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

Abstract

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, openshell 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 (Ph 2 -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.

A Tale of Two Transitions: Unraveling Two Distinct Polymorph Transition Mechanisms in One n-Type Single Crystal for Dynamic Electronics

“…However, as the temperature increases through the II-III transition, the biradical concentration abruptly increases conducive to forming new spin-spin interactions 27,33 . Typically, in molecules where the biradical ground state is dominant, the major packing motifs are either face-on dimer pairs when unhindered 30,62 or ladder-like stacking 31,63 when steric hinderance prevents the former. In both cases, the high spin centers (where the radical is most localized) will line up and, in some circumstances, form a pseudo σ-bond 12,30,33,62 .…”

α,α′-Diamino-p-quinodimethanes with Three Stable Oxidation States

“…Herein, for the first time, we report the isolation and thorough characterization of α,α′-diamino-substituted-p-quinodimethane derivatives III (Scheme 1). Moreover, our study shows that III exhibits two reversible one-electron oxidation processes under the formation of isolable three oxidation states: dication, radical cation (a class of π-conjugated open-shell compound 12 ), and neutral, which are interconvertible to each other.…”

Recent Advances in Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds

“…In 2019, Chen and co-workers reported the synthesis of a bisphenalenyl radical cation [ 136.3 ] •+ ( Scheme 136 ). 273 Treatment with triflic acid caused demethylation of the methoxy groups in 136.2 , which was followed by cyclization to generate the dipyrylium salt [ 136.3 ]OTf 2 after stirring in tetrachloroethane at 120 °C for 12 h. Reduction of the dication [ 136.3 ] 2+ in the presence of either strong reducing reagents (i.e., Na, K, and Zn) or mild ones (e.g., sodium dithionite) provided the π-radical cation [ 136.3 ] •+ , while the corresponding neutral species could not be obtained. The electronically stabilized π-radical cation [ 136.3 ] •+ shows multiple short intermolecular contacts (<3.4 Å) in its X-ray crystal structure.…”