Bottom-Up Preparation of Twisted Graphene Nanoribbons by Cu-Catalyzed Deoxygenative Coupling

Abstract

Graphene nanoribbons (GNRs) are promising in organic optoelectronic materials, and their properties largely depend on the size, edge, and conformation. Herein, the fully armchair-edged GNRs (AGNRs) with lengths up to 2.65 nm by using a Cu-catalyzed deoxygenative coupling as a key step. The resulting AGNRs (2HBT, 3HBT, and 4HBT) possess highly twisted π-scaffolds, and the torsion angles between the adjacent triphenylene moieties are larger than 32°, as proved by crystallographic analyses. Theoretical and spectroscopic studies show that the butoxy groups endow AGNRs with electron-rich features, the extension of the π-system from 2HBT to 4HBT reinforces S₀ →S₁ excitation, and the distortion of the π-scaffold enhances the fluorescence quantum yield (Φ_F ). In particular, 4HBT has the lowest oxidation potential (E_ox ¹ =0.55 V vs. SCE) and displays red fluorescence with a Φ_F value of 81 %.

Keywords: Deoxygenative Coupling; Fluorescence; Graphene Nanoribbons; Polycyclic Aromatics; Twisted Nanoribbons.