Mechanical-Bond-Protected, Air-Stable Radicals.

Radical templation centered around a heterotrisradical tricationic inclusion complex DB⊂DAPQT, assembled from an equimolar mixture of a disubstituted 4,4'-bipyridinium radical cation (DB) and an asymmetric cyclophane bisradical dication (DAPQT), affords a symmetric [2]catenane (SC·7PF) and an asymmetric [2]catenane (AC·7PF) on reaction of the 1:1 complex with diazapyrene and bipyridine, respectively. Both these highly charged [2]catenanes have been isolated as air-stable monoradicals and characterized by EPR spectroscopy. X-ray crystallography suggests that the unpaired electrons are delocalized in each case across two inner 4,4'-bipyridinium (BIPY) units forming a mixed-valence (BIPY) state inside both [2]catenanes, an observation which is in good agreement with spin-density calculations using density functional theory.

Redox-Active Macrocycles for Organic Rechargeable Batteries.

Organic rechargeable batteries, composed of redox-active molecules, are emerging as candidates for the next generation of energy storage materials because of their large specific capacities, cost effectiveness, and the abundance of organic precursors, when compared with conventional lithium-ion batteries. Although redox-active molecules often display multiple redox states, precise control of a molecule's redox potential, leading to a single output voltage in a battery, remains a fundamental challenge in this popular field of research. By combining macrocyclic chemistry with density functional theory calculations (DFT), we have identified a structural motif that more effectively delocalizes electrons during lithiation events in battery operations-namely, through-space electron delocalization in triangular macrocyclic molecules that exhibit a single well-defined voltage profile-compared to the discrete multiple voltage plateaus observed for a homologous macrocyclic dimer and an acyclic derivative of pyromellitic diimide (PMDI).

Chiral Redox-Active Isosceles Triangles.

Designing small-molecule organic redox-active materials, with potential applications in energy storage, has received considerable interest of late. Herein, we report on the synthesis, characterization, and application of two rigid chiral triangles, each of which consist of non-identical pyromellitic diimide (PMDI) and naphthalene diimide (NDI)-based redox-active units. (1)H and (13)C NMR spectroscopic investigations in solution confirm the lower symmetry (C2 point group) associated with these two isosceles triangles.