Surfactant-Triggered Nanoarchitectonics of Fullerene C₆₀ Crystals at a Liquid-Liquid Interface

Here, we report the structural and morphological modulation of fullerene C₆₀ crystals induced by nonionic surfactants diglycerol monolaurate (C₁₂G₂) and monomyristate (C₁₄G₂). C₆₀ crystals synthesized at a liquid-liquid interface comprising isopropyl alcohol (IPA) and a saturated solution of C₆₀ in ethylbenzene (EB) exhibited a one-dimensional (1D) morphology with well-defined faceted structure. Average length and diameter of the faceted rods were ca. 4.8 μm and 747 nm, respectively. Powder X-ray diffraction pattern (pXRD) confirmed a hexagonal-close packed (hcp) structure with cell dimensions ca. a = 2.394 nm and c = 1.388 nm. The 1D rod morphology of C₆₀ crystals was transformed into "Konpeito candy-like" crystals (average diameter ca. 1.2 μm) when the C₆₀ crystals were grown in the presence of C₁₂G₂ or C₁₄G₂ surfactant (1%) in EB. The pXRD spectra of "Konpeito-like" crystals could be assigned to the face-centered cubic (fcc) phase with cell dimensions ca. a = 1.4309 nm (for C₁₂G₂) and a = 1.4318 nm (for C₁₄G₂). However, clusters or aggregates of C₆₀ lacking a uniform morphology were observed at lower surfactant concentrations (0.1%), although these crystals exhibited an fcc crystal structure. The self-assembled 1D faceted C₆₀ crystals and "Konpeito-like" C₆₀ crystals exhibited intense photoluminescence (PL) (∼35 times greater than pC₆₀) and a blue-shifted PL intensity maximum (∼15 nm) compared to those of pC₆₀, demonstrating the potential use of this method for the control of the optoelectronic properties of fullerene nanostructures. The "Konpeito-like" crystals were transformed into high surface area nanoporous carbon with a graphitic microstructure upon heat-treatment at 2000 °C. The heat-treated samples showed enhanced electrochemical supercapacitance performance (specific capacitance is ca. 175 F g^-1, which is about 20 times greater than pC₆₀) with long cyclic stability demonstrating the potential of the materials in supercapacitor device fabrication.