Porous materials are important in a wide range of applications including molecular separations and catalysis. We demonstrate that covalently bonded organic cages can assemble into crystalline microporous materials. The porosity is prefabricated and intrinsic to the molecular cage structure, as opposed to being formed by non-covalent self-assembly of non-porous sub-units. The three-dimensional connectivity between the cage windows is controlled by varying the chemical functionality such that either non-porous or permanently porous assemblies can be produced. Surface areas and gas uptakes for the latter exceed comparable molecular solids. One of the cages can be converted by recrystallization to produce either porous or non-porous polymorphs with apparent Brunauer–Emmett–Teller surface areas of 550 and 23 m2 g-1, respectively. These results suggest design principles for responsive porous organic solids and for the modular construction of extended materials from prefabricated molecular pores.

Porous organic cages

Two-dimensionally extended, polycyclic heteroaromatic molecules (heterocyclic nanographenes) are a highly versatile class of organic materials, applicable as functional chromophores and organic semiconductors. In this Review, we discuss the rich chemistry of large heteroaromatics, focusing on their synthesis, electronic properties, and applications in materials science. This Review summarizes the historical development and current state of the art in this rapidly expanding field of research, which has become one of the key exploration areas of modern heterocyclic chemistry.

Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds: Synthetic Routes, Properties, and Applications

Designing pi-conjugated polymers for organic electronics

Over the last two decades the field of metallosupramolecular self-assembly has emerged as a promising research area for the development of intricate, three-dimensional structures of increasing complexity and functionality. The advent of this area of research has strongly benefited from design principles that considered the ligand geometry and metal coordination geometry, thus opening up routes towards rationally designed classical (Archimedean or Platonic) architectures. In this tutorial review, we will focus on more recent developments in the design and synthesis of three-dimensional suprastructures which have non-classical architectures (non-Archimedean/Platonic solids) and we will explicitly address the secondary effects responsible for their formation. Three classes of metallosupramolecular assemblies will be discussed: architectures formed through the combination of a single ligand and metal, heteroleptic structures and heterometallic structures. It is hoped that our exposition may suggest how different principles employed in these three classes of structures might be combined to create even greater complexity and potential for function.

Building on architectural principles for three-dimensional metallosupramolecular construction

Porphyrins and other tetrapyrrole macrocycles possess an impressive variety of functional properties that have been exploited in natural and artificial systems. Different metal centres incorporated within the tetradentate ligand are key for achieving and regulating vital processes, including reversible axial ligation of adducts, electron transfer, light-harvesting and catalytic transformations. Tailored substituents optimize their performance, dictating their arrangement in specific environments and mediating the assembly of molecular nanoarchitectures. Here we review the current understanding of these species at well-defined interfaces, disclosing exquisite insights into their structural and chemical properties, and also discussing methods by which to manipulate their intramolecular and organizational features. The distinct characteristics arising from the interfacial confinement offer intriguing prospects for molecular science and advanced materials. We assess the role of surface interactions with respect to electronic and physicochemical characteristics, and describe in situ metallation pathways, molecular magnetism, rotation and switching. The engineering of nanostructures, organized layers, interfacial hybrid and bio-inspired systems is also addressed.

Porphyrins at interfaces

Chemists use template-directed synthesis to position molecular components so that they can be covalently linked into complex molecules that are not readily accessible by classical synthetic methods. But as larger structures are targeted, the synthesis of the templates themselves becomes challenging. O'Sullivan et al. now show that 'molecular Verniers', based on the principle of moire pattern formation, can solve this problem. Using a Vernier template with six binding sites and molecular building blocks with four porphyrins acting as binding sites, the authors create a 12-porphyrin nano-ring with a diameter of 4.7 nanometres. The ease and efficiency of this synthesis establishes Vernier templating as a powerful new strategy for producing large monodisperse macromolecules. Templates are widely used to arrange molecular components so they can be covalently linked into complex molecules that are not readily accessible by classical synthetic methods. But, as larger structures are targeted, the synthesis of the templates themselves becomes challenging. It is now shown that 'molecular Verniers' can solve this problem: using a template with six binding sites and molecular building blocks with four porphyrins acting as binding sites, a 12-porphyrin nano-ring with a diameter of 4.7 nm is created. The ease and efficiency of this synthesis establishes Vernier templating as a powerful new strategy for producing large monodisperse macromolecules. Templates are widely used to arrange molecular components so they can be covalently linked into complex molecules that are not readily accessible by classical synthetic methods1,2,3,4,5,6,7. Nature uses sophisticated templates such as the ribosome, whereas chemists use simple ions or small molecules. But as we tackle the synthesis of larger targets, we require larger templates—which themselves become synthetically challenging. Here we show that Vernier complexes can solve this problem: if the number of binding sites on the template, nT, is not a multiple of the number of binding sites on the molecular building blocks, nB, then small templates can direct the assembly of relatively large Vernier complexes where the number of binding sites in the product, nP, is the lowest common multiple of nB and nT (refs 8, 9). We illustrate the value of this concept for the covalent synthesis of challenging targets by using a simple six-site template to direct the synthesis of a 12-porphyrin nano-ring with a diameter of 4.7 nm, thus establishing Vernier templating as a powerful new strategy for the synthesis of large monodisperse macromolecules.

Corentin Rinfray

Papers

Vernier templating and synthesis of a 12-porphyrin nano-ring