Molecular Conductance through a Quadruple‐Hydrogen‐Bond‐Bridged Supramolecular Junction

A series of self‐complementary ureido pyrimidinedione (UPy) derivatives modified with different aurophilic anchoring groups were synthesized. Their electron transport properties through the quadruple hydrogen bonds in apolar solvent were probed employing the scanning tunneling microscopy break junction (STMBJ) technique. The molecule terminated with a thiol shows the optimal electron transport properties, with a statistical conductance value that approaches 10^?3 G₀. The ¹H NMR spectra and control experiments verify the formation of quadruple hydrogen bonds, which can be effectively modulated by the polarity of the solvent environment. These findings provide a new design strategy for supramolecular circuit elements in molecular electronics.     

Activation of Electron‐Deficient Quinones through Hydrogen‐Bond‐Donor‐Coupled Electron Transfer

Quinones are important organic oxidants in a variety of synthetic and biological contexts, and they are susceptible to activation towards electron transfer through hydrogen bonding. Whereas this effect of hydrogen bond donors (HBDs) has been observed for Lewis basic, weakly oxidizing quinones, comparable activation is not readily achieved when more reactive and synthetically useful electron‐deficient quinones are used. We have successfully employed HBD‐coupled electron transfer as a strategy to activate electron‐deficient quinones. A systematic investigation of HBDs has led to the discovery that certain dicationic HBDs have an exceptionally large effect on the rate and thermodynamics of electron transfer. We further demonstrate that these HBDs can be used as catalysts in a quinone‐mediated model synthetic transformation.     

Hydrogen‐Bonded Organic Aromatic Frameworks for Ultralong Phosphorescence by Intralayer π–π Interactions

Ultralong organic phosphorescence (UOP) based on metal‐free porous materials is rarely reported owing to rapid nonradiative transition under ambient conditions. In this study, hydrogen‐bonded organic aromatic frameworks (HOAFs) with different pore sizes were constructed through strong intralayer π–π interactions to enable ultralong phosphorescence in metal‐free porous materials under ambient conditions for the first time. Impressively, yellow UOP with a lifetime of 79.8 ms observed for PhTCz‐1 lasted for several seconds upon ceasing the excitation. For PhTCz‐2 and PhTCz‐3, on account of oxygen‐dependent phosphorescence quenching, UOP could only be visualized in N₂, thus demonstrating the potential of phosphorescent porous materials for oxygen sensing. This result not only outlines a principle for the design of new HOFs with high thermal stability, but also expands the scope of metal‐free luminescent materials with the property of UOP.     

Phase‐Transfer‐Catalysed Synthesis of Pyrroloindolines and Pyridoindolines by a Hydrogen‐Bond‐Assisted Isocyanide Cyclization Cascade

A cascade reaction that generates pyrrolo‐ and pyridoindoline motifs from isocyanide precursors under phase‐transfer conditions is described. This transformation proceeds at room temperature in the presence of a quaternary ammonium catalyst and base to generate functionalized products containing an all‐carbon quaternary stereocentre. Quantum chemical calculations demonstrated that intramolecular general acid catalysis plays a key accelerating role through stabilization of developing charge in the transition state, and that the reaction is best described as a 5‐endo dig cyclization, rather than an anionic 6π electrocyclization. Investigations employing chiral phase‐transfer catalysts have given promising selectivities to date.     

A C3‐Symmetric Macrocycle‐Based,Hydrogen‐Bonded,Multiporous Hexagonal Network as a Motif of Porous Molecular Crystals

A C₃‐symmetric π‐conjugated macrocycle combined with an appropriate hydrogen bonding module (phenylene triangle) allowed the construction of crystalline supramolecular frameworks with a cavity volume of up to 58 %. The frameworks were obtained through non‐interpenetrated stacking of a hexagonal sheet possessing three kinds of pores with different sizes and shapes. The activated porous material absorbed CO₂ up to 96 cm³ g^?1 at 195 K under 1 atm.     

Isolation of a Hydrogen‐Bonded Complex Based on the Anthranol/Anthroxyl Pair: Formation of a Hydrogen‐Atom Self‐Exchange System

A hydrogen‐bonded complex was successfully isolated as crystals from the anthranol/anthroxyl pair in the self‐exchange proton‐coupled electron transfer (PCET) reaction. The anthroxyl radical was stabilized by the introduction of a 9‐anthryl group at the carbon atom at the 10‐position. The hydrogen‐bonded complex with anthranol self‐assembled by π–π stacking to form a one‐dimensional chain in the crystal. The conformation around the hydrogen bond was similar to that of the theoretically predicted PCET activated complex of the phenol/phenoxyl pair. X‐ray crystal analyses revealed the self‐exchange of a hydrogen atom via the hydrogen bond, indicating the activation of the self‐exchange PCET reaction between anthranol and anthroxyl. Magnetic measurements revealed that magnetic ordering inside the one‐dimensional chain caused the inactivation of the self‐exchange reaction.     

