Near-field infrared nanospectroscopy reveals guest confinement in metal-organic framework single crystals

TL;DR

This study demonstrates the use of advanced near-field infrared spectroscopy techniques combined with DFT calculations to visualize and confirm guest molecule encapsulation within MOF crystals at the nanoscale.

Contribution

It introduces a novel methodology combining s-SNOM, nanoFTIR, and DFT to analyze host-guest interactions in MOFs at the nanoscale, enabling detailed vibrational characterization.

Findings

Confirmed luminescent guest molecule encapsulation in MOF crystals

Mapped local molecular vibrations revealing host-guest interactions

Established a new nanoscale characterization approach for porous materials

Abstract

Metal-organic frameworks (MOFs) can provide exceptional porosity for molecular guest encapsulation useful for emergent applications in sensing, gas storage, drug delivery and optoelectronics. Central to the realisation of such applications however is the successful incorporation of a functional guest confined within the host framework. Here we demonstrate, for the first time, the feasibility of scattering-type scanning near-field optical microscopy (s-SNOM) and nano-Fourier transform infrared (nanoFTIR) spectroscopy, in concert with density functional theory (DFT) calculations to reveal the vibrational characteristics of the Guest@MOF systems. Probing individual MOF crystals, we pinpoint the local molecular vibrations and thus, shed new light on the host-guest interactions at the nanoscale. Our strategy not only confirms the successful encapsulation of luminescent guest molecules in the porous host framework in single crystals, but further provides a new methodology for nanoscale-resolved physical and chemical identification of wide-ranging framework materials and designer porous systems for advanced applications.