Fig. 4. Changes in the UV-vis absorption spectra starting from (a) (E)-S2 (24 μM in CH₂Cl₂, 298 K) upon irradiation with 405 nm light to PSS₄₀₅ and (b) upon subsequently irradiating with 455 nm light to PSS₄₅₅. Enlarged spectra at the isosbestic point of (c) E to Z isomerization and (d) Z to E back-switching. (e) Plots of the absorption at λ = 403 nm upon sequential irradiation with 405 nm and 455 nm light. (f) Changes in ¹H NMR spectra of (i) (E)-S2 (2.9 mM in CD₂Cl₂, 298 K, 500 MHz), (ii) upon irradiation with 405 nm light to PSS₄₀₅, and (iii) upon subsequent irradiation with 455 nm light to PSS₄₅₅.