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

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-gamma-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)]center dot 4H(2)O}(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 pi-pi and C-H/center dot center dot center dot pi 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 pi 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.