Single-Crystal-to-Single-Crystal [2 + 2] Photocycloaddition Reaction in a Photosalient One-Dimensional Coordination Polymer of Pb(II)

In
a remarkable example, we report a one-dimensional coordination
polymer (CP) of Pb­(II) showing photosalient (PS) properties triggered
by [2 + 2] cycloaddition of olefinic ligands, which is seldom observed
in CPs. Macroscopic rod-shaped crystals show various photomechanical
effects such as jumping, splitting, rolling, and breaking upon UV
illumination. In this rare example, we could determine the solid-state
structure of the 100% dimerized product and three intermediate structures,
even after the shattering of crystals into small pieces. Detailed
mechanistic investigation from the single-crystal data indicates that
the strain generated in the unit cell due to anisotropic expansion
played a bigger role for the PS effects. Nucleated growth of the photoproduct
crystal created different domains inside the single crystal, which
multiplied the already developed stress leading to the photomechanical
movements. This example falls in the gray area of a clean single-crystal-to-single-crystal
(SCSC) transformation and violent PS effect. Such photochemical behavior
has never been reported before.