Emergent Pressure-Induced Reactivity of 4,4’-Azopyridine-Templated Hybrid Metal Oxides

We show that the ordered installation of 4,4’-azopyridine ligands featuring reactive azo groups within layered hybrid inorganic–organic metal oxides produces enhanced pressure-induced reactivity relative to the molecular compound alone or previously reported hybrids. Using in situ X-ray diffraction measurements along with vibrational and optical spectroscopies, as well as ex situ neutron elastic and inelastic scattering, vibrational, solid-state NMR, and EPR spectroscopies and mass spectrometry, we examine the structural and electronic evolution of both organic and inorganic components under compression. We find that, in contrast to the molecular solid, the pressure-induced reactivity in the hybrid structure occurs to a greater degree and at lower onset pressure. This collective analysis reveals sharp irreversible piezochromism and partial structural strain/disorder, yet the inorganic oxide framework is retained. The root of these changes is shown to be molecular oligomerization up to seven or more monomer units through an inherently distinct mechanism from previously reported intermolecular bond formation in similar hybrid oxides, even showing the emergence of EPR-active species. These findings show how judicious molecular and material modification within a hybrid architecture can direct chemical reactivity under pressure and provide a pathway to systems with designer optical, electronic, and stress-responsive properties.