A two-fold interpenetrated microporous bi-pillared-layer framework of Fe(II), {[Fe(2,6-napdc)(4,4'-bipy)](EtOH)(H₂O)}$_n$ (1) (2,6-napdc =2,6-naphthalenedicarboxylate; 4,4'-bipy=4,4'-bipyridine) composed of mixed ligand system has been synthesized and structurally characterized. The 2,6-napdc linkers form a 2D corrugated sheet of {Fe(2,6-napdc)}$_n$ by linking the secondary building unit of Fe₂(CO₂)₂ in the $ac$ plane, which are further connected by double 4,4'-bipy pillars resulting in a bi-pillared-layer type 3D framework. The 3D framework is two-fold interpenetrated and exhibits a 3D channel structure ($4.0 \times 3.5, 1.5 \times 0.5$ and $2.2 \times 2.1$ Ų) occupied by the guest water and ethanol molecules. Framework 1 shows high thermal stability, and the desolvated framework (1′) renders permanent porosity realized by N₂ adsorption profile at 77K (BET surface area of $\tilde 52$ m² g^-1). Moreover, the framework 1′ also uptakes different solvent vapours (water, methanol and ethanol) and their type-I profile suggest strong interaction with pore surfaces and overall hydrophilic nature of the framework. Temperature dependent magnetic measurements suggest overall antiferromagnetic behaviour in compound 1.

The metal–organic frameworks (MOFs) or porous coordination polymers (PCPs) are a class of porous, crystalline material with numerous possibilities of real-world applications including storage, separation, catalysis, sensing etc. The possibility of intrinsic crystallinity and virtually infinite metal/metal-oxo node and organic linker combination make it a perfect material for photophysical studies. In the last decade, luminescent MOFs have emerged as an excellent modular material for various optical applications, and here, we have discussed about its design strategies. In this review, with relevant examples we have highlighted the rational design approach, possible applications (light emitting diodes, sensing) and future directions in luminescent MOFs