Reversible Laser-Induced Bending of Pseudorotaxane Crystals

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.