Segregation of Constitutional Isomers of Some Aromatic Amines Exploiting the Changes of Photo-Luminescence Behaviour of Isoreticular Metal-Organic Frameworks

Three different two dimensional Cd(II)-based metal-organic frameworks (MOFs) have been synthesized by utilizing same N,N'-donor ligand and three different functionalized dicarboxylate linkers namely isophthalate, 5-nitroisophthalate and 5-hydroxyisophthalate for compound 1, 2 and 3 respectively. The compounds that are isoreticular bi-walled 2D frameworks, show dual fluorescence emission spectra for their π-π* and n-π* excitation. Compound 1 is consists of unsubstituted bridging isophthalate whereas 2 and 3 are made with bridging isophthalate that are substituted by electron withdrawing -NO₂ group and electron donating -OH group respectively. These different electronic environments in three MOFs are found effective to respond differently towards the constitutional isomers of aromatic amines having suitable electronic environment. Compound 1 responses towards non-polar -CH₂ group containing picolylamine moieties, showing maximum fluorescence emission enhancement for 2-picolylamine in comparison to 3- and 4- isomer of picolylamine derivates. Compound 2, consisting electron withdrawing -NO₂ group, responses more significantly towards the electron rich phenylenediamines showing maximum quenching in case of m-phenylenediamine compared to their ortho and para isomers. The change of functionalisation from -NO₂ to -OH in 3, helps to detect the electron deficient aminopyridines; where the maximum fluorescence quenching has been observed in presence of 3-aminopyridine in contrast to its other isomers.