Hydrogen-bonded Self-assembly Research Articles

Biomimetic, highly adhesive, supramolecular nano-coatings for fire-safe polymeric foams

Constructing fire-protective coatings has been to be an effective strategy for reducing fire hazards of polymeric materials. However, it remains a huge challenge to fabricate high-performance flame retardant coatings with biodegradability, excellent mechanical and thermal properties, as well as strong adhesion. Herein, inspired by snails exhibiting strong adhesion to a variety of surfaces by interfacial hydrogen-bonding, a biomimetic, highly adhesive, supramolecular nano-coating consisting of a tannic acid (TA)-functionalized hexagonal boron nitride nanosheets (TA-BNNS), TA and polyvinyl alcohol (PVA) was prepared by using a hydrogen-bond self-assembly strategy of solvent volatilization regulation. TA-BNNS was prepared via an efficient and green ball milling exfoliation method under mild conditions. Dynamically regulating the hydrogen bonds between PVA and TA molecules through the volatilization of ethanol was to achieve physical cross-linking. Then such a nanocoating was applied for surface treatment of rigid polyurethane foam (RPUF), which exhibiting excellent flame retardant properties. Compared to pure RPUF, the peak heat release rate (PHRR) and peak smoke production rate (PSPR) of the TA/PVA@BNNS coated RPUF were reduced by ~52.4 % and ~53.4 %, respectively. Therefore, this work provides new approach to the design and manufacture of green, efficient and non-toxic flame retardant materials.

(Invited) Hole-Transporting Materials for Perovskite Solar Cells: A Theoretical Insight

Hole-transporting materials (HTMs) are a crucial component in obtaining high power conversion efficiencies (PCEs) in perovskite-based solar cells (PSCs). They play the important roles of extracting the photogenerated holes, formed within the perovskite film, and transporting them to the electrodes. Among the wide number of chemical structures proposed as HTMs for PSCs, small organic molecules have received special attention with spiro-OMeTAD (2,2´,7,7´-tetrakis(N,N-di-p-methoxyphenylamine)-9,9´-spirobifluorene) as a reference.1 In this communication, we first focus on how the donor ability and hole reorganization energy change with the chemical structure of the HTM. Sulfur-rich compounds, such as the anthracene-tetrathiophene ATT-OMe system displayed in Figure 1a, that have been used as HTMs in PSCs achieving remarkable PCEs, are theoretically described.2 Second, we investigate a series of HTMs based on fused polyheteroaromatic molecules incorporating 7-azaindole terminal moieties bearing hydrogen-bond donor and hydrogen-bond acceptor sites (Figure 1b). The 7-azaindole units induce the hydrogen-bond self-assembly of the conjugated molecules thus increasing the supramolecular ordering in the HTM layer. The effects of this ordering on the charrier transport in the HTM semiconducting layer are theoretically discussed.3 Third, we briefly present how the optical properties (energy bandgap) of Cs2AgBiBr6 lead-free double perovskites can be tuned by substituting the monovalent Ag1+ and trivalent Bi3+ cations by divalent Sn2+, Ge2+ and Zn2+ cations.4 Figure 1. Chemical structure of the sulfur-rich ATT-OMe (a) and the H-bond-promoting ADAI (b) HTM molecules. Both HTMs are based on an anthracene central core. References J. Urieta, I. García-Benito, A. Molina-Ontoria, N. Martín, Chem. Soc. Rev. 2016, 47, 8541.I. Zimmermann, J. Urieta-Mora, P. Gratia, J. Aragó, G. Grancini, A. Molina-Ontoria, E. Ortí, N. Martín, M. K. Nazeeruddin, ACS Appl. Mater. Interfac. 2017, 7, 1601674.P. Gómez, S. Georgakopoulos, M. Más-Montoya, J. Cerdá, J. Pérez, E. Ortí, J. Aragó, D. Curiel, J. Mater. Chem. C 2021, 13, 8620.P. Sebastiá-Luna, J. Calbo, N. Albiach-Sebastián, M. Sessolo, F. Palazón, E. Ortí, H. J. Bolink, Chem. Mater. 2021, 33, 8028. Figure 1

