Cracking under Internal Pressure: Photodynamic Behavior of Vinyl Azide Crystals through N2 Release

• DOI: 10.1021/jacs.0c07830
• Publication Date: 2020-09-29T20:15:59Z
• Authors: Dylan J. Shields; Durga Prasad Karothu; Karthik Sambath; Ranaweera A. A. U...; Stefan Schramm; Alexander Duncan; Benjamin Duncan; Jeanette A. Krause; Anna D. Gudmundsd...; Panče Naumov
• Keywords: Internal energy; Crystal (programming language)

When exposed to UV light, single crystals of the vinyl azides 3-azido-1-phenylpropenone (1a), 3-azido-1-(4-methoxyphenyl)propenone (1b), and 3-azido-1-(4-chlorophenyl)propenone (1c) exhibit dramatic mechanical effects by cracking or bending with release N2. Mechanistic studies using laser flash photolysis, supported quantum calculations, show that each degrades through a vinylnitrene intermediate. However, despite having very similar crystal packing motifs, three compounds distinct photomechanical responses in bulk crystals. While 1a delaminate gaseous N2 indiscriminately under paraffin oil, 1b 1c visibly expand, bend, fracture, mainly along specific crystallographic faces, before releasing The photochemical analysis suggests observed expansion is due internal pressure exerted product lattices these materials. Lattice energy nanoindentation experiments, significant differences respective lattice energies. calculations identify critical features structures where elastic accumulates during gas release, which correspond direction cracks. This study highlights hitherto untapped potential elicit response motility photoreactive molecular