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.