Triplet Shelving in Fluorescein and Its Derivatives Provides Delayed, Background-Free Fluorescence Detection

Fluorescence from the xanthene dyes rose bengal, erythrosine B, eosin Y, and fluorescein is modulated by reversibly optically populating and depopulating their long-lived triplet states through coillumination with a second, long-wavelength laser. Here, we show that repumping the S1 state from the triplet generates strong, nanosecond-lived optically activated delayed fluorescence (OADF), microseconds to milliseconds after primary pulsed...