Fig. 2.

Synthesis and mechanism of probe PFF-1. a Mechanism of photoactivation and fluxionality of PFF-1. b Synthesis of probes PFF-1 and 2 through their common intermediate 3. c Fluorescence increase of compounds PFF-1 and 2 upon photoirradiation at 410 nm in buffered aqueous solutions. Bars represent average values of three independent measurements (N = 3) and error bars indicate standard deviation (±). d Calculated potential energy surface for ring opening of the Z isomer of probe PFF-1. The structures of “open” and “closed” correspond to those in panel (a). Relative energies were obtained at the B3LYP/def2-TZVP/IEFPCM(H₂O) level of theory