Test‐Strip‐Based Fluorometric Detection of Fluoride in Aqueous Media with a BODIPY‐Linked Hydrogen‐Bonding Receptor

The measurement of biologically relevant anions, such as fluoride, is an important task in analytical chemistry, in particular, for dental health and osteoporosis. Although a large number of fluoride probes are known, the applicability under relevant conditions is limited to a few examples. To improve this situation, BODIPY‐amidothiourea dyes with varying hydrogen‐bond donating strengths were developed, the most H‐acidic of which ( 1 c ) could detect F^? from an inorganic source (NaF) in 50 % aqueous solution (DMSO/water 1:1, v/v) with 0.01 ppm sensitivity through selective fluorescence quenching by a photoinduced electron‐transfer (PET) process. Use of the probe and a reference dye with a test‐strip assay and a portable and rapidly recording lateral‐flow fluorescence reader made determination of F^? in neat aqueous solutions, such as spiked water samples and toothpaste extracts, possible in a self‐referenced manner, achieving a detection limit of 0.2 ppm.     

Conformationally Complex π‐Conjugated Molecular and Polymeric Materials: New Challenges for Organic Synthesis

No protection? A unique, albeit fairly specialized, example of what promises to be a useful retrosynthetic consideration for those designing complex π‐molecular systems, namely, using conformation as a protecting group to shield a given reactive site in lieu of protecting‐group manipulation, is described (see scheme).

     

Rational Construction of 2D and 3D Borromean Arrayed Organic Crystals by Hydrogen‐Bond‐Directed Self‐Assembly

Borromean organic networks: The rigid and trigonal pyramidal molecule, 1,3,5‐tris(4‐carboxyphenyl)adamantane (TCA), self‐assembles into a 2D Borromean linked network by hydrogen bonds. Different linkers (methanol, phenazine, 4,4′‐bipyridine, and 4,4′‐azopyridine) result in more complex Borromean networks or a 3D polycatenation network.

     

The Quest of Excited‐State Intramolecular Proton Transfer via Eight‐Membered Ring π‐Conjugated Hydrogen Bonding System

Searching for eight‐membered ring π‐conjugated hydrogen bonding (8‐MR H‐bonding) systems with excited‐state intramolecular proton transfer (ESIPT) property is seminal and synthetically challenging. In this work, a series of π‐conjugated molecules ( 8‐HB‐1 , 8‐HB‐L1 and 8‐HB‐2 ) potentially possessing 8‐MR H‐bonding are strategically designed, synthesized and characterized. The configurations of these three potential molecules are checked by their X‐ray structures, among which 8‐HB‐L1 (a structurally locked 8‐HB‐1 core chromophore) is proved to be an 8‐MR H‐bonding system, whereas 8‐HB‐1 and 8‐HB‐2 are too sterically hindered to form the 8‐MR intramolecular H‐bond. The ESIPT property of 8‐HB‐L1 is confirmed by the dual fluorescence consisting of normal and proton‐transfer tautomer emissions. The insight into the ESIPT process of 8‐HB‐L1 is provided by femtosecond fluorescence upconversion measurements together with computational simulation. The results demonstrate for the first time a successful synthetic route to attain the 8‐MR H‐bonding molecule 8‐HB‐L1 with ESIPT property.     

The Temperature‐Dependent Hydrogen‐Bonding Signature of Lipids Monitored in the Far‐Infrared Domain

Phospholipids are studied by means of Fourier transform infrared (FTIR) spectroscopy in the mid‐ and far‐infrared spectral ranges, thereby establishing the hydrogen‐bonding continuum as a function of the temperature. The well‐known mid‐infrared spectrum of the phospholipid layer clearly shows a temperature‐dependent phase transition. In the far‐infrared region (from 300 to 50 cm^?1), an alternation of the interaction between the phospholipids and water molecules is found. The hydrogen‐bonding network ensemble and bound water molecules can be monitored in this spectral region. The lipid structure is found to strongly influence the intermolecular hydrogen‐bonding interplay. Thus, studies in the far‐infrared region provide significant information—at the molecular level—about the intermolecular hydrogen‐bonding signature of self‐assembled phospholipids.     

