Photochemically driven shape changes of crystalline organic nanorods

Area of Science:

• Materials Science
• Organic Chemistry
• Nanotechnology

Background:

• Organic crystals can undergo photochemical reactions.
• Nanostructure properties differ significantly from bulk materials.
• Photodimerization is a known photochemical process.

Purpose of the Study:

• To synthesize and characterize 9-tert-butylanthroate (9-TBAE) nanorods.
• To investigate the effect of UV light on 9-TBAE nanorods.
• To explore the potential of organic nanostructures for photochemical energy conversion.

Main Methods:

• Synthesis of nanorods using an Al2O3 template and solvent annealing.
• UV irradiation to induce photodimerization.
• Characterization using transmission electron microscopy (TEM) and atomic force microscopy (AFM).
• X-ray crystallography of monomer and photodimer.

Main Results:

• Uniform 15% expansion along the nanorod axis upon UV-induced [4+4] photodimerization.
• Nanorods maintained structural integrity, unlike random 9-TBAE crystals which disintegrated.
• Evidence of a crystal-to-crystal photoreaction mechanism leading to increased molecular volume.
• High surface-to-volume ratio in nanorods likely facilitates strain relief.

Conclusions:

• Organic nanostructures can undergo controlled photochemical expansion.
• Photochemical energy can be converted into mechanical motion at the nanoscale.
• The strain relief in nanorods is crucial for maintaining structural integrity during photoreaction.