The photochemistry of the series 4a-d can be assigned to a reversible photoinduced E/Z isomerization process, in which the direct switch corresponds to the conversion of the The time-evolution of the absorption spectrum for all the compounds under irradiation at 375 nm and 300 nm was also analyzed in the same solvents. UV-Vis spectra of the direct and reverse switch are given in Figure for 4c,d and in figures S6 and S7 for 4a,b. As expected, under irradiation at 375 nm one can observe the decrease of the bands corresponding to the ππ* transition for the E-isomer comprised between 370 nm and 385 nm depending on the chromophore. On the other hand, the back switch from PSS to GS is confirmed by the increase of the same band under irradiation at 300 nm. As shown in Table , at the GS, the E/Z ratio is independent on the nature of the solvent (more than 92% E-isomer for all compounds). Nevertheless, the efficiency of the photoisomerization varies with both the solvent and donor groups. For a given solvent, the conversion rates for compound 4c are close to those previously determined for compounds 4a and 4b (about 80%, 80%, and 50% in CDCl3, Acetonitrile-d3, DMSO-d6, respectively). A significant decrease in photoisomerization efficiency was observed in ethanol-d6 with increased carbon chain length and thus hydrophobicity (around 50% for 4c vs. 65% for 4b). This could be due to the limited solubilization and possible self-aggregation. Compound 4d showed conversion rates evaluated at more than 70% in CDCl3 while it is only 37% in DMSO-d6 and 15% in Ethanol-d6.