Pore size dynamics in interpenetrated metal organic frameworks for selective sensing of aromatic compounds

• Unique exciplex emission response to different monoaromatic compounds.
• Metal-organic framework undergoes structural changes with analyte binding.
• Fluorescence and sorption experiments show high selectivity for toluene and p-xylene.
• Competitive binding selectivity has affects the interpretation of sensor response.

The two-fold interpenetrated metal-organic framework, [Zn2(bdc)2(dpNDI)]n (bdc = 1,4-benzenedicarboxylate, dpNDI = N′N′-di(4-pyridyl)-1,4,5,8-naphthalenediimide) can undergo structural re-arrangement upon adsorption of chemical species changing its pore structure. For a competitive binding process with multiple analytes of different sizes and geometries, the interpenetrated framework will adopt a conformation to maximize the overall binding interactions. In this study, we show for binary mixtures that there is a high selectivity for the larger methylated aromatic compounds, toluene and p-xylene, over the small non-methylated benzene. The dpNDI moiety within [Zn2(bdc)2(dpNDI)]n forms an exciplex with these aromatic compounds. The emission wavelength is dependent on the strength of the host-guest CT interaction allowing these compounds to be distinguished. We show that the sorption selectivity characteristics can have a significant impact on the fluorescence sensor response of [Zn2(bdc)2(dpNDI)]n towards environmentally important hydrocarbons based contaminants (i.e., BTEX, PAH).

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