Supramolecular Pi

Significance

Supramolecular π-conjugated molecules, nanocarbons, are of great interest for the development of next-generation optoelectronic and spintronic materials. Small molecule mimetics enable practical solution-phase synthesis and processing but present the challenge of reproducing the unique electronic properties of their nanocarbon parent structures. A particular challenge is the stabilization of open-shell structures, which engender distinct optoelectronic and magnetic properties. Described is the robust synthesis and characterization of a persistent open-shell conjugated small molecule that shows antiambipolar charge transport and anti-Kasha doublet fluorescent emission.

Comment

The tricyclic phenalenyl moiety is known to stabilize unpaired spin densities and is smoothly incorporated into the structure of 5 by the addition of doubly lithiated 2 to commercially available 1. Oxidation with DDQ and hydrogenation yields diketone 3. Condensation with hydroxyl amine followed by acetylation yields 4, which is primed for cyclization. Treatment with Fe(acac)₃ yields the pyrido-quinoline core via a Friedel–Crafts N-arylation (Org. Lett. 2013, 15, 4254) and facile dehydrogenation. Methylation with methyl triflate and reduction with triethylamine yields radical cation 5. Notably, 5 is the first molecular material to show anti-ambipolar charge transport properties.