Excited state proton and electron transfer reactions of acridinedione dyes with amines

The excited singlet and triplet state reactions of a set of interesting bifunctional molecules, acridinedione dyes with amines were studied in 2:1 acetonitrile-water. The dyes absorb around 370-390 nm and emit around 430-450 nm. The dyes (N-H) show a new emission with a maximum around 500-520 nm in the presence of highly basic amines which is similar to the deprotonated form, which is formed by excited state proton transfer from the dye to the amine. Electron transfer from the amine to the dye is observed in the case of weakly basic amines and N-R compounds. The triplet of the dyes absorb around 620-670 nm. No proton transfer is observed from the dye to the amine in the triplet state. An electron transfer followed by a proton transfer from the amine to the dye resulting in the ketyl radical formation is observed. For highly basic amines and the dyes with N-H substitution, a further deprotonation of the ketyl radical is observed. The radical cation of the amine is observed in the singlet as well as the triplet reaction, evidencing electron transfer from the amine to the dye.