Chemical Functionalisation and Photoluminescence of Graphene Quantum Dots

Abstract

Chemical modification of graphene quantum dots (GQDs) can influence their physical and chemical properties; hence, the investigation of the effect of organic functional groups on GQDs is of importance for developing GQD-organic hybrid materials. Three peripherally functionalised GQDs having a third-generation dendritic wedge (GQD-2), long alkyl chains (GQD-3) and a polyhedral oligomeric silsesquioxane group (GQD-4) were prepared by the Cu(I) -catalysed Huisgen cycloaddition reaction of GQD-1 with organic azides. Cyclic voltammetry indicated that reduction occurred on the surfaces of GQD-1-4 and on the five-membered imide rings at the periphery, and this suggested that the functional groups distort the periphery by steric interactions between neighbouring functional groups. The HOMO-LUMO bandgaps of GQD-1-4 were estimated to be approximately 2 eV, and their low-lying LUMO levels (<-3.9 eV) were lower than that of phenyl-C61 -butyric acid methyl ester, an n-type organic semiconductor. The solubility of GQD-1-4 in organic solvents depends on the functional groups present. The functional groups likely cover the surfaces and periphery of the GQDs, and thus increase their affinity for solvent and avoid precipitation. Similar to GQD-2, both GQD-3 and GQD-4 emitted white light upon excitation at 360 nm. Size-exclusion chromatography demonstrated that white-light emission originates from the coexistence of differently sized GQDs that have different photoluminescence emission wavelengths.

Chirality‐Embedded Nanographenes

“…The photoemission spectra of GQD‐ 1 a and GQD‐ 1 b showed broad emissions in the visible region, similar to previous reports . The size of ( R )‐GQD‐ 1 a was determined by atomic force microscopy (AFM; Figure ).…”

“…The nanographene was functionalized by attaching organic amines onto edge‐oxidized nanographene (GQD‐ 2 ), which was produced by the oxidative cutting of graphite with a mixture of HNO 3 and concentrated H 2 SO 4 at 120 °C for 24 h followed by neutralization with Na 2 CO 3 and de‐ionization in a dialysis membrane with 2 kD . Treatment of GQD‐ 2 with oxalyl chloride followed by the reaction with ( R )‐, ( S )‐, or rac ‐phenylethylamine in DMF gave ( R )‐, ( S )‐, or rac ‐GQD‐ 1 a , respectively.…”

A Supramolecular Polymer Network of Graphene Quantum Dots

“…The introduction of the hydrogen‐bonding functional groups was confirmed by ATR‐IR spectroscopy, and C−H vibrations at 2917 and 2849 cm −1 and C=O vibrations at 1750–1650 cm −1 were observed (Figure a). These absorptions were in good agreement with those of 4 and 5 . The 1 H NMR spectra of GQD‐ 2 b – e supported the functionalization; the signals of the organic functional groups installed into GQD‐ 2 b – e appeared in regions similar to those of 4 and 5 (Figure b).…”

Near‐Infrared‐Emitting Nitrogen‐Doped Nanographenes

“…The change in the HOMO–LUMO gaps was reflected in the PL spectra (Figure ). The PL of both nanographenes was observed in a long‐wavelength region ( λ max =667 nm for GQD‐ 1 a and 621 nm for GQD‐ 1 b ) compared to GQD‐ 2 and previously reported edge‐functionalized nanographenes . For example, the nanographene carrying a POSS groups showed PL at λ max =515 nm.…”

“…Because of the importance of the NIR light within the in vivo window (650–900 nm) for biological applications such as cell imaging, the development of nanographenes that emit NIR light is important. Herein, we report the synthesis of nitrogen‐doped nanographenes (GQD‐ 1 a and GQD‐ 1 b ; Figure ) by post‐modification of edge‐oxidized nanographene (GQD‐ 2 ). By utilizing the ring‐closing reaction between a benzene‐1,2‐dicarboxylic‐acid‐type moiety with 1,8‐naphthalenediamine derivatives, which produces a perimidine framework, π‐extension was realized on the edge of GQD‐ 2 .…”