In various lab processes we observe that some organic crystals exhibit macroscopic motion in the presence of light; we refer to these crystals as photodynamic. Though photodynamic behavior is generally unpredictable in crystals, even with knowledge of the crystal packing, including an azido chromophore increases the chance of observing photodynamic response, as they release nitrogen gas upon exposure to light. Release of nitrogen gas from within the azido crystal lattice, is likely to result in photodynamic activity. Given that the azide crystals can be photodynamic, the next step is to determine how the azido crystals will respond to nitrogen gas release, as there are a variety of possibilities from bending to bubbling to cracking. With the knowledge of how to control the photodynamic activity of azide crystals, they could see use as, for example, actuators in microscopic machines and would be light activated, leading to high energy efficiency. We will discuss studies of different azido-stilbenes crystals, based on product studies, transient spectroscopy, and calculations. Our results indicate that the type of photodynamic activity observed depends largely on arrangement of molecules within the crystal lattice and their associated intermolecular forces and properties.

Crystal packing is integral to predicting reactivity of photodynamic azide crystals

ACS Spring 2022

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