Coaxially Conductive Organic Wires Through Self-Assembly.

Here, we describe the synthesis of the hexameric macrocyclic aniline (MA[6]), which spontaneously assembles into coaxially conductive organic wires in its oxidized and acidified emeraldine salt (ES) form. Electrical measurements reveal that ES-MA[6] exhibits high electrical conductivity (7.5 × 10-2 S·cm-1) and that this conductivity is acid-base responsive. Single-crystal X-ray crystallography reveals that ES-MA[6] assembles into well-defined trimeric units that then stack into nanotubes with regular channels, providing a potential route to synthetic nanotubes that are leveraged for ion or small molecule transport. Ultraviolet-visible-near-infrared absorbance spectroscopy and electron paramagnetic spectroscopy showcase the interconversion between acidic (conductive) and basic (insulating) forms of these macrocycles and how charge carriers are formed through protonation, giving rise to the experimentally observed high electrical conductivity.

Stringing the Perylene Diimide Bow.

This study explores a new mode of contortion in perylene diimides where the molecule is bent, like a bow, along its long axis. These bowed PDIs were synthesized through a facile fourfold Suzuki macrocyclization with aromatic linkers and a tetraborylated perylene diimide that introduces strain and results in a bowed structure. By altering the strings of the bow, the degree of bending can be controlled from flat to highly bent. Through spectroscopy and quantum chemical calculations, it is demonstrated that the energy of the lowest unoccupied orbital can be controlled by the degree of bending in the structures and that the energy of the highest occupied orbital can be controlled to a large extent by the constitution of the aromatic linkers. The important finding is that the bowing results not only in red-shifted absorptions but also more facile reductions.

Controlling Singlet Fission by Molecular Contortion.

Singlet fission, the generation of two triplet excited states from the absorption of a single photon, may potentially increase solar energy conversion efficiency. A major roadblock in realizing this potential is the limited number of molecules available with high singlet fission yields and sufficient chemical stability. Here, we demonstrate a strategy for developing singlet fission materials in which we start with a stable molecular platform and use strain to tune the singlet and triplet energies. Using perylene diimide as a model system, we tune the singlet fission energetics from endoergic to exoergic or iso-energetic by straining the molecular backbone. The result is an increase in the singlet fission rate by 2 orders of magnitude. This demonstration opens a door to greatly expanding the molecular toolbox for singlet fission.