Existence of multi-radical and closed-shell semiconducting states in post-graphene organic Dirac materials

Abstract

Post-graphene organic Dirac (PGOD) materials are ordered two-dimensional networks of triply bonded sp 2 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.

2D Hexagonal Covalent Organic Radical Frameworks as Tunable Correlated Electron Systems

“…Recently, we proposed a new class of sp 2 carbon‐based SL materials based on linking trivalent triarylmethyl (TAM) αC‐containing radical molecules to form 2D covalent organic radical frameworks (CORFs). [ 8,9 ] Since our prediction, some example 2D CORFs have been experimentally prepared. [ 10–12 ] Herein, we focus on 2D CORFs with hexagonal connectivity based on the graphene‐like honeycomb lattice (2D hex‐CORFs), which we predicted to exhibit spin‐polarized antiferromagnetic (AF) ground states and low energy valence bond quinoidal gapped states, linked by an intervening semimetallic transition state.…”

“…[ 10–12 ] Herein, we focus on 2D CORFs with hexagonal connectivity based on the graphene‐like honeycomb lattice (2D hex‐CORFs), which we predicted to exhibit spin‐polarized antiferromagnetic (AF) ground states and low energy valence bond quinoidal gapped states, linked by an intervening semimetallic transition state. [ 9 ] Compared to the delocalized semimetallic state, the more stable AF and valence bond states have lower space group symmetries and thus can be described as emerging through symmetry breaking. [ 9,13 ] The first experimental examples of a 2D hex‐CORF were indeed found to exhibit an AF ground state.…”

“…[ 9 ] Compared to the delocalized semimetallic state, the more stable AF and valence bond states have lower space group symmetries and thus can be described as emerging through symmetry breaking. [ 9,13 ] The first experimental examples of a 2D hex‐CORF were indeed found to exhibit an AF ground state. [ 10,11 ] 2D hex‐CORFs can be seen as expanded graphene lattices where chemical linkers, rather than external strain, increase the distance between the threefold connected carbon sites.…”

Tailoring Bond Topologies in Open-Shell Graphene Nanostructures

“…8 The past decade has witnessed the realization of interesting classes of open-shell PAHs including zigzag graphene nanoribbons, 9 acenes, [10][11][12][13] anthenes, 14 triangulene 15 and post-graphene organic Dirac materials. 16,17 However, their synthesis via solution-based chemistry remains challenging due to the high intrinsic reactivity arising from unpaired electron densities. 18 In this regard, on-surface synthesis, utilizing surface-driven catalytic reactions of rationally-designed stable precursor molecules under ultra-high vacuum (UHV) conditions, provides a valuable synthetic toolbox toward atomicallyprecise synthesis of PAHs hitherto unattainable via solution chemistry, and allows atomic-scale investigation of structural and electronic properties using scanning probe microscopies.…”

$${\mathscr{P}}{\mathscr{T}}$$-symmetric interference transistor

“…But despite long-term and intensive efforts since its origin in the early 70s 4 , molecular electronics (ME) has not yet presented any experimentally realized candidate to replace the silicon transistor as a “wheel-horse” of the modern IC industry. High expectations were held and are still in place with graphene 5 and post graphene organic Dirac materials 6 . During past period ME mainly concentrated on the attempts to reproduce typical elements of silicon electronics 7 – 12 .…”