Hydrogen-Bonded Self-assembly of Supramolecular Donor–Acceptor Complexes of (E)-Bis(18-crown-6)azobenzene with Bis(ammoniopropyl) Derivatives of Bipyridine and Dipyridylethylene in Acetonitrile

Hydrogen-Bonded Self-assembly of Supramolecular Donor–Acceptor Complexes of (E)-Bis(18-crown-6)azobenzene with Bis(ammoniopropyl) Derivatives of Bipyridine and Dipyridylethylene in Acetonitrile

Continuous Making, Stretch Breaking, and Exciton Dynamics of a Red-Emissive Organic Submicrometer-Sized Triangular Pyramid

Highly photoluminescent, single-component self-assembly being scalable and sustainable has a profound commercial significance. In this article, the challenges that we address in development of self-assembly of π-conjugated molecules are ─(i) feeble photoluminescence caused by poor molecular orientational ordering and (ii) costly fluorescent monomer owing to lack of an atom/step/energy economical synthetic method. We have discovered that a bright yellow fluorescent xanthene analog capable of instantly forming self-assembly can be synthesized by a home-built coil-in-spiral reactor using an inexpensive precursor, pyrogallol. Stimuli such as temperature (35 °C), acid fumes, and apolar solvent can trigger the formation of red-emissive self-assembly. In solution orientation of about 13 molecules yielding hydrogen-bonded self-assembly has a direct resemblance with a Coulomb-coupled J-aggregate highlighted in the Kasha model. After photoexcitation, the excited state dynamics of the monomer progress via three pathways: (i) relaxation (2 ± 0.3 ps), (ii) solvation (19.5 ± 3 ps), and (iii) decay (2.5 ns). On the other hand, self-assembly exciton evolves via two pathways: (i) relaxation (81 ± 25 ps) and (ii) decay (∼1 ns). In the solid state, the self-assembly retains the submicron-sized trigonal pyramidal structures by layer-by-layer stacking of triangular plates. This self-assembly doped in polymer even exhibits mechanofluorescence. Our study will pave way the use of this photoluminescent self-assembly for improved performance of organic/sustainable electronics and stretchable electronics.

Chain-Length-Dependent Hydrogen-Bonded Self-Assembly of Terminally Functionalized Discrete Polyketones

Here, we report the synthesis and the chain-length-dependent self-assembling behaviors of discrete di-, tetra-, and hexaketones terminally functionalized with hydrogen-bonding carboxyl (C1, C2, and C3) and 3-acylaminopyridine groups (P1, P2, and P3). These polyketones were prepared by the coupling reactions of silylated analogues of 3,3-dimethylpentane-2,4-dione and t-butyl 2,2-dimethyl-3-oxobutanoate and the subsequent hydrolysis or amidation with 3-aminopyridine. Single-crystal X-ray diffraction analysis revealed that C1 and C2 form helical assemblies in which the components are connected by the dimerization of terminal carboxyl groups, whereas the longer C3 showed infinite hydrogen-bonded chains mediated by 1,4-dioxane used as a crystallization solvent. Pyridine-terminated P1 exhibited a three-dimensional hydrogen-bonded network owing to multiple NH···N(pyridine) hydrogen bonds in the solid state. P2 generated a double-helix-like fiber structure in the crystalline state. Among the pyridine-terminated polyketones P1–P3, only P2 showed gelation behavior in chloroform (100 mM concentration) at 25 °C. The scanning electron microscopy measurement of xerogel P2 revealed the formation of rod-like structures with a thickness of approximately 0.5–3.5 μm. These results demonstrate that the precise control of the polyketone chain length can significantly alter hydrogen-bonded self-assembly in the solid state and in solution even with the same terminal structures.

