Topology-Mediated Enhanced Polaron Coherence in Covalent Organic Frameworks

Abstract

We employ the Holstein model for polarons to investigate the relationship among defects, topology, Coulomb trapping, and polaron delocalization in covalent organic frameworks (COFs). We find that intrasheet topological connectivity and π-column density can override disorder-induced deep traps and significantly enhance polaron migration by several orders of magnitude in good agreement with recent experimental observations. The combination of percolation networks and micropores makes trigonal COFs ideally suited for charge transport followed by kagome/tetragonal and hexagonal structures. By comparing the polaron spectral signatures and coherence numbers of large three-dimensional frameworks having a maximum of 180 coupled chromophores, we show that controlling nanoscale defects and the location of the counteranion is critical for the design of new COF-based materials yielding higher mobilities. Our analysis establishes design strategies for enhanced conductivity in COFs that can be readily generalized to other classes of conductive materials such as metal–organic frameworks and perovskites.

2D Conjugated Covalent Organic Frameworks: Defined Synthesis and Tailor-Made Functions

“…The topology greatly influences the conductivity and magnetic properties of 2D conjugated COFs. For example, in contrast to the kagome, tetragonal, and hexagonal COFs, it has been reported that the trigonal counterparts are more advantageous for charge transport and that the Lieb lattice is promising in ferromagnetism . Interestingly, combining building blocks with C 2 and D 2 h symmetries can either render COFs with uniform rhombic pores or COFs with a kagome lattice comprising both triangular and hexagonal pores.…”

Reaction Pathways toward Sustainable Photosynthesis of Hydrogen Peroxide by Polymer Photocatalysts

“…Conjugated polymers, especially those with fully π-conjugated two-dimensional (2D) structures, exhibit an array of electronic structure characteristics, which make them attractive for applications in solar-to-chemical energy conversion. , Rational design and synthesis of conjugated polymers with ordered topological structures could extend π-delocalization over the entire framework, resulting in efficient charge transfer. In addition, recent theoretical calculations have also revealed that the charge transport properties of 2D conjugated polymer networks are highly dependent on the lattice symmetry. , For example, 2D conjugated polymers with the kagome lattice typically display flat or nearly flat bands around the Fermi energy. These flat bands are indicative of very high charge-carrier effective masses, which are not favorable for achieving high carrier mobilities.…”

Connecting the dots for fundamental understanding of structure–photophysics–property relationships of COFs, MOFs, and perovskites using a Multiparticle Holstein Formalism

“…Building upon the 3D Holstein polaron model that was recently developed to investigate the effect of defects, domain size, chemical doping, and topology on the mid-IR photophysical signatures and charge transport properties of COFs, 216,217 future studies will go beyond a simple single chain analysis and focus on developing 3D vibronic exciton models for various COF topologies. Explicit inclusion of intra-and inter-framework electronic interactions, Frenkel and charge separated exciton states, and strong electron-phonon coupling on equal footing is necessary to investigate the spectral changes in both the UV-vis absorption and emission lineshapes of COFs.…”

“…In this context, taking advantage of sparse matrix techniques and MPI parallelization on multinode clusters, we have shown that it is possible to extend the application of multiparticle modeling to large "vibronic" 3D systems, with negligible loss of accuracy. 216,217 The article is organized as follows: In Section 2 we briefly discuss the MHF. Section 3 highlights the photophysical signatures of Frenkel, charge-transfer, and Wannier-Mott excitons in organic (polymers and COFs) and hybrid (MOFs and perovskites) materials.…”