Fig. 5: Fluorescence photoswitching based on intramolecular electron transfer.

a Photochromism and molecular structure of 7. b Absorption and fluorescence spectra of each component of 7 in 1,4-dioxane. Absorption spectra of the open-ring isomer of the DAE unit (black), the closed-ring isomer of the DAE unit (blue), and the PBI unit (red) and fluorescence spectrum of the PBI unit (green). c Relative fluorescence quantum yields as a function of the dielectric constant for the open-ring isomer 7a (open-circle) and the closed-ring isomer 7b (closed-circle). d Non-destructive fluorescence readout capability of both open- and closed-ring isomers of 7. Fluorescence intensities at 568 nm under excitation at 532 nm of 7a (open-circle) and 7b (closed-circle) were plotted against irradiation time. e Single-molecule fluorescence photoswitching in a poly(methyl acrylate) (PMA) thin film containing 7. Sequential wide-field fluorescence images of 7 embedded in PMA film (upper) and the corresponding fluorescence intensity trajectory of a single molecule of 7, represented as a white circle in the upper images. (Reprinted with permission from Fukaminato et al.⁴¹. Copyright 2011 American Chemical Society)