Azido azole-1,3,4-triazine fused energetic materials: A bioinspired strategy for tuning thermal stability and sensitivity of metal-free primary explosives via hierarchical hydrogen-bond self-assembly

Primary explosives are useful but they usually pose low thermal stability and underlying safety threat to manufacturers and users. It is highly desirable yet challenging to develop next-generation primary explosives with lead-free, environmentally friendly, high-dense, thermostable and safe organic energetic materials for replacement. Here, inspired by biosystem’s architecture, we report a simple and efficient hierarchical hydrogen-bond self-assembly strategy to synthesize high-performance primary explosives with enhanced thermal stability (Tonset > 200 °C) and decreased sensitivity (40 J). Owing to the above-efficient strategy, 7-azide-3-(1H-tetrazol-5-yl)-[1,2,4]triazolo[5,1-c] [1,2,4]triazin-4-amine-2- oxide (EM-4) and 7-azide-4-amino-3-nitro-[1,2,4]triazolo[5,1-c][1,2,4]triazine (EM-6) feature high densities of 1.825 and 1.816 g cm−3, much superior to their analogues 7-azide-3-(1H-tetrazol-5-yl)-[1,2,4]triazolo[5,1-c][1,2,4]triazin-4-amine (EM-3) and 8-azide-4-amino-3,7-dinitropyrazolo-[5,1-c][1,2,4]triazine (EM-9), comparable to that of 6-azido-8-nitrotetrazolo[1,5-b]-pyridazine-7-amine (ANTP). Meanwhile, EM-3 (Td = 225 °C), EM-4 (Td = 290 °C) and EM-6 (Td = 210 °C) exhibit better thermal stability and lower sensitivities (IS = 40 J) than those representative metal-free primary explosives (Td = 114–193 °C, IS = 0.25–17 J). The as-synthesized materials all feature superior performance to those of commercially scale-up and industrial applicable primary explosive 2-diazo-4,6-dinitrophenol (DDNP). Moreover, the calculated detonation velocity of EM-6 reaches up to 9029 m s−1, which is comparable to that of 6-nitro-7-azido-pyazol[3,4-d][1,2,3]triazine-2-oxide (ICM-103) but EM-6 features better thermal stability and safety performance. Bioinspired organic primary explosive may open a new gate for the design and development of more thermostable, higher dense and safer initiating substances towards future advanced applications.

CO2-responsive tunable persistent luminescence in a hydrogen-bond organized two-component ionic crystal.

A reversible CO2-responsive luminescent material was constructed by a facile hydrogen-bond self-assembly of a two-component ionic crystal. The modification of CO2 on the ionic crystal not only alternates the green afterglow, but also endows the material with inverse excitation wavelength dependence for multicolor emission.

Photoinduced hydrogen-bonded self-assembly of cation-capped complexes and novel photoswitchable supramolecular devices based on (aza)-18-crown-6-containing styryl dyes bearing a long N-ammonioalkyl substituent

Herein, we report the synthesis and quantitative studies of novel photocontrollable ionophores.

Carbon vacancies enriched carbon nitride nanotubes for Pd coordination environment optimization: Highly efficient photocatalytic hydrodechlorination and CO2 cycloaddition

The use of easily available solar energy to achieve pollutants efficient degradation and waste carbon resource CO2 utilization under mild conditions is highly desired. Herein, novel carbon vacancies enriched nanotubes graphitic carbon nitride (SCNT-500) has been successfully fabricated via melamine (MA) supramolecular hydrogen-bonded self-assembly in the presence of H2SO4. Pd NPs loaded carbon vacancies enriched carbon nitride nanotubes (Pd/SCNT-500) were used for photocatalytic chlorophenols hydrodechlorination and CO2 cycloaddition with styrene oxide. Up to 6.93 s-1 4-chlorophenol hydrodechlorination TOF and obviously improved CO2 cycloaddition efficiency could be realized with Pd/SCNT-500. The improved photocatalytic efficiency should be related to the morphology and carbon vacancies based Pd coordination environment optimization. Such as, the surface area increased nanotubes structure promoted light harvesting along with photoelectrons and holes generation; the carbon vacancies improved excited electrons capture, photoinduced carriers recombination inhibition along with substrates adsorption with electron rich Pd NPs. Mechanism studies not only demonstrated the important role of atomic hydrogen and Pd coordination environment optimization in the chlorophenols hydrodechlorination, but also confirmed the promotion ability of photogenerated electrons on CO2 cycloaddition.

Multi-responsive fluorescent switches and iodine capture of porous hydrogen-bonded self-assemblies

Porous nanoribbons from gels may act as smart materials for applications in iodine absorption and fluorescence sensing for gaseous nitrobenzene, and could reversibly change its fluorescence color under shearing force and solvent annealing.

