A Concise Synthetic Strategy for Accessing Ambient Stable Bisphenalenyls toward Achieving Electroactive Open-Shell π‑Conjugated Materials

Open-shell,
π-conjugated molecules represent exciting next-generation
materials due to their unique optoelectronic and magnetic properties
and their potential to exploit unpaired spin densities to engineer
exceptionally close π–π interactions. However,
prior syntheses of ambient stable, open-shell molecules required lengthy
routes and displayed intermolecular spin–spin coupling with
limited dimensionality. Here we report a general fragment-coupling
strategy with phenalenone that enables the rapid construction of both
biradicaloid (Ph2-s-IDPL, 1) and radical [10(OTf)] bisphenalenyls in ≤7
steps from commercial starting materials. Significantly, we have discovered
an electronically stabilized π-radical cation [10(OTf)] that shows multiple intermolecular closer-than-vdW contacts
(<3.4 Å) in its X-ray crystal structure. DFT simulations reveal
that each of these close π–π interactions allows
for intermolecular spin–spin coupling to occur and suggests
that 10(OTf) achieves electrostatically enhanced intermolecular
covalent-bonding interactions in two dimensions. Single crystal devices
were fabricated from 10(OTf) and demonstrate average
electrical conductivities of 1.31 × 10–2 S/cm.
Overall, these studies highlight the practical synthesis and device
application of a new π-conjugated material, based on a design
principle that promises to facilitate spin and charge transport.