Fig. 4. (a) UV-Vis spectra of o-R-A¹₂L₃ during ring-closing, and (b) c-R-A¹₂L₃ during the ring-opening process (CH₃CN/CHCl₃, v : v = 1 : 1, 1 × 10⁻⁵ mol L⁻¹, 298 K). (c) Cycled signals for absorbance at 538 nm during alternative ring-closing/opening processes (left), and color change photos (right). (d) Time-dependent ¹H NMR spectral evolution of o-R-A¹₂L₃ under UV irradiation (400 MHz, CD₃OD, 298 K).