Radical Activity of Binary Melamine-Based Hydrogen-Bonded Self-Assemblies

Melamine cyanurate and melamine barbiturate self-assembled materials were prepared and studied by the electron paramagnetic resonance (EPR) spectroscopy, optical and scanning electron microscopy, X-ray powder diffraction (XRD). Both optical and electron microscopy show the formation of microscale crystalline particles possessing complex layered structures with a highly stable appearance. Both assemblies tend to form twinned crystals, which in the barbiturate case leads to multiple twinning in every particle. Optical microscopy shows high anisotropy and birefringence of both materials. XRD data represent a high crystallinity of melamine barbiturate and much lower for melamine cyanurate. Studied materials reveal the ability to incorporate radicals that correlate with their crystal structure quality. It is attributed to the structure-dependent stabilization of active radical superoxide species in structure voids or defects. In the example of melamine barbiturate, it is shown that the number of active paramagnetic centers increases at ca. 22% when a substance is irradiated with UV + Vis light. It reaches saturation in approximately 20 min, whereas only ca. 14% decrease was observed in a week.

Two-dimensional infrared spectral explorations into bilayer and monolayer self-assemblies of amphiphilic polypeptides

Poly(2-(3-((2-hydroxyethyl)amino)-3-oxopropyl)ethyleneamido) (PHAOE) is an amphiphilic polypeptide. The self-assembly is significant, but the ultrafast dynamic analyses of the peptide self-assembly are exiguous and worth further exploring. In this investigation, the temporal dynamic characteristics of the aggregates and unaggregated PHAOEs are mined by the two-dimensional infrared (2D IR) spectroscopy. The homogeneous and inhomogeneous diffusion processes of the carbonyl stretching modes of the unaggregated PHAOEs are slower than those of the self-assemblies. The inhomogeneous spectral diffusion proportion of the biopolymer PHAOE in methanol is greater than that in dimethyl sulfoxide (DMSO). The solvation shells surround the aggregates and unaggregated PHAOEs in the protic solvent methanol, but there are not any solvation shells around the aggregates or unaggregated PHAOEs in the dipolar solvent DMSO. The massive hydrogen-bonded monolayer self-assembly has merely an aggregate of PHAOEs and no solvation shell in DMSO. But the hydrogen-bonded bilayer self-assembly has a self-assembled methanol shell and an interior aggregate of PHAOEs in methanol. The self-assemblies of PHAOEs motivate the methanols to self-assemble. The large delocalized amide structure results in the fast spectral diffusion of the carbonyl stretching mode.Communicated by Ramaswamy H. Sarma

Hydrogen bonding-based self-assembly technology for high-performance melt blending TPU/PA6 polymers

Toughness and tensile strength are important mechanical properties of polymers. However, it is generally very challenging to improve the toughness without an obvious decrease in the tensile strength, and vice versa, which greatly limits the applications of polymers. Here we developed a novel hydrogen bonding-based self-assembly technology for melt blending polymers to achieve a notable improvement in toughness without an obvious decrease in the tensile strength. Thermoplastic polyurethane (TPU)/polyamide 6 (PA6) blend was selected a model composite and its elongation at break increased significantly from 1150% (0 wt% PA6) to 1350% (7.5 wt% PA6) and 1375% (10 wt% PA6), without an obvious decrease in the tensile strength. We deeply investigated the relationship between microcosmic self-assembly and macroscopic mechanical properties in polymer melt blends. It was found that the hard and soft segment groups (urethane and ester) of TPU form new hydrogen bonds with the amide group of PA6 through hydrogen-bonded self-assembly during the melt blending process, while the intrinsic hydrogen bonding structure of TPU was obviously shielded and weakened. As a result, the TPU/PA6 melt blends showed a notable improvement in toughness without an obvious decrease in the tensile strength. Since most previous self-assembly studies were carried out in solution and there was little work focused on the industrial convenient melt blending method, our study paves the way for further studies on both theoretical studies and practical applications of polymer blends.

Occurrence of Chiral Nanostructures Induced by Multiple Hydrogen Bonds.

