Supramolecular Control of Photoswitching in a Chiral Azobenzene

The photochemical behaviour of azobenzene photoswitches is strongly influenced by molecular structure and the surrounding chemical environment, while supramolecular interactions offer an additional means of modulating their switching response. We report the synthesis and photoswitching behaviour of chiral azobenzene derivatives incorporating a BINOL framework and thiourea hydrogen-bonding groups. The thiourea-containing photoswitch 1 undergoes reversible E→Z and Z→E photoisomerization while retaining its chiroptical response. Concentration-dependent NMR and DLS studies indicate self-association of 1, particularly in CDCl3, accompanied by a pronounced retardation of E→Z photoisomerization. Comparison with the thiourea-free analogue 8 suggests that, in addition to general concentration effects, thiourea-mediated interactions contribute to this behaviour. Addition of chloride leads to changes in the thiourea N–H resonances and increases the Zisomer content at the photostationary state from approximately 50% to 70%. Although the effect on the apparent E→Z half-life is modest, chloride binding also increases the thermal lifetime of the Z-isomer. These results show that thiourea-based association and guest binding influence the photochemical and thermal behaviour of the chiral azobenzene system.