An Attempt to Determine Fluorescein’s S–T Transition Probability and a Preliminary Investigation of the Behavior of Its Semiquinone in an Alkaline Solution

Abstract
An attempt to obtain a reliable value of \varphiS-T for fluorescein in an alkaline solution has been unsuccessful since the values for EDTA and ATU were quite different. It has been found that a large quantity of semiquinone is produced when EDTA is used as a reducing agent. In the case of ATU, the quantity of semiquinone produced is very small. Semiquinone in an alkaline solution reverts to the oxidized dye by the second-order thermal reaction and, quite astonishingly, mostly by the reaction 2DH → 2D+H2. The photochemical behavior of leuco-fluorescein has been investigated to some extent in the presence of and in the absence of a reducing agent.