Fig. 3. (A–D) UV-vis spectra of PSP1, PSP2, PSP3 and PSP4 solution in DCM, recorded before and after 330 nm monochromatic irradiation at 25 °C. The red dashed lines denote the spectra recorded post 330 nm irradiation; the purple solid lines represent the spectra recorded immediately after 330 nm irradiation; the green solid lines indicate the spectra recorded after 500 nm irradiation of the 330 nm irradiated solutions. (E–H) UV-vis spectra recorded upon addition of PSP1, PSP2, PSP3 and PSP4, to 330 nm irradiated DCM blank solvents. Molar concentrations were between 50 and 150 μM. Enlargements of UV-vis spectra in (A–H) are available in the ESI, Fig. S8.† The laser power at 330 and 500 nm irradiation was kept at 6.5 mW ± 5.2% and 8.5 mW ± 13%, respectively. (I–L) Plots of AMC/ASPvs. time for PSP1, PSP2, PSP3 and PSP4, respectively. Note that the protonated form of MC (MCH+) also exists but is grouped into the ‘MC’ label in AMC (i.e., absorbance of the opened form) for the sake of simplicity. The absorbance of the ‘MC’ label in this case (AMC) corresponds to the λmax of the colored species in the visible range, and the ASP refers to the absorbance at λmax of the respective spiropyran. The AMC/ASP ratio is used instead of AMC to factor in the concentration difference between experiments assuming AMC/ASP ∼ cMC/cSP with εMC/εSP = constant. The number of photons (Np) was converted into time via eqn S1.† The gray areas in (J–L) highlight the actual photochromic response of polymer solutions upon 330 nm irradiation.
