DPEPOFPhCz). The last two are quaternary with fluorenyls as linking bridges, diphenylphosphine oxide (DPPO) moieties as electron acceptors and diphenylethers and carbazolyls as two different kinds of electron donors. Owing to the fine‐organised molecular structures and the mixed indirect and multi‐insulating linkages, all of these hosts achieve the same first triplet energy levels (T₁) of 2.86 eV for exothermic energy transfer to phosphorescent dopants. The first singlet energy levels (S₁) and the carrier injection/transportation ability of the hosts were accurately modulated, so that DPESPOFPhCz and DPEPOFPhCz revealed extremely similar optoelectronic properties. However, the T₁ state of the former is localised on fluorenyl, whereas the carbazolyl mainly contributes to the T₁ state of the latter. A lower driving voltages and much higher efficiencies of the devices based on DPESPOFPhCz indicated that the chromophore‐localised T₁ state can suppress the quenching effects through realising independent contributions from the different functional groups to the optoelectronic properties and the embedding and protecting effect on the T₁ states by peripheral carrier transporting groups.