Modulation of the fluorescence of graphene oxide micro-flakes with addition of peripheral benzimidazole group

Graphene oxide (GO) is peripherally modified with the addition of 4-(1H-benzimidazol-2-yl) benzaldehyde using a Debus-Radziszewski reaction with its ortho-quinone groups. The GO content of ortho-quinone is enhanced by the oxidation of catechol groups using molybdic acid in a Froehde reaction. Following a Knoevenagel condensation of the peripherally substituted benzimidazole with methyl cyanoacetate, a fluorescent intramolecular charge-transfer (ICT) chromophore is introduced in the GO structure, forming a new fluorescent material called GO-BI (graphene oxide with benzimidazole). Its micro-flake particle has emission concentrated in its border, as revealed by confocal and total internal reflection fluorescence microscopy (TIRFM) images. The emission spectrum of the GO-BI micro-particle is centered on 525 nm and the fluorescence decay is biexponential, with two main components of 1.6 and 7.0 ns when excited at 473 nm.