Intrinsic Emission from Nanographenes

Top-down approaches have been widely used as convenient methods for the production of nanographenes. To understand the photoemission properties of nanographenes, their separation and the optical properties of the individual fractions is important. By using a combination of size-exclusion and silica-gel-adsorption chromatography, we separated lipophilic nanographenes that contained para-methoxybenzyl groups. The mixture consisted of large (average 19.8 nm) and small (average 4.9 nm) nanographenes, whilst unreacted carboxy groups remained in the latter group. Optical measurements revealed that oxygen-containing functional groups had little influence on the photoemission of the nanographenes, thus indicating that the intrinsic emission, that is, emission from the sp² surfaces, was responsible for the photoemission. Two photoemission bands were observed for all of the fractions, which likely originated from the edge and inner parts of nanographene.