Mechanoluminescent MOF nanoplates: spatial molecular isolation of light-emitting guests in a sodalite framework structure

Abstract: Mechanoluminescent materials have a wide range of promising nanotechnological applications, such as photonics based sensors and smart optoelectronics. Examples of mechanoluminescent metal-organic framework (MOF) materials, however, are relatively scarce in the literature. Herein, we present a previously undescribed Guest@MOF system, comprising Perylene@ZIF-8 nanoplates which will undergo a reversible 442 nm <->502 nm photoemission switching when subject to a moderate level of mechanically induced pressure (~10s MPa). The nanoplates were synthesized via a high-concentration reaction (HCR) strategy at ambient conditions, to yield a crystalline ZIF-8 framework hosting the highly luminous Perylene guests; the latter confined within the porous sodalite cages of ZIF-8. Remarkably, we show that in a solid-state condition, it is the spatial isolation and nano-partitioning of the luminescent guests that bestow a unique solution-like optical properties measured in the host-guest assembly. We elucidate how the switchable red- or blue-shifts of the visible emission can be accomplished by mechanically modifying the nanoscale packing of the underlying nanoplates. Theoretical calculations suggest that the elasticity of the host sodalite cage coupled with the intermolecular weak interactions of the confined guest are underpinning the unique mechanoluminescent behavior observed.