Supramolecular Nanostructures of Structurally Defined Graphene Nanoribbons in the Aqueous Phase

Abstract

Structurally well‐defined graphene nanoribbons (GNRs) have attracted great interest because of their unique optical, electronic, and magnetic properties. However, strong π–π interactions within GNRs result in poor liquid‐phase dispersibility, which impedes further investigation of these materials in numerous research areas, including supramolecular self‐assembly. Structurally defined GNRs were synthesized by a bottom‐up strategy, involving grafting of hydrophilic poly(ethylene oxide) (PEO) chains of different lengths (GNR‐PEO). PEO grafting of 42–51 % percent produces GNR‐PEO materials with excellent dispersibility in water with high GNR concentrations of up to 0.5 mg mL−1. The “rod–coil” brush‐like architecture of GNR‐PEO resulted in 1D hierarchical self‐assembly behavior in the aqueous phase, leading to the formation of ultralong nanobelts, or spring‐like helices, with tunable mean diameters and pitches. In aqueous dispersions the superstructures absorbed in the near‐infrared range, which enabled highly efficient conversion of photon energy into thermal energy.

Synthetic Engineering of Graphene Nanoribbons with Excellent Liquid-Phase Processability

“…The resultant thin-film FETs exhibited a maximum carrier mobility of ∼0.3 cm 2 V −1 s −1 under a low voltage (20 V), highlighting the applicability of GNR-PEO in FETs [55]. As the third representative application, the photothermal conversion of GNR superstructures has recently been demonstrated in the aqueous phase [30]. With NIR absorption and excellent water dispersibility, the GNR-PEO superstructures in water exhibited high photothermal conversion with an efficiency of 31%, superior to those of many conventional low-dimensional nanomaterials, such as single-walled carbon nanotubes, graphene oxide, gold nanoparticles, 2D molybdenum disulfide, and 2D manganese dioxide ( Figure 6) [30].…”

“…Although alkyl chain-functionalized GNRs can self-organize into monolayers at the solid-liquid interface ( Figure 1F), their poor dispersibility in organic solvents limits the diversity of GNR supramolecular nanostructures. In contrast, polymer functionalization provides GNRs with enhanced dispersibility and amphiphilicity, enabling the supramolecular self-assembly of the resultant GNRs both at the solid-liquid interface and in solution [30,55]. For example, GNR-PEOs with different PEO lengths show controllable supramolecular behavior (see Figure 4 for the self-assembly of GNR-PEO400, GNR-PEO1000, and GNR-PEO2000; the numbers represent the molecular weights of the PEO chains).…”

“…After achieving excellent solution processability, a number of potential applications for GNRs processed from the liquid phase have been developed [27,30,38,55,[62][63][64][65]. As one of the typical examples, GNR-film-based chemical sensors have been fabricated using GNR 1 with lengths of N500 nm and widths of ∼0.78 nm.…”

“…As the third representative application, the photothermal conversion of GNR superstructures has recently been demonstrated in the aqueous phase [30]. With NIR absorption and excellent water dispersibility, the GNR-PEO superstructures in water exhibited high photothermal conversion with an efficiency of 31%, superior to those of many conventional low-dimensional nanomaterials, such as single-walled carbon nanotubes, graphene oxide, gold nanoparticles, 2D molybdenum disulfide, and 2D manganese dioxide ( Figure 6) [30]. The excellent photothermal conversion performance affords great opportunities for the application of GNRs in photothermal tumor therapy, antisepsis, and other applications.…”

“…(B-D) Typical transmission electron microscopy images of the superstructures formed by GNR-PEO400 (B), GNR-PEO1000 (C), and GNR-PEO2000 (D) in water. Adapted, with permission, from[30].…”