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A combination of self-complementary hydrogen bonding and metal–ligand interactions allows stereocontrol in the self-assembly of prochiral ligand scaffolds. A unique, non-tetrahedral M₄L₆ structure is observed upon multicomponent self-assembly of 2,7-diaminofluorenol with 2-formylpyridine and Fe(ClO₄)₂. The stereochemical outcome of the assembly is controlled by self-complementary hydrogen bonding between both individual ligands and a suitably sized counterion as template. This hydrogen-bonding-mediated stereoselective metal–ligand assembly allows the controlled formation of nonsymmetric discrete cage structures from previously unexploited ligand scaffolds.

Abracadabra: The stereoselective self-assembly of an unsymmetrical metal–ligand cage can be controlled by self-complementary hydrogen bonding between alcohol-containing ligands as well as between ligands and suitable anion guests.

While single-molecule sensing offers the ultimate detection limit, its throughput is often restricted as sensing events are carried out one at a time in most cases. 2D and 3D DNA origami nanostructures are used as expanded single-molecule platforms in a new mechanochemical sensing strategy. As a proof of concept, six sensing probes are incorporated in a 7-tile DNA origami nanoassembly, wherein binding of a target molecule to any of these probes leads to mechanochemical rearrangement of the origami nanostructure, which is monitored in real time by optical tweezers. Using these platforms, 10 pM platelet-derived growth factor (PDGF) are detected within 10 minutes, while demonstrating multiplex sensing of the PDGF and a target DNA in the same solution. By tapping into the rapid development of versatile DNA origami nanostructures, this mechanochemical platform is anticipated to offer a long sought solution for single-molecule sensing with improved throughput.

DNA origami nanostructures were used as expanded platforms for multiplex mechanochemical sensing with improved throughput at the single-molecule level. Topological rearrangements of the DNA origami nanoassemblies in response to the binding of specific targets were monitored in real time by using optical tweezers.

We report on multicomponent self-sorting to form open circular helicates of different sizes from a primary monoamine, Fe^II ions, and dialdehyde ligand strands that differ in length and structure by only two oxygen atoms. The corresponding closed circular helicates that are formed from a diamine—a molecular Solomon link and a pentafoil knot—also self-sort, but up to two of the Solomon-link-forming ligand strands can be accommodated within the pentafoil knot structure and are either incorporated or omitted depending on the stage that the components are mixed.

It takes all sorts: Tris(bidentate) ligand strands that differ in length by just two atoms self-sort into circular helicates of different sizes with a monoamine and into different molecular topologies—a molecular Solomon link and a pentafoil knot—with a diamine (see picture).

Dynamic covalent bonds are extensively employed in dynamic combinatorial chemistry. The metathesis reaction of disulfide bonds is widely used, but requires catalysis or irradiation with ultraviolet (UV) light. It was found that diselenide bonds are dynamic covalent bonds and undergo dynamic exchange reactions under mild conditions for diselenide metathesis. This reaction is induced by irradiation with visible light and stops in the dark. The exchange is assumed to proceed through a radical mechanism, and experiments with 2,2,6,6-tetramethylpiperidin-1-yloxyl (TEMPO) support this assumption. Furthermore, the reaction can be conducted in different solvents, including protic solvents. Diselenide metathesis can also be used to synthesize diselenide-containing asymmetric block copolymers. This work thus entails the use of diselenide bonds as dynamic covalent bonds, the development of a dynamic exchange reaction under mild conditions, and an extension of selenium-related dynamic chemistry.

Diselenide bonds are dynamic covalent bonds. Their metathesis can be induced by irradiation with visible light and likely proceeds through a radical mechanism, as the exchange reaction between two different diselenides was suppressed by the addition of the radical scavenger 2,2,6,6-tetramethylpiperidine N-oxide (TEMPO).

[n]Cycloparaphenylenes behave as molecular templates of “perfectly chemically defined” single-wall carbon nanotubes. These [n]CPP molecules have electronic, mechanical, and chemical properties in size correspondence with their giant congeners. Under mechanical stress, they form charge-transfer salts, or complexes with fullerene, by one-electron concave–convex electron transfer.

[n]Cycloparaphenylenes behave as molecular templates of “perfectly chemically defined” single-wall carbon nanotubes. These [n]CPP molecules have electronic, mechanical, and chemical properties in size correspondence with their giant congeners. Under mechanical stress, they form charge-transfer salts, or complexes with fullerene, by one-electron concave–convex electron transfer.

A cyclic tetramer of pyrene, [4]cyclo-2,7-pyrenylene ([4]CPY), was synthesized from pyrene in six steps and 18 % overall yield by the platinum-mediated assembly of pyrene units and subsequent reductive elimination of platinum. The structures of the two key intermediates were unambiguously determined by X-ray crystallographic analysis. DFT calculations showed that the topology of the frontier orbitals in [4]CPY was essentially the same as those in [8]cycloparaphenylene ([8]CPP), and that all the pyrene units were fully conjugated. The electrochemical analyses proved the electronic properties of [4]CPY to be similar to those of [8]CPP. The results are in sharp contrast to those obtained for the corresponding linear oligomers of pyrene in which each pyrene unit was electronically isolated. The results clearly show a novel effect of the cyclic structure on cyclic π-conjugated molecules.

Changing the landscape: A cyclic tetramer of pyrene, [4]cyclo-2,7-pyrenylene ([4]CPY), was synthesized by the platinum-mediated cyclotetramerization and subsequent dehydrogenation. DFT calculations and electrochemical analyses showed that the electronic structure of [4]CPY was completely altered from that of pyrene and linear oligopyrenes. The results clearly show there is modulation of the topology of molecular orbitals upon formation of a cyclic structure.

An overview of some recent developments of the chemistry of molecular donor materials for organic photovoltaics (OPV) is presented. Although molecular materials have been used for the fabrication of OPV cells from the very beginning of the field, the design of molecular donors specifically designed for OPV is a relatively recent research area. In the past few years, molecular donors have been used in both vacuum-deposited and solution-processed OPV cells and both fields have witnessed impressive progress with power conversion efficiencies crossing the symbolic limit of 10 %. However, this progress has been achieved at the price of an increasing complexity of the chemistry of active materials and of the technology of device fabrication. This evolution probably inherent to the progress of research is difficult to reconcile with the necessity for OPV to demonstrate a decisive economic advantage over existing silicon technology. In this short review various classes of molecular donors are discussed with the aim of defining possible basic molecular structures that can combine structural simplicity, low molecular weight, synthetic accessibility, scalability and that can represent possible starting points for the development of simple and cost-effective OPV materials.

Various classes of molecules used as donor materials in heterojunction organic solar cells are presented. Special emphasis is placed on molecular structures that combine low molecular weight, (in general inferior to 500) structural simplicity and synthetic accessibility with reasonable yield. Such systems are discussed as possible working structures for the development of simple and cost-effective materials for organic photovoltaics.