Antiaromatic Covalent Organic Frameworks Based on Dibenzopentalenes

Abstract

Despite their inherent instability, 4n pi-systems have recently received significant attention due to their unique optical and electronic properties. In dibenzopentalene, benzanellation stabilizes the highly antiaromatic pentalene core, without compromising its amphoteric redox behavior or small HOMO–LUMO energy gap. However, incorporating such molecules in organic devices as discrete small molecules or ill-defined amorphous polymers can limit the performance (e.g. due to solubility in the electrolyte solution or low internal surface area). Covalent organic frameworks, on the contrary, are highly ordered, porous, and crystalline materials that can provide a platform to align molecules with specific properties in a well-defined, ordered environment. We synthesized the first antiaromatic framework materials and obtained a series of three highly crystalline and porous covalent organic frameworks based on dibenzopentalene. Potential applications of such antiaromatic bulk materials were explored: COF films show a conductivity of 4 × 10^(−8) S cm^(−1) upon doping and exhibit photoconductivity upon irradiation with visible light. Investigations as battery electrode materials demonstrate their ambipolar nature and the ability to store both anions and Li ions with enhanced charge storage capabilities compared to an aromatic COF or the conductive carbon material. This work showcases antiaromaticity as a new design principle for functional framework materials.

Covalent Organic Frameworks as Electrode Materials for Alkali Metal‐ion Batteries

“…The capacity retention was still 76.4 % after more than 500 cycles at 2 C when the material was compounded with CNTs for LIBs, and the capacity retention after 1000 cycles reaches an excellent 84 % at 5 C for MIBs. [108] Lu et al combined various modification methods such as high active sites, carbon material composite, and introduction of heteroatoms to designed a COFs cathode material S@TAPT-COFs@rGO with excellent comprehensive performance. [99] By replacing TAPA with TAPT containing triazine ring, more active sites C=N were introduced into the structure (Figure 10d).…”

Strategic design of covalent organic frameworks (COFs) for photocatalytic hydrogen generation

“…98 Herein, by virtue of donor-acceptor combination, the migration of photogenerated electrons from the donor to the acceptor ligand is favored by a push-pull effect. 60…”

“…[57][58][59] Additionally, COFs can be structurally predesigned and functionalized by varying their organic synthons as per requirements. 60 The chemical and thermal stability of COFs is an added advantage in inhibiting photocorrosion during photocatalysis. Thus, COFs are applied for many photocatalytic transformations, including water splitting to hydrogen and oxygen evolution, CO 2 reduction, and organic transformations.…”

Concealed antiaromaticity

“…9 Besides antiaromatic molecules with two degenerate SOMOs and a diradical character y0 of 1 (referred to as truly antiaromatic molecules in this article), there are molecules with a formal 4n πelectron system but reduced diradical character (between 0 and 1). 10 These molecules -including pentalene, dibenzopentalene, s-indacene, and biphenylene (Figure 1c) and their derivatives as well as different cyclooctatetraene derivatives -are often also referred to as antiaromatic, [11][12][13][14][15][16][17][18] even when the diradical character is low. However, the classification of such molecules as antiaromatic has been criticized, particularly for polycyclic molecules that feature both formal 4n and 4n+2 πelectron systems (such as dibenzopentalene and biphenylene, Figure 1c right).…”