Intersystem crossing rates and saturation parameters in the triplet state for rhodamine, fluorescein, and acridine dyes

Abstract

The saturation of the population in the triplet state T1 using a laser excitation ESR technique was observed directly at 77 K. The saturation parameters Isat and the singlet-to-triplet intersystem crossing rate kST were determined for acridine red (AO), rhodamine S (RS), rhodamine B (RB), rhodamine 6G (R6G), fluorescein disodium salt (FDS), 2′,7′-dichlorofluorescein (DF), eosin Y (EY), eosin B (EB), acridine orange (AR), and acridine yellow (AY) in rigid ethanolic solutions. On the basis of the results, the intersystem crossing mechanisims of rhodamine (type R), fluorescein (type F), and acridine (type A) types of the ten dyes are discussed.