Fig. 4: Visualization of photochromic procedures.

a Photochromic images and b the proposed reversible photochromic mechanism of AB-SA, DAMB-SA, DAMB-SAB, and DAMB-SAN upon UV and Day light irradiation. c The UV-DRS spectra of AB-SA in its reversible photochromic processes. Inset: The plots of the visible absorption maximum of AB-SA (469 nm) versus the irradiation and recover time, respectively. d The plots of the IL/IS versus the irradiation and recover time, respectively. IL and IS represent the absorption intensity at the long and short wavelength in the visible region, respectively.