with respect to TFA), and equilibration at rt for 24 h. Please note that direct addition of TFA and Et3N to the same solution of (Z)-1 also results in a slight decrease in molar absorptivity as is observed here after the full switching cycle has been completed (Supplementary Fig. ). c, UV-vis spectra starting with (Z)-1 (0.076 mM in degassed CHCl3, 1 cm quartz cuvette) where irradiation with 365 nm, 385 nm, 455 nm, 465 nm, 525 nm, for 2-10 min did not cause any spectral changes, yet after addition of TFA (5.5 μL, 4.7 × 10 2 equiv.) and irradiation with 455 nm the absorption shifted bathochromically.