Selective Identification and Encapsulation of Biohazardous <i>m</i>-Xylene among a Pool of Its Other Constitutional C₈ Alkyl Isomers by Luminescent d¹⁰ MOFs: A Combined Theoretical and Experimental Study

Abstract

Separation of C₈ alkyl-aromatics (<i>o</i>-xylene, <i>m</i>-xylene, and <i>p</i>-xylene) remains one of the most challenging tasks to date due to their similar physical and chemical properties. Cd²⁺- and Zn²⁺-based luminescent metal-organic frameworks (MOFs) have been synthesized for the selective identification of <i>m</i>-xylene in a pool of other isomers by fluorometric methods. Inhibition of the photoinduced electron transfer process is the prime reason for fluorescence enhancement, owing to the comparable molecular orbital energies for <i>m</i>-xylene in comparison with <i>o</i>- and <i>p</i>-xylene. Density functional theory calculations signify that the extraordinary selectivity is mainly due to the high dipole moment of <i>m</i>-xylene that might enhance the ring current, leading to a strong π-π interaction with the MOF's co-ligand. As a practical application, fluorometric sensing could be used for the estimation of <i>m</i>-xylene in different solvent media. Moreover, X-ray structural analysis reveals that the Zn²⁺-MOF can encapsulate <i>m</i>-xylene selectively within its framework among other constitutional isomers, which also emphasizes its capability for practical implementation.