Dye-Encapsulated Zeolitic Imidazolate Framework (ZIF-71) for Fluorochromic Sensing of Pressure, Temperature, and Volatile Solvents

TL;DR

This study introduces a new fluorescent hybrid material, RhB@ZIF-71, that exhibits multiple sensing capabilities for pressure, temperature, and volatile solvents through nanoconfinement effects, enabling smart sensing applications.

Contribution

The paper presents a novel host-guest MOF-based sensor with tunable fluorochromic responses for pressure, temperature, and solvents, demonstrating multifunctionality and high sensitivity.

Findings

Pressure causes linear red shift in emission, indicating mechanochromic response.

Temperature induces linear thermochromic scaling in emission.

Volatile organic compounds are detected via solvatochromic shifts.

Abstract

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.