Reaction of ˙H, ˙OH, O˙−and specific one-electron oxidants with 3,3,6,6-tetramethyl-3,4,6,7,9,10-hexahydro-(1,8) (2H,5H)-acridinedione Ground- and excited-state and transient acid–base properties

Abstract

Acridinedione dye is able to exist in neutral, protonated and deprotonated forms in acid–base conditions. The neutral form shows an absorption at 400 nm and emits at 463 nm. The absorption under acidic conditions is blue shifted and the emission intensity at 463 nm decreases with the formation of a new emission peak. In basic solution, the dye is deprotonated and absorbs at 470 nm and emits at 525 nm. The ground- and excited-state pK_a have been calculated. The pulse radiolysis experiments were carried out with specific one-electron oxidants, such as Br₂˙⁻, N₃˙, Cl₂˙⁻, I₂˙⁻. They show transient absorption bands at 305 and 630 nm. Pulse radiolysis of acidic solutions of the dye show transient bands with absorption maxima at 315 and 545 nm and are assigned to a solute radical cation, which deprotonates in neutral solutions. The reaction of ˙H, ˙OH and O˙⁻ with the dye has been studied and the transient absorption bands in the neutral solution are assigned to a neutral carbon centred radical, which deprotonates in basic solution. The pK_a values of the transient species are determined. The redox potential for the one-electron oxidation of the dye is determined as 1.01 ± 0.02 V vs. NHE which compares well with the value obtained by an electrochemical method.