Poly(ethylene oxide) Functionalized Graphene Nanoribbons with Excellent Solution Processability

Abstract

Structurally well-defined graphene nanoribbons (GNRs) have attracted great interest as next-generation semiconductor materials. The functionalization of GNRs with polymeric side chains, which can widely broaden GNR-related studies on physiochemical properties and potential applications, has remained unexplored. Here, we demonstrate the bottom-up solution synthesis of defect-free GNRs grafted with flexible poly(ethylene oxide) (PEO) chains. The GNR backbones possess an armchair edge structure with a width of 1.0-1.7 nm and mean lengths of 15-60 nm, enabling near-infrared absorption and a low bandgap of 1.3 eV. Remarkably, the PEO grafting renders the GNRs superb dispersibility in common organic solvents, with a record concentration of ∼1 mg mL(-1) (for GNR backbone) that is much higher than that (<0.01 mg mL(-1)) of reported GNRs. Moreover, the PEO-functionalized GNRs can be readily dispersed in water, accompanying with supramolecular helical nanowire formation. Scanning probe microscopy reveals raft-like self-assembled monolayers of uniform GNRs on graphite substrates. Thin-film-based field-effect transistors (FETs) of the GNRs exhibit a high carrier mobility of ∼0.3 cm(2) V(-1) s(-1), manifesting promising application of the polymer-functionalized GNRs in electronic devices.

Fluorescence from graphene nanoribbons of well-defined structure

“…Raman and FTIR spectra of both GNR samples were in agreement with our previous reports, which supported their GNR structures (see figure S7 and S8 in ESI) [14,22]. The first structure studied in this paper, 4-CNR, is described on figure 1(a).…”

“…4-CNR and p-ANR were prepared adapting reported procedures, through the solution-mediated intramolecular oxidative cyclodehydrogenation, or "graphitization", of tailor-made polyphenylene precursors [14,22,26]. Raman and FTIR spectra of both GNR samples were in agreement with our previous reports, which supported their GNR structures (see figure S7 and S8 in ESI) [14,22].…”

“…In this paper we report on a detailed study of the PL properties of two bottom-up-synthesized GNRs with defined structures, namely 4-CNR and p-ANR [14,22], following the name code used in Ref [3]. Both GNRs show broad PL lines and a large Stokes shift.…”

“…In contrast, there is an obvious lack of knowledge about their optical properties. Optical absorption spectroscopy has been reported, showing the dependence of the gap on the width of the GNR [12,14,[20][21][22]. The comparison between reflectivity measurements on GNRs grown on gold and ab-initio calculations recently highlighted the excitonic nature of the optical transitions, with exciton binding energy as high as 1.5-1.8 eV [23].…”

“…Likewise, pump/probe ultrafast transient absorption experiments demonstrated exciton-exciton annihilation and biexciton stimulated emission, with a bi-exciton binding energy of ∼250 meV [24]. Nevertheless, the photoluminescence (PL) properties of GNRs have remained largely underexplored [22,25].…”