"Clicked" Hydrazone Photoswitches

The length of the linker connecting a photoswitch to a material significantly influences the latter's properties, with "zero-length" linkers being ideal for optimal photomodulation. The 1,2,3-triazole formed through the "click" reaction between an azide and an alkyne has been used as such a linking motif in various areas of research spanning from materials to biological chemistry. However, its effect, as well as that of its regioisomers, on the photoswitching properties has not been fully elucidated. Here, we report on a series of triazole-containing hydrazone photoswitches, investigating how the connectivity (1,4 vs 1,5) between the triazole and the switch affects the photoswitching properties. The structure-property analysis and DFT/TD-DFT calculations show that the switching efficiency of N-connected 1,4-triazole hydrazones is lower than their C-connected counterparts, while the 1,5-triazole hydrazone exhibits an overall better photoswitching efficiency.