Photoreduction of organic dyes in ketone amine systems

Photopolymerization Reactions Initiated by a Visible Light Photoinitiating System: Dye/Amine/Bis(trichloromethyl)-Substituted-1,3,5-Triazine

“…From the reduction potential of the dyes used previously, [28] one can estimate the upper limit of the oxidation potential of A9: E ox f -0.6 V/SCE, which is close to the value published for aminoalkyl radicals (-1.0 V/SCE for trimethylaminyl radical). [29] Assuming that this value is valid, the reduction of RB or EOY by the aminoalkyl radical is not favorable.…”

“…But, due to the short excited state lifetime of the singlet state of RB and the fact that the back electron transfer reaction is expected more significant in the singlet state than in the triplet state, the main source of radicals is issued from the triplet state. [26,27] In addition, it was shown that the aminoalkyl radical arising from the triethanolamine can react with the ground state of certain cationic organic dyes (methylene blue, phenosafranine, thiopyronine, crystal violet for example) through an electron transfer reaction: [28] Dye + A9 e Dye9 -+ A +…”

“…The rate constant of this reaction is high (10 9 m -1 N s -1 ), [28] which means that the free enthalpy of this reaction is near or below 0 eV (D ET G = E ox (A9) -E red (dye)). From the reduction potential of the dyes used previously, [28] one can estimate the upper limit of the oxidation potential of A9: E ox f -0.6 V/SCE, which is close to the value published for aminoalkyl radicals (-1.0 V/SCE for trimethylaminyl radical).…”

Direct and ketone-sensitized photoconversion of 1-nitro-9,10-anthraquinone to 1-amino-9,10-anthraquinone mediated by donor radicals

“…This is different for the other radical reactions because of the formation of ketyl and alcohol radicals in equal amount. The benzophenone/donor system has been employed for reduction of related dyes [37,38]. The rate constant of radical termination in aqueous solution is 2.4 Â 10 9 , 1.5 Â 10 9 and 1.1 Â 10 9 M À1 s À1 for methanol, ethanol and 2-propanol, respectively, and the rate constant of termination of 2-propanol radicals in acetonitrile is 1 Â 10 9 M À1 s À1 [41,43,44].…”

“…For this purpose benzophenone, acetophenone or acetone were used. The benzophenone/acetonitrile/alcohol system has been employed for reduction of cationic dyes [37,38]. The third goal aimed at the reduction of 1-aminoAQ which is a subsequent photoreaction of 1-nitroAQ.…”