Figure 1.

(a) Generalized molecular structures of the spiro (SP) and merocyanine (MC) states of naphthoxazine (NISO) with details of the orthogonal, optically-triggered transitions between the two states. (b) Schematic of photochromic Förster resonance energy transfer (FRET) in the Cy-NISO probes. Optical switching between SP and MC states of NISO results in a time-varying change in FRET efficiency with concomitant modulation of the intensity of Cy fluorescence. (c) Optical modulation of the intensity of Cy fluorescence over multiple cycles of optical switching of the populations of the SP and MC states of NISO. The grey bars represent periods when the sample is exposed to 365/405 nm and the blue bars the periods the sample is exposed to 532–632 nm. The height of each bar represents the intensity of Cy fluorescence at specific times during the course of optical switching.