Modulation of Fluorescence Emissions of Copper(II) 2,2′‐biquinoline‐4,4′‐dicarboxylates

Interplay of weak interactions of di‐aqua‐bis‐ethylenediammine copper(II) 2,2′‐biquinoline‐4,4′‐dicarboxylate hydrate ( 1 ) were used to modulate solid state fluorescence emissions. Complex 1 forms porous self‐assembly in solid state by hydrogen bonds between cations, anions and lattice water molecules. Fluorescence spectroscopy, thermogravimetry, powder XRD, IR‐spectroscopy and surface analysis were used to establish the breakdown and regeneration of porous hydrogen bonded sub‐assemblies by dehydration and rehydration. Complex 1 is non‐fluorescent in solid state but anhydrous form of the complex 1 is highly fluorescent. In the solid state self‐assembly of the complex 1, π‐stacking among biquinoline rings contributes to quenching. Dehydration of solid sample of complex 1 generates a fluorescent state, and subsequent absorption of moisture by the anhydrous complex quenches fluorescence. In solution, competition between chelation by ethylenediamine and coordination by 2,2′‐biquinoline‐4,4′‐dicarboxylic acid with copper(II) ions is reflected in the ON and OFF states generated by judicious manipulation of chelation effects. Complex 1 is one among a series of bis‐chelated ethylendiamine copper(II) aromatic carboxylate complexes which have layered structures. It is also a precursor of nano‐dimensional copper oxide; 25–50 nm size copper oxide particles are formed by thermal decomposition of complex 1 at 500 °C.