Developing artificial systems to mimic the emergence of chirality is of vital importance in better understanding the mysterious origin of natural homochirality and guiding the design of advanced chiroptical materials. Herein, we present a DNA-inspired control over the emergence of supramolecular nanoscale chirality in multiple hydrogen-bonded self-assemblies. N-Terminated aromatic amino acids bearing serine and aromatic domains could self-assemble into lamellar microsheets without nanoscale chirality, ascribed to their pronounced molecular stacking preference on two-dimensional orientations. Significantly, when achiral bipyridine-, melamine-, and imidazole-based molecular binders that could potentially form hydrogen-bonded complexes with these aromatic amino acids were introduced, the induced chiral nanostructures from the resulting coassemblies were observed. Melamine and its derivatives presented an excellent capability to generate ordered supramolecular structures and induce the nanoscale chirality. Assisted by the key duplex hydrogen bonds between the melamine core and serine segments, chiral nanotubes and ribbons were obtained. This study reveals that multiple hydrogen bonds are the prerequisite for inducing the emergence of chiral nanostructures from integrated coassemblies.

Modular fabrication of fluorescent sensors via hydrogen-bonding self-assembly

Fluorescent molecular sensors offer a sensitive and straightforward approach to monitoring biologically or environmentally important targets. However, obtaining high-performance chemosensors are still challenging in terms of laborious synthesis and low success rate. Herein we report a general and efficient strategy for fabrication of complex fluorescent chemosensors. Noncovalent synthesis of supramolecular sensors was realized by self-assembly of structurally simple subunits bearing hydrogen-bonding linkers. Based on the selected use of three recognition subunits and three signalling subunits, an array of fluorescent sensory co-assemblies with different subunits combination patterns were fabricated for sensitive detection of bisulfite, saccharides, carbon dioxide or chemical warfare agents. The multiplicity and ratios of these subunits can be flexibly adjusted to obtain desirable functions such as signal amplification, ratiometric responses and simultaneous multitarget monitoring.

Scalable one-step synthesis of hydroxylated boron nitride nanosheets for obtaining multifunctional polyvinyl alcohol nanocomposite films: Multi-azimuth properties improvement

Introducing hydroxyl (OH) groups onto the surface of chemically inert hexagonal boron nitride (h-BN) is conducive to the exfoliation and functionalization of h-BN, meanwhile could enhance the intermolecular forces with polymer as well. However, chemical inertness generated by partially ionized BN bonds makes the introduction of OH groups still remains a challenge. Here, we reported a scalable one-step thermal calcination method for the fabrication of OH-functionalized h-BN nanosheets (OH-BN). Then, transparent, strong, and flexible as well as flame retardant nanocomposite films of as-prepared OH-BN and PVA were prepared through an aqueous solution casting technique. Due to hydrogen-bond self-assembly and crystalline-region self-relief, elongation at break, tensile strength, and Young's modulus of PVA nanocomposite film were simultaneously increased by 109.3%, 73.6%, and 144.4% with as low as 0.2 wt % OH-BN. Besides, the self-stiffness phenomenon that damages the material elasticity during dynamic service process of PVA nanocomposite films was effectively hindered. Meanwhile, the superior visible light transmittance and higher absorption quality to UV-light were also confirmed, which promoted its practical use in artificial cornea materials. Attributing to the well-dispersed state and layered structure, incorporated OH-BN presented a barrier function to suppress the delivery of thermal degradation products of PVA matrix, thus enhancing thermal stability and fire safety. Herein, we come to a conclusion that the scalable one-step synthesis of OH-BN and environmentally friendly fabrication of PVA/OH-BN nanocomposite films as well as excellent properties greatly contribute to the development of the practical application of h-BN nanosheets, thus obtaining multifunctional composite materials.

Conformation and Visual Distinction between Urea and Thiourea Derivatives by an Acetate Ion and a Hexafluorosilicate Cocrystal of the Urea Derivative in the Detection of Water in Dimethylsulfoxide.

