Fig. 6: Addressability of the four states of diaryl-HI 4b.

a Overview of the multi-stimuli addressability (visual light, temperature, acid, and base concentration) of the four states of diaryl-HI 4b. Species are colored for distinction, Z-4b in blue, E-4b in red, Z-[4b-H]⁺ in black, E-[4b-H]⁺ in purple. b Enrichment of the thermodynamically less stable neutral E-4b species (black) via TFA addition and neutralization with NEt₃ at –78 °C. Addition of large excess of TFA to a E/Z-4b mixture (gray) leads to complete conversion to E-[4b-H]⁺ (purple). Subsequent addition of an equal excess of NEt₃ at –78 °C leads to the enrichment of 91% of thermodynamically less stable neutral E-4b (black). The molar absorption coefficients of pure Z-4b (blue) and E-4b (red) species are depicted as references. c ¹H NMR titration experiment adding excess of TFA-d₁ (0–647 equiv., spectrum 1–38) to a thermally equilibrated, Z-4b enriched mixture (spectrum 1–38, 601 MHz, 1.12 mm in toluene-d₈, 25 °C). The stepwise complete population of the E-isomer and corresponding depopulation of the Z-isomer is shown. Source data are provided in a Source Data file.