We have studied surface transformations of two polycyclic aromatic hydrocarbons (pyrene and anthracene) covalently attached to the surfaces of modified quartz, indium tin-oxide (ITO) and gold. We applied two immobilization strategies. For quartz and ITO we prepared acid chloride terminated monolayers and reacted the acid chloride moieties with the amino groups of aminopyrene or aminoanthracene. For gold substrates, we self-assembled monolayers of 11-mercaptoundecanoic acid, transformed the carboxylic groups into interchain anhydrides, and then attached aminopyrene (or aminoanthracene) through the amide bonds.
We investigated the surface bound molecules using steady-state emission spectroscopy and cyclic voltammetry. It was shown that the immobilized polycyclic aromatic hydrocarbons can be electrochemically or photochemically oxidized into reactive radical cations. These radicals react with water molecules and are transformed into intermediate monohydroxy derivatives. The further oxidation of monohydroxy compounds results in the formation of dihydroxy/dione systems. It was found that the final products of pyrene oxidation are 1,6 and 1,8 pyrenediones/dihydroxypyrenes. The oxidation of anthracene results in formation of 1,4-anthracenedione/dihydroxyanthracene couple.