Structures of different solvates and solute–solvent interactions of 4-(3-(4-nitrophenyl)urido)benzoate (L1) and methyl-4-(3-(4-nitrophenyl)thiourido)benzoate (L2) with different solvents are analyzed. The solution of L1 with tetrabutylammonium acetate (TBAA) in dimethylsulfoxide (DMSO) is colorless, but a similar solution of L2 with TBAA is orange. On the other hand, respective solutions of these urea and thiourea derivatives with tetrabutylammonium fluoride (TBAF) in DMSO are orange. Urea derivative L1 facilitates the reaction of TBAF with glass to form tetrabutylammonium hexafluorosilicate, which on further interaction with L1 forms cocrystal 2L1·(TBA)2SiF6. Reorganization of hydrogen-bonded self-assembly of 2L1·(TBA)2SiF6 in DMSO caused by water is established by a dynamic light scattering study. With an increase in the amount of water in the solution, visual color changes from orange to colorless, and the color changes are reversed upon the addition of a dehydrating agent such as molecular sieves. Solvates of L1 with DMSO, dimethylformamide (DMF), and dimethylacetamide are quasi-isostructural. The respective self-assembly of these solvates differs due to orientations of aromatic rings and the carbomethoxy group across the thioamide/amide bond. Significant differences in self-assemblies of the respective DMSO solvate of L1 and L2 are observed; self-assembly of the former has dimeric subassemblies as repeat units, whereas the latter has monomeric subassemblies. DMF solvates of L1 and dimethylacetamide of L1 are built by dimeric subassemblies to form self-assembled structures, but these subassemblies differ in the orientation of the carbomethoxy group across the urea units.

Effect of topology structure on the electrochemical behavior of hydrogen-bonded self-assembled Poly(4-vinylpyridine) -ferrocenyl dendron complexes

In this report, two new redox-responsive complexes with different dendritic tail chain number (P4VP- nFc, n = 1, 2) were prepared via the hydrogen-bonded self-assembly of poly(4-vinylpyridine) and ferrocenyl-modified percec-type dendrons. These complexes exhibited a crystalline phase for P4VP-1Fc and liquid crystalline for P4VP-2Fc at room temperature. The cyclic voltammetry measurement shows that the electrode process of P4VP-nFc (n = 1, 2) films was diffusion controlled and the reversibility of the electrode process for the P4VP-2Fc films became better than that for the P4VP-1Fc. Moreover, the redox peak current |ip| increased with increasing dendritic tail chain number n in the complex, because the complex film formed with 2Fc-COOH has the looser stacking of alkyl chains, which was favorable for the electrolyte diffusion and charge transfer. The present results demonstrate that the electrochemical activity of the redox-responsive poly(4-vinylpyridine) -ferrocenyl dendron complex can be easily tuned using the dendritic tail chain with different numbers. These complexes may be used as new kinds of modified electrodes.

Enabling Light Work in Helical Self-Assembly for Dynamic Amplification of Chirality with Photoreversibility.

Light-driven transcription and replication are always subordinate to a delicate chirality transfer. Enabling light work in construction of the helical self-assembly with reversible chiral transformation becomes attractive. Herein we demonstrate that a helical hydrogen-bonded self-assembly is reversibly photoswitched between photochromic open and closed forms upon irradiation with alternative UV and visible light, in which molecular chirality is amplified with the formation of helixes at supramolecular level. The characteristics in these superhelixes such as left-handed or right-handed twist and helical length, height, and pitch are revealed by SEM and AFM. The helical photoswitchable nanostructure provides an easily accessible route to an unprecedented photoreversible modulation in morphology, fluorescence, and helicity, with precise assembly/disassembly architectures similar to biological systems such as protein and DNA.

Bioinspired Strategy to Reinforce PVA with Improved Toughness and Thermal Properties via Hydrogen-Bond Self-Assembly.

Despite the high strength and stiffness of polymer nanocomposites, they usually display lower deformability and toughness relative to their matrices. Spider silk features exceptionally high stiffness and toughness via the hierarchical architecture based on hydrogen-bond (H-bond) assembly. Inspired by this intriguing phenomenon, we here exploit melamine (MA) to reinforce poly(vinyl alcohol) (PVA) via H-bond self-assembly at a molecular level. Our results have shown that due to the formation of physical cross-link network based on H-bond assembly between MA and PVA, yield strength, Young's modulus, extensibility, and toughness of PVA are improved by 22, 25, 144, and 200% with 1.0 wt % MA, respectively. Moreover, presence of MA can enhance the thermal stability of PVA to a great extent, even exceeding some nanofillers (e.g., graphene). This work provides a facile method to improve the mechanical properties of polymers via H-bond self-assembly.