Stimuli-responsive materials, such as thermochromics, have found mass usage and profitability in manufacturing and process control. Imparting charge-transfer-based functional supramolecular materials with tunable thermochromism emerges as an ideal strategy to construct optically responsive multifunctional assemblies. Herein, the authors report a new series of thermochromic charge-transfer-based supramolecular materials assembled in water. These assemblies are composed of a bis-bipyridinium-derived acceptor and a series of commercially available donors—namely, the neurotransmitter melatonin and its analogue bioisosteres. When the chemical structure of the donors are tailored, the strength of the charge-transfer interactions can be tuned. Thermochromic aerogels and inks of these materials are prepared, with a large selection of colors, in environment-friendly solvents and demonstrate tunable thermochromic transition temperatures ranging from 45 to 105 °C. Favorable compatibility of these materials with commercial inks and inkjet printers afford excellent pattern quality with extended color options. Mechanistic studies reveal that the two types of water molecules were bound to the supramolecular complexes with differing strengths, and that the more weakly bound water is responsible for the thermochromic transitions.

•Highly efficient and scalable synthesis of a hydrogen-bonded, conjugated ladder polymer•Rigid coplanar polymer backbones with well-defined intermolecular interactions•Solution-processed yet solvent-resistant polymer thin films•Polymer precursor with pre-fused rings gives highly graphitic carbon materialsRigid molecular backbones and strong intermolecular interactions are crucial for a wide range of functional properties of polymeric materials, such as stability under extreme conditions, mechanical strength, and electronic conductivity. Achieving these features in synthetic polymers opens a new way to innovative industrial materials by integrating sustainable and affordable production with exotic properties and high performance. The challenges associated with this class of materials, however, are twofold: the difficulty in precision chemical synthesis and the resulting poor solubility and processability. This work represents an important advance in the synthesis of rigid ladder-type macromolecules equipped with regulated intermolecular non-covalent bonds. These structural features are integrated with solution processability, allowing for feasible manipulation of this type of robust polymeric material under harsh conditions. This strategy provides a unique way to approach the design and large-scale production of highly rigid, strongly self-associated macromolecules possessing unique material functions.Rigid coplanar ladder polymers equipped with regulated intermolecular interactions promise unique solid-state properties. Efficient synthesis and solution processing of these materials, however, are challenging because of their extremely poor solubility. Herein, we describe a highly efficient, gram-scale synthesis of a hydrogen-bond-containing ladder polymer through an approach free of metal catalyst. The quinacridone-derived repeating unit features multiple self-complementary intermolecular hydrogen bonds along the rigid backbone. Using a reversible hydrogen-bond protection strategy, we were able to fully characterize this insoluble polymer in solution and process it into smooth thin films. In the solid state, the material demonstrated excellent resistance to organic solvents, aqueous acids, and thermal treatments, rendering a solution-processed, solvent-resistant thin film. This unique property allows for solution manipulation of robust polymer materials for applications associated with extreme operating or processing conditions. This scalable fused-ring polymer also demonstrated promising potential as a precursor for graphitic carbon materials.Download high-res image (175KB)Download full-size image

Fully conjugated ladder polymers (cLPs), in which all the backbone units on the polymer main-chain are π-conjugated and fused, have attracted great interest owing to their intriguing properties, remarkable chemical and thermal stability, and potential suitability as functional organic materials. The synthesis of cLPs can be, in general, achieved by two main strategies: single-step ladderization and post-polymerization ladderization. Although a variety of synthetic methods have been developed, the chemistry of cLPs must contend with structural defects and low solubility that prevents complete control over synthesis and structural characterization. Despite these challenges, cLPs have been used for a wide range of applications such as organic light emitting diodes (OLEDs) and organic field effect transistors (OFETs), paralleling developments in processing methods. In this perspective, we discuss the background of historical syntheses including the most recent synthetic approaches, challenges related to the synthesis and structural characterization of well-defined cLPs with minimum levels of structural defects, cLPs' unique properties, and wide range of applications. In addition, we propose outlooks to overcome the challenges limiting the synthesis, analysis, and processing of cLPs in order to fully unlock the potential of this intriguing class of organic materials.

AbstractWell-defined, fused-ring aromatic oligomers represent promising candidates for the fundamental understanding and application of advanced carbon-rich materials, though bottom-up synthesis and structure–property correlation of these compounds remain challenging. In this work, an efficient synthetic route was employed to construct extended benzo[k]tetraphene-derived oligomers with up to 13 fused rings. The molecular and electronic structures of these compounds were clearly elucidated. Precise correlation of molecular sizes and crystallization dynamics was established, thus demonstrating the pivotal balance between intermolecular interaction and molecular mobility for optimized processing of highly ordered solids of these extended conjugated molecules.

Molybdenum disulfide (MoS2) is a promising earth-abundant and low-cost electrocatalyst for the hydrogen evolution reaction (HER). In this study, we describe a stepwise synthetic approach comprising vapor transport, reduction, and topochemical sulfidation for creating 3D arrays of MoS2 nanosheets directly integrated onto carbon fiber paper (CFP) substrates. The sulfidation process results in a high density of edge sites along both the edges and the basal planes of MoS2. The obtained materials characterized by a high density of exposed edge sites exhibit promising electrocatalytic performance, including an overpotential (η10) of 245 mV at 10 mA/cm2, a Tafel slope of 81 mV/dec, and a turnover frequency (TOF) of 1.28 H2/s per active site at −0.2 V vs RHE in a 0.5 M acidic solution. The electrocatalytic properties of the MoS2 nanosheets are observed to be substantially enhanced by interfacing with solution-deposited buckminsterfullerene nanoclusters (nC60). A coverage of ca. 2% of nC60 yields a hybrid electrocatalyst exhibiting an η10 value of 172 mV, a Tafel slope of 60 mV/dec, and a TOF value of 2.33 H2/s per active site at −0.2 V vs RHE. The enhancement of electrocatalytic activity is found to derive from interfacial charge transfer at nC60/MoS2 p–n heterojunctions. The high conductivity of the interfacial layer formed as a result of charge transfer from nC60 to MoS2 is thought to substantially mitigate the limitations imposed by the poor basal plane conductivity of undoped MoS2. The hybrid catalysts illustrate an important design principle involving the use of structured interfaces to enhance the catalytic activity of low-dimensional materials.Keywords: chemical vapor deposition; electrocatalyst; fullerene; hydrogen evolution reaction; molybdenum disulfide

