Carlos

A P-fused double helicene consisting of a highly distorted benzene ring, with a bending angle of 23°, has been synthesized by a tandem intramolecular phospha-Friedel–Crafts reaction. Despite the distortion and reduced aromaticity, the double helicene shows thermal and chemical stability. These are important features that make these compounds attractive for applications as a new C₂-symmetric bisphosphine ligand. The simple strategy proposed in this work can be used to prepare a diverse range of distorted molecules.

Bent on helices: A P-fused double helicene consisting of a highly distorted benzene, with a bending angle of 23°, has been synthesized by a tandem intramolecular phospha-Friedel–Crafts reaction. Despite distortion and reduced aromaticity, the proposed molecule shows thermal and chemical stability, and can be converted into the corresponding C₂-symmetric bis(phosphine).

Two-dimensional covalent organic frameworks (2D COFs) provide a unique platform for the molecular design of electronic and optoelectronic materials. Here, the synthesis and characterization of an electroactive COF containing the well-known tetrathiafulvalene (TTF) unit is reported. The TTF-COF crystallizes into 2D sheets with an eclipsed AA stacking motif, and shows high thermal stability and permanent porosity. The presence of TTF units endows the TTF-COF with electron-donating ability, which is characterized by cyclic voltammetry. In addition, the open frameworks of TTF-COF are amenable to doping with electron acceptors (e.g., iodine), and the conductivity of TTF-COF bulk samples can be improved by doping. Our results open up a reliable route for the preparation of well-ordered conjugated TTF polymers, which hold great potential for applications in fields from molecular electronics to energy storage.

An electroactive COF: A two-dimensional covalent organic framework (COF) containing well-known tetrathiafulvalene (TTF) units is synthesized (see figure). The presence of TTF units endows the TTF-COF with electron-donating ability, and the open frameworks of TTF-COF are amenable to doping with electron acceptors (e.g., iodine). In addition, the conductivity of TTF-COF bulk samples can be improved by doping.

A new class of brightly phosphorescent Pt(II) compounds that contain an N^∧C-chelate phenyl-1,2,3-triazolyl ligand (ptrz) and an N^∧C-chelate pyridyl-1,2,4-triazolyl ligand (pytrz) in the central core is achieved. The impact of various substituent groups on phosphorescence of this class of molecules is examined. Crystal structural analyses revealed that this class of compounds has a great tendency to form stacked dimers—one of which is persistent even in the gas phase—leading to excimer emission. The introduction of bulky substituents, such as diphenyl amino (NPh₂) or trityl (CPh₃), is found to greatly diminish the excimer emission. Using this approach, several highly efficient blue and green phosphorescent Pt(II) compounds with λ_em at ≈450–460 nm and Φ_p ≈ 0.70 to 1.00 are obtained. These molecules are highly robust with exceptionally high thermal stability. Bright bluish-green electrophosphorescent devices with external quantum efficiencies as high as 16.7% are fabricated.

Bright blue and green phosphorescent Pt(II) complexes with an N^∧C chelate 1,2,3-triazolyl ligand and an N^∧N chelate 1,2,4-trizolyl ligand, near unity quantum efficiencies and high thermal stability are achieved. Steric blocking and the rigidity enhancement around the Pt(II) core by large substituent groups at the para-position are found to be critical in the bright phosphorescence of this new class of compounds.

Reactions between the U-shaped binuclear Cu^I complex A that bears short metal–metal distances and the cyano-capped monotopic π-conjugated ligands 1–5 that carry gradually bulkier polyaromatic terminal fragments lead to the formation of π-stacked supramolecular assemblies 6–10, respectively, in yields of 50–80 %. These derivatives have been characterized by multinuclear NMR spectroscopic analysis and X-ray diffraction studies. Their solid-state structures show the selective formation of U-shaped supramolecular assemblies in which two monotopic π-conjugated systems present large (6, 7, and 9) or medium (8 and 10) intramolecular π overlap, thus revealing π–π interactions. These assemblies self-organize into head-to-tail π-stacked dimers that in turn self-assemble to afford infinite columnar π stacks. The nature, extent, and complexity of the intermolecular contacts within the head-to-tail π-stacked dimer depend on the nature of the terminal polyaromatic fragment carried by the cyano-capped monotopic ligand, but it does not alter the result of the self-assembling process. These results demonstrate that the dinuclear molecular clip A that bears short metal–metal distances allows selective supramolecular assembly processes driven by the formation of intra- and intermolecular short π–π interactions in the resulting self-assembled structures; thus, demonstrating that their shape is not only dictated by the symmetry of the building blocks. This approach opens perspectives toward the formation of extended π-stacked columns based on dissymmetrical and functional π-conjugated systems.

Stretching into infinity: A general approach to π-stacked dissymmetrical supramolecular assemblies is described. The reaction of a series of dissymmetrical cyano-capped monotopic π-conjugated systems with a U-shaped Cu^I dinuclear molecular clip results in the formation of U-shaped π-stacked supramolecular assemblies that self-assemble in the solid state along infinite columns of interacting π systems, regardless of the nature of the π-conjugated system (see picture).