Increasing attention is being given to the development of covalent organic frameworks (COFs) that are based on monolayers of fully π-conjugated structures. At first glance, such two-dimensional (2D) polymer networks could simply be viewed as a mere extension into a second dimension of the quasi-one-dimensional (1D) conjugated polymers at the origin of the field of organic electronics. However, such a view misses essential characteristics coming specifically from 2D lattice symmetry. Our aims in this Perspective are twofold. We seek (i) to provide a conceptual, chemistry-oriented theoretical description of the impact on the electronic structure of this extension from 1D to 2D and (ii) to establish chemical structure–symmetry–electronic property relationships for this class of 2D π-conjugated COFs.

Branched-alkyl-substituted poly(thieno[3,4-c]pyrrole-4,6-dione-alt-3,4-difluorothiophene) (PTPD[2F]T) can be used as a polymer acceptor in bulk heterojunction (BHJ) solar cells with a low-band-gap polymer donor (PCE10) commonly used with fullerenes. The "all-polymer" BHJ devices made with PTPD[2F]T achieve efficiencies of up to 4.4 %. While, to date, most efficient polymer acceptors are based on perylenediimide or naphthalenediimide motifs, our study of PTPD[2F]T polymers shows that linear, all-thiophene systems with adequately substituted main chains can also be conducive to efficient BHJ solar cells with polymer donors.

Experimental details, synthesis and analysis of the monomers and polymers, additional figures, and additional characterization data (PDF).

Theoretical and experimental investigations of diacetylene-linked COFs with remarkable charge-transport properties.