Primary processes in the photochemistry of rhodamine dyes

Abstract Quantum yields for intersystem crossing in rhodamine 6G, N,N′-diethylrhodamine and rhodamine B as well as their triplet—triplet (T—T) absorption spectra were measured in aqueous solutions. The main pathways of rhodamine singlet excited state decay are fluorescence and internal conversion. The main pathways of rhodamine triplet state decay radiationless deactivation, quenching by impurities and by ion radicals, T—T interaction and self-quenching. The process of the electron transfer is considered to be the result of T—T interaction and self-quenching of rhodamine triplets in plain aqueous solutions. Triplet states of rhodamine dyes play a major role in redox reaction that occur in the presence of exogenic electron donors and acceptors. The kinetic decay of half-reduced and half-oxidized rhodamine species was studied. The peculiar properties of rhodamine 6G photoreactions occurring in alcohol solutions are considered. The rate constants of the rhodamine triplet and ion radical decay processes are determined.