,r-Extended Rubrenes via Dearomative Annulative ,r-Extension Reaction

Among a large variety of organic semiconducting materials, rubrene (5,6,11,12-tetraphenyltetracene) represents one of the most prominent molecular entities mainly because of its unusually high carrier mobility. Toward finding superior rubrene-based organic semiconductors, several synthetic strategies for related molecules have been established. However, despite its outstanding properties and significant attention in the field of materials science, late-stage functionalizations of rubrene remains undeveloped, thereby limiting the accessible chemical space of rubrene-based materials. Herein, we report on a late-stage pi-extension of rubrene by dearomative annulative pi-extension (DAPEX), leading to the generation of rubrene derivatives having an extended acene core. The Diels-Alder reaction of rubrene with 4-methyl-1,2,4-triazoline-3,5-dione occurred to give 1:1 and 1:2 cycloadducts which further underwent iron-catalyzed annulative diarylation. The thus-formed 1:1 and 1:2 adducts were subjected to radical-mediated oxidation and thermal cycloreversion to furnish one-side and two-side pi-extended rubrenes, respectively. These pi-extended rubrenes displayed a marked red shift in absorption and emission spectra, clearly showing that the acene pi-system of rubrene was extended not only structurally but also electronically. The X-ray crystallographic analysis uncovered interesting packing modes of these pi-extended rubrenes. Particularly, two-side pi-extended rubrene adopts a brick-wall packing structure with largely overlapping two-dimensional face-to-face pi-pi interactions. Finally, organic field-effect transistor devices using two-side pi-extended rubrene were fabricated, and their carrier mobilities were measured. The observed maximum hole mobility of 1.49 x 10-3 cm2V-1 s-1, which is a comparable value to that of the thin-film transistor using rubrene, clearly shows the potential utility of two-side pi-extended rubrene in organic electronics.

Automated summary

In this study, we successfully achieved a late-stage pi-extension of rubrene using dearomative annulative pi-extension (DAPEX), leading to the generation of rubrene derivatives with an extended aromatic core. These pi-extended rubrenes displayed a marked red shift in absorption and emission spectra, indicating the extension of the rubrene's aromatic pi-system both structurally and electronically. Furthermore, organic field-effect transistor devices using two-side pi-extended rubrene were fabricated, demonstrating the potential utility of these compounds in organic electronics with a comparable carrier mobility to rubrene thin-film transistors.