Fig. 2.

Reversible photoswitching of tetra-o-methoxyazobenzene 4 in water. (A) Yellow/blue light-induced isomerization of 4. (B) The ¹H NMR spectra of inclusion complex 4 ⊂ 1 obtained by encapsulating cis-4 (Upper) and trans-4 (Lower) (500 MHz, D₂O, 298 K). (C) Changes in the UV/Vis absorption spectrum of cis-4 ⊂ 1 following exposure to blue light (5 min) and then to yellow light (90 min). (D) Eight cycles of reversible photoisomerization of 4 within 4 ⊂ 1, followed by UV/Vis absorption spectroscopy.