Quenching of triplet chlorophyll-a by aromatic nitrogen compounds

Abstract

Flash excitation of chlorophyll-a in outgassed ethanol solution gives a high yield of the long-lived triplet state. Various types of aromatic nitrogen compound have been found of quench the triplet via an electron transfer reaction. Thus, nitrobenzenes and aromatic heterocyclic compounds act as electron acceptors with triplet chlorophyll-a and quenching leads to formation of chlorophyll-a radical cations and quencher radical anions. Decay of the transient absorption observed by flash spectroscopy is due to back electron transfer. On the other hand, aromatic amines react with triplet chlorophyll-a to yield the chlorophyll-a radical anion and the amine radical cation. Here, reduced chlorophyll-a decays via oxidation with an impurity within the system.