The synthesis of a carbazole-derived, well-defined ladder polymer was achieved under thermodynamic control by employing reversible ring-closing olefin metathesis. This unique approach featured mild conditions and excellent efficiency, affording the ladder polymer backbone with minimum levels of unreacted defects. Rigorous NMR analysis on a 13C isotope-enriched product revealed that the main-chain contained less than 1% of unreacted precursory vinyl groups. The rigid conformation of the ladder-type backbone was confirmed by photophysical analysis, while the extended rod-like structure was visualized under scanning tunneling microscope. Excellent solubility of this polymer in common organic solvents allowed for feasible processing of thin films using solution-casting techniques. Atomic force microscopy and grazing incident X-ray scattering revealed a uniform and amorphous morphology of these films, in sharp contrast to the polycrystalline thin films of its small molecular counterpart.

Active conformational control is realized in a conjugated system using intramolecular hydrogen bonds to achieve tailored molecular, supramolecular, and solid-state properties. The hydrogen bonding functionalities are fused to the backbone and precisely preorganized to enforce a fully coplanar conformation of the π-system, leading to short π–π stacking distances, controllable molecular self-assembly, and solid-state growth of one-dimensional nano-/microfibers. This investigation demonstrates the efficiency and significance of an intramolecular noncovalent approach in promoting conformational control and self-assembly of organic molecules.

Side-chain manipulation of isoindigo-thiophene derived conjugated polymers was achieved by statistical copolymerization of two different isoindigo monomers decorated with t-Boc groups and polyisobutylene chains, respectively. The long polyisobutylene side-chains ensured solution-processability of the polymers while the t-Boc groups served as a cleavable H-bond inhibitor. By post-film-casting thermal treatment, the t-Boc groups could be removed efficiently to generate a H-bond cross-linked polymer network, which demonstrated excellent solvent resistance. Organic field-effect transistor devices made from these thin films demonstrated retained electronic properties after being immersed in organic solvents. By taking advantage of the post-annealing solvent resistant feature, multilayered films of the polymers could be fabricated using multiple “casting–annealing–casting–annealing” cycles.

Ladder-type conjugated molecules with a low band gap and low LUMO level were synthesized through an N-directed borylation reaction of pyrazine-derived donor–acceptor–donor precursors. The intramolecular boron–nitrogen coordination bonds played a key role in rendering the rigid and coplanar conformation of these molecules and their corresponding electronic structures. Experimental investigation and theoretical simulation revealed the dynamic nature of such coordination, which allowed for active manipulation of the optical properties of these molecules by using competing Lewis basic solvents.

A highly efficient and feasible “condensation followed by annulation” synthetic approach was developed to afford a subset of 9-ring-fused quinacridone derivatives on a 10 g scale. Despite the amenable intermolecular hydrogen-bonding ability of these rigid molecules, good solubility in common organic solvents and solution processability into uniformed thin films were achieved. Integrated advantages in the synthesis and properties make these compounds ideal building blocks for high-performance dyes and optoelectronic materials.

The synthesis of a carbazole-derived, well-defined ladder polymer was achieved under thermodynamic control by employing reversible ring-closing olefin metathesis. This unique approach featured mild conditions and excellent efficiency, affording the ladder polymer backbone with minimum levels of unreacted defects. Rigorous NMR analysis on a 13C isotope-enriched product revealed that the main-chain contained less than 1% of unreacted precursory vinyl groups. The rigid conformation of the ladder-type backbone was confirmed by photophysical analysis, while the extended rod-like structure was visualized under scanning tunneling microscope. Excellent solubility of this polymer in common organic solvents allowed for feasible processing of thin films using solution-casting techniques. Atomic force microscopy and grazing incident X-ray scattering revealed a uniform and amorphous morphology of these films, in sharp contrast to the polycrystalline thin films of its small molecular counterpart.

Fully conjugated ladder polymers (cLPs), in which all the backbone units on the polymer main-chain are π-conjugated and fused, have attracted great interest owing to their intriguing properties, remarkable chemical and thermal stability, and potential suitability as functional organic materials. The synthesis of cLPs can be, in general, achieved by two main strategies: single-step ladderization and post-polymerization ladderization. Although a variety of synthetic methods have been developed, the chemistry of cLPs must contend with structural defects and low solubility that prevents complete control over synthesis and structural characterization. Despite these challenges, cLPs have been used for a wide range of applications such as organic light emitting diodes (OLEDs) and organic field effect transistors (OFETs), paralleling developments in processing methods. In this perspective, we discuss the background of historical syntheses including the most recent synthetic approaches, challenges related to the synthesis and structural characterization of well-defined cLPs with minimum levels of structural defects, cLPs' unique properties, and wide range of applications. In addition, we propose outlooks to overcome the challenges limiting the synthesis, analysis, and processing of cLPs in order to fully unlock the potential of this intriguing class of organic materials.