Polycyclic aromatic hydrocarbons radical cation mechanism

Such polycyclic aromatic hydrocarbons as anthracene or heteroaromatics as acridine, phenazine and 2,4,5-triphenyl oxazole act as Jt-donors for the Jt-acceptors AN and alkyl methacrylates [50-53]. Again, the interaction of the donor excited states with vinyl monomers leads to exciplex formation. But, the rate constants (k ) of these quenching processess are low compared to other quenching reactions (see Table 1). The assumed electron transfer character is supported by the influence of the donor reduction potential on the k value (see Table 1), and the detection of the monomer cation radicals with the anthracene-MMA system. Then, the ion radicals initiate the polymerization, the detailed mechanism of which is unsolved,... 

Abstract The study of the fate of electronically excited radical and radical cation of aromatic hydrocarbons is an emerging topic in modern chemical dynamics. Observations like low quantum yield of fluorescence and photostability are of immediate concern to unravel the mechanism of ultrafast nonradiative internal conversion dynamics in such systems. The radical cations of polycyclic aromatic hydrocarbons (PAHs) have received considerable attention in this context and invited critical measurements of their optical spectroscopy in a laboratory, in striving to understand the enigmatic diffuse interstellar bands (DIBs). 

Although a mechanism involving a radical cation has been proposed for the Scholl reaction, as indicated by the paramagnetic properties of many polycyclic aromatic hydrocarbons (PAHs) when they are treated with Lewis acids or concentrated sulfuric acid, it is assumed that the Scholl reaction occurs in a manner similar to the Friedel-Crafts Alkylation, involving an arenium cation instead of a radical cation. In detail, the Scholl reaction of hexaphenylbenzene involves the complexation between a Lewis acid and aromatic nucleus, electrophilic addition, and deprotonation,as illustrated here. In the presence of NaCl or HCl, chloride is beneficial for the elimination of aryl hydrogen by the formation of hydrogen chloride, as indicated by the bold chloride. 

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