Diarylethene microcrystals make directional jumps upon ultraviolet irradiation

Area of Science:

• Materials Science
• Photochemistry
• Solid-State Physics

Background:

• Diarylethenes are photochromic compounds known for reversible structural changes upon light irradiation.
• Photochemical reactions in solids can induce mechanical stress within the crystal lattice.
• Surface instabilities can arise from mechanical stresses in crystalline materials.

Purpose of the Study:

• To investigate the photomechanical effects in microcrystals of a specific diarylethene derivative.
• To understand the relationship between photoinduced molecular changes and macroscopic crystal behavior.
• To explore the potential mechanisms, such as Grinfeld surface instability, driving these photomechanical phenomena.

Main Methods:

• Synthesis and characterization of diarylethene microcrystals: 1,2-bis[5'-methyl-2'-(2"-pyridyl)thiazolyl]perfluorocyclopentene.
• Photoirradiation experiments using ultraviolet light to induce reversible photocyclization.
• In-situ observation of crystal behavior, including directional jumps and surface morphology changes.
• Analysis of induced uniaxial stress and its relaxation dynamics within the crystal lattice.

Main Results:

• Microcrystals of the diarylethene derivative undergo distinct directional jumps upon photoirradiation.
• Absorbed energy thresholds (around 10 microJ) trigger stress relaxation via these jumps.
• Prevention of jumps leads to the formation of parallel, equidistant cracks on crystal surfaces.
• Observed photomechanical effects are consistent with Grinfeld surface instability.

Conclusions:

• Diarylethene microcrystals exhibit significant photomechanical responses to ultraviolet light.
• Reversible photocyclization drives internal stress, leading to macroscopic crystal movements or fracture.
• Grinfeld surface instability is a plausible mechanism explaining the observed photomechanical effects and crack formation.