Rational design of a pyrene based luminescent porous supramolecular framework: excimer emission and energy transfer

Abstract

Here we report a rational design and synthesis approach to construct a porous luminescent supramolecular framework by modulating the spatial arrangement of aromatic linkers directed by coordination to a metal ion. A metal–organic complex, {Cd(oxo-pba)₂(H₂O)₂}_n (1) has been synthesized using a functionalized pyrene linker, 1-pyrene-γ-oxo-butyric acid (oxo-pba) and this structure is extended to a 2D supramolecular framework through non-covalent interactions. Using Zn(II) as a metal center we have also synthesized {[Zn(oxo-pba)₂(bpy)]·4H₂O}_n (2), which has a similar chemical structure as compound 1, except 2,2′-bipyridine chelator occupies the positions of the coordinated water molecules. Further, compound 2 extends via several π–π and C–H⋯π interactions to form a 3D porous supramolecular structure as supported by CO₂ (195 K) and different solvent vapour adsorption studies. Compounds 1 and 2 both show bright pyrene excimer emission. Furthermore, the porosity and aromatic π electron decorated pore surface of compound 2 has been exploited for noncovalent encapsulation of a suitable acceptor dye acridine orange (AO) and an efficient energy transfer from the framework to encapsulated dye was observed.