P=O-containing dibenzopentaarenes: facile synthesis, structures and optoelectronic properties

Incorporation of heteroatoms into polyarenes has been developed as an effective approach to alter their intrinsic structures and properties. Herein, we designed and synthesized two P=O-containing dibenzopentaarene isomers (5a and 5b) and studied their structures and properties, along with those of dibenzopentaarenes containing six-membered Si- and B-heterocycles (3 and 4). These heterocyclic polyarenes have similar frameworks to well-known heptazethrene, and thus can be regarded as members of the heteroatom-doped zethrene system. The heterocycles greatly affect not only the molecular and packing structures but also the electronic structures and properties. Notably, while compounds 3 and 4 adopt almost planar geometries, 5a possesses a clearly curved conformation, leading to its brick-type slipped and dense pi-pi stacking mode. Moreover, the electron-withdrawing P=O groups endow 5a and 5b with simultaneously lowered lowest unoccupied molecular orbital (LUMO)/highest occupied molecular orbital (HOMO) levels, whereas the p-pi conjugation of the B atoms in 4 leads to its smaller energy gap and thus remarkably red-shifted absorption and fluorescence bands by over 80 nm, though all of these molecules possess similar closed-shell structures. This study thus deepens the understanding of heteroatom-doping effects, which may be expanded to develop other heteroatom-doped zethrene materials.

Automated summary

Incorporation of heteroatoms into polyarenes has been proven to be an effective method to modify their structures and properties. In this study, P=O-containing dibenzopentaarene isomers (5a and 5b) were designed and synthesized, and their structures and properties were investigated alongside dibenzopentaarenes containing Si and B heterocycles (3 and 4). The incorporation of heterocycles greatly influenced the molecular and packing structures, as well as the electronic structures and properties of the polyarenes.