Abstract
The photoisomerization of molecules is widely used to control the structure of soft matter in both natural and synthetic systems. However, the structural dynamics of the molecules during isomerization and their subsequent response are difficult to elucidate due to their complex and ultrafast nature. Herein, we describe the ultrafast formation of higher-orientation of liquid-crystalline (LC) azobenzene molecules via linearly polarized ultraviolet light (UV) using ultrafast time-resolved electron diffraction. The ultrafast orientation is caused by the trans-to-cis isomerization of the azobenzene molecules. Our observations are consistent with simplified molecular dynamics calculations that revealed that the molecules are aligned with the laser polarization axis by their cooperative motion after photoisomerization. This insight advances the fundamental chemistry of photoresponsive molecules in soft matter as well as their ultrafast photomechanical applications.
Highlights
The photoisomerization of molecules is widely used to control the structure of soft matter in both natural and synthetic systems
We examine the molecular motion of photoresponsive LC azobenzene molecules by picosecond timeresolved electron diffraction measurements and molecular dynamics calculations
The loosely packed azobenzene molecules 1 are irradiated with a pulse of linearly polarized ultraviolet light (UV) light
Summary
The photoisomerization of molecules is widely used to control the structure of soft matter in both natural and synthetic systems. Our observations are consistent with simplified molecular dynamics calculations that revealed that the molecules are aligned with the laser polarization axis by their cooperative motion after photoisomerization This insight advances the fundamental chemistry of photoresponsive molecules in soft matter as well as their ultrafast photomechanical applications. We report the ultrafast orientation in a single direction of LC azobenzene molecules in a smectic B phase using picosecond time-resolved electron diffraction and model calculations based on molecular dynamics. Great advances in ultrashortpulsed and ultrabright electron sources have been made recently, and time-resolved electron diffraction can be used to elucidate the structural dynamics of organic molecular crystals[31] Very recently, this technique has been applied to more complex soft materials[32]. Our findings show that the trans-to-cis isomerization induced in the azobenzene-molecule-based LC assembly via linearly polarized ultraviolet (UV) light induces ultrafast higher orientation
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