Abstract
Post-graphene organic Dirac (PGOD) materials are ordered two-dimensional networks of triply bonded sp2 carbon nodes spaced by π-conjugated linkers. PGOD materials are natural chemical extensions of graphene that promise to have an enhanced range of properties and applications. Experimentally realised molecules based on two PGOD nodes exhibit a bi-stable closed-shell/multi-radical character that can be understood through competing Lewis resonance forms. Here, following the same rationale, we predict that similar states should be accessible in PGOD materials, which we confirm using accurate density functional theory calculations. Although for graphene the semimetallic state is always dominant, for PGOD materials this state becomes marginally meta-stable relative to open-shell multi-radical and/or closed-shell states that are stabilised through symmetry breaking, in line with analogous molecular systems. These latter states are semiconducting, increasing the potential use of PGOD materials as highly tuneable platforms for future organic nano-electronics and spintronics.
Highlights
Post-graphene organic Dirac (PGOD) materials are ordered two-dimensional networks of triply bonded sp[2] carbon nodes spaced by π-conjugated linkers
Hybrid functionals (i.e. functionals which incorporate a fraction of Hartree–Fock-like exchange (HFE)) are being widely adopted by material’s modellers[36], especially for capturing the most subtle electronic features displayed by many systems
density functional theory (DFT) calculations employing generalised gradient approximation (GGA) functionals over-delocalise valence electrons, and cannot stabilise the localised states found in experimental observations
Summary
Post-graphene organic Dirac (PGOD) materials are ordered two-dimensional networks of triply bonded sp[2] carbon nodes spaced by π-conjugated linkers. A series of 2D conjugated networks were predicted to present Dirac cones in their bandstructures[10] These networks present a common basic skeleton: a hexagonal array of triply bonded sp[2] carbon atoms (or nodes of the hexagonal network) connected by π-conjugated linkers (see Fig. 1a). Due to the common basic structure shared by all materials depicted in Fig. 1b (i.e. hexagonal lattice of sp[2] carbon nodes connected by π-conjugated linkers), it is chemically reasonable to expect that these extended resonance forms should lead to the accessibility of similar electronic states in all cases
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