Rational Design of Nanofibers and Nanorings through Complementary Hydrogen‐Bonding Interactions of Functional π Systems

A simple protocol to create nanofibers and ‐rings through a rational self‐assembly approach is described. Whereas the melamine–oligo(p‐phenylenevinylene) conjugate 1 a self‐aggregates to form ill‐defined nanostructures, conjugate 1 b , which possesses an amide group as an additional interactive site, self‐aggregates to form 1D nanofibers that induce gelation of the solvent. AFM and XRD studies have shown that dimerization through the melamine–melamine hydrogen‐bonding interaction occurs only for 1 b . Upon complexation with 1/3 equivalents of cyanuric acid (CA), conjugate 1 a provides well‐defined, ring‐shaped nanostructures at micromolar concentrations, which open to form fibrous assemblies at submillimolar concentrations and organogels in the millimolar concentration range. Apparently, the enhanced aggregation ability of 1 a by CA is a consequence of columnar organization of the resulting discotic complex 1 a ₃ ? CA. In contrast, coaggregation of 1 b with CA does not provide well‐defined nanostructures, probably due to the interference of complementary hydrogen‐bonding interactions by the amide group.     

Modulating Photo‐ and Electroluminescence in a Stimuli‐Responsive π‐Conjugated Donor–Acceptor Molecular System

Functional organic materials that display reversible changes in fluorescence in response to external stimuli are of immense interest owing to their potential applications in sensors, probes, and security links. While earlier studies mainly focused on changes in photoluminescence (PL) color in response to external stimuli, stimuli‐responsive electroluminescence (EL) has not yet been explored for color‐tunable emitters in organic light‐emitting diodes (OLEDs). Here a stimuli‐responsive fluorophoric molecular system is reported that is capable of switching its emission color between green and orange in the solid state upon grinding, heating, and exposure to chemical vapor. A mechanistic study combining X‐ray diffraction analysis and quantum chemical calculations reveals that the tunable green/orange emissions originate from the fluorophore's alternating excited‐state conformers formed in the crystalline and amorphous phases. By taking advantage of this stimuli‐responsive fluorescence behavior, two‐color emissive OLEDs were produced using the same fluorophore in different solid phases.     

Hydrogen‐Bond‐Assisted “Gold Cold Fusion” for Fabrication of 2D Web Structures

Keeping their cool : Fabrication of a 2D weblike nanonetwork of gold was successfully demonstrated through a two‐step procedure including complexation of gold precursors to a weblike supramolecular assembly of surfactant followed by in situ reduction of the precursors to gold. Molecular assemblies stabilized by hydrogen bonding provided a sound template, leading to the highly integrated structure of gold through room‐temperature (cold) nanostructure fusion.

     

Solution‐Processed Bulk‐Heterojunction Photovoltaic Cells Based on Dendritic and Star‐Shaped D‐π‐A Organic Dyes

A series of D ‐π‐A organic dendritic and star‐shaped molecules based on three various chromophores (i.e., the truxene nodes, triphenylamine moieties as the donor, and benzothiadiazole chromophore as the acceptor) and their corresponding model compounds are facilely developed. Their photophysical and electrochemical properties are investigated in detail by UV/Vis absorption and photoluminescent spectroscopy, and cyclic voltammetry. By changing the various conjugated spacers (i.e., single bond, double bond, and triple bond) among the three chromophores of dendritic series, their photophysical properties (that is, the one‐photon absorption range and two‐photon absorption cross‐section values) are effectively modulated. All D ‐π‐A conjugated oligomers show a broad and strong absorption band from 250 to 700 nm in thin films. Solution‐processed bulk‐heterojunction photovoltaic devices using our oligomer as donor and PCBM as acceptor are fabricated and measured. The power conversion efficiency of the devices based on our oligomers continuously increases from DBTTr to TRTD2A as a result of an increasing relative absorption intensity in longer wavelength region by changing the donor‐acceptor ratio and conjugated spacers between the donor and acceptor. The power conversion efficiency of the devices based on TRTD2A was 0.54 % under the illumination of AM 1.5 and 100 mW cm^?2, which is the highest value recorded based on D ‐π‐A conjugated oligomers containing triphenylamine moieties and benzothiadiazole chromophores with truxene to date.     

A Platinum(II) Terpyridine Metallogel with an L‐Valine‐Modified Alkynyl Ligand: Interplay of Pt⋅⋅⋅Pt, π–π and Hydrogen‐Bonding Interactions

A series of platinum(II) terpyridine complexes with L ‐valine‐modified alkynyl ligands has been synthesized. A complex with an unsubstituted terpyridine and one valine unit on the alkynyl is shown to be capable of gel formation, which is in sharp contrast to the gelation properties of the corresponding organic counterparts. Upon sol–gel transition, a drastic color change from yellow to red is observed, which is indicative of the involvement of Pt ??? Pt interactions. Through the concentration‐ and temperature‐dependent UV/Vis absorption, emission, circular dichroism, and ¹H NMR studies, the contribution of hydrogen bonding, Pt ??? Pt and π–π stacking interactions as driving forces for gelation have been established, and the importance of maintaining a delicate balance between different intermolecular forces has also been illustrated.