Spatial photocontrol of the passive optical output direction of the elastic molecular crystals based on acylhydrazone derivatives

The photo-reactive acylhydrazone derivatives (4-FBAc, 4-ClBAc, 4-BrBAc and 4-IBAc) had been prepared, and they could undergo reversible E-Z isomerization reactions in the crystals under UV (365 nm) irradiation and heating condition. Meanwhile, the significant photomechanical behaviors were observed for the crystals with different shapes. The crystals of 4-FBAc (block-like), 4-ClBAc (block-like) and 4-BrBAc (rod-like) showed lightinduced cracking, salient and cracking behaviors, respectively. Interestingly, the crystals of 4-FBAc (needle-like) and 4-IBAc (needle-like) bent away from the UV light (E-*Z isomerization) firstly, then bent toward the source with the increasing of the irradiation or heating time (structure relaxation and Z-*E isomerization). The theoretical study also showed that the molecules could undergo reversible E-Z isomerization reactions under UV irradiation and heating condition. Interestingly, the passive optical (635 nm) output direction of the crystal of 4FBAc could be controlled by UV light. When mechanical force was applied or removed, the needle-like crystals of 4-FBAc and 4-IBAc exhibited reversible elastic bending properties. Analysis of the single crystal data suggested that C-HMIDLINE HORIZONTAL ELLIPSIS pi and H-bonds were responsible for the flexibility. So, the elastic organic molecular crystals based on acylhydrazone derivatives could be used as the candidate for crystal actuators and position-controllable optical transducer.

Automated summary

The study investigates the reversible E-Z isomerization reactions and photomechanical behaviors of photo-reactive acylhydrazone derivatives in crystals. Different shaped crystals exhibit varying properties under light exposure, suggesting potential applications in crystal actuators and position-controllable optical transducers.