  Luminescent metal-organic frameworks (MOFs) offer a multifunctional platform
for creating non-invasive sensors and tuneable optoelectronics. However,
fluorochromic materials that are photophysically resilient and show high
sensitivity towards different physical and chemical stimuli are scarce. We
report a facile host-guest nanoconfinement strategy to construct a fluorescent
hybrid material with multiple sensing capabilities. We design and fabricate a
new Guest@MOF material: comprising a zeolitic MOF (ZIF-71) as a nanoporous host
for encapsulating rhodamine B (RhB dye) guest molecules, resulting in the
RhB@ZIF-71 system with mechanochromic, thermochromic, and solvatochromic
sensing response. The fluorochromic sensing properties stem from the
nanoconfinement effect that ZIF-71 imposes on RhB monomers, yielding the H- or
J-type aggregates with tuneable photophysical and photochemical properties. For
mechanochromism, the external pressure causes an emission red shift in a linear
fashion, switching RhB guests from H-type to J-type aggregates through a shear
deformation. For thermochromism, we demonstrate a linear scaling as a function
of temperature due to the spatial restriction imposed on J-type aggregates
incarcerated in ZIF-71 pores. Harnessing the solvatochromism of RhB@ZIF-71, we
identified three diverse groups of volatile organic compounds. The multimodal
sensing response pave the way to smart applications like photonic pressure
sensors, non-invasive thermometers, and ultrasensitive chemosensors.
