Vanishing Electronic Band Gap in Two-Dimensional Hydrogen-Bonded Organic Frameworks

Abstract

We introduce the concept of two-dimensional donor–acceptor (DA) hydrogen-bonded organic frameworks (HOFs) as a general design strategy to realize low-band-gap flat-band materials. We report the electronic structure calculations for a series of hexagonal and tetragonal DA-HOFs from aromatic quinones and cyclic fused oligopyrroles. Density functional theory calculations show that these HOFs possess reasonable binding energies (∼10 kcal/mol). The HOFs show very strong charge transfer interactions that enhance the DA abilities while maintaining localized orbital distributions. This leads to vanishingly low band gaps (E g ∼ 0.02–0.07 eV) but with extremely flat bands (bandwidth <0.06 eV). The partial filling of these bands via p- or n-doping leads to Stoner ferromagnetism, with stabilization energies up to 100 meV. Stacking the layers results in the metallization of the porous networks with varying energy dispersions. The symmetry of the band structures can be easily modified by the chemical constituent to represent, for example, Kagome and Lieb lattices.

Progresses and Perspectives of Near-Infrared Emission Materials with “Heavy Metal-Free” Organic Compounds for Electroluminescence

“…As previously mentioned, the effects on tuning the energy gap are mainly related to the individual molecules without consideration of intermolecular interaction. The intermolecular interaction, for instance, the molecular π-π stacking, hydrogen bonding and charge transfer could also have the influence on altering the band gap of the molecules in the solid states [ 71 , 72 , 73 , 74 , 75 ]. According to the above approaches, researchers have designed and organized NIR luminescent materials.…”

Connecting the Dots for Fundamental Understanding of Structure-Photophysics-Property Relationships of COFs, MOFs, and Perovskites using a Multiparticle Holstein Formalism

“…Different stacking arrangements such as cofacial vs. slip-stacked configurations directly influence the degree of charge transfer, polaron migration, and energy transfer along the π-stacks. 273,277,341,342 Strong cofacial interactions between the planar monomers with large π surface area experience significant wave function overlap between the stacks and facilitate more efficient polaronic hopping through the columns. Current investigations in our group are focused on characterizing spectral signatures in the mid-IR energy region for different packing arrangements in COFs.…”

“…Current investigations in our group are focused on characterizing spectral signatures in the mid-IR energy region for different packing arrangements in COFs. 273,277,341,342 In the eclipsed configuration, π-stacking maintains an "in-phase" registry where the donors line up with the donors and the acceptors line up with the acceptors as shown in Fig. 2b.…”

π-Conjugated Materials: Here, There, and Everywhere

“…29 Liu and Perepichka have reported electronic structure calculations for a series of two-dimensional hydrogen-bonded organic frameworks (2D HOFs) that allow designing low gap materials. 30 The incorporation of π-conjugated units in coordination polymers and metal−organic frameworks and the subsequent complexation of polycyclic aromatic hydrocarbons and fullerenes has been proven as an efficient approach to enhance charge transport. For example, Tatay, Marti ́-Gastaldo, and coworkers have produced conductive ultrathin films of 2D Hofmann-type coordination polymers using pillaring linkers of a different nature.…”

“…Ryu and Baek have reported the synthesis of different 2D COFs constituted of different benzothiazole units that show photocatalytic activity in CO 2 conversion . Liu and Perepichka have reported electronic structure calculations for a series of two-dimensional hydrogen-bonded organic frameworks (2D HOFs) that allow designing low gap materials …”