ナノグラフェンの有機合成化学による構造修飾と機能発現

抄録

Nanographenes, known as graphene quantum dots, are graphene fragments with a few to tens of nanometers. Due to the quantum size effect, nanographenes have bandgaps with a few eV and display photoemission in the visible region. These properties make nanographenes attractive research targets. Nanographenes can be obtained by the oxidative cleavage of parent carbons such as graphite and carbon fiber with strong oxidants. We have employed a mixture of concentrated sulfuric acid and 60% nitric acid as oxidants. Although as obtained products are the nonstoichiometric mixture of nanographenes, their size separation with dialysis membranes offers nanographenes with narrower lateral size distribution that displays excitation-wavelength-independent photoemission. Nanographenes carry a large number of carboxylic acid groups at the edge that can be utilized for chemical functionalization by organic synthesis. An example is the installation of 4-propargyloxy benzylamine at the edge. The reactive triple bonds on the resulting nanographenes allow to conduct the Cu(I) catalyzed click reactions, yielding edge-functionalized nanographenes. The click reaction of the nanographene with 1^st, 2^nd, and 3^rd generation dendritic wedges produces white-light-emitting nanographenes and the installation of both long alkyl chains and ureidopyrimidinone groups, which form self-complementary four-fold hydrogen bonds, into the edge drives the self-assembly of the functionalized nanographenes to organize polymer-like structures that function as organogelators. This article focuses on the chemical modification of nanographenes by organic synthesis.