Reversible Laser-Induced Bending of Pseudorotaxane Crystals

Abstract

This study investigated the dynamic photoresponse of pseudorotaxane crystals with azobenzene and ferrocenyl groups in the axle component. X-ray crystallography showed pseudorotaxanes with a methylazobenzene group and a dibromophenylene ring in the cyclic component to exhibit twisting of the trans-azobenzene groups at torsion angles of 17° and 38°, respectively. Repeated alternating laser irradiation of the crystals at 360 and 445 nm produced bending of 20-30° in opposite directions, with no evidence of decay. Under 445 nm irradiation, bending took place within 0.3 s. A crystal of nonsubstituted pseudorotaxane showed bending of only 2° under 360 nm irradiation due to multiple π-π interactions between the planar trans-azobenzene groups. The pseudorotaxane crystals have two chromophores, bent rapidly and reversibly on irradiation at rates depending on the molecular structure.

Light‐Responsive Arylazopyrazole Gelators: From Organic to Aqueous Media and from Supramolecular to Dynamic Covalent Chemistry

“…We attributet his to the photoisomerization of the hydrogelator.S imilar to G1, E-G2i se xpected to provide as tiffer material due to the face-to-face hydrogen bonding and the p-p interactions between the gelators.O nt he contrary,t he Z-G2 loses the additional p-p interactions between the AAPs due to their twisted structure. [53][54][55] Thus, ad iminished elastic modulus (G')w as observed. During the visible light irradiation (l = 520 nm), the storagem odulusw as restored.…”

“…This gel fully liquefies upon irradiation with UV light due to the photoisomerization of AAP from the planar E isomer to the twisted Z isomer. [53][54][55] Ther esulting twisted configuration of Z-G1 prevents intermoleculars tacking, resultingi naclear solution.U pon green light irradiation, the planar E isomer is re-obtained, the intermoleculari nteractions are restored, and an organogel is reformed that passes the inverted vial test. As ac ontrol experiment as ample of the organogel was irradiatedf or 2.5h with infrared light (980 nm), which does not induce isomerization of the AAP unit.…”

“…However,i ti sk nownt hat the photoisomerization of azobenzenes results in an equilibrium,t he photostationary state (PSS), which is typicallya round 80 %i n both directions E to Z and Z to E. [51] This phenomenon of incomplete photoisomerization can be even worse in solidphase materials due to the reduced dynamics required for isomerization of the azobenzene. [52,53] To address this limitation, arylazopyrazoles (AAPs) have been recently introduced as improvedl ight-responsive molecular switches. [54][55][56] In further studies, we have investigated, with others, the properties of AAPs [57] as molecular switches and developeds everal supramolecular systemsr anging from colloidal host-guest complexes, [58,59] foams, [60] adhesives, [61] and DNA complexes.…”

“…However, it is known that the photo‐isomerization of azobenzenes results in an equilibrium, the photostationary state (PSS), which is typically around 80 % in both directions E to Z and Z to E . This phenomenon of incomplete photoisomerization can be even worse in solid‐phase materials due to the reduced dynamics required for isomerization of the azobenzene . To address this limitation, arylazopyrazoles (AAPs) have been recently introduced as improved light‐responsive molecular switches .…”

Photomechanical Azobenzene Crystals

“…Besides co-crystals, molecular machines such as rotaxanes are also composed of multi-components with an axial molecule and a ring molecule. Photo-reactive pseudorotaxane crystals of 23-25 were constructed with an axial element with azobenzene and a ring element with different substituents [45]. The pseudorotaxanes with different substituents afforded crystal structures with differing intra-and intermolecular π-π